• Covalent?bonding occurs between two?nonmetals
• A covalent bond involves the?electrostatic?attraction?between nuclei of two atoms and the bonding electrons of their outer shells
• No?electrons?are?transferred?but only?shared?in this type of bonding

The positive nucleus of each atom has an attraction for the bonding electrons shared in the covalent bond

• Non-metals?are able to?share?pairs of electrons to form different types of covalent bonds
• Sharing electrons in the covalent bond allows each of the 2 atoms to achieve an electron configuration similar to a noble gas
  • This makes each atom more stable

Covalent bonds & shared electrons table

Dot & cross diagrams

• Dot and cross diagrams?are used to represent covalent bonding
• They show just the?outer?shell?of the atoms involved
• To differentiate between the two atoms involved,?dots?for electrons of one atom and?crosses?for electrons of the other atom are used
• Electrons are shown in?pairs?on dot-and-cross diagrams

Single covalent bonding

Hydrogen, H₂

Covalent bonding in hydrogen

Chlorine, Cl₂

Covalent bonding in chlorine

Hydrogen Chloride, HCl

Covalent bonding in hydrogen chloride

Ammonia, NH₃

Covalent bonding in ammonia

Methane, CH4

Covalent bonding in methane

Ethane, C₂H₆

Covalent bonding in ethane

Double covalent bonding

Oxygen, O₂

Covalent bonding in oxygen

Carbon dioxide, CO₂

Covalent bonding in carbon dioxide

Ethene, C₂H₄

Covalent bonding in ethene

Triple covalent bonding

Nitrogen, N₂

Covalent bonding in nitrogen

• In some instances, the central atom of a covalently bonded molecule can accommodate?more?or?less?than 8 electrons in its outer shell
• Being able to accommodate?more?than 8 electrons in the outer shell is known as?‘expanding the octet rule’
• Accommodating?less?than 8 electrons in the outer shell means than the central atom is?‘electron deficient’
• Some examples of this occurring can be seen with Period 3 elements

Sulfur dioxide,?SO₂ – dot and cross diagram

Phosphorus pentachloride, PCl₅?– dot and cross diagram

Sulfur hexafluoride, SF₆?– dot and cross diagram