Biology CH2a

Element

Cannot be broken down into other substances by chemical reactions.

Matter

Anything that takes up space and has mass.

Chemistry

The study of matter.

Compound

Two or more elements in a fixed ratio.

Atom

Smallest unit having the properties of an element.

Subatomic particles

The composition of an atom, including protons, electrons, and neutrons.

Proton

Positively charged particle in the center of an atom, 1 dalton, determines chemical identity.

Electron

Negatively charged particle that orbits the nucleus, has negligible mass, and moves at the speed of light.

Neutron

Neutral particle in the center of an atom, 1 dalton.

Atomic mass

The total number of protons and neutrons in an atom.

Atomic Number

The number of protons in an atom.

Isotope

Different atomic form of the same element, with the same number of protons but a different number of neutrons.

Electron shell

Represents energy levels in an atom.

Valence shell

The outermost shell of an atom that contains valence electrons.

Valence electrons

Outermost electrons with high energy.

Covalent bond

The sharing of a pair of valence electrons between two atoms (strongest bond).

Hydrogen bond

A weak bond where partial positive hydrogen is attracted to an electronegative atom.

Ionic bond

Attraction between oppositely charged ions (medium strength).

Ion

A charged atom or molecule.

Molecule

Made of two or more atoms bonded by covalent bonds.

Electronegativity

The affinity for electrons; the more electronegative an atom, the more it pulls shared electrons to itself.

Polar covalent bond

A bond between elements with different electronegative values.

Nonpolar covalent bond

A bond between elements that have the same electronegativity.

Van Der Waals interaction

A weak attraction when atoms are so close that their outer electron shells barely touch.

Cohesion

Hydrogen bonds cause water molecules to stay close to each other.

Adhesion

The clinging of one substance to another.

Surface tension

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

Kinetic Energy

The energy of motion.

Thermal Energy

Kinetic energy associated with the random movement of atoms or molecules.

Temperature

The average kinetic energy of the molecules in a body of matter.

Heat

The energy associated with molecular movement; a large amount of energy is required to disrupt water.

Calorie

The energy required to raise 1 gram of water by 1°C.

Kilocalorie

A food calorie, equivalent to 1000 calories.

Specific heat

The amount of heat that must be absorbed or lost for 1 gram of a substance to change by 1°C.

Heat of vaporization

The energy needed to convert a liquid into a gas.

Solvent

The dissolving agent of a solution.

Solute

The substance that is dissolved in a solution.

Solution

A liquid that is a homogeneous mixture of two or more substances.

Aqueous solution

A solution in which water is the solvent.

Hydrophilic

Substances that are attracted to water and will dissolve in it (polar, ionic).

Hydrophobic

Substances that are not attracted to water and will not dissolve in it (nonpolar).

Acid

A compound that ionizes to release hydrogen ions and increase H+ concentration in a solution.

Base

A compound that ionizes to release OH- or directly combines with H+ to decrease H+ concentration.

Alkaline

A term used to describe a base.

pH

A measure of hydrogen ion concentration, or hydrogen potential.

Buffer

Substances that can resist changes in pH.

Acid rain

Rain with a pH of 4.5 and below.

Ocean acidification

The process of ocean absorption of CO2, which combines with water to form carbonic acid.