CHAPTER 2 ATOMS & MOLECULES

C, H, O , N

most common elements in living things

ATOM

smallest unit of an element that retains the element's

ATOMIC NUMBER

fixed number of protons in the atomic nucleus

ATOMIC MASS UNIT (AMU)

mass of a subatomic particle

ATOMIC MASS

the total number of protons neutrons

ISOTOPES

atoms of the same element with varying numbers of neutrons

RADIOISOTOPE

unstable and tend to decay to a more stable isotope

ORBITALS

regions of 3-D space in which electrons move

VALENCE SHELL

outermost electron shell, which the most energetic electrons occupy

INORGANIC COMPOUNDS

small, simple substances (ex: water, simple acids & bases, and simple salts)

ORGANIC COMPOUNDS

large, complex carbon-containing compounds

MOLECULAR MASS OF A COMPOUND

the sum of the atomic masses of the component atoms of a single molecule

1 MOLE

the amount of a compound whose mass in grams is equivalent to its molecular mass

BOND ENERGY

energy necessary to break a chemical bond

COVALENT BONDS

share electrons between atoms to fill each atom's valence shell

COVALENT MOLECULE

consists of atoms joined by covalent bonds

Ex. hydrogen gas (H2)

COVALENT COMPOUND

unlike atoms linked by covalent bonds (ex methane gas CH4)

LEWIS STRUCTURE

a simple way of representing valence electrons by placing dots around the element's chemical symbol

ORBITAL HYBRIDIZATION

atoms form covalent bonds that require orbitals in valence shells to become rearranged, affecting the shape of the end molecule

ELECTRONEGATIVITY

measure of an atom's attraction for shared electrons in chemical bonds

NONPOLAR COVALENT BOND

covalently bonded atoms with similar electronegativities/ similar shared electrons

POLAR COVALENT BOND

covalent bond between atoms that differ in electronegativity

ION

an atom or group

HYDROGEN BONDS

relatively weak bonds that are very important in living organisms

VAN DER WAALS

Weak attractions between molecules or parts of molecules that result from transient local partial charges.

COHESION

occurs when water molecules stick to one another

ADHESION

the ability of water to stick to other substances

CAPILLARY ACTION

tendency of water to move in narrow tubes

SURFACE TENSION

occurs when molecules at water's surface crowd together, producing a strong layer

HYDRATION

the process in which an ion is surrounded by water molecules arranged in a specific manner

ACID

substance that dissociates in solution to yield hydrogen ions & anion; a proton donor

BASE

substance that dissociates in solution to yield a hydroxide ion and cation; a proton acceptor

BUFFER

a substance that resists changes in pH when acid or base is added

SALT

compound in which the hydrogen ion of an acid is replaced by some other cation