Covalent Bonding

COVALENT BONDING

Bonding

• Each shared pair of electrons forms a covalent bond between nonmetal atoms.
• Two pairs of electrons in the area of overlap form a covalent bond.

Dative or Coordinate bonds

• Sometimes the electrons in the pair come from the same atom. The resulting covalent bond is called a dative/coordinate bond.
• Ammonium ions NH4+ contain a dative bond. The ammonium ion is formed when an alkaline solution of ammonia NH3 reacts with an acid. This forms H+ ions.
• The H+ ion has no electrons of its own so it accepts and shared a non binding pair of electron from the outer shell of the nitrogen atom. This gives the hydrogen 2 electrons filling its shell.
• The dative bond is represented by an arrow. The direction of the arrow shows us which atom the pair of electrons has come from. It points to the atom accepting the electrons.

Shapes of molecules

• Count number of electrons surrounding the central atom.
• Divide this by 2 to get the electron pairs. These are negatively charged. They repel each other and get as far apart as possible.
• Non bonding pairs of electrons are called lone pairs.
• Strongest repulsion: lone pair/lone pair
• Lone pair/bonding pair
• Weakest repulsion: bonding pair/bonding pair

Giant Covalent Structures:

• The covalent substances sometimes consist of giant 3D networks of atoms. The atoms are fixed in position by covalent bonds. These are called giant covalent structures.
• Substances with giant covalent structures aren't soluble in water. Their particles carry no charge. So polar water molecules aren't attracted to them. They can't provide the huge amounts of energy needed to break the structure apart. These substances don't conduct electricity as there are no free ions or electrons to carry the charge.
• HAVE HIGH MELTING POINTS
• INSOLUBLE IN WATER
• THEY DONT CONDUCT ELECTRICITY EXCEPT GRAPHITE

GRAPHITE

• Diamond and GRAPHITE are allotropes of carbon. These are different forms of the same element.
• The electrons hold the layers together by weak forces. Therefore the layers can slide over each other easily. The electrons holding the layers together are held together loosely to the carbon atoms. These can drift between the layers in GRAPHITE.
• Graphite does not melt when heated. It sublimes and turns into a gas.

Simple molecular structures

• Substances with low melting points and boiling points have simple molecular structures.