3.1.3.4 Bonding and Physical Properties

It is when a solid turns into a liquid by supplying more energy. This energy is needed to weaken the forces between molecules

The heat energy change

A liquid gaining energy and becoming a gas Enthalpy change of vaporisation is the energy needed to do this

They are solids with a regular structure

Ionic, metallic, molecular, macromolecular

Have strong electrostatic attractions between oppositely charged ions = high melting points Requires a lot of energy to seperate the ions

Exist as a lattice of positive ions embedded in a sea of delocalised electrons Strong metallic bonds causes high melting temperature

Consists of molecules held in a regular array by intermolecular forces Covalent bonds within the molecules hold the atoms together but they do not act between the molecules Intermolecular forces are weaker so they have lower melting points and low enthalpies of melting

Macromolecular crystal Stong covalent bonds join ioding atoms to form I2 Iodine has a large number of electrons so van der waals forces are strong Crystals are soft and break easily Low melting temperature Doesn’t conduct electricty

When covalent bonds extend throughout the structure High melting points

Macromolecular structure Each carbon atom forms four covalent bonds with other carbon atoms Tetrahedron with bond angles of 109.5 Very hard material Very high melting point Doesn't conduct electricity

Layers of flat trigonal pyramids Carbons are held together by strong bonds This creates a strong connection along the layers This leaves a free electron in a p-orbital which becomes delocalised and carries charge Weak Van der Waals forces between layers Soft material High melting temperature because of the covalent bonds Conducts electricity along the layers

Simple molecular