h) Metallic crystals

1.46 understand that a metal can be described as a giant structure of positive
ions surrounded by a sea of delocalised electrons

Metals have a giant structure of positive ions, surrounded by a 'sea of delocalised electrons.' So, a metal is a lattice of positive ions in a sea of delocalised, or free, electrons. These electrons are not attached to a particular atom and can move freely. 

1.47 explain the electrical conductivity and malleability of a metal in terms of its

structure and bonding.

As metals have delocalised electrons and electrons carry electricity, they are good conductors of electricity. The free electrons carry electrical current through the material and do this easily.

The structure of a metal is composed of rows of atoms on top of eachother, The atoms are all the same size and the layers will therefore be able to slide easily over one another, making them malleable.