Chemistry | Kumaran Kumarathurai

Elements and the periodic table

The main groups of the periodic table and the first 20 elements.

Alkali metals

Group 1 – soft, highly reactive metals such as sodium and potassium that react violently with water.

Alkaline earth metals

Group 2 – reactive metals such as magnesium and calcium, less violent than the alkali metals.

Transition metals

Groups 3-12 – hard, conductive metals such as iron, copper and gold, often with several oxidation states.

Halogens

Group 17 – highly reactive non-metals such as fluorine, chlorine and iodine that readily form salts.

Noble gases

Group 18 – stable, largely inert gases such as helium and neon with a full outer electron shell.

Non-metals

Elements such as carbon, nitrogen and oxygen that typically form covalent bonds and are essential to life.

The first 20 elements

Symbol	Name	Atomic number	Atomic mass (u)
H	Hydrogen	1	1.008
He	Helium	2	4.003
Li	Lithium	3	6.94
Be	Beryllium	4	9.012
B	Boron	5	10.81
C	Carbon	6	12.011
N	Nitrogen	7	14.007
O	Oxygen	8	15.999
F	Fluorine	9	18.998
Ne	Neon	10	20.180
Na	Sodium	11	22.990
Mg	Magnesium	12	24.305
Al	Aluminium	13	26.982
Si	Silicon	14	28.085
P	Phosphorus	15	30.974
S	Sulfur	16	32.06
Cl	Chlorine	17	35.45
Ar	Argon	18	39.948
K	Potassium	19	39.098
Ca	Calcium	20	40.078

Chemical notation

Symbols and abbreviations found in chemical equations.

States of matter

(s)

Solid

(l)

Liquid

(g)

Gas

(aq)

Aqueous (dissolved in water)

Common ions

H⁺

Hydrogen ion

Acids release H⁺ ions

OH⁻

Hydroxide ion

Bases release OH⁻ ions

Na⁺

Sodium ion

Cl⁻

Chloride ion

SO₄²⁻

Sulfate ion

NO₃⁻

Nitrate ion

NH₄⁺

Ammonium ion

Reaction notation

→

Yields

Shows the direction of the reaction

⇌

Equilibrium

The reaction can go both ways

Δ

Heating

Indicates the reaction requires heat

↓

Precipitate

A solid forms out of the solution

↑

Gas evolved

A gas is released by the reaction

Basic formulas

Central calculations for amount of substance, concentration and gases.

Name	Formula
Amount of substance	n = m / M
Concentration	c = n / V
Ideal gas law	p · V = n · R · T
pH value	pH = −log[H⁺]
Density	ρ = m / V
Mass fraction of solution	w% = (mₛ₠₡₢₠₡ / mₜ₠ₜ₊₋) · 100%

History of chemistry

From ancient alchemy to modern quantum chemistry.

Antiquity – Middle Ages

Alchemy

Alchemists in Egypt, China and the Arab world experiment with substances in the pursuit of gold and immortality, developing early laboratory techniques.

1661

Robert Boyle

Boyle publishes "The Sceptical Chymist" and introduces the modern notion of an element as a pure substance that cannot be broken down further.

1789

Lavoisier's law of conservation

Antoine Lavoisier formulates the law of conservation of mass and, with his systematic naming, lays the foundation for modern chemistry.

1803

Dalton's atomic theory

John Dalton proposes that matter is made of indivisible atoms, and that elements differ by the weight of their atoms.

1869

Mendeleev's periodic table

Dmitri Mendeleev arranges the elements by their properties and correctly predicts the existence of elements not yet discovered.

Around 1900

Radioactivity

Marie and Pierre Curie discover radioactive elements such as radium and polonium, paving the way for nuclear and radiation chemistry.

1900s–today

Quantum chemistry and modern chemistry

The development of quantum mechanics explains atoms' electron structure, and modern chemistry today spans materials science to drug development.

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🧪 Chemistry