Chemistry
🔒 Log in to trackPeriodic table, elements and record-holders
🔒 Log in to trackHistory of classification
| Scientist | Contribution |
|---|---|
| Döbereiner | Triads (e.g. Li, Na, K) |
| Newlands | Law of octaves (every 8th element similar) |
| Mendeleev | Periodic table based on atomic mass; left gaps and predicted eka-aluminium (gallium), eka-silicon (germanium) |
| Moseley | Modern periodic law — properties depend on atomic number |
- The modern (long form) table has 18 groups (vertical) and 7 periods (horizontal); 118 named elements.
- Group 1 — alkali metals (Li, Na, K…); Group 2 — alkaline earth metals (Be, Mg, Ca…); Group 17 — halogens (F, Cl, Br, I); Group 18 — noble gases (He, Ne, Ar, Kr, Xe, Rn).
- Across a period (left → right): atomic size decreases, metallic character decreases, electronegativity increases. Down a group: size increases, metallic character increases.
- Fluorine is the most electronegative element.
Record-holders (static favourites)
| Record | Answer |
|---|---|
| Most abundant element in the universe | Hydrogen |
| Most abundant element in Earth's crust | Oxygen (then silicon) |
| Most abundant metal in Earth's crust | Aluminium (then iron) |
| Most abundant gas in the atmosphere | Nitrogen (about 78%), then oxygen (about 21%), then argon |
| Most abundant element in the human body | Oxygen (by mass) |
| Lightest element / lightest metal | Hydrogen / Lithium |
| Metal that is liquid at room temperature | Mercury (Bromine is the liquid non-metal) |
| Metal that melts in the palm | Gallium (about 30 °C) |
| Hardest natural substance | Diamond |
| Best conductor of electricity | Silver (then copper) |
| Most malleable and ductile metal | Gold |
| Metal with the highest melting point | Tungsten |
| Non-metal that conducts electricity | Graphite |
| Lustrous non-metal | Iodine |
Noble gases and their uses
- Helium — balloons and airships (light, non-inflammable), breathing mix for deep-sea divers.
- Neon — advertising signs (orange-red glow). Argon — filled in electric bulbs. Xenon — flash lamps. Radon — radioactive.
- Metalloids: boron, silicon, germanium, arsenic, antimony, tellurium.
Detailed notes
How the table grew
Chemists kept discovering elements, so they needed a map. Döbereiner noticed triads (Li–Na–K: the middle element's mass is the average of the other two). Newlands arranged elements by mass and found every 8th one similar — the law of octaves. Mendeleev made the real breakthrough: a table built on atomic mass, in which he left gaps and predicted unknown elements — his eka-aluminium turned out to be gallium and eka-silicon, germanium. Finally H.G.J. Moseley showed that properties depend on atomic number, not mass — the modern periodic law — and the modern table was born.
Reading the modern table
The modern (long-form) table has 18 vertical groups and 7 horizontal periods; 118 elements are named today. Elements in a group share outer-shell electrons (valency), so they behave alike.
| Region | Members |
|---|---|
| Group 1 | Alkali metals — Li, Na, K (very reactive, stored in kerosene) |
| 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 (salt-formers) |
| Group 18 | Noble (inert) gases — He, Ne, Ar, Kr, Xe, Rn |
| Two bottom rows | Lanthanides and Actinides (includes uranium) |
Trends — the two directions
- Across a period (left → right): atomic size decreases, metallic character decreases, electronegativity (pull on electrons) increases. Sodium is a metal; chlorine at the far right is a non-metal.
- Down a group (top → bottom): atomic size increases, metallic character increases, so reactivity of metals grows (K is wilder than Na).
- Fluorine is the most electronegative element; caesium is the most electropositive (reactive) stable metal.
Record-holders — the static-GK list
| Record | Answer |
|---|---|
| Most abundant element in the universe | Hydrogen |
| Most abundant element in Earth's crust | Oxygen (then silicon — 'OSAIC': O, Si, Al, Fe, Ca) |
| Most abundant metal in the crust | Aluminium (then iron) |
| Most abundant gas in the atmosphere | Nitrogen (≈ 78%) |
| Most abundant element in the human body | Oxygen (most abundant metal in body: calcium) |
| Lightest element / gas | Hydrogen |
| Lightest metal | Lithium |
| Only liquid metal at room temperature | Mercury (gallium melts in the palm, ~30 °C) |
| Only liquid non-metal | Bromine |
| Hardest natural substance | Diamond (an allotrope of carbon) |
| Softest mineral | Talc |
| Best conductor among metals | Silver (graphite conducts among non-metals) |
| Most ductile and malleable metal | Gold |
| Highest melting point metal | Tungsten (used as bulb filament) |
| Densest natural element | Osmium |
| First man-made element | Technetium |
| Non-metal that conducts electricity | Graphite |
Symbols from Latin names
Several chemical symbols come from Latin: 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. Exams love these mismatch traps — sodium is NOT 'So'.
Quick revision
- Döbereiner triads → Newlands octaves → Mendeleev (mass, gaps) → Moseley (atomic number).
- 18 groups, 7 periods, 118 elements; group 1 alkali, 2 alkaline earth, 17 halogens, 18 noble gases.
- Across period: size ↓, metal character ↓. Down group: size ↑, metal character ↑.
- Fluorine most electronegative; caesium most electropositive stable metal.
- Records: H–universe, O–crust, Al–crust metal, N–air, Ca–body metal; Li lightest metal; Hg liquid metal; Br liquid non-metal; Au most ductile; W highest melting point.
Types of questions asked
Every way this subtopic shows up in exams — how to recognise it, the formula or logic to use, and a solved example.
Type 1: Element record-holdersvery common5 practice Q
'Most abundant element/metal in the crust/body/universe', 'lightest metal', 'only liquid metal/non-metal', 'hardest natural substance', 'first man-made element'.
- Abundance chain: H (universe) → O (crust; then Si, Al, Fe) → Al (crust metal; then Fe) → N (air 78%) → O (body; Ca is the body's top metal).
- Oddities: Li lightest metal, Hg liquid metal, Br liquid non-metal, graphite conducts, Au most ductile, W highest melting point, technetium first man-made.
- In 'odd one out' questions, check for these records first.
Example: The most abundant metal in the Earth's crust is —
Aluminium (about 8%), ahead of iron. Oxygen is the most abundant element overall.
Type 2: Symbols from Latin namescommon2 practice Q
A wrong-symbol pair (Na–sodium, K–potassium, Fe–iron, Ag–silver, Au–gold, Pb–lead) is given and the mistake must be found.
- Memorise the Latin list: natrium–Na, kalium–K, ferrum–Fe, cuprum–Cu, argentum–Ag, aurum–Au, plumbum–Pb, stannum–Sn, hydrargyrum–Hg, stibium–Sb, wolfram–W.
- In 'wrong symbol' questions the answer is almost always one of these eleven.
- Others follow the English name (He, Ca, Zn…).
Example: Which symbol–element pair is wrong? (a) Fe–Iron (b) Au–Gold (c) Ag–Silver (d) So–Sodium
(d) — sodium's symbol is Na (Latin natrium), not 'So'.
Type 3: History of classificationcommon3 practice Q
'Law of octaves was given by…', 'Mendeleev's table was based on…', 'modern periodic law depends on…', 'eka-silicon is now called…'.
- Chain: Döbereiner triads → Newlands octaves → Mendeleev (atomic mass, gaps, predictions) → Moseley (atomic number = modern law).
- Mendeleev's predictions: eka-aluminium = gallium, eka-silicon = germanium.
- Periods run by increasing atomic number today, not mass.
Example: Mendeleev's eka-silicon is today's —
Germanium (eka-aluminium became gallium).
Type 4: Groups, periods and trendscommon2 practice Q
'Across a period atomic size…', 'down a group metallic character…', which group an element belongs to, number of groups/periods.
- Fixed numbers: 18 groups (vertical), 7 periods (horizontal), 118 elements.
- Across a period: size shrinks, metallic character falls, electronegativity rises; down a group: size grows, metallic character rises.
- Most reactive non-metal sits at the top-right (F); most reactive metals at the bottom-left (Cs, Fr).
Example: On moving down a group, the metallic character of elements —
Increases — outer electrons get farther from the nucleus and are lost more easily (K is more reactive than Na).
Type 5: Group families (alkali, halogens, noble gases)common2 practice Q
'Which group contains halogens/noble gases?', 'why are group 18 gases inert?', 'which metal is stored in kerosene?'.
- Group 1 alkali metals (Li, Na, K — soft, reactive, kerosene-stored); group 2 alkaline earth (Be, Mg, Ca).
- Group 17 halogens (F, Cl, Br, I — form salts, F most electronegative).
- Group 18 noble gases (He, Ne, Ar, Kr, Xe, Rn) have full outer shells, hence inert; He tops the list, Rn is radioactive.
Example: Noble gases are chemically inert because —
Their outermost electron shells are complete, so they neither give, take nor share electrons easily.
Shortcut tricks
⚡ Crust order: 'OSAIC' — Oxygen, Silicon, Aluminium, Iron, Calcium
So the most abundant element is O and the most abundant metal is Al.
Example: Most abundant metal in the Earth's crust?
Aluminium.
⚡ Two liquids at room temperature
Mercury — metal; Bromine — non-metal. Gallium and caesium melt just above room temperature.
Where students lose marks
Saying Mendeleev's table was based on atomic number — it used atomic mass; Moseley used atomic number.
Answering iron for the most abundant metal in the crust — it is aluminium.
Answering oxygen for the most abundant gas in air — it is nitrogen.
Practice sets — 16 questions
Sets of 10, mixed across the question types above. Each answer comes with a step-by-step explanation.
Topic test · 10 questions
Suggested time 3 min · wrong answers go to your mistake notebook automatically.