Chemical bonding: how atoms are held together in elements and compounds
Atoms form bonds because they do not have a full outer shell of electrons (except the noble group)
There are three types of bonding:
When a metal bonds with a non-metal, electrons are transferred. Charged particles called ions are formed.
The metal loses electron(s) to form positive ions.
Non-metals gain electron(s) to form negative ions.
Metal/non-meyal compounds are ionic. They have a full outer shell of electrons, like noble gases.
Ionic compounds are neutral. The charges on their ions cancel out. This helps us work out the formulae.
1. Positive and negative charges must add up to zero e.g. NaCl is +1 and -1 so it adds up to zero. Sometimes you need two of one ion for the neutral charges.
2. For ions which contain more than one atom you must put a bracket round the whole ion and then put a number at the bottom of the bracket.
3. Sometimes you need to put a number at the bottom of both ions to make the charges add up to zero.
An ion is an atom with a charge - it has gained or lost electron(s).
Electrons are negative. Protons are postive. Ions with opposite charges attract. When oppisitely charged ions attract and join, they form an ionic bond.
To form a neutral compound, positive and negative charges must be equal.
Sometimes an ion consists of a small group of atoms.
Stock Notation - if an element can have differnet ions, the name is shown as: e.g. Iron (II)
Properties of Ionic Compounds:
-made of crystals
-high melting point
-soluble in water
-only conduct electricity when dissolved in water
Giant Ionic Structures
-oppositely charged ioons are attracted to each other
-this attraction forms a strong ionic bond
-the charge on an ion acts in all directions
-the ions arrange themselves
-called Giant Ionic Lattice
-electrostatic force means a force between opposite charges
Many non-metal elements exist as diatomic atoms. Covalent bonding is the of two non-metals. In covalent bonding a pair of electrons, one forom each atom, is share between.
Atoms are held together by sharing…