Atomic Structure and the Periodic Table: a full term of science

Ten ready-to-teach lessons for Year 10 Chemical sciences. Print this pack and the term is prepared: every lesson comes with a step-by-step plan, the questions to ask, a student worksheet, cut-out cards, a class sheet or exit tickets, an assessment kit and worked answers.

Start here: five minutes to Monday

1. Skim the term at a glance on the next page.
2. Print the lesson you need. Each lesson is three A4 sheets: plan, worksheet, and cards, a class sheet or tickets.
3. Gather the few items under “You need” on the plan. Most come from the classroom or the science prep room.
4. Open the free interactive unit on your board or projector. Every plan tells you which picture to show and when.
5. Teach straight from the plan. Timings, talk prompts, misconceptions and worked answers are all on the one page.

For any Year 10 science teacher

The pack suits a chemistry specialist and a teacher working outside their own subject alike: each plan explains the idea in plain words, lists the misconceptions students bring, and gives worked answers. The big idea of the term: the periodic table is a picture of how atoms are built. The protons name an element; the shells in use set its row and the outer electrons its column, so elements in a column behave alike and properties change steadily along a row.

Two ways to run each lesson

Every lesson works as one 60-minute block, or as two 30-minute sessions; the split point is marked in every plan. Look ahead: Lesson 2 needs six sealed mystery boxes made before the lesson, Lesson 3 needs flame test splints soaked overnight, and Lesson 9 needs a set of element samples and a conductivity tester for each group.

Safety and care in one look

The Lesson 3 flame tests are a teacher demonstration. The group 1 metals and the halogens are shown on video only. In Lesson 6 students add a little magnesium and calcium to water, with safety glasses and no flames nearby. In Lesson 9 samples are handled with tongs, and everyone washes their hands.

The term at a glance

One lesson a week for a term. Each lesson stands on the ones before it, so run them in order where you can.

How the sequence builds

Lesson 1 opens the atom, and Lesson 2 follows the evidence that built that picture. Lesson 3 adds the electron shells, so that Lesson 4 can rebuild the table from them and Lesson 5 can meet the man who built it without knowing about electrons. Lessons 6 and 7 study three families down their columns, Lesson 8 walks along a row, and Lesson 9 maps metals and non-metals. Lesson 10 brings it together.

Curriculum links (Australian Curriculum V9)

The whole term teaches the Science Understanding descriptor AC9S10U06 quoted on the cover. The lessons also work these Science Inquiry and Human Endeavour descriptors:

Assessment in this pack

• Every plan ends with “Answers and look-fors”: what meeting the idea sounds like in a Year 10 voice, with working.
• The assessment sheet near the front has a class observation checklist and a three-level rubric.
• Lesson 10 is the summative pair: the group 2 task, plus the “Show what we know” check.

Materials for the whole term

One gathering session covers all ten lessons, and most of it is already in the science prep room. Three things are worth doing ahead: tape the six mystery boxes shut for Lesson 2, soak the flame test splints overnight before Lesson 3, and find two short videos from a reliable education source for Lessons 6 and 7.

The one-trip list

• From the prep room: a Bunsen burner, splints, the five chloride solutions, test tubes, universal indicator, calcium granules, magnesium ribbon, element samples, tongs and conductivity testers.
• From the classroom: shoe boxes, tape, scissors, calculators, rulers and coloured pencils.
• From home or a shop: six small objects for the mystery boxes.

Safety and care in one look

• Flame tests are a teacher demonstration: safety glasses, a heatproof mat, and used splints into a beaker of water.
• Group 1 metals and the halogens are shown on video only. Calcium and magnesium go into water in small amounts, with safety glasses and no flames nearby.
• Element samples are handled with tongs; magnesium is not burnt; sulfur stays on its watch glass; everyone washes their hands.

Assessment without extra work

The term assesses itself. Every lesson plan ends with worked answers and look-fors, and Lesson 10 is the summative pair: the group 2 task, in which students predict strontium from its neighbours and identify a mystery element from its structure and properties, and the final check. This sheet is the place to note what you see along the way.

The three levels

Class observation checklist

A tick a lesson is plenty; the Lesson 10 task and check fill the gaps.

Word wall cards

Cut out the cards and build the wall as the words arrive: atom, nucleus, proton, neutron, electron, atomic number, mass number and isotopes in Lesson 1; model in Lesson 2; electron shell and electron configuration in Lesson 3; period and group in Lesson 4; alkali metals in Lesson 6; halogens and noble gases in Lesson 7; ionisation energy in Lesson 8; metalloid in Lesson 9.

Dear families

This term in science, Year 10 studies what atoms are made of and how the periodic table is organised: why the elements sit where they do, and how an element’s place tells chemists how it will behave.

Along the way your student will build a model of a box they cannot open, watch metals colour a flame, rebuild the periodic table from cards, follow how Mendeleev predicted elements nobody had yet found, drop calcium into water, and test which elements conduct electricity.

Try this at home

• Hunt for elements in the kitchen: aluminium foil, copper in a power cord, iron in a pan, and sodium and chlorine joined in table salt.
• Watch fireworks or a gas flame: the colours come from metals, such as sodium’s yellow-orange and copper’s blue-green.
• Look at a glowing red-orange sign: the light comes from neon gas.
• Check a food label for elements: calcium, iron, potassium and sodium all appear, as compounds.

What to ask your scientist

• What is inside an atom, and how do we know when nobody can see one?
• Why are the elements arranged in rows and columns?
• How did Mendeleev predict elements before anyone found them?
• Why does potassium react with water faster than sodium?

A small note on safety: practical work this term includes a teacher’s flame test demonstration and small amounts of calcium and magnesium in water, with safety glasses. The most reactive elements are shown on video only.

Warm regards,

The Year 10 science team

Printed from the free seegongsik Atomic Structure and the Periodic Table teaching pack · seegongsik.com/au/y10/chemical/AC9S10U06/pack

Inside the atom

Every atom is built from three particles. Protons, with a charge of +1, and neutrons, with no charge, pack into a tiny nucleus that holds almost all of the mass. Electrons, with a charge of −1 and about 1/1836 of a proton’s mass, sit in shells around it. The number of protons is the atomic number, and it alone names the element; the protons plus the neutrons give the mass number. A neutral atom has as many electrons as protons. Atoms of one element with different numbers of neutrons are isotopes. The nucleus is roughly 100 000 times narrower than the atom, so an atom is mostly empty space.

We are learning to

• describe the charge, mass and place of protons, neutrons and electrons,
• use the atomic number and the mass number to count the particles in an atom,
• explain what isotopes are.

Success criteria

• I can count the protons, neutrons and electrons in an atom from its atomic number and mass number.
• I can explain how two atoms of chlorine can have different masses.

You need

• the particle cards (third sheet), one set per pair, with scissors; calculators,
• the worksheet (next sheet), one per student.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the foil, the board and Parts A and B in Session A, and the card sort and Part C in Session B.

Watch for these ideas

• “A different mass number means a different element.” Only the number of protons decides the element; isotopes differ in neutrons.
• “Electrons circle the nucleus like planets.” That is an old model (Lesson 2); shells are energy levels, not paths.
• “An atom is a solid ball.” It is mostly empty space; the push you feel from a desk comes from the electrons repelling each other.

Make it easier, make it bigger

• Easier: work through sodium-23 together: protons = atomic number, electrons = protons, neutrons = mass number − atomic number.
• Bigger: hydrogen has three isotopes, hydrogen-1, hydrogen-2 and hydrogen-3. How many protons, neutrons and electrons does each have?

Answers and look-fors

• Part A: proton +1, mass 1, in the nucleus; neutron no charge, mass 1, in the nucleus; electron −1, mass about 1/1836 (almost 0), in shells around the nucleus.
• Part B: helium-4 2, 2, 2; carbon-14 6, 8, 6; sodium-23 11, 12, 11; chlorine-35 17, 18, 17; chlorine-37 17, 20, 17; potassium-39 19, 20, 19 (protons, neutrons, electrons). Chlorine-35 and chlorine-37 are isotopes: both have 17 protons and 17 electrons, but 18 and 20 neutrons.
• Part C: 1. 10⁻¹⁰ ÷ 10⁻¹⁵ = 10⁵ = 100 000 times. 2. 1 mm × 100 000 = 100 000 mm = 100 m, about the width of a sports oval. 3. Mostly empty space, with the electrons moving through it.
• Part D: proton B, E, F, I, L; neutron D, H, K; electron A, C, G, J.
• Bigger: each has 1 proton and 1 electron; they have 0, 1 and 2 neutrons.

Inside the atom

A. The three particles

B. Count the particles

Atomic number = the number of protons. Mass number = protons + neutrons. A neutral atom has as many electrons as protons.

C. How empty is an atom?

An atom is about 10⁻¹⁰ m across. Its nucleus is about 10⁻¹⁵ m across.

D. Sort the particle cards

Which particle?

Cut out the three headings and the twelve cards. Sort each card under the particle it describes.

Teacher note: the answer letters are in the plan. The three piles are different sizes.

Models of the atom

Nobody has looked inside an atom, yet chemists have a detailed model of one. The model was built in steps, and each step was forced by new evidence. Democritus reasoned that matter must end in pieces that cannot be cut. Dalton’s solid atoms explained why elements combine in fixed ratios. Thomson found the electron and placed it in a ball of positive charge. Rutherford’s team fired alpha particles at gold foil and found the nucleus. Bohr put the electrons in shells to explain the colours atoms give out, and Chadwick found the neutron. Students first model a box they cannot open, then match each model of the atom to its evidence.

We are learning to

• explain how a model is built from evidence we cannot see directly,
• describe how the model of the atom changed as new evidence appeared,
• link each model of the atom to the evidence behind it.

Success criteria

• I can describe my model of the mystery box, and keep my evidence apart from my guesses.
• I can explain why the gold foil results meant Thomson’s model had to change.

You need

• six shoe boxes, each taped shut around one small object (a marble, a die, a cotton reel, a key, an eraser, a cork), numbered 1 to 6,
• the model cards (third sheet), one set per pair, with scissors; the worksheet (next sheet), one per student.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the boxes and the board in Session A, and the matching and Part C in Session B.

Watch for these ideas

• “The old models were wrong, so they were useless.” Each explained the evidence of its day, and was kept until new evidence asked for more.
• “Scientists saw atoms and drew them.” Every model here came from indirect evidence, as with the mystery boxes.
• “Bohr’s model is the last word.” Today’s model describes where electrons are likely to be; shells still explain the periodic table well.

Make it easier, make it bigger

• Easier: hand out the model cards in date order, so students only look for the evidence.
• Bigger: if the positive charge were spread through the atom, as Thomson pictured, what should the alpha particles have done?

Answers and look-fors

• Part A: results vary; look for evidence (a rolling sound, a slide, a thud, the weight) kept apart from the model (the guess).
• Part B: G with A, D with J, E with L, B with H, K with F, I with C. In date order: Democritus, Dalton, Thomson, Rutherford, Bohr, Chadwick.
• Part C: 1. A very few alpha particles bounced back, and only a tiny, dense, positive centre could turn them round; most passed straight through, so the atom is mostly empty. 2. It has no charge, so it is not bent by electric or magnetic fields and is hard to detect. 3. No: each model explained the evidence of its day and was improved when new evidence came; Dalton’s model still explains why elements combine in fixed ratios.
• Bigger: they should all have passed through with only small changes of direction; none should have bounced back.

Models of the atom

A. The mystery box

Tilt the box, roll it and listen. Do not open it.

B. Match the models

Pair each model with its evidence. Write the pairs of letters, then lay the pairs out in date order.

C. Questions

Models and their evidence

Cut out the twelve cards. Six describe a model of the atom; six describe the evidence or reason behind one. Match each pair.

Teacher note: the pairs are in the plan. Every card has exactly one partner.

Electron shells

Electrons do not sit just anywhere around the nucleus: they fill shells, each with a set energy, from the inside out. For the first 20 elements the shells hold 2, then 8, then 8, then the rest, so calcium is 2, 8, 8, 2. This configuration is the element’s address: the number of shells in use gives its period (row) and the electrons in the outer shell give its group (column). Heat can lift an electron to a higher shell; when it falls back, the atom gives out light of an exact energy, so each metal colours a flame its own way. That was the evidence Bohr’s shells explained.

We are learning to

• write the electron configuration of the first 20 elements,
• draw an atom as a shell diagram,
• read the period and the group from a configuration.

Success criteria

• I can write the configuration of any of the first 20 elements and draw its shell diagram.
• I can explain why each metal gives a flame its own colour.

You need

• for a teacher demonstration: a Bunsen burner on a heatproof mat, safety glasses, wooden splints soaked overnight in solutions of lithium, sodium, potassium, calcium and copper(II) chlorides, and a beaker of water for used splints,
• the worksheet (next sheet), one per student, and the exit tickets (third sheet), cut into four.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the flames, the board and Parts A and B in Session A, and Part C, the sharing and the ticket in Session B.

Watch for these ideas

• “Electrons go into any shell.” They fill from the inside out: 2 in the first shell, then 8, then 8 for the first 20 elements.
• “The colour comes from the chlorine.” Every splint holds a chloride, yet the colours differ: the metal makes the colour.
• “The group is just the outer electrons.” For groups 13 to 18 add 10; helium, with a full first shell of 2, sits in group 18.

Make it easier, make it bigger

• Easier: give the shell sizes as four boxes (2, 8, 8, 2) to fill in order, and work beryllium and magnesium together.
• Bigger: some street lights glow yellow-orange because they hold sodium. What is happening inside the sodium atoms?

Answers and look-fors

• Part A: lithium chloride red; sodium chloride yellow-orange; potassium chloride lilac; calcium chloride orange-red; copper(II) chloride blue-green.
• Part B (configuration; period; group): helium 2; 1; 18. beryllium 2, 2; 2; 2. nitrogen 2, 5; 2; 15. fluorine 2, 7; 2; 17. neon 2, 8; 2; 18. magnesium 2, 8, 2; 3; 2. aluminium 2, 8, 3; 3; 13. phosphorus 2, 8, 5; 3; 15. argon 2, 8, 8; 3; 18. calcium 2, 8, 8, 2; 4; 2.
• Part C: oxygen 2, 6; sodium 2, 8, 1; chlorine 2, 8, 7, each drawn as rings of electrons around a nucleus labelled with its protons.
• Exit ticket: 1. 2, 8, 6. 2. Period 3, group 16. 3. Heat lifts electrons to a higher shell; as they fall back they give out light, and the colour is set by that element’s shells.
• Bigger: the electric current lifts electrons in the sodium atoms to a higher shell; as they fall back, they give out yellow-orange light.

Electron shells

A. Coloured flames

B. Fill the shells

Shells fill from the inside out and hold 2, then 8, then 8, then the rest. Shells in use = period. Outer electrons give the group.

C. Draw the atoms

Draw the nucleus with its number of protons, then each shell as a ring with its electrons as dots.

Exit tickets

Arrange the table

Lay the first 20 elements out by their electrons and the periodic table appears. Each card shows an element’s configuration: the number of shells in use sets its row, and its outer electrons set its column. The elements in a column then share an outer shell, and they turn out to behave alike: lithium, sodium and potassium are soft metals that react with water, fluorine and chlorine are reactive non-metals, and helium, neon and argon hardly react at all. The cards also show each element’s mass. In order of mass, argon (39.9) and potassium (39.1) swap places and argon lands among the reactive metals; in order of protons, the atomic number, every element sits with its family.

We are learning to

• arrange elements in the periodic table from their electron configurations,
• describe what the elements in a period, and in a group, have in common,
• explain why the table is in order of atomic number rather than mass.

Success criteria

• I can place any of the first 20 elements in the table from its configuration.
• I can explain why argon comes before potassium although it is heavier.

You need

• the element cards (third sheet), one set per pair, with scissors; a printed periodic table to check against at the end,
• the worksheet (next sheet), one per student.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the cards, the board and the building in Session A, and Part B and the check in Session B.

Watch for these ideas

• “The table is in order of mass.” It is in order of atomic number; argon and potassium, and a few pairs further on, show the difference.
• “Hydrogen is an alkali metal.” It has one outer electron, so it heads group 1, but it is a gas and behaves differently.
• “Elements in a row behave alike.” A row runs from metals to non-metals; the families are in the columns.

Make it easier, make it bigger

• Easier: place hydrogen, helium, lithium and neon together first, then let pairs finish the grid.
• Bigger: beryllium (2, 2) and helium (2) both have 2 outer electrons. Why does helium sit above neon, and not above beryllium?

Answers and look-fors

• Part A: period 1: H He; period 2: Li Be B C N O F Ne; period 3: Na Mg Al Si P S Cl Ar; period 4: K Ca. Hydrogen and helium sit at the two ends of period 1, and potassium and calcium start period 4.
• Part B: 1. The same number of outer electrons, and so similar behaviour. 2. The same number of shells in use. 3. In order of mass, argon would fall under sodium with the reactive metals and potassium under neon with the gases that do not react; by protons (18 and 19) each sits with its family. 4. Like them it has one outer electron; unlike them it is a gas, not a metal.
• Bigger: helium’s only shell is full, like neon’s outer shell, so it hardly reacts; beryllium is a reactive metal.

Arrange the table

A. Build the table

Lay out the cards: shells in use give the row, outer electrons give the column. Then copy each symbol into the grid.

B. Questions

The first twenty elements

Cut out the twenty cards. Lay them out so that each row and each column means something.

Teacher note: the finished grid is in the plan. Mass is the relative atomic mass.

Mendeleev’s gaps

In 1869 Dmitri Mendeleev laid out the 63 elements then known in order of atomic mass, starting a new row whenever an element with familiar behaviour came round again. Where the pattern called for an element nobody had found, he left a gap, and in 1871 he described three of the missing elements in detail. The one he called eka-silicon, below silicon, was found in 1886 and named germanium, and it matched his forecast closely. Students use the same idea: they estimate germanium from its neighbours, then compare their estimate with the forecast and the measured values. Mendeleev knew nothing of protons or electrons. His table worked because mass mostly rises with atomic number, and because he trusted families over mass when the two disagreed.

We are learning to

• use the patterns in the periodic table to predict the properties of an element,
• compare a prediction with measured values and judge how close it is,
• explain how successful predictions convinced other chemists that the table was right.

Success criteria

• I can estimate a property of germanium from its neighbours and compare it with the measured value.
• I can explain why leaving gaps made Mendeleev’s table more convincing, not less.

You need

• the worksheet (next sheet), one per student; calculators,
• the exit tickets (third sheet), cut into four.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the gap, the board and Part A in Session A, and Parts B and C and the ticket in Session B.

Watch for these ideas

• “Mendeleev just listed the elements by mass.” He broke the order of mass when families disagreed, and he left gaps.
• “A forecast that is a little off has failed.” What counts is a definite forecast made before anyone could check it, and how close it came.
• “Mendeleev used electrons to build his table.” The electron was found in 1897, almost 30 years later; shells explained his table afterwards.

Make it easier, make it bigger

• Easier: average only the two neighbours in the same column, silicon and tin, for each property.
• Bigger: gallium, Mendeleev’s eka-aluminium, melts at 29.8 °C. What would happen to a piece held in your hand?

Answers and look-fors

• Part A: 1. (28.1 + 69.7 + 74.9 + 118.7) ÷ 4 = 72.9. 2. (2.33 + 5.91 + 5.73 + 7.27) ÷ 4 = 5.31 g/cm³. 3. (57.6 + 114.1) ÷ 2 = 85.9 °C.
• Part B: our estimates from Part A; GeO₂ and GeCl₄, from silicon’s and tin’s oxide and chloride. Measured: mass 72.6, density 5.32 g/cm³, chloride boils at 86.5 °C.
• Part C: 1. Here the density (5.31 against 5.32) is closest, and every estimate is within 1% of the measured value. 2. He gave exact values before the element was found, and they could have been wrong; when germanium matched, the pattern was shown to be real. 3. They would have doubted his table: a pattern that makes risky forecasts can be tested, and could have failed.
• Exit ticket: 1. To keep elements that behave alike in the same column, leaving room for elements not yet found, whose properties he could then predict. 2. A careful measurement can still be wrong (the first sample was not pure); a strong pattern can show where to check again, and a better measurement settles it. 3. The family: argon goes before potassium, and tellurium before iodine, because of how they behave, which today we know follows the number of protons.
• Bigger: it melts in your hand, since body temperature is about 37 °C.

Mendeleev’s gaps

A. Estimate from the neighbours

Mendeleev estimated each missing element from the elements around its gap. Germanium’s neighbours on today’s table:

B. Forecast and measurement

C. Questions

Exit tickets

Reactive metals

The alkali metals of group 1 each have one outer electron, and they react by losing it. Down the group that electron sits in a shell further from the nucleus, with more inner shells in between, so it is held less tightly and lost more easily. Lithium fizzes steadily on water, sodium melts into a ball and races about, and potassium bursts into a lilac flame. Each makes hydrogen and an alkaline solution: 2Na + 2H₂O → 2NaOH + H₂. Group 2 shows the same trend more gently: magnesium barely reacts with cold water, while calcium, one shell further down, fizzes steadily. The group 1 metals are too reactive for students to handle, so they are shown on video; students test magnesium and calcium themselves.

We are learning to

• describe how the metals of groups 1 and 2 react with water,
• explain why reactivity increases down a group of metals, using the shells,
• describe a trend in a property from a graph.

Success criteria

• I can explain why potassium reacts with water faster than sodium.
• I can compare magnesium and calcium in water and link the difference to their places in group 2.

You need

• a short video of lithium, sodium and potassium added to water, from a reliable education source,
• for each group: two test tubes in a rack, water, universal indicator, 2 cm of clean magnesium ribbon, two or three calcium granules, safety glasses; no flames nearby,
• the worksheet (next sheet), one per student, and the class results sheet (third sheet), on the board or a bench.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the jar, the board, the video and Part A in Session A, and the test tubes, the graph and Part D in Session B.

Watch for these ideas

• “More protons pull the outer electron tighter.” The outer electron is further out, with more inner shells in between, so it is held less tightly.
• “The metal dissolves like sugar.” It reacts: new substances, hydrogen and a hydroxide, form.
• “The bubbles are air or steam.” They are hydrogen; with potassium the heat of the reaction sets the hydrogen alight.

Make it easier, make it bigger

• Easier: describe lithium together, then students look for what changes with sodium and potassium.
• Bigger: caesium is two places below potassium. Predict how it reacts with water, and what state it is in on a 30 °C day.

Answers and look-fors

• Part A: lithium floats and fizzes steadily; sodium melts into a ball, races over the surface and fizzes fast; potassium races about and bursts into a lilac flame. Each time the water turns alkaline.
• Part B: magnesium gives few or no bubbles in the time, and the indicator stays green or turns slightly blue; calcium fizzes steadily, the water turns cloudy, and the indicator turns blue to purple.
• Part C: Li 180.5 °C, Na 97.8 °C, K 63.5 °C, Rb 39.3 °C, Cs 28.5 °C; the melting point falls steadily down the group.
• Part D: 1. The reactions get faster and more violent down the group. 2. The outer electron is in a shell further from the nucleus, with more inner shells in between, so it is held less tightly and lost more easily. 3. Calcium reacted faster: it is below magnesium in group 2, so the same trend holds. 4. Lower than 28.5 °C, following the trend; nobody has collected enough francium to measure it.
• Bigger: even more violently than potassium; it melts at 28.5 °C, so on a 30 °C day it is a liquid.

Reactive metals

A. Group 1 on video

B. Magnesium and calcium in water

Safety glasses on. No flames. Add the metal to water with three drops of universal indicator, and watch for two minutes.

C. Melting points down group 1

D. Questions

Class results: magnesium and calcium in water

Each group adds what it saw. Write none, a few or many for the bubbles. Do all the groups agree on which metal reacts faster?

A group that disagrees is worth a closer look: was its magnesium ribbon clean, and its water cold?

Halogens and noble gases

At the right of the table sit two very different families. The halogens of group 17 have seven outer electrons and react by gaining one more. Down the group the outer shell is further from the nucleus, so it pulls in an extra electron less strongly: fluorine is the most reactive and iodine the least, the opposite of group 1. A more reactive halogen pushes a less reactive one out of its compounds, so chlorine water turns potassium bromide solution orange as bromine is set free. The noble gases of group 18 already have full outer shells, so they hardly react at all. In both groups the boiling point rises down the group, and the halogens change from gases to a liquid to a solid. Halogens are toxic, so the reactions are shown on video.

We are learning to

• describe and graph trends down groups 17 and 18,
• explain why halogens become less reactive down the group while alkali metals become more reactive,
• explain why the noble gases hardly react.

Success criteria

• I can predict which halogen will push out another, and explain why.
• I can use a graph to predict the boiling point of the next noble gas.

You need

• a short video of chlorine water, bromine water and iodine solution added to potassium chloride, bromide and iodide solutions,
• the family cards (third sheet), one set per pair, with scissors; the worksheet (next sheet), one per student; two coloured pencils each.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the families, the board and the graph in Session A, and the video, the cards and Part D in Session B.

Watch for these ideas

• “Every group gets more reactive going down.” Metals that lose electrons do; halogens, which gain one, get less reactive.
• “Noble gases never react.” They hardly react; chemists have made a few compounds of xenon and krypton.
• “Chlorine in pools is chlorine gas.” Pools use chlorine compounds dissolved in water; the gas itself is toxic.

Make it easier, make it bigger

• Easier: plot the halogens together, then students plot the noble gases on their own.
• Bigger: astatine comes below iodine. Predict its state at room temperature and whether iodine would push it out of its compounds.

Answers and look-fors

• Part A: halogens F₂ −188 °C, Cl₂ −34 °C, Br₂ 59 °C, I₂ 184 °C; noble gases He −269 °C, Ne −246 °C, Ar −186 °C, Kr −153 °C, Xe −108 °C. Both rise down the group; every noble gas and the first two halogens are below room temperature, so they are gases.
• Part B: chlorine water with potassium bromide: colour change; chlorine water with potassium iodide: colour change; bromine water with potassium chloride: no change; bromine water with potassium iodide: colour change; iodine solution with potassium chloride: no change; iodine solution with potassium bromide: no change. Chlorine pushes out bromine and iodine, and bromine pushes out iodine.
• Part C: group 1 C, E, G, H, J; group 17 B, I, K, L; group 18 A, D, F.
• Part D: 1. Chlorine is more reactive: its outer shell is closer to the nucleus, so it pulls in an extra electron more strongly and takes it from the bromide. 2. Their outer shells are already full, so they have no need to gain or lose electrons. 3. About −60 °C following the trend; radon boils at −62 °C.
• Bigger: a solid, darker than iodine; iodine is more reactive, so it would push astatine out.

Halogens and noble gases

A. Boiling points down two groups

Plot each group in its own colour against the period. The halogens run from period 2 to 5, the noble gases from period 1 to 5.

B. Which halogen wins?

From the video: write colour change or no change.

C. Sort the family cards

D. Questions

Which family?

Cut out the three headings and the twelve cards. Sort each card under the family it describes.

Teacher note: the answer letters are in the plan. The three piles are different sizes.

Across a period

Walk along period 3 and every step adds a proton to the nucleus and an electron to the same outer shell. The growing charge pulls that shell in tighter, so the atoms shrink from sodium (186 pm) to chlorine (99 pm), and it takes more and more energy to pull an outer electron away: the first ionisation energy roughly triples from sodium (496 kJ/mol) to argon (1 521 kJ/mol). Along the way the elements change from metals (sodium, magnesium, aluminium) through a metalloid (silicon) to non-metals, ending with the noble gas argon. The ionisation energy graph has two small dips, at aluminium and at sulfur. They are real anomalies, measured again and again, and a finer structure inside each shell explains them in senior chemistry.

We are learning to

• graph and describe the trends in atomic radius and ionisation energy across a period,
• explain the trends with the charge on the nucleus and the shells,
• pick out anomalies in a data set and describe them honestly.

Success criteria

• I can explain why atoms get smaller across period 3.
• I can point to the two anomalies on my graph and describe them.

You need

• the worksheet (next sheet), one per student; rulers and a coloured pencil,
• the exit tickets (third sheet), cut into four.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the question, the board and the graph in Session A, and Part C and the ticket in Session B.

Watch for these ideas

• “More electrons make a bigger atom.” Across a period the extra electrons join the same shell, and the extra protons pull it in.
• “An anomaly means the data are wrong.” A measured anomaly that repeats is real: it points to something the simple model leaves out.
• “Ionisation energy is the energy an atom has.” It is the energy needed to remove its outermost electron.

Make it easier, make it bigger

• Easier: plot the first three points together, and describe the radius trend aloud before anyone writes.
• Bigger: use the shells to explain why sodium loses an electron so easily in reactions, while argon does not react at all.

Answers and look-fors

• Part A: the radius falls steadily, from 186 pm for sodium to 99 pm for chlorine.
• Part B: Na 496, Mg 738, Al 578, Si 787, P 1 012, S 1 000, Cl 1 251, Ar 1 521 kJ/mol: rising overall, with dips at Al and S.
• Part C: 1. Each step adds a proton, so the nucleus pulls harder on the same outer shell and draws it in. 2. It rises: the outer electrons are closer to a more strongly charged nucleus, so they are harder to remove. 3. At aluminium and at sulfur the value drops below the one before; the dips are repeatable, so they are real, and the simple shell model does not explain them. 4. Between aluminium and silicon: sodium to aluminium are metals, silicon is a metalloid, and phosphorus to chlorine are non-metals.
• Exit ticket: 1. Magnesium: both use three shells, but sulfur’s 16 protons pull its shells in more than magnesium’s 12. 2. Chlorine. 3. The dips appear every time the values are measured, so they are real; they show where the simple model needs more detail.
• Bigger: sodium’s single outer electron is far out and loosely held; argon’s full outer shell is held tightly and complete.

Across a period

A. Period 3

1 pm (picometre) is a millionth of a millionth of a metre. Argon forms no bonds, so its radius is not measured the same way.

B. Graph the ionisation energy

C. Questions

Exit tickets

Metals and non-metals

Most elements are metals: shiny, good conductors of heat and electricity, and able to bend or be hammered into shape. They fill the left and the middle of the table. The non-metals, on the right, are mostly dull, brittle solids or gases that do not conduct. Between them, along a staircase that runs from boron down to tellurium, sit the metalloids, such as silicon and germanium: shiny but brittle, and conducting a little, more when warm. That is why silicon makes computer chips: how well it conducts can be controlled. Students test eight elements, then sort twelve element cards by their properties. One sample breaks the pattern: carbon, as graphite, conducts, yet carbon is a non-metal, so no single test decides.

We are learning to

• describe the properties of metals, non-metals and metalloids,
• classify an element from the results of several tests,
• explain why one property alone is not enough to classify an element.

Success criteria

• I can classify eight elements from my test results and say where they sit on the table.
• I can explain why graphite does not make carbon a metal.

You need

• for each group: copper wire, aluminium foil, an iron nail, a zinc strip, magnesium ribbon, a pencil lead, a lump of sulfur on a watch glass, a lump of silicon if the prep room has one; tongs; a conductivity tester made of a battery, a bulb or LED and leads with clips,
• the element property cards (third sheet), one set per pair, with scissors; the worksheet (next sheet), one per student.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the question, the board and the tests in Session A, and the cards and Part C in Session B.

Watch for these ideas

• “Shiny means metal.” Silicon and iodine are shiny, and neither is a metal; test several properties.
• “Metals are all hard.” Sodium and potassium can be cut with a knife, and mercury is a liquid.
• “Non-metals never conduct.” Graphite, a form of carbon, conducts well; one property alone does not decide.

Make it easier, make it bigger

• Easier: test the copper and the sulfur together first, so students see a clear metal and a clear non-metal side by side.
• Bigger: the metalloids sit on a staircase between the metals and the non-metals. Why does it make sense for mixed properties to sit there?

Answers and look-fors

• Part A: copper wire: shiny, conducts, bends, metal; aluminium foil: shiny, conducts, bends, metal; iron nail: shiny, conducts, bends a little, metal; zinc strip: shiny, conducts, bends, metal; magnesium ribbon: shiny, conducts, bends, metal; carbon (pencil lead): grey, conducts, snaps, non-metal; sulfur lump: dull, does not conduct, crumbles, non-metal; silicon lump: shiny, conducts very little or not at all, brittle, metalloid.
• Part B: metal A, D, E, G, H; non-metal B, I, J, L; metalloid C, F, K.
• Part C: 1. Graphite conducts, but it is brittle, and carbon’s other properties and its reactions are those of a non-metal; a single test cannot decide. 2. On a staircase between the metals and the non-metals, such as boron, silicon and germanium. 3. It conducts a little, and chip makers can control exactly how much by adding tiny amounts of other elements.
• Bigger: properties change gradually along a period, so the elements where metal behaviour gives way to non-metal behaviour have some of each.

Metals and non-metals

A. Test the elements

Use tongs. Press the sulfur and the silicon gently with a spatula; do not try to bend them. Wash your hands afterwards.

B. Sort the property cards

C. Questions

Metal, non-metal or metalloid?

Cut out the three headings and the twelve cards. Sort each element by the properties on its card.

Teacher note: the answer letters are in the plan. The three piles are different sizes.

Show what we know

The term comes together. In the task, students meet group 2. They are given the atomic radius, the first ionisation energy and the reaction with cold water for beryllium, magnesium, calcium and barium, and they predict all three for strontium from its neighbours and the trends, explaining each with the shells. Then they identify a mystery element from its number of protons and its properties. After the task they sit the eight-question final check, and the class plays the unit quiz as a game on the board.

We are learning to

• use the structure of atoms to explain trends down a group,
• predict the properties of an element from its place in the table,
• identify an element from its structure and properties.

Success criteria

• I can predict strontium’s properties and explain my predictions with the shells.
• I can answer the final check on my own.

You need

• the task (next sheet) and the final check (third sheet), one each per student; calculators,
• the interactive unit open on the board for the quiz; mini whiteboards if you have them.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the warm-up and the task in Session A, and the final check and the quiz in Session B.

Watch for these ideas

• Students who average without a reason: the average is a fair start, but they should say why strontium sits between calcium and barium.
• Students who write strontium as 2, 8, 8, 2: that is calcium; beyond calcium the shells hold more, and the task needs only the outer shell.
• Students who expect group 2 to get less reactive down the group, like the halogens: these metals lose electrons, as group 1 does.

Make it easier, make it bigger

• Easier: give strontium’s period and group, so students can spend their time on the predictions.
• Bigger: radium sits below barium. Predict its reaction with cold water, and its ionisation energy compared with barium’s.

Answers and look-fors

• Task: 1. Radius about (197 + 222) ÷ 2 ≈ 210 pm (measured 215 pm); ionisation energy about (590 + 503) ÷ 2 ≈ 547 kJ/mol (measured 550 kJ/mol); it reacts with cold water faster than calcium and more slowly than barium. 2. Down the group each atom has one more shell, so the outer electrons are further from the nucleus, with more shells in between; they are held less tightly, so less energy removes them. 3. Period 5, group 2. 4. 2, 8, 4: period 3, group 14. 5. A metalloid: shiny but brittle, and it conducts a little. 6. Silicon.
• Final check: 1. the neutron. 2. 14 neutrons and 13 electrons. 3. the same number of outer electrons. 4. 2, 8, 5: period 3, group 15. 5. To keep elements that behave alike in the same column, leaving room for elements not yet found, whose properties he could then predict. 6. they get smaller. 7. Potassium’s outer electron is in its fourth shell, further from the nucleus with more shells in between, so it is held less tightly and lost more easily. 8. A metalloid: it conducts a little, which a non-metal would not, but it is brittle, which a metal would not be.
• Bigger: even faster than barium; a lower ionisation energy than barium’s, since its outer electrons are another shell further out.
• Mark the task against the rubric in the assessment kit; the check covers the atom, shells, the table and trends.

Group 2, and a mystery element

Part 1. The missing member

Here are five members of group 2. Strontium’s values have been left out.

Part 2. The mystery element

Element Q has 14 protons. It is a shiny grey solid that shatters when struck, and it conducts electricity a little, more when it is warm.

Show what we know