Atoms, Molecules and PH

Element

A distinct type of substance or matter. Each element has atoms that contain a unique number of protons in the nucleus.

Atom

Smallest unit of matter. The fundamental unit of an element, made of protons, neutrons, and electrons.

Ion

An atom or molecule that carries a full charge—positive if it contains more protons than electrons, and negative if it contains more electrons than protons.

Molecule

A structure made of two or more atoms held together by covalent bonds.

Covalent bond

An attraction between two atoms based on shared electrons.

Electronegativity

The tendency for an atom's nucleus to attract the shared electrons in a covalent bond.

Polar covalent bond

An asymmetry in the position of shared electrons, due to differences in the electronegativities of the atoms involved, that creates a partial positive charge on one atom and a partial negative charge on the second atom.

Nonpolar covalent bond

Equal sharing of electrons, due to equal or roughly equal electronegativities of the atoms involved.

Hydrogen bond

An attraction between a partial positive charge on a hydrogen atom and a partial negative charge on another atom

Hydrophilic molecule

a molecule that can readily interact with the partial charges on water.

Hydrophobic molecule

a molecule that contains mostly nonpolar covalent bonds and cannot readily interact with the partial charges on water.

Ion

an atom or molecule that carries a full charge.

Acid

an ion or molecule that releases a proton.

Base

an ion or molecule that acquires a proton.

pH scale

a method for expressing the concentration of protons in a solution—specifically, the negative of the base 10 logarithm of the proton concentration