2.1 - Bonding, structure, and the properties of matter

2.1.1 Chemical bonds

- There are three types of strong chemical bonds: ionic, covalent and metallic.
- In Ionic bonds, the positive and negative charges are attracted to each other. It can only occur in compounds where metals are combined with non-metals.
- In Covalent bonds, the electrons are shared between the atoms. It happens in most non-metallic elements and in most non-metal compounds.
- In Metallic bonds, the electrons are shared between the atoms, but the atoms are held together by a network of metal ions. It occurs in metals.

2.1.2 Ionic bonds

- Ions are atoms that have a positive or negative charge formed by the gain or loss of electrons.
- The loss or gain of electrons gives the ion a full outer shell of electrons.
- A full outer shell needs to have 8 electrons. Metals lose electrons, and non-metals gain electrons.
- Since most of GCSE only focuses up to Calcium, for our purposes:

Group 1 elements lose 1 electron
Group 2 elements lose 2 electrons
Group 3 elements lose 3 electrons
Group 4 elements gain 4 electrons
Group 5 elements gain 3 electrons
Group 6 elements gain 2 electrons
Group 7 elements gain 1 electron
Group 8 elements do not gain or lose electrons

- Negative ions are called anions and form when atoms gain electrons, they have more electrons than protons.
- Positive ions are called cations and form when atoms lose electrons, they have more protons than electrons.
- Here's how it's represented (image stolen from spec):
ionic bonding dot-and-cross

2.1.3 Ionic Structures

Giant Ionic Lattices

- This is a regular arrangement of alternating positive and negative ions.
- The ions are tightly packed together, and the electrons are evenly distributed.
- It is held together by the strong electrostatic forces of attraction between the ions, forming the basis of ionic bonding.
- Due to the electrostatic forces, the lattice structures have high melting and boiling points.
- They allow regular shaped crystals to be formed. giant ionic lattice _{also stolen from the spec}

Ball-and-stick structure advantages/disadvantages

Advantages	Disadvantages
Provides a clear, 3D visualization of ionic lattice structures. Shows the relative positions and arrangement of ions in the lattice. Makes it easier to understand how ions are connected in a crystalline structure. Helps in visualizing bond angles and coordination numbers.	Oversimplifies ionic bonding by using sticks, which don't exist in real ionic crystals. Does not accurately represent the true sizes of the ions involved. May give the impression of localized bonds, which are not present in ionic lattices. Can be misleading in terms of the scale between the ions and the bonds.

2.1.4 Covalent bonding

_{(images from spec)}
- When atoms share pairs of electrons, they form strong covalent bonds.
- Covalently bonded substances may consist of small molecules, for example water (H₂O).
- However, some covalently bonded substances have very large molecules, such as polymers, for example polyethylene (C₂H₆).
- In addition, some covalently bonded substances have giant covalent structures, such as diamond and silicon dioxide.

Representing covalent bonds

- The covalent bonds in molecules and giant structures can be represented in the following forms:

Pros and cons of each representation

Model	Limitations
Dot and Cross Diagrams	Does not show the actual shape of the molecule. Does not show how atoms are arranged in space. Implies electrons are fixed, whereas they are actually delocalised or shared clouds. Does not show the relative sizes of atoms.
Ball and Stick Models	Bonds are shown as sticks, but real bonds are not rigid sticks. Atoms are shown far apart, when in reality they are much closer together. Does not accurately represent the movement of electrons or ions.
2D Diagrams	Cannot show the 3D arrangement of atoms. Cannot show bond angles accurately. Oversimplified; may give a misleading idea of structure.
3D Diagrams	Hard to draw for complex or giant structures. Does not show how electrons are shared or transferred. Cannot show the actual movement or vibration of atoms.

Polymers

- Polymers can be respesented in this form, where n is a large number:

2.1.5 Metallic bonding

- Metals consist of giant structures of atoms arranged in a regular pattern.
- The electrons in the outer shell of metal atoms are delocalised and so are free to move through the whole structure, which results strong metallic bonds in the form of giant structures (lattices).