1.40 explain, using dot and cross diagrams, the formation of covalent compounds by electron sharing for the following substances:

i hydrogen

ii chlorine

iii hydrogen chloride

iv water
Just one example of a dot cross diagram.


v methane

vi ammonia

vii oxygen

viii nitrogen

ix carbon dioxide

x ethane

xi ethene

1.39 understand covalent bonding as a strong attraction between the bonding pair of electrons and the nuclei of the atoms involved in the bond

Covalent bonding part II

During covalent bonding, the sharing of electrons between 2 non-metals, the electrons become attracted to the nucleus of each ion in a bond, this is electrostatic attraction.

1.38 describe the formation of a covalent bond by the sharing of a pair of electrons between two atoms

Covalent bonds

When two non-metallic elements combine together they often share  electrons between them. When an atom of hydrogen, H and an atom of chlorine, Cl, combine to form hydrogen chloride, HCl, the atoms come close enough together for their outer electron (valence) shells to overlap.

TRIPLE: 1.36 &1.37 describe an ionic crystal as a giant three-dimensional lattice structure held together by the attraction between oppositely charged ions

Giant ionic lattice structure

As you can see from the diagram, this is a giant ionic lattice. When an ionic compound forms, the positively charged ions attract the negatively charged ions and arrange themselves into a three-dimensional structure called an ionic lattice. The arrangement of the ions in the ionic lattice of sodium chloride is shown above. 

1.32 explain, using dot and cross diagrams, the formation of ionic compounds by electron transfer, limited to combinations of elements from Groups 1, 2, 3 and 5, 6, 7

Dot and cross diagrams

Dot and cross diagrams are used to show electron transfers, and the creation of ions.

As you can see, the magnesium atom gives 2 electrons to the oxygen atom, so an ionic bond is created and therefore, 2 ions are created; the magnesium atom becomes a positive ion, losing 2 electrons and the oxygen atom becomes a negative ion, gaining 2 electrons.