1. Basic Concepts of Chemistry

Chemistry is the branch of science that studies the composition, structure, properties and changes of matter.

• Physical Chemistry: Study of the physical principles governing chemical systems.
• Organic Chemistry: Study of carbon-containing compounds.
• Inorganic Chemistry: Study of elements and compounds other than most carbon-based compounds.
• Analytical Chemistry: Identification and measurement of chemical substances.
• Biochemistry: Study of chemical processes in living organisms.

2. Matter and Its States

Matter is anything that has mass and occupies space.

• Melting: Solid changes into liquid.
• Freezing: Liquid changes into solid.
• Vaporisation: Liquid changes into gas.
• Condensation: Gas changes into liquid.
• Sublimation: Solid changes directly into gas.
• Deposition: Gas changes directly into solid.

3. Atomic Structure

An atom consists of a central nucleus surrounded by electrons.

• Atomic number: Number of protons in the nucleus.
• Mass number: Total number of protons and neutrons.
• Isotopes: Atoms of the same element with the same atomic number but different mass numbers.
• Isobars: Atoms of different elements having the same mass number.
• Valency: Combining capacity of an atom.

4. Periodic Table

The modern periodic table arranges elements according to increasing atomic number.

• There are 7 periods and 18 groups in the modern periodic table.
• Group 1 elements are called alkali metals, except hydrogen.
• Group 2 elements are called alkaline earth metals.
• Group 17 elements are called halogens.
• Group 18 elements are called noble gases.
• Elements in the same group generally have similar valence-electron configurations.
• Metallic character generally increases down a group and decreases from left to right across a period.
• Atomic size generally decreases across a period and increases down a group.

5. Chemical Bonding

Chemical bonding is the force that holds atoms or ions together in a chemical substance.

• Ionic bond: Formed by transfer of electrons, usually between a metal and a non-metal.
• Covalent bond: Formed by sharing of electrons between atoms.
• Coordinate bond: A covalent bond in which both shared electrons are supplied by one atom.
• Metallic bond: Attraction between metal ions and delocalised electrons.
• Hydrogen bond: A relatively weak attraction involving hydrogen bonded to a highly electronegative atom.

6. Chemical Reactions

A chemical reaction is a process in which one or more substances are converted into new substances.

• Combination reaction: Two or more substances combine to form one product.
• Decomposition reaction: One compound breaks down into simpler substances.
• Displacement reaction: A more reactive element displaces a less reactive element.
• Double displacement reaction: Exchange of ions between two compounds.
• Redox reaction: Oxidation and reduction occur simultaneously.
• Oxidation: Commonly involves loss of electrons or addition of oxygen.
• Reduction: Commonly involves gain of electrons or removal of oxygen.

7. Acids, Bases and Salts

• Acids: Substances that donate hydrogen ions in aqueous solution according to the Brønsted–Lowry concept.
• Bases: Substances that accept hydrogen ions or produce hydroxide ions in aqueous solution, depending on the definition used.
• Neutralisation: Reaction between an acid and a base to form salt and usually water.
• pH scale: Commonly ranges from 0 to 14 for many aqueous solutions under ordinary conditions.
• pH below 7 is generally acidic, pH 7 is neutral at 25°C, and pH above 7 is generally basic.

8. Metals and Non-metals

• Metals are generally lustrous, malleable, ductile and good conductors of heat and electricity.
• Non-metals are generally poor conductors, although graphite is a notable exception.
• Mercury is a metal that is liquid at room temperature.
• Bromine is a non-metal that is liquid at room temperature.
• Metals generally form positive ions by losing electrons.
• Non-metals generally form negative ions or share electrons.
• Alloy: Mixture or solid solution containing a metal and one or more other elements.

9. Carbon and Its Compounds

Carbon forms a large number of compounds because of its tetravalency and ability to form chains and rings.

• Catenation: Ability of carbon atoms to bond with one another to form chains and rings.
• Tetravalency: Carbon generally forms four covalent bonds.
• Hydrocarbons: Compounds containing only carbon and hydrogen.
• Alkanes: Saturated hydrocarbons with single bonds.
• Alkenes: Hydrocarbons containing at least one carbon-carbon double bond.
• Alkynes: Hydrocarbons containing at least one carbon-carbon triple bond.
• Isomerism: Existence of compounds with the same molecular formula but different arrangements of atoms.

10. Solutions and Mixtures

• Solution: Homogeneous mixture of a solute and a solvent.
• Solute: Substance dissolved in a solvent.
• Solvent: Component that dissolves the solute.
• Suspension: Heterogeneous mixture containing particles that may settle down.
• Colloid: Mixture containing dispersed particles intermediate in size between those of a solution and a suspension.
• Solubility: Maximum amount of a substance that dissolves in a given amount of solvent under specified conditions.

11. Chemistry in Everyday Life

• Soap: Sodium or potassium salts of higher fatty acids.
• Detergents: Cleansing agents that work effectively in hard water as well as soft water, depending on their composition.
• Antiseptics: Substances applied to living tissues to reduce or prevent infection.
• Disinfectants: Substances used on non-living surfaces to destroy or reduce harmful microorganisms.
• Antacids: Substances used to neutralise excess stomach acid.
• Preservatives: Substances used to slow spoilage of food and other products.
• Fertilisers: Materials that supply essential nutrients to plants.
• Polymers: Large molecules made from repeating structural units called monomers.

12. Fuels and Combustion

• Fuel: Substance that releases usable energy through a chemical or nuclear process.
• Combustion: Chemical reaction involving a fuel and an oxidant, often oxygen, accompanied by heat.
• Complete combustion: Burning with sufficient oxygen, often producing carbon dioxide and water from hydrocarbons.
• Incomplete combustion: Burning with insufficient oxygen, which may produce carbon monoxide or soot.
• Calorific value: Heat released by complete combustion of a unit quantity of fuel.
• Coal, petroleum and natural gas are conventional fossil fuels.
• Biogas mainly contains methane.
• Hydrogen can be used as an energy carrier and fuel in suitable systems.

13. Environmental Chemistry

• Air pollution: Presence of harmful substances in the atmosphere.
• Water pollution: Contamination of water that makes it harmful or unsuitable for use.
• Greenhouse effect: Warming caused by the absorption and re-emission of infrared radiation by greenhouse gases.
• Global warming: Long-term rise in Earth’s average surface temperature, largely due to human activities in the modern era.
• Ozone layer: Region of the stratosphere containing relatively high ozone concentration that absorbs much of the Sun’s harmful ultraviolet radiation.
• Acid rain: Precipitation made more acidic mainly by atmospheric sulphur and nitrogen compounds.
• Eutrophication: Excessive nutrient enrichment of water bodies.
• Biodegradable substances: Materials that can be broken down by biological activity.

14. Basic Biochemistry

• Carbohydrates: Important sources of energy, such as glucose and starch.
• Proteins: Polymers of amino acids that perform structural and functional roles in living organisms.
• Fats: Energy-rich compounds that also support insulation and cell functions.
• Vitamins: Organic compounds required in small amounts for normal growth and metabolism.
• Enzymes: Biological catalysts that speed up biochemical reactions.
• DNA: Molecule that stores genetic information in living organisms.
• RNA: Nucleic acid involved in various roles in gene expression and protein synthesis.
• Chlorophyll: Green pigment involved in photosynthesis.

15. Important Chemistry Facts

16. Quick Revision Facts

• Avogadro constant is approximately 6.022 × 10²³ per mole.
• The SI unit of amount of substance is the mole.
• The chemical symbol of gold is Au.
• The chemical symbol of silver is Ag.
• The chemical symbol of iron is Fe.
• Ozone has the molecular formula O₃.
• Water has the molecular formula H₂O.
• Carbon dioxide has the molecular formula CO₂.
• Ammonia has the molecular formula NH₃.
• Common salt is sodium chloride, NaCl.
• Rust mainly contains hydrated iron(III) oxides.
• Diamond and graphite are allotropes of carbon.