Chemistry
🔒 Log in to trackPeriodic table, elements and record-holders
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| 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.
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'.
Question types you will see
Each type: how to recognise it, the method step by step, and one question to try.
Element record-holders
'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.
The most abundant metal in the Earth's crust is —
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Aluminium (about 8%), ahead of iron. Oxygen is the most abundant element overall.
Symbols from Latin names
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…).
Which symbol–element pair is wrong? (a) Fe–Iron (b) Au–Gold (c) Ag–Silver (d) So–Sodium
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(d) — sodium's symbol is Na (Latin natrium), not 'So'.
History of classification
'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.
Mendeleev's eka-silicon is today's —
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Germanium (eka-aluminium became gallium).
Groups, periods and trends
'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).
On moving down a group, the metallic character of elements —
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Increases — outer electrons get farther from the nucleus and are lost more easily (K is more reactive than Na).
Group families (alkali, halogens, noble gases)
'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.
Noble gases are chemically inert because —
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Their outermost electron shells are complete, so they neither give, take nor share electrons easily.
Shortcuts that save time
So the most abundant element is O and the most abundant metal is Al.
Most abundant metal in the Earth's crust?
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Aluminium.
Mercury — metal; Bromine — 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 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.
Quick revision
Read this the night before the exam.
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.
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.