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Covalent Bonding
Covalent Bond formed when two atoms share a pair of electrons.
Covalent bonding forms molecules. These can have single bonds, double bonds or triple bonds.
Single Bond – H2O
Double Bond – O2
Triple Bond
Covalent Bonding
- Usually liquids or gases
- Low melting and boiling points
- Do not conduct electricity
- Do not dissolve easily in water
Types of Bonds
σ (sigma) bond
- formed with an end-on overlap of orbitals
- always formed in covalent bonds
- strongest type of covalent bond
π (pi) bond
- formed with a sideways overlap of orbitals
- in a double bond, there is one sigma bond and one pi bond
- in a triple bond, there is one sigma bond and two pi bonds
Non-polar Covalent Bond electrons are shared equally between two atoms e.g. H2
Polar Covalent Bond electrons are shared unequally between two atoms e.g. H2O
- The atom with the lesser share of electrons becomes slightly positively charged – δ+
- The atom with the greater share of electrons becomes slightly negatively charged – δ-
The polarity can be determines by calculating the difference in electronegativity between the two elements
- >1.7 – ionic
- 0 – pure covalent
- <1.7 – polar covalent
Usually, polar and ionic substances dissolve in polar substances. Non-polar substances dissolve in non-polar substances.
Electronegativity
Electronegativity the relative attraction of an atom for shared pairs of electrons in a covalent bond i.e. the ability to attract shared electrons to itself
- measured on the Pauling scale
- decreases down the group (screening effect, increased atomic radius)
- increases across the period (increased nuclear charge, decreased atomic radius)
