Important Chemical Terms and Definitions:
Formation of Fossil fuels
Fossil fuels
Fossil fuels are formed from the remains of plants and animals that lived hundreds of
millions years ago. (coal, petroleum and natural gas are fossil fuels)
Petroleum
Petroleum is formed from dead sea animals, that are buried underground under high
temperature and pressure for a long time.
Coal
Coal is formed from dead plants, that are buried underground under high temperature and
pressure for a long time.
Natural gas
Natural gas is formed from dead sea animals and plants, that are buried underground under
high temperature and pressure for a long time.
Atomic Structure
Full atomic symbol
Atomic number
Number of protons.
Mass number
The sum of number of protons and neutrons.
Isotopes
Isotopes are different atoms of the same element with the same number of protons but
different numbers of neutrons.
Why isotopes of the same element have the same chemical properties?
It is because they have the same electronic arrangement.
Why elements of the same group have similar chemical properties?
It is because they have the same number of outermost shell electrons.
Avogadro’s constant
The number of atoms/molecules/formula units in one mole of a substance.
Relative atomic mass
Weighted average of relative isotopic masses.
Relative molecular mass
Sum of relative atomic masses of all atoms in a molecule.
Formula mass
Sum of relative atomic masses of all atoms in a formula unit.
Molar mass
The mass of a substance per mole.
Empirical formula
The formula which shows the simplest whole number ratio of atoms
Molecular formula
The real formula which shows the actual number of atoms.
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Chemical Bondings/Forces
Octet rule
Atoms tend to attain the stable electronic arrangement of the nearest noble gas.
Metallic bond
The (non-directional) electrostatic attraction between (positive) metal (cat)ions and the
sea of delocalized electrons.
Ionic bond
The (non-directional) electrostatic attraction between cations and anions.
How ionic bond is formed? It is formed by the transfer of electron(s) from an atom to another atom.
Covalent bond
The (directional) electrostatic attraction between the (proton in) nucleus of the atoms
and the bond pair electrons.
How covalent bond is formed? It is formed by the sharing of electron(s) between atoms.
Dative covalent bond
A covalent bond formed between two atoms where bond pair electrons are contributed
by the same atom.
Atomicity
The number of atoms in a molecule of an element or a compound (e.g. Cl2 is a diatomic
molecule, He is a monoatomic molecule).
Hydrogen bond
The electrostatic attraction between a hydrogen atom in a very polar bond with the lone
pair of electrons of a very electronegative atom (such as N, O, F).
Van der Waals forces
The weak electrostatic attractive forces between molecules, arising from the interaction
between polar and/or non-polar molecules.
Electronegativity of atoms
The power of that atom in a molecule to attract bonding electrons.
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Volumetric Analysis
Standard solution
A solution with known concentration.
Primary standard
A primary standard is a substance of known high purity which may be dissolved in
a known volume of solvent to give a standard solution.
Criteria for a primary standard:

Readily available

Chemicall stable

High solubility in water

High purity

Involatile

Does not absorb water vapor from air
Purpose of titration
It is used to determine the amount/concentration of a substance (analyte).
Equivalence point
A point when an acid and an alkali have just completely reacted with each other.
End point
A point when the indicator changes color sharply (and permanently).
Acid
A (covalent molecular) compound that dissolves in water to form hydrogen ion (or
hydronium ion) as the only cation.
Base
Bases react with acids to form salt and water only.
Alkali
Bases that are soluble in water and react with acids to form salt and water only./ A
substance that dissolves in water to form hydroxide ions as the only anion.
Basicity
Maximum number of hydrogen ions produced by one acid molecule. (e.g. HCl is
monobasic, CH3COOH is monobasic, H2SO4 is dibasic, H3PO4 is tribasic)
Strong acid/alkali
An acid/alkali that completely dissociates in water.
Weak acid/akali
An acid/alkali that partially/slightly dissociates in water.
Carbon compounds
Saturated hydrocarbons
Saturated hydrocarbons are hydrocarbons that contain only single bonds between
carbon atoms.
Unsaturated hydrocarbons
Unsaturated hydrocarbons are hydrocarbons that have double or triple covalent
bonds between (adjacent) carbon atoms.
Functional group
An atom or a group of atoms responsible for most of the compound’s chemical
properties.
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Reactions
A reaction in which one element displaces another element from its compound (a
Displacement reaction
more reactive metal always displaces the less reactive metal)
Neutralization
A reaction between an acid and a base, with salt and water as the only products.
Cracking
A process of breaking down larger molecules into smaller ones.
Addition polymerization
A reaction when monomer molecules join together to form polymer molecules,
WITHOUT the elimination of small molecules (e.g. H2O, HCl)
Condensation polymerization
A reaction when monomer molecules join together to form polymer molecules,
WITH the elimination of small molecules (e.g. H2O, HCl)
Redox Reactions
Reducing agent
The substance that undergoes oxidation.
Oxidising agent
The substance that undergoes reduction.
Primary cells
A chemical cell that is not rechargeable, converting chemical energy to electrical energy.
Secondary cells
A chemical cell that is rechargeable, converting chemical energy to electrical energy.
Chemical Equilibrium
Le Châtelier’s Principle
It states that when a chemical system at equilibrium is disturbed by a change in
conditions (e.g. temperature, pressure), the equilibrium position will shift in a direction
that counteract the change.
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Standard enthalpy change
Standard conditions
Pressure: 1 atm
Temperature: 25oC
Concentration: 1.0 M
Substances in standard state (most stable form at 1 atm and 25oC
Standard enthalpy change
Enthalpy change of reaction measured under standard conditions.
of reaction
Standard enthalpy change
Enthalpy change when one mole of the substance is completely burnt in oxygen under
of combustion
standard conditions.
Standard enthalpy change
Enthalpy change when one mole of the water is produced from neutralization between
of neutralization
an acid and an alkali under standard conditions.
Standard enthalpy change
Enthalpy change when one mole of substance is formed from its constituent elements
of formation
in their standard states under standard conditions.
Hess’ Law
The overall enthalpy change of a chemical reaction is the same, regardless of the
route of the reaction, provided that the initial and final states are the same.
Rate of reaction (molar volume of gas)
Avogadro’s Law
Equal volumes of all gases at the same temperature and pressure contain the same
number of molecules.
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