Atoms and Bonding

What is a valence electron?

Electron located in the outermost shell, participating in chemical bonding by being shared, lost, or gained by an atom to become more stable

What are the 3 forms of primary bonding?

• Ionic

• Covalent

• Metallic

Ionic Bonding

Electrons are transferred between atoms; creates charged particles (ions)

Covalent Bonding

Electrons are shared between atoms and firmly localised between them

Metallic Bonding

Electrons are shared between atoms but delocalised over a large distance

What are the 2 forms of secondary bonding?

• Fluctuating dipoles

• Permanent dipoles

What are fluctuating dipoles? (Van der Waals)

Constantly changing regions of slight positive/negative charge within an atom/molecule caused by the movement of electrons

What are permanent dipoles?

Separation of positive and negative charge within a molecule, caused by the unequal sharing of electrons in a covalent bond. This asymmetry creates a slightly positive (δ+) end and a slightly negative (δ-) end, making the molecule polar (i.e. hydrogen bonding)

Properties of Metals (Metallic bonding)

• Electrical and thermal conductivity

• Ductile and strong

• Various melting points

• May form alloys

• Magnetic

• Shiny

Properties of Polymers (Covalent, Van der Waals, H-bonding)

• Electrical and thermal insulation

• Low density

• Low melting point

• Low strength

• Flexible

If a materials electrons are bound, what effects will it have on its properties?

The material will provide electrical and thermal insulation

What are intrachain (or intramolecular) bonds?

Hold atoms within a single molecule or polymer chain (generally stronger/more stable than interchain bonds)

What are interchain (or intermolecular) bonds?

Weaker forces that hold separate molecules or chains together

What causes a material to have a lower melting point, less strength and more flexibility?

Having strong intrachain bonds, but weaker interchain bonds

Properties of Ceramics (Ionic or covalent bonding)

• Electrical and thermal insulation

• Hard and brittle

• High melting point

• Environmental resistance

• Always compounds

If a materials bonds are stronger, what effects will it have on its properties?

• Higher melting temperature

• Higher modulus