covalent bonds

🤔 Covalent Bond Formation

Covalent bonds are formed when atoms share electrons in their outer shells (valence shells). This typically occurs between non-metal atoms, which are located on the right-hand side and upper part of the periodic table. Examples of common non-metals include carbon, nitrogen, oxygen, and halogens.

Non-metals tend to have valence shells that are half or more than half full. Because of their strong attraction for additional electrons, it is energetically unfavorable for them to lose electrons; therefore, they share electrons instead.

The sharing of electrons happens through the overlapping of orbitals, creating a bonding orbital or covalent bond containing two electrons. Depending on the available space in the outer shell, atoms can form single, double, or triple bonds.

📊 Representing Covalent Bonds

Covalent bonds can be represented in two ways:

  • Straight line: A single line represents a single covalent bond.

  • Dot and cross diagrams: These diagrams illustrate only the valence electrons involved in bonding. (See separate video on dot and cross diagrams for more details).

🤝 Characteristics of Covalent Bonds

  • Directional: Covalent bonds are fixed in position, unlike ionic bonds which are formed by electrostatic attraction.

  • Strong: The close proximity of atoms due to orbital overlap results in strong bonds.

  • Non-Polar: Electrons are generally shared equally, resulting in little to no polarity.

🧱 Covalent Structures: Small vs. Giant

There are two main types of covalent structures:

  • Small molecules: Examples include water (H₂O) and other simple organic molecules.

  • Giant covalent structures: Examples include diamond and silicon dioxide (SiO₂). These form large, continuous lattices or chains.

🌡 Physical Properties and Covalent Compounds

The properties of covalent compounds are greatly influenced by the type of structure:

Structure TypeMelting/Boiling PointVolatilityElectrical Conductivity

Small molecules

Low

High

Poor

Giant structures

Very high

Very Low

Poor (except for graphite)

💎 Giant Covalent Structures: An In-depth Look

Giant covalent structures like diamond involve many atoms bonded together in a continuous network. In diamond, each carbon atom forms four covalent bonds with four other carbon atoms. This creates an extremely strong, rigid structure.

The high melting and boiling points of giant covalent compounds are a result of the need to break strong covalent bonds to change their state.

🔬 Allotropes of Non-Metals

Allotropes are different structural forms of the same element. Diamond is an allotrope of carbon; other examples of allotropes include the fullerenes (e.g., C₇₀, buckminsterfullerene).

🤔 Identifying Covalent Compounds

The following are examples of covalent compounds:

  • Carbon dioxide (CO₂)

  • Carbon monoxide (CO)

  • Methanol (CH₃OH)

  • C₇₀ (Fullerene)

  • Silicon dioxide (SiO₂)

These compounds exhibit properties consistent with covalent bonding, such as low melting points (for small molecules) and poor electrical conductivity. Their constituent elements are primarily non-metals.