Chemical Bonding
- Formation of ions
- Formation of ionic bonds & covalent bonds
- Properties of ionic & covalent compounds
- Structure of simple, molecular & giant molecular structures

Noble Gas Structure
- Eg. He, Ne, Ar, Kr, Xe
- Each atom has 8 valence electrons (except for He)
- Single atoms
- Do not form compounds
- Described as unreactive
- Stable due to fully filled outer shells

The Octet Rule
- All atoms without a fully filled outer shell is unstable
- Unstable atom would try to gain stability by surrounding itself with an octet (8) of electrons
- Octet Rule

Helium (He)
- 2 outer electrons
- Stable atom because outer shell is fully filled
- Duplet Rule

Valency
- Number of electrons needed to fill up the outer shell
- Number of electrons in excess to the atom, stopping the atom from having a fully filled outer shell

Formation of Ions
- Charged particle formed from an atom/group of atoms by the loss/gain of electrons
- Metals formed positively charged ions called Cations.
- Non-metals formed negatively charged ions called Anions.

Formation of Positive Ions
- Formed by loss of electrons
- Metals tend to form positive ions because most metal atoms have less than 4 electrons in the outer shell. Hence it is more likely to lose the few electrons than to gain many more to achieve octet structure.

Formation of Negative Ions
- Formed by the gain of electrons
- Non-metals tend to form negative ions because most non-metals have more than 4 electrons in the outer shell. Hence, it is more likely for the atoms to gain a few more electrons to complete the octet than to transfer their outer electrons to other atoms.

Ions
- Positive and negative ions can be formed by a group of atoms, known as polyatomic ions

Ionic Bonds
- Formed between metals and non-metals
- Involves the formation of both positively charged ions (cations) and negatively charged ions (anions)
- Involves the transfer of electrons from one atom to another
- All metal atoms are known as electron donors and all non-metal atoms are known as electron receivers.

Ionic Compounds
- Made up of oppositely charged ions, NOT molecules
- Oppositely charged ions are arranged together in a giant ionic structure
- Lattice structure/Crystal lattice
- THree-dimensional network of atoms/ions which are packed together in a regular pattern
- Held together very tightly because oppositely charged ions attract one another strongly
- High melting and boiling points
- In order for the ionic solid to melt, a very large amount of heat energy is needed to break up the strong ionic bonds
- All ionic compounds are solids at room temperature
- Substances with low melting and boiling points are known as volatile
- Ionic compounds - Non-volatile
- Solubility:
       - Most ionic compounds can dissolve in water
       - Water molecules can separate the positive ions from the negative ions
       - Ionic compounds do not dissolve in organic solvents
- Able to conduct electricity in the molten (liquid) state) and as an aqueous solution
- Moving ions acts as charges carriers to conduct electricity

Covalent Bonds
- Two non-metals reacting with each other
- Bond formed by the sharing of electrons is called Covalent Bond
- In the case of ionic bonding, atoms would achieve stable duplet/octet structure by donating or receiving electrons. All non-metal atoms have a choice of whether to undergo ionic or covalent bonding depending on the nature of the other reactants.

Molecules of Compounds
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Atomic Structure

Atoms are made up of three different particles - protons, neutrons and electrons. They are called sub-atomic particles.
Protons and neutrons are tightly packed together in the centre of an atom, forming the nucleus of the atom. Protons and neutrons are known as nucleons.
An atom contains an equal number of positively charged protons and negatively charged electrons.
Proton number
- Also known as atomic number
- Represented by the symbol Z
- Different atoms have different numbers of protons

Nucleon number
- Total number of protons and neutrons in an atom
- Represented by the letter A
- Also known as mass number
Nucleon number (A) = number of protons + number of neutrons

Isotopes
- Atoms of the same element with the same number of protons but different number of neutrons
- Same chemical properties but slightly different physical properties
- Emit high energy radiation called radioisotopes

Electrons
- Move around the nucleus in regions known as electron shells
- The way the electrons are arranged in an atom is also known as the atoms' electron structure or electronic configuration

Valence Electrons
- The shell that is furthest from the nucleus
- Also known as outer shell
- Chemical properties of an element depend on the number of valence electrons