Bond Strength


Bond strength is the measure of how strong a bond is in terms of the energy needed to make and break the bond

A bond strength is also a bonds energy this is referred to as the energy that is required to break a bond between two atoms. These value often differ with covalent, metallic and ionic bonds.

In a covalent molecule we can measure the strength it takes to break the bond. We measure this energy in kj/mol which is the amount of energy in kilojoules it takes per mole of substance. This value is often averaged over a range of compounds due to the influence of different atoms on these bonds with electronegativities. For example the energy required to break the bond between carbon and hydrogen atoms is 415KJ/mol but this bond energy would be different depending on what other atoms are bonded to the carbon.

The strength of a bond between two atoms is also influenced by the number of electron pairs. For example when two atoms share one pair of electrons this is called a single bond, but when a par of atoms share two pairs of electrons this is a double bond. When comparing a single bond to a double bond, double bonds require a lot more energy to break the bond between the two atoms. For example a nitrogen bonded to another nitrogen can have different bond strengths based on how many bonds it has between the atoms. A nitrogen that is double bonded requires 418KJ/mol where as a single bonded nitrogen molecule requires 160KJ/mol.

Bond strength is also often related to bond length the shorter a bond in general the stronger it is. This is evident when looking at the trend in bond energies down a group as in general down a group the atoms increase in size and the nucleus is further away from the bonded electrons. For example looking at the bon between a carbon atom and different halogens we can see a trend. The bond between carbon and fluorine requires 439kj/mol of energy to break the bond compared to the bond between carbon and bromine which requires 275kj/mol. This is because the bromine atom is much larger in size compared to the fluorine atom.

When measuring the bond energy in ionic compounds the energy that it takes to break apart the lattice structure of an ionic compound. Separating ionic compounds from their lattices is an endothermic process requiring energy to be put in. The amount of energy required to break apart a lattice depends on the size of the ion and charge of the ions involved in the lattice. For example the lattice of lithium fluoride contains a lithium atom with a +1 charge and a fluoride atom with a -1 charge. This lattice requires 1023 Kj/mol to separate the ions. This is compared to 3900Kj/mol of energy required to separate the lattice of magnesium oxide where the magnesium ion has a +2 charge and the oxygen has a -2 charge. This shows that the larger the charge on the ions the more energy is required to break apart the lattice.

Terms in section
Bond strength

Bond strength is the term used to describe the amount of energy required to break a bond attraction between two atoms or ions

Bond energy

Bond energy is the term used to describe the amount of energy required to break a bond attraction between two atoms or ions measured in kj/mol


kj/mol is the abbreviation of kilojoules per mole which is a term used to describe the amount of energy in kilojoules that is put into a number of moles of atoms


A mole is the term used to describe the number of atoms in a substance. One mole is equal to 6.02x10^23 atoms


Electronegativity is the ability of an atom to attract electrons in its bond determined by the nuclear charge, number of protons and the number of shells.


The electron is the smallest sub atomic particle that make up the atom. Has a negative charge and is located in shells that orbit the nucleus

Single bond

A single bond is the term used to. describe a shared pair of electrons in a covalent bond

Double bond

A double bond is the term used to describe the sharing of two pairs of electrons in a covalent bond


Endothermic is a term used to describe a chemical process where heat energy is taken in by chemicals and turned into chemical potential energy. Energy has to be put in to get the process/reaction to work an the temperature of the surroundings decreases


A lattice is a term given to an ordered arrangement of points in a 3D shape creating a regular arrangement of atoms and ions


Electronegativity of the Elements


Intermolecular Forces in Covalent Compounds