In this lesson, we will learn:
• To understand the two major types of bonding in chemical compounds
• To explain why both types exist and when they are likely to form.
• How to predict the formula of ionic and covalent compounds.
• Chemical molecules are held together by intramolecular forces - chemical bonds between the constituent atoms they are made of.
• One major type of chemical bond is the ionic bond: ∘ Ionic bonding is the forces of attraction caused by oppositely charged ions interacting with each other. It occurs between metal and non-metal atoms. ∘ In trying to obtain a full outer shell, metal atoms can transfer outer shell electrons from themselves to non-metal atoms. This creates a positive metal ion which lost electrons, and a negative non-metal ion which gained electrons. ∘ The transfer of electrons is driven by the stability of having a full outer shell, and the difference in electronegativity - the non-metal atom should have a much higher electronegativity than the metal atom. ∘ The ionic bond created is strong due to the oppositely charged ions attracting one another. ∘ Examples of simple ionic compounds are sodium chloride, NaCl, or magnesium oxide, MgO. ∘A quick tip: Ionic bonds will form between elements on opposite sides in the periodic table.
• Another major type of chemical bond is the covalent bond: ∘ Covalent bonding is the force of attraction created when two atoms share a pair of electrons between them – one from each atom, between both their nuclei. It occurs between non-metal atoms with similar electronegativity. ∘ The force of attraction and stability of this bond comes from the electrons being attracted to the nuclei of both atoms involved, while the electron pair being shared means both atoms have their outer shell being filled. ∘ Covalent bonding occurs widely between non-metal atoms. Their similarity in electronegativity leads to the electrons being shared and no single atom losing or gaining electrons, unlike in ionic bonding. ∘A quick tip: Covalent bonds form between nonmetals and elements close to each other in the periodic table.
• Both ionic and covalent bonding are examples of intramolecular forces. Their forces occur between the atoms or ions that make up a chemical substance itself, not between the separate molecules of the substance. They are both strong forces – simple ionic compounds often have melting points of several hundred degrees Celsius, as do some large covalent structures.
• You can use the valence of an atom to work out the formula of covalent and ionic compounds: ∘ For each element, find the number of valence electrons (the number would be the group number). (E.g. N has 5 valence electrons, H has 1). ∘ For both atoms to make the compound, fill in the outer shell and find the number of unpaired electrons. This is the valence of the atom. (E.g. N has a valence of 3 due to 3 unpaired electrons, H has 1). ∘ Cross the valence of each atom with the other – this is the number of atoms of the element that will combine to form the compound. (N = 1, H = 3 makes NH3, a covalent compound).
Building on bonding
Identify whether covalent or ionic bonds will form between these elements.
Will the following pairs of atoms form a covalent or ionic compound? Explain why.
Identify covalent or ionic compounds and predict their formula using valence.
Predict whether these atoms will form a covalent or ionic compound together, then predict the formula of their compound:
Ionic and covalent bonding
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