Structure and bonding

There are 3 types on chemical bonds.

Ionic, metallic and covalent

For ionic the particles are oppositely charged ions.

For covalent the atoms share pairs of electrons

For mettalic the atoms share delocalised electrons

Ionic compounds are giant structures of ions

Ionic compounds are held together by strong electrostatic forces of attraction between oppositely charged ions.

Ionic compounds form a giant ionic lattice. In a giant ionic lattice every positive ion is surrounded by negative ions, and every negative ion is surrounded by positive ions.

In a giant ionic lattice, there are very strong forces of attraction between the positive and negative ions. These strong electrostatic forces of attraction hold the positive and negative ions in place. The electrostatic forces are also called ionic bonds and they act in all directions.

Properties of ionic compounds :

• High melting and boiling points because the strong electrostatic forces of attraction require a great deal of heat energy

• They cant conduct electricity when they are solid. This is because the ions are locked in place by the strong electrostatic forces of attraction. However, they can conduct electricoty when they are melted or dissolved in water, thats because the ions are now able to move and carry the charge around the whole structure.

Limitation of dot and cross diagram :

• They dont tell you the shape of the molecule

Limitation of two dimensional stick :

• Unable to tell which electron in the covalent bond came from which atom

Limitation of ball and stick :

• The ions are widely spaced but in reality they are packed together

How bonding and structure are related to the properties of substances

Small molecules

In small molecules, each molecule contains only a few atoms with strong covalent bonds between these atoms. Different molecules are held together by weak intermolecular forces of attraction.

An example is water.

Properties

• Low melting and boiling points because only the intermolecular forces need to be overcome to melt or boil the substances, not the bonds between the atoms. This doesnt require a lot of energy as the intermolecular forces of attraction are very weak.

• They are normally as a gas or liquid at room temperature.

Polymers

They have very large molecules.

The atoms in Polymers are linked to other atoms by strong covalent bonds.

Properties

• The intermolecular forces between polymer molecules are relatively strong which require energy to overcome

• these substances are solids at room temperature.

Giant covalent structures

All of the atoms in these structures are linked to other atoms by strong covalent bonds.

Eg Diamond

Properties

• High meting or boiling points because they have strong intermolecular forces which need to be overcome to melt or boil the substances. This requires a lot of energy

• Solid at room temperture

Structure and bonding of carbon

Graphite

Graphite is a giant covalent structure.

Made only of carbon and each carbon atom bonds to three others forming hexagonal rings in layers. Each carbon atom has one spare electron which is delcolised therefore free to move around the whole structure.

The layers can slide over eachother because they are no covalently bonded therefore are held together weakly, making it relatively soft when compared to daimond.

They have delocalised electrons which are free to move around the whole structure and carry charge allowing the electrical current to flow.

Nanotubes

The carbon atoms within them are made of cylindrical tubes. There tensile strength is why they are used in electronics

Graphene

Consists of one layer of graphite. Their strong covalent bonds is they are strong materials conducting electricity. They are useful in composites and high tech electronics.

Nanoparticles

They are used in medicines, electronics, cosmetics and catalysts. However they can be hazardous to health and ecosystem so its important they are researched further.