BIO121 Chapter 2

Montco BIO121 Chapter 2 Key Terms

acid

A substance that increases the hydrogen ion (H⁺) concentration in a solution

adhesion

The attraction between different kinds of molecules

aqueous solution

A solution in which water is the solvent

atom

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

atomic mass

The total mass of an atom; also called atomic weight. Given as a whole number, the atomic mass approximately equals the mass number

atomic number

The number of protons in each atom of a particular element

base

A substance that decreases the hydrogen ion (H⁺) concentration in a solution

buffer

A chemical substance that minimizes changes in pH by accepting hydrogen ions from or donating hydrogen ions to solutions

chemical bond

An attraction between two atoms resulting from a sharing of outer-shell electrons or the presence of opposite charges on the atoms. The bonded atoms gain complete outer electron shells

chemical reaction

The making and breaking of chemical bonds, leading to changes in the composition of matter

cohesion

The sticking together of molecules of the same kind, often by hydrogen bonds

compound

A substance containing two or more elements in a fixed ratio

covalent bond

A type of strong chemical bond in which two atoms share one or more pairs of valence electrons

electron

A subatomic particle with a single negative electrical charge. One or more electrons move around the nucleus of an atom

electron shell

A level of electrons at a characteristic average distance from the nucleus of an atom

electronegativity

The attraction of a given atom for the electrons of a covalent bond

element

A substance that cannot be broken down to other substances by chemical means

evaporative cooling

The process in which the surface of an object becomes cooler during evaporation, a result of the molecules with the greatest energy changing from the liquid to the gaseous state

heat

Thermal energy in transfer from one body of matter to another

hydrogen bond

A type of weak chemical bond formed when the slightly positive hydrogen atom of a polar covalent bond in one molecule is attracted to the slightly negative atom of a polar covalent bond in another molecule (or in another region of the same molecule)

ion

An atom or group of atoms that has gained or lost one or more electrons, thus acquiring an electrical charge

ionic bond

A chemical bond resulting from the attraction between oppositely charged ions

isotope

One of several atomic forms of an element, each with the same number of protons but a different number of neutrons

mass number

The sum of the number of protons and neutrons in an atom’s nucleus

matter

Anything that occupies space and has mass

molecule

Two or more atoms held together by covalent bonds

neutron

A subatomic particle having no electrical charge, found in the nucleus of an atom

nonpolar covalent bond

A type of covalent bond in which electrons are shared equally between two atoms of similar electronegativity

nucleus

(1) An atom’s central core, containing protons and neutrons. (2) The organelle of a eukaryotic cell that contains the genetic material in the form of chromosomes, made of chromatin

ocean acidification

Process by which the pH of the ocean is lowered (made more acidic) when excess atmospheric CO₂ dissolves in seawater

pH scale

A measure of the acidity of a solution, ranging in value from 0 (most acidic) to 14 (most basic)

polar covalent bond

A covalent bond between atoms that differ in electronegativity. The shared electrons are pulled closer to the more electronegative atom, making it slightly negative and the other atom slightly positive

polar molecule

A molecule containing polar covalent bonds and having an unequal distribution of charges in different regions of the molecule

product

An ending material in a chemical reaction

proton

A subatomic particle with a single positive electrical charge, found in the nucleus of an atom

radioactive isotope

An isotope whose nucleus decays spontaneously, giving off particles and energy

reactant

A starting material in a chemical reaction

salt

A compound resulting from the formation of an ionic bond

solute

A substance that is dissolved in a solution

solution

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

solvent

The dissolving agent of a solution. Water is the most versatile solvent known

surface tension

A measure of how difficult it is to stretch or break the surface of a liquid. Water has a high surface tension because of the hydrogen bonding of surface molecules