Covalent bonds are formed between two non-metals, while ionic bonds are formed between a metal and a non-metal. Both types of bonds involve forming complete outer electron shells.
Covalent bond:
This bond involves sharing electrons between two non-metals. Because electrons are shared between the elements, this means that the elements will gain a full outer electron shell.
Structures formed by Covalent Bonds:
Covalently bonded atoms can form a covalent structure. This has a low melting point and boiling point. Therefore it is usually a gas at room temperature. Examples of covalently bonded molecules include O2 (oxygen), H2O (water) and HCl (hydrogen chloride).
Here is an example of a covalent bond (found in water):

Figure 4 - Covalent bonding in water
Ionic bond:
This occurs between a positive ion and a negative ion. An ion is a charged atom. The positive ion is a metal, and the negative ion is a non-metal. The negative ion transfers its excess electrons to the positive ion. The ions are therefore held in place by electrostatic interactions between positive and negative ions.

Figure 5 – Ionic bonding in NaCl
Structures involving ionic bonds:
Ionic lattices are the structure formed from ionic bonds. These have a high melting point and boiling point. When dissolved in water, the ions are free to move in solution. Therefore, they can conduct electricity (which is the flow of charge). Ionic lattices only conduct electricity when dissolved in solution. An example of an ionic lattice is NaCl (sodium chloride) – table salt.
Conclusions:
Ionic bonds are formed between metal and non-metal, while covalent bonds are formed between two nonmetals.
Ionic bonds involve the formation of ions and ions are held in place by electrostatic interaction.
Covalent bonds involve the sharing of electrons between atoms (not IONS)Ionic bonds can form an ionic lattice.
Covalently bonded molecules can form a covalent structure.

Describe the trend in reactivity in group 1 alkali metals.

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