Biology Chapter 2: chemical context of life

Matter

Anything that takes up space and has mass.

Element

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

Molecule

Two or more atoms held together by bonds.

Compound

A substance consisting of two or more different elements combined in a fixed ratio.

Isotopes

Different atomic forms of the same element with the same number of protons but different numbers of neutrons, resulting in differing atomic masses.

Valence Electrons

Electrons in the outer shell of an atom that determine much of its chemical reactivity.

Duet Rule

Row 1 atoms are stable with 2 valence electrons.

Octet Rule

Row 2 atoms tend to gain, lose, or share electrons to achieve 8 valence electrons, resulting in a configuration similar to noble gases.

Covalent Bonds

Involve sharing a pair of valence electrons, with single bonds sharing 1 pair, double bonds sharing 2 pairs, and triple bonds sharing 3 pairs.

Polar Covalent Bond

Occurs with a moderate difference in electronegativity, resulting in unequal sharing of electrons and partial charges.

Ionic Bond

Forms when there is a very large difference in electronegativity, leading one atom to take an electron from another, creating oppositely charged ions.

Hydrogen Bonds

Weak attraction between hydrogen and another electronegative atom, involving attraction between partial positive and partial negative charges.

Chemical Reaction

The making and breaking of chemical bonds that changes the composition of matter.

Reactants

The substances you start with in a chemical reaction.

Products

The substances produced in a chemical reaction.

Chemical Equilibrium

Occurs when the forward reaction rate equals the reverse reaction rate, although biological systems rarely reach equilibrium due to constantly changing concentrations.