Chapter 2: The Chemical Basis of Life Study Guide.

Matter

Anything that occupies space and has mass.

Element

A substance that cannot be broken down into simpler substances by chemical means.

Compound

A substance made of two or more elements in a fixed ratio.

Atom

The smallest unit of matter that retains the properties of an element.

Trace element

An element essential for life but required in very small amounts.

Protons

Positive charge, found in nucleus, mass ~1 amu.

Neutrons

Neutral charge, found in nucleus, mass ~1 amu.

Electrons

Negative charge, orbit nucleus, negligible mass.

Atomic number

The number of protons in the nucleus.

Mass number

The number of protons + neutrons.

Isotope

Atoms of the same element with different numbers of neutrons.

Radioactive isotope

An isotope with an unstable nucleus that decays over time, releasing radiation.

Electron configuration

Arrangement of electrons that determines chemical behavior by filling outer shells.

Valence electrons

Electrons in the outermost shell that participate in bonding.

Electronegativity

An atom’s ability to attract shared electrons in a bond.

Covalent bond

A bond formed when two atoms share electrons.

Nonpolar covalent bond

Shared electrons are distributed equally between atoms.

Polar covalent bond

Shared electrons are distributed unequally due to electronegativity differences.

Hydrogen bond

Weak attraction between hydrogen in one polar molecule and an electronegative atom in another.

Ionic bond

Bond formed when electrons are transferred, creating oppositely charged ions.

Cation

Positively charged ion (lost electrons).

Anion

Negatively charged ion (gained electrons).

Chemical reaction

Process where bonds are broken and formed; reactants change into products.

Reactant

Starting substance in a chemical reaction.

Product

Substance formed as a result of a chemical reaction.

Cohesion

Attraction between molecules of the same substance.

Adhesion

Attraction between molecules of different substances.

Surface tension

Measure of how difficult it is to stretch or break the surface of a liquid.

Capillary action

Ability of water to move upward through narrow tubes due to cohesion and adhesion.

Evaporative cooling

Cooling that occurs when water molecules with the most energy evaporate.

High specific heat

Property of water that allows it to resist temperature changes.

Ice insulation

Ice floats because hydrogen bonds make it less dense than liquid water.

Universal solvent

Water dissolves many substances due to polarity and hydrogen bonding.

Solution

A homogeneous mixture of substances.

Solvent

Substance that dissolves another substance.

Solute

Substance that is dissolved in a solvent.

Aqueous solution

A solution where water is the solvent.

Acid

Substance that donates H+ ions to a solution (pH < 7).

Base

Substance that accepts H+ ions or donates OH

Buffer

Substance that minimizes changes in pH by accepting or donating H+.

pH scale

Measures concentration of H+ ions in a solution; 0 = acidic, 7 = neutral, 14 = basic.