The Periodic Table, Grade 7: Atomic Number, Groups, Metals and Non-Metals
Six elements on the table in front of your Grade 7 class do not have names. They have placeholders: Uut, Uuq, Uup, Uuh, Uus and Uuo.
They were all named in 2016. Elements 113 to 118 are nihonium, flerovium, moscovium, livermorium, tennessine and oganesson, and every current table prints them that way.
We checked our own wall chart before writing this. Period 7 on it reads Nh, Fl, Mc, Lv, Ts and Og, and it says 118 confirmed elements. So the chart on the wall is right and the table on the desk is out of date, which is an unusually satisfying thing to be able to tell a class.
The six elements that changed their names
| Number | Old placeholder | Name now | Symbol | Named after |
|---|---|---|---|---|
| 113 | Uut | Nihonium | Nh | Nihon, Japan. The first element named in Asia |
| 114 | Uuq | Flerovium | Fl | Georgy Flerov, a Soviet physicist |
| 115 | Uup | Moscovium | Mc | The Moscow region |
| 116 | Uuh | Livermorium | Lv | Livermore, in California |
| 117 | Uus | Tennessine | Ts | Tennessee. It ends in -ine because it sits in the halogen group |
| 118 | Uuo | Oganesson | Og | Yuri Oganessian, one of only two people ever to have an element named after them while still alive |
The placeholders were never names. Un-un-tri-um is just Latin for one-one-three with an ending stuck on it, a holding label used until a discovery is confirmed and the discoverers get to choose. All six were confirmed and named in 2016, which makes this the easiest correction in the grade and the most satisfying to explain.
Where this fits in the curriculum
| Subject | Natural Sciences |
|---|---|
| Grade | 7 |
| Term | 2 |
| Strand | Matter and Materials |
| Topic | The Periodic Table of Elements |
| Status | Class activities. Nothing here is formally assessed |
| Marks | The topic revision is 20. Our worksheet is 40 |
Reading one block on the table
Every element sits in its own block with two numbers, and a Grade 7 only needs to be sure which is which.
| What it is | Where it sits | What it means |
|---|---|---|
| Atomic number | The smaller number | How many protons the atom has. It is what makes the element that element, and it is what the table is sorted by |
| The bigger number | Usually below the symbol | How heavy the atom is compared with other atoms |
One thing to watch if you teach across grades. You will see the larger number called the mass number. It is really the relative atomic mass, which is an average across the forms an element comes in, and that is why so many of them are not whole numbers.
Mass number belongs to a single atom and is always a whole number. A Grade 7 does not need the distinction, but a learner who memorises the wrong word here has to unlearn it in Grade 10.
Groups and periods: the two directions
- A group is a column, read downwards. Elements in a group behave alike, which is the whole reason the table is shaped this way
- A period is a row, read across. Atomic number goes up by one with every step to the right
The quickest way to prove the table is doing something real: look down group 1 and you get lithium, sodium and potassium, three soft metals that all fizz in water and get more violent as you go down. Look down group 18 and you get helium, neon and argon, which react with almost nothing at all. That pattern is what Mendeleev spotted, and he left gaps for elements nobody had found yet.
The first period is the odd one. It has only hydrogen and helium in it, which catches learners out on any question that asks what else shares a period with helium.
Metals, non-metals and semimetals
| Metals | Non-metals | Semimetals | |
|---|---|---|---|
| Look | Shiny | Dull | Shiny, but brittle |
| Electricity | Conduct well | Do not conduct | Conduct a little, which is the useful bit |
| Heat | Conduct well | Do not | In between |
| Hit it | Bends and flattens | Shatters | Shatters |
| At room temperature | Solid, except mercury | Solids, liquids and gases | Solid |
There are only six semimetals worth knowing: boron, silicon, germanium, arsenic, antimony and tellurium, and they run in a staircase down the right-hand side between the metals and the non-metals. Silicon is by far the most common, and being halfway between a conductor and an insulator is exactly what makes a computer chip possible.
The two exceptions that are worth more than the rule.
Graphite conducts electricity, and it is a non-metal. It is carbon, it is in every pencil in the room, and a class can test it in thirty seconds.
Diamond has one of the highest melting points of any substance known. Also carbon. Same element as the graphite, arranged differently.
Carbon breaking two of the non-metal rules at once, in two forms a learner has heard of, teaches the idea better than the table does.
The heating step that cannot work, and can break your test tubes
You will see an instruction to compare iron, aluminium and copper by heating each one in a test tube to see whether it melts easily.
None of them will melt. The test tube will go first.
What is being heated Melts or softens at Soda glass test tube Softens around 700 °C Borosilicate test tube Softens around 820 °C Aluminium 660 °C Copper 1 085 °C Iron 1 538 °C A school burner will not reach copper or iron at all. Aluminium is the dangerous one: it sits below the softening point of glass, so if the flame is hot enough you get molten aluminium in a sagging tube.
What to do instead. Compare published melting points as a reading exercise, and if you want the class to actually watch something melt, use solder or candle wax. Both melt well under 250 °C and neither will cost you a tube.
The other three parts of that comparison are all fine. Shine, the magnet test and the conductivity circuit all work exactly as set, and they are the parts worth the lesson time.
The conductivity circuit, which is the part that works
- Build a simple circuit: a cell, a bulb and two leads, with a gap left in it
- Bridge the gap with the sample, holding a crocodile clip on each end
- Bulb lights, it conducts. Bulb stays dark, it does not
- Test a pencil lead as well as the metals. That is the graphite, and the bulb will light
The magnet test is worth doing in the same round. Iron is attracted, aluminium and copper are not, and it is the fastest way to show that "metal" and "magnetic" are not the same word.
Pictures that are not elements
In the metals-against-non-metals comparison you will see dull illustrated with cardboard boxes, brittle with a broken wine glass, and liquid with a flask of coloured solution.
None of those is an element, and in a topic about the Periodic Table that matters. Cardboard is not on the table. Glass is not on the table.
Turn it into the exercise it should have been: ask the class to name a real element for each property. Dull, sulfur. Brittle, sulfur again. Liquid at room temperature, bromine or mercury, and only those two. It takes three minutes and it is a better question than the one printed.
Optical fibres are not made of silicon
You will see optical fibres described as thin tubes of glass made from silicon and germanium. There are three separate mistakes in that.
What it says What is actually true Made from silicon Made from silica, which is silicon dioxide. Silicon on its own is a grey, opaque, metallic-looking solid. You cannot see through it Made from germanium Germanium dioxide is added in tiny amounts to the core to bend light a little more strongly than the outer layer does. That difference is what keeps the light inside A tube A solid strand, with a core down the middle and a cladding around it. Nothing is hollow The reason given for fibre cables being light is also wrong. They are light because each strand is about the thickness of a human hair, not because silicon is a light element.
Three statements about elements that are not true
| The claim | What is actually the case |
|---|---|
| "Stainless steel does not rust" | It resists rust. Chromium forms an invisible oxide film over the surface that heals itself when scratched. Break that film and keep it broken, and stainless steel rusts. Salt water does it. Leave a cheap stainless blade in seawater for a week and look |
| "Gold and silver do not corrode" | Gold does not. Silver does. That black film on old silver is tarnish, which is silver sulfide, and tarnishing is corrosion. It comes from tiny amounts of sulfur compounds in the air |
| "Chlorine, in the form of an acid, cleans swimming pools" | Pool chlorine is a salt, not an acid. It is usually a hypochlorite or a chlorinated isocyanurate. Pool acid is a completely separate product, usually hydrochloric acid, and its job is to bring the pH down, not to sanitise |
The pool one is worth getting right for a reason that has nothing to do with marks.
Mixing pool acid with pool chlorine releases chlorine gas. Almost every house with a pool has both containers standing in the same store room, and a learner who has been taught that the chlorine is the acid has been given exactly the wrong idea about two things that must never be poured together.
It is thirty seconds of a lesson and it is the part a class should take home.
Three elements that surprise a class
| Element | Melts at | Why it is worth a minute |
|---|---|---|
| Mercury | -39 °C | The one metal that is liquid in the classroom |
| Caesium | 28,5 °C | A metal that melts on a hot Highveld day |
| Gallium | 29,8 °C | A metal that melts in your hand. Body heat is enough |
Sodium melts at 98 °C, which is below the boiling point of water. "Metals melt at high temperatures" is a habit, not a rule, and three counter-examples fix it faster than any definition.
One spelling that costs marks
The element is phosphorus. Phosphorous is an adjective, and it turns up misspelt often enough to be worth saying out loud once.
Same trap as sulfur, which is the spelling used in South African curriculum material and on our charts, although sulphur is still common in older books.
If it does not work
| Problem | Cause | Fix |
|---|---|---|
| The metal will not melt in the test tube | It never will. The tube softens first | Do not run that step. Compare published melting points, and melt solder or wax if you want it visible |
| A learner says elements 113 to 118 have no names | The table in front of them is out of date | Show them the wall chart. Period 7 ends Nh, Fl, Mc, Lv, Ts, Og |
| The bulb will not light on any sample | The circuit itself is broken | Touch the two crocodile clips together first. If the bulb does not light then, the fault is the circuit, not the sample |
| Graphite lights the bulb and the class says the test failed | Nothing. Graphite really does conduct | That is the result. It is the exception worth teaching |
| Aluminium is not attracted to the magnet and a learner calls it a non-metal | Magnetic and metallic are being treated as the same thing | Only a few metals are magnetic. Most are not |
| The relative atomic masses are not whole numbers | They are averages across the forms of the element | Correct as printed. Round them for Grade 7 work |
The table itself
If you came here for the Periodic Table rather than the lesson, the two we stock are the A1 Periodic Table wall chart at R85 and the large format poster at R700. Both are current: period 7 ends Nh, Fl, Mc, Lv, Ts, Og, and both state 118 confirmed elements.
We checked the actual product before saying so, rather than taking the supplier's word for it, because a table is the one thing in a science classroom that quietly goes out of date while hanging on the wall.
How the 40 marks are made up
| Part | Marks |
|---|---|
| Reading the table: atomic number, groups and periods | 10 |
| The six elements that were renamed | 6 |
| Metals, non-metals and semimetals | 10 |
| The heating step, and why it cannot work | 6 |
| Elements in everyday life, and the claims that fail | 8 |
Nothing in this topic is formally assessed. The topic revision is 20 marks and it adds up correctly. Our worksheet is 40 and the split above is ours.
Free worksheet and marking memo
Both free, no sign up, straight to the PDF.
- Learner worksheet, 40 marks, including the renaming table and the melting point comparison
- Marking memorandum, with what to accept and the five answers that look right and score nothing
Related practicals
- Atoms, Elements, Compounds and Mixtures, Grade 8. Where this goes next year
- Properties of Materials, Grade 7. Melting point and conductivity, same term
- Separating Mixtures, Grade 7. Elements and compounds put to work
What you need to run it
| Item | Price | What it is for |
|---|---|---|
| Periodic Table wall chart, A1 | R85 | The one thing this topic needs. Current, with all 118 |
| Periodic Table, large format poster | R700 | For a lab or a corridor, readable from the back |
| AA battery holder with leads | R6,50 | The conductivity circuit |
| Bulb, MES E10 | R20,64 | The thing that lights up |
| Crocodile leads, pack of 10 | R58 | Five circuits from one pack |
| Alnico bar magnets with keeper | R500 | The magnet test. One pair does a whole class |
| Test tubes, borosilicate | R4 | For the tests that are not the heating one |
| Test tube holder, wire | R35 | Never hold a hot tube in your fingers |
| Safety goggles | R30 | Anything involving a flame |
The honest version of this topic is that it needs one purchase. A circuit for the conductivity test is about R90 worth of parts that most schools already own, the magnets last forever, and the rest is reading. What a Grade 7 class actually needs is a table on the wall that is not six elements out of date.
The charts are in educational wall charts, and the electrical parts are in physical sciences.