2.1 AP bio

Matter

Anything that takes up space and has mass.

Atoms

The basic units of matter that make up all substances.

Elements

Pure substances that cannot be broken down into other substances by chemical reactions.

Compounds

Pure substances consisting of two or more elements in a fixed ratio.

Atomic Mass Unit

The mass of one proton or one neutron.

Essential Elements for Life

About 25 elements necessary for living organisms.

Major Elements in Living Matter

Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N) make up 96% of living matter.

Remaining Essential Elements

Phosphorus (P), Calcium (Ca), Sulfur (S), Potassium (K) make up most of the remaining 4%.

Isotopes

Forms of an element with different numbers of neutrons and different mass numbers.

Chemical Reactivity

Atoms tend to complete or empty their partially filled outer (valence) electron shell.

Ionic Bonds

Bonds formed by the transfer of electrons, resulting in + (cation) and - (anion) ions.

Covalent Bonds

Bonds formed by sharing a pair of electrons between two atoms.

Hydrogen Bonds

Weak bonds formed between a positive hydrogen atom in one molecule and a negative atom in another.

Polar Covalent Bonds

Bonds where a pair of electrons is not shared equally between two atoms, leading to a polar molecule.

Water Molecule

Composed of oxygen and hydrogen, with a polar structure resulting in unique properties of water.