Chapter 2: Water and Carbon – The Chemical Basis of Life (Biological Science, 8th Edition)

Vocabulary flashcards covering key terms from Chapter 2: atoms, isotopes, bonds, and electronegativity.

Element

A chemical substance made of only one type of atom.

Atom

The smallest unit of an element; electrically neutral.

Nucleus

The center of an atom containing protons and neutrons.

Proton

+Positively charged subatomic particle in the nucleus; +1 charge.

Neutron

Electrically neutral subatomic particle in the nucleus; no charge.

Electron

Negatively charged subatomic particle orbiting the nucleus; −1 charge.

Atomic number

The number of protons in the nucleus of an atom.

Mass number

The sum of protons and neutrons in an atom.

Isotope

Different forms of an element with different numbers of neutrons; same number of protons but different masses; most are stable, some are radioactive.

Radioactive isotope

An isotope that is unstable and decays over time.

CHNOPS

The six elements that make up over 99% of atoms in living organisms: carbon, hydrogen, nitrogen, oxygen, phosphorus, sulfur.

Covalent bond

A chemical bond formed when two or more atoms share electrons (e.g., H2, H2O).

Molecule

A chemical substance in which two or more atoms are held together by covalent bonds.

Compound

A chemical substance made of atoms of different elements (e.g., H2O, NaCl).

Electronegativity

The tendency of an atom to attract shared electrons toward its nucleus; in biology, O > N > C ≈ H.

Bond polarity

Unequal sharing of electrons in a covalent bond, leading to partial positive and partial negative charges.

Unpaired electrons

The number of unpaired electrons in an atom’s outer shell determines how many covalent bonds it can form.