Chemistry
🔒 Log in to trackPeriodic table, elements and record-holders
🔒 Log in to trackThe periodic table arranges all elements in order of atomic number. Its columns are groups and its rows are periods. Elements in one group behave alike, and properties change in a steady way across a period and down a group. Exams also ask fixed record-holders and Latin-name symbols.
How the table grew
Chemists needed a map for the elements they kept finding. Four names matter.
| Scientist | Idea |
|---|---|
| Döbereiner | Triads, such as Li, Na, K |
| Newlands | Law of octaves: every 8th element is similar |
| Mendeleev | Table built on atomic mass, with gaps left for unknown elements |
| Moseley | Modern periodic law: properties depend on atomic number |
Mendeleev predicted eka-aluminium and eka-silicon. They turned out to be gallium and germanium.
Watch: Mendeleev used atomic mass. Moseley used atomic number.
Reading the modern table
The modern table has 18 groups (vertical) and 7 periods (horizontal). It names 118 elements. Elements in one group have the same number of outer electrons, so they behave alike.
| Region | Members |
|---|---|
| Group 1 | Alkali metals: Li, Na, K. Very reactive. |
| Group 2 | Alkaline earth metals: Be, Mg, Ca |
| Groups 3-12 | Transition metals: Fe, Cu, Zn, Ag, Au |
| Group 17 | Halogens: F, Cl, Br, I |
| Group 18 | Noble gases: He, Ne, Ar, Kr, Xe, Rn |
| Two bottom rows | Lanthanides and actinides |
Noble gases have full outer shells. This is why they are inert.
Trends in the table
- Across a period (left to right): atomic size falls. Metallic character falls. Electronegativity (pull on electrons) rises.
- Down a group (top to bottom): atomic size rises. Metallic character rises. Metals get more reactive, so K is wilder than Na.
Sodium is a metal. Chlorine, at the far right, is a non-metal. Fluorine is the most electronegative element.
Tip: Picture the table. Reactive non-metals sit at the top right. Reactive metals sit at the bottom left.
Record-holders
| Record | Answer |
|---|---|
| Most abundant in the universe | Hydrogen |
| Most abundant in Earth's crust | Oxygen, then silicon |
| Most abundant metal in the crust | Aluminium, then iron |
| Most abundant gas in air | Nitrogen (about 78%) |
| Most abundant in the human body | Oxygen (top metal: calcium) |
| Lightest element / lightest metal | Hydrogen / Lithium |
| Liquid metal / liquid non-metal | Mercury / Bromine |
| Metal that melts in the palm | Gallium (about 30 °C) |
| Hardest natural substance | Diamond |
| Softest mineral | Talc |
| Best metal conductor | Silver |
| Most ductile and malleable metal | Gold |
| Highest melting point metal | Tungsten |
| Densest natural element | Osmium |
| First man-made element | Technetium |
| Non-metal that conducts | Graphite |
The crust order is OSAIC: Oxygen, Silicon, Aluminium, Iron, Calcium.
Symbols from Latin names
Some symbols come from Latin names. They are common exam traps.
| Symbol | Latin name | Element |
|---|---|---|
| Na | natrium | Sodium |
| K | kalium | Potassium |
| Fe | ferrum | Iron |
| Cu | cuprum | Copper |
| Ag | argentum | Silver |
| Au | aurum | Gold |
| Pb | plumbum | Lead |
| Sn | stannum | Tin |
| Hg | hydrargyrum | Mercury |
| Sb | stibium | Antimony |
| W | wolfram | Tungsten |
Watch: The symbol for sodium is Na, never So.
Noble gases and metalloids
- Helium: balloons, airships and deep-sea diver breathing mixes.
- Neon: advertising signs with an orange-red glow.
- Argon: filled inside electric bulbs.
- Xenon: flash lamps. Radon is radioactive.
- Metalloids: boron, silicon, germanium, arsenic, antimony, tellurium.
Question types you will see
Each type: how to recognise it, the method step by step, and one question to try.
Element record-holders
The question says 'most abundant', 'lightest metal', 'only liquid metal', 'hardest natural substance' or 'first man-made element'.
Match the phrase to the record table.
Abundance chain: H (universe), O (crust), Al (crust metal), N (air), O (body).
Oddities: Li lightest metal, Hg liquid metal, Br liquid non-metal, graphite conducts.
In odd-one-out questions, check the records first.
These records are fixed facts, so recall is the only route.
The most abundant metal in the Earth's crust is which?
Show solutionHide solution
Oxygen is the top element but not a metal.
Aluminium (about 8%) comes before iron.
Aluminium
Symbols from Latin names
A list of symbol and element pairs is given, and you must find the wrong pair.
Learn the eleven Latin symbols.
Check each pair against the Latin name.
The wrong pair is almost always one of these eleven.
Other symbols follow the English name (He, Ca, Zn).
The Latin names explain symbols that do not match the English name.
Which pair is wrong? (a) Fe-Iron (b) Au-Gold (c) Ag-Silver (d) So-Sodium
Show solutionHide solution
Sodium comes from natrium.
Its symbol is Na.
(d)
History of classification
The question asks who gave the law of octaves, what Mendeleev's table was based on, or what eka-silicon is now called.
Recall the chain: Döbereiner, Newlands, Mendeleev, Moseley.
Mendeleev used atomic mass and left gaps.
Eka-aluminium became gallium. Eka-silicon became germanium.
Modern periods follow atomic number.
Each step fixed a weakness in the one before it.
Mendeleev's eka-silicon is today's which element?
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Mendeleev left a gap under silicon.
The element found later fits that gap.
Germanium
Groups, periods and trends
The question asks how size or metallic character changes across a period or down a group, or how many groups exist.
Remember the fixed numbers: 18 groups, 7 periods, 118 elements.
Across a period: size and metallic character fall.
Down a group: size and metallic character rise.
Most reactive non-metal is F. Most reactive metals are at the bottom left.
More shells down a group put the outer electrons farther away, so they leave easily.
Moving down a group, what happens to metallic character?
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Outer electrons are farther from the nucleus.
They are lost more easily, so K is more reactive than Na.
It increases
Group families (alkali, halogens, noble gases)
The question asks which group holds halogens or noble gases, why group 18 is inert, or which metal is kept in kerosene.
Group 1 is alkali: Li, Na, K. They are soft, reactive and kept in kerosene.
Group 17 is halogens: F, Cl, Br, I.
Group 18 is noble gases with full outer shells.
Helium is first in group 18. Radon is radioactive.
A full outer shell means the atom has no need to give, take or share electrons.
Why are noble gases chemically inert?
Show solutionHide solution
Look at the outer shell.
It is already complete.
Their outer shells are full, so they do not give, take or share electrons easily
Shortcuts that save time
Oxygen, Silicon, Aluminium, Iron, Calcium. So the top element is O and the top metal is Al.
Which is the most abundant metal in the Earth's crust?
Show solutionHide solution
Read OSAIC and skip the non-metals O and Si.
The first metal is aluminium.
Aluminium
Mercury is the liquid metal. Bromine is the liquid non-metal. Gallium and caesium melt just above room temperature.
Mistakes to avoid
Where most students lose marks on this subtopic.
Saying Mendeleev's table used atomic number.
Mendeleev used atomic mass. Moseley used atomic number.
Naming iron as the most abundant metal in the crust.
It is aluminium. Iron comes second.
Naming oxygen as the most abundant gas in air.
It is nitrogen, about 78%. Oxygen is about 21%.
Writing the symbol of sodium as So.
Use the Latin name: natrium gives Na.
Thinking size grows across a period.
Size falls left to right and rises down a group.
Quick revision
Read this the night before the exam.
Döbereiner triads, Newlands octaves, Mendeleev atomic mass, Moseley atomic number.
18 groups, 7 periods, 118 elements.
Group 1 alkali, group 2 alkaline earth, group 17 halogens, group 18 noble gases.
Across a period size and metallic character fall. Down a group both rise.
Fluorine is the most electronegative element.
Hydrogen: universe. Oxygen: crust. Aluminium: crust metal. Nitrogen: air.
Li lightest metal, Hg liquid metal, Br liquid non-metal, Au most ductile, W highest melting point.
Practice: 16 questions
Sets of 10, mixed across the question types above. Every answer has a step-by-step explanation.
Topic test · 10 questions
Suggested time 3 min · wrong answers go to your mistake notebook automatically.