Biology Chapter 2 Notes

Matter

Anything that has mass and takes up space.

Atom

The smallest unit of matter that forms all chemical substances.

Compound

Substances that consist of two or more different elements combined at a fixed ratio.

Essential Elements

About 20-25% of the 92 natural elements required for life.

Trace Elements

Elements required by an organism in only minute quantities.

Protons

Subatomic particles with a positive charge found in the nucleus.

Neutrons

Subatomic particles that are neutral and found in the nucleus.

Electrons

Subatomic particles with a negative charge found in orbitals.

Isotope

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

Atomic Number

Equals the number of protons in an atom.

Atomic Mass

The total mass of an atom, which is the number of protons plus the number of neutrons.

Covalent Bond

A chemical bond where electrons are shared to fill valence shells.

Ionic Bond

A bond formed by the transfer of electrons, resulting in cations and anions.

Hydrogen Bond

The attraction between a hydrogen atom from one molecule and an electronegative atom from another molecule.

Chemical Reaction

A process where one or more substances are changed into other substances.

Hydrophilic

Substances that readily dissolve in water, often having ionic or polar covalent bonds.

Hydrophobic

Substances that do not dissolve in water, often being nonpolar molecules.

Buffers

Substances that minimize changes in concentrations of H+ and OH- in a solution.