Chapter 2 Basic Chemistry

Matter

Anything that takes up space and has mass.

Element

A substance that cannot be broken down to other substances by chemical reactions.

Compound

A substance consisting of two or more elements in a fixed ratio with characteristics different from those of its elements.

Atomic Number

The number of protons in an atom's nucleus.

Atomic Mass

Approximately equal to the sum of protons and neutrons in an atom's nucleus.

Isotope

Atoms of the same element that differ in the number of neutrons.

Valence Electrons

Electrons in the outermost shell that determine the chemical behavior of an atom.

Covalent Bond

A bond formed by the sharing of a pair of valence electrons by two atoms.

Electronegativity

An atom's attraction for the electrons in a covalent bond.

Ionic Bond

A bond formed when one atom takes an electron from another atom, resulting in oppositely charged ions.

Hydrogen Bond

A weak bond formed when a hydrogen atom covalently bonded to one electronegative atom is attracted to another electronegative atom.

Van der Waals Interactions

Weak attractions between molecules that result from transient local partial charges.

Chemical Reaction

The making and breaking of chemical bonds.

Chemical Equilibrium

Reached when the rates of the forward and reverse reactions are equal, and concentrations of reactants and products remain constant.

Half-life

The time required for half of a sample of a radioactive isotope to decay.

Emergent Properties

Characteristics that arise from the arrangement and interactions of parts within a system.

Potential Energy

Stored energy that matter possesses due to its location or structure.

Kinetic Energy

The energy of motion.

Molecule

A group of two or more atoms bonded together.

Trace Elements

Elements required by organisms in minute quantities, such as iron (Fe), iodine (I), and zinc (Zn).