Biology - Topic 1 Biological Molecules

Chemistry For Life

The single basic unit of all elements is an atom. When the atoms of more elements react they form a compound. An atom is made from a nucleus containing positive protons and neutral neutrons surrounded by negatve electrons. When an atom has a full outer shell of electrons it is stable and does not react. However, most atoms do not have a full shell of outer electrons. In chemical reactions, changes occur to give a full outer shell through either ionic or covalent bonding. 

Ionic Bonding-The atoms involved in the reaction donate or recieve electrons. The atom gains one or more electrons and becomes a negative ion (anion). The other atom, looses one or more electrons and becomes a positive ion (cation). Strong forces of attractiion called ionic bonds hold oppositely charged ions together. 

Covalent Bonding-  The atoms involved in the reaction…