Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Covalent bonding is the electrostatic attraction between a shared pair of electrons and the positively charged nuclei of the atoms involved, typically occurring between two non-metals.
The primary goal of covalent bonding is for atoms to achieve a stable electron configuration, usually an octet ( electrons in the outer shell), similar to noble gases. Hydrogen is an exception, seeking a duet ( electrons).
Lewis Dot and Cross diagrams are used to represent the valence electrons and how they are shared. Dots represent electrons from one atom, while crosses represent electrons from the other.
Covalent bonds can be single ( pair of shared electrons, e.g., ), double ( pairs, e.g., ), or triple ( pairs, e.g., ).
Simple molecular substances, such as and , have low melting and boiling points because the intermolecular forces (forces between molecules) are weak, even though the covalent bonds within the molecules are very strong.
Giant covalent structures (like diamond, graphite, and ) consist of a repeating lattice of atoms held together by strong covalent bonds, resulting in extremely high melting points and hardness.
Covalent compounds generally do not conduct electricity in any state (except for graphite) because they do not contain mobile ions or delocalized electrons.
📐Formulae
💡Examples
Problem 1:
Draw the Lewis structure and describe the bonding in a water molecule ().
Solution:
Oxygen has valence electrons and needs more to complete its octet. Each Hydrogen has valence electron and needs more. Oxygen shares one electron with each Hydrogen atom, forming two single covalent bonds.
Explanation:
The resulting molecule has two bonding pairs of electrons and two 'lone pairs' on the Oxygen atom. The chemical formula is .
Problem 2:
Explain why Carbon Dioxide () exists as a gas at room temperature while Silicon Dioxide () is a solid with a very high melting point.
Solution:
is a simple molecular structure with weak intermolecular forces. is a giant covalent lattice.
Explanation:
In , only a small amount of energy is needed to overcome the weak forces between molecules. In , many strong covalent bonds must be broken throughout the entire structure, which requires a huge amount of thermal energy.
Problem 3:
Represent the triple bond in Nitrogen gas () using a dot and cross diagram concept.
Solution:
Each Nitrogen atom has valence electrons (). To achieve an octet, each atom must share electrons.
Explanation:
The two Nitrogen nuclei share electrons total (3 pairs). This is represented as , where the three lines indicate a triple covalent bond.