Chemical Bonds and Molecular Structures in Biology

Chemical Bonds

A combination between two or more atoms to form a compound (new substance).

Ionic Bond

Electrons are completely transferred from one atom to another, resulting in ions held together electrostatically.

Covalent Bond

Formed when atoms share electrons, resulting in a molecule.

Example of Ionic Bond

NaCl: Sodium and chlorine combine to form sodium chloride, table salt.

Example of Covalent Bond

H2O: Hydrogen and oxygen combine to make water.

Salt Characteristics

Salts have a crystalline structure, high melting temperature, usually dissolve in water, and the resulting solution is a conductor.

Molecule

Formed when atoms share electrons.

Lewis Dot Diagrams

A technique for visualizing valence electrons to determine which atoms will bond to each other.

Bonds in Lewis Dot Diagrams

Bonds are shown as shared electrons or as a line for a single bond or two lines for a double bond.

Polar Bonds

Valence electrons are not shared equally between atoms in a bond or molecule.

Examples of Polar Bonds

O—H, C—O, N—H.

Hydrophilic Molecules

Molecules with polar bonds that often dissolve well in water.

Hydrophobic Molecules

Molecules with non-polar bonds that often dissolve poorly in water.

Common Biological Elements in Polar Bonds

Oxygen and Nitrogen.

Hydrogen Bonds

Typically between different molecules, much weaker than covalent bonds.

Characteristics of Water

Hydrogen bonds are responsible for many unique characteristics of water.

Hydrophilic Substances

Dissolve easily in water, include ionic compounds and molecules with N's and O's.

Hydrophobic Substances

Do not dissolve easily in water, include molecules made up mostly of C's and H's.