Chapter 2: The Chemical Context of Life

matter

anything that takes up space and has mass

element

a substance that cannot be broken down to othert substances by chemical reactions

compound

a substance consisting of two or more elements in a fixed ratio

essential elements (%, list)

96%; carbon, hydrogen, oxygen, and nitrogen

remaining 4% of elements in living matter

calcium, phosphorus, potassium, sulfur

trace elements

those rquired by an organism in only minute quantities; boron, chromium, cobalt, copper, fluorine, iodine, iron, manganese, molybdenum, selenium, silicon, tin, vanadium, and zinc

atom

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

neutrons

no charge; 1 amu; nucleus

protons

positive charge; 1 amu; nucleus

electrons

negative charge; 1/1836 amu; orbit nucleus

atomic number

the number of protons in an element's nucleus

mass number

the sum of protons plus neutrons in the nucleus

atomic mass

the atoms total mass; approximated by mass number

AZXC

mass number, atomic number, element symbol, charge

isotopes

two atoms of an element that differ in number of neutrons

radioactive isotopes

decay spontaneously, giving off particles and energy

half-life

the time it takes for half of a sample to decay

energy

the capacity to cause change

potential energy

the energy that matter has because of its location or structure

electron shell/energy level

an electron's state of potential energy

valence electrons

in the outermost shell; determine chemical behavior of an atom

orbital

the three-dimensional space where an electron is found 90% of the time; each electron shell consists of a specific number of orbitals

chemical bonds

attractions that hold atoms close together

covalent bond

sharing electrons between nonmetals (right side of table); the shared electrons count as part of each atom's valence shell

hydrogen bonds

attractive forces; not real bonds; very weak individually, strong collectively; forms when a hydrogen atom covalently bonded to one electronegative atom is also attracted to another electronegative atom

molecule

two or more atoms held together by covalent bonds

single/double bond

the sharing of 1 / 2 pairs of electrons

valence

an atom's bonding capacity

electronegativity

an atom's attraction for the electrons in a covalent bond

nonpolar covalent bond

the atoms share the electron equally

polar covalent bond

one atom is more electronegative, and the atoms do not share the electron equally; causes a partial positive or negative charge for each atom or molecule

ion

a charged atom or molecule

cation

positively charged ion

anion

negatively charged ion

ionic compounds

salts; compounds formed by ionic bonds

van der waals interactions

attractions between molecules that are close together as a resuolt of electrons that are not evenly distributed within the atoms

chemical reactions

the making and breaking of chemical bonds

reactants

the starting molecules of a chemical reaction

products

the final molecules of a chemical reaction

chemical equilibrium

when the forward and reverse reactions occur at the same rate

ionic bonding

transferring electrons from a metal to a nonmetal