Introduction chemistry for biologists

Hydrolysis

A reaction that uses water to break chemical bonds in a molecule.

Condensation reaction (Dehydration synthesis)

Two molecules join to form a larger molecule, usually with water released.

Redox reaction

A reaction involving the transfer of electrons between reactants.

Oxidation

Loss of electrons (or gain of oxygen) during a reaction.

Reduction

Gain of electrons (or loss of oxygen) during a reaction.

Neutralization reaction

Acid and base react to form water and a salt.

Acid

Substance that increases hydrogen ion (H+) concentration in water (pH < 7).

Base

Substance that increases hydroxide ion (OH-) concentration in water (pH > 7).

Hydrogen ion (H+)

The positively charged ion that determines acidity in solution.

Hydroxide ion (OH-)

The negatively charged ion that contributes to basicity in solution.

pH

A measure of how acidic or basic a solution is, based on [H+] in mol/L.

pH scale

Logarithmic 0–14 scale expressing acidity or basicity.

Ionization

Dissociation of a molecule into ions in solution.

Strong acid

An acid that completely ionizes in water (e.g., HCl).

Weak acid

An acid that only partially ionizes in water, with equilibrium.

Strong base

A base that completely ionizes in water (e.g., NaOH).

Weak base

A base that partially ionizes in water.

Buffer

Substance or system that resists pH changes by neutralizing added acids or bases. (proteins, amino acids, carbonic acid)

Intramolecular Bonds

Bonds within Molecules

Intermolecular Bonds

Bonds between Molecules

Types of intramolecular bonds

• Ionic Bonds

• Covalent Bonds

• Polar Covalent Bonds

An ionic bond

forms when one atom transfers electrons to another atom (usually form between metals and non-metals)

A covalent bond

forms when two or more non-metals share one or more pairs of electrons.

A polar covalent bond

is a special type of covalent bond. It is formed when there is an unequal sharing of valence electrons between atoms in the pair, with one atom pulling harder on the electrons than the other.

Dipole molecules

one end being slightly positive and the other, slightly negative.

Electronegativity

is a measure of an atom’s ability to attract electrons in a chemical bond.

There are three types of intermolecular bonds which are collectively called van der Waals forces are

1. London forces

2. Dipole-dipole forces

3. Hydrogen bonds

London forces

• Hold non-polar molecules together

• Very weak forces of attraction

• Momentary dipoles are created by the electrons contained within the compound, which are constantly in motion.

Dipole-dipole forces

Hold polar molecules together.

Hydrogen bonding

Is formed between the electropositive hydrogen dipole and an electronegative dipole of oxygen, chlorine, or fluorine.