Chapter 2: Chemical Basis of Life

matter

anything that occupies space and has mass

element

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

atom

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

compound

a substance containing two or more elements in a fixed ratio

molecule

two or more atoms held together by covalent bonds

proton

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

neutron

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

electron

a subatomic particle with a single negative electrical charge, one or more electrons move around the nucleus of an atom

isotope

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

ion

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

ionic bond

a chemical bond resulting from the attraction between oppositely charged ions

covalent bond

a strong chemical bond in which two atoms share one or more pairs of outer-shell electrons

hydrogen bond

a type of weak chemical bond formed when the partially positive hydrogen atom participating in a polar covalent bond in one molecule is attracted to the partially negative atom participating in a polar covalent bond in another molecule (or in another regi

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

nonpolar covalent bond

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

cohesion

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

adhesion

the attraction between different kinds of molecules

acid

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

base

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

buffer

a chemical substance that resists changes in pH by accepting hydrogen ions from or donating hydrogen ions to solutions