ap bio vocab ch. 2

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matter
anything that occupies space and has mass
element
a substance that cannot be broken down to other substances by ordinary chemical means
compound
a substance consisting of two or more different elements combined in a fixed ratio
trace elements
account for less than .01% of human body weight but are still essential to the body, iron
proton
a subatomic particle with a single positive charge
electron
a subatomic particle with a single negative charge
neutron
a subatomic particle that is electrically neutral or has no charge
nucleus
an atom's central core
atomic number
the number of protons in an element
mass number
the sum of the number of protons and neutrons in an element's nucleus
atomic mass
approximately equal to the mass number
isotopes
contain the same number of protons and behave identically in chemical reactions but have different numbers of neutrons
radioactive isotope
an isotope in which the nucleus decays and gives off radioactivity
electron shells
certain energy levels where electrons move around the nucleus
chemical bonds
attractions that hold atoms close together
molecule
two or more atoms held together by covalent bonds form this
electronegativity
an atom's attraction for shared electrons
nonpolar covalent bonds
bond that is formed in molecules where the identical atoms exert an equal pull on the electrons
polar covalent bond
a bond produced by unequal sharing of electrons
polar molecule
a molecule that has an unequal distribution of charges
ion
an atom or molecule with an electrical charge resulting from a gain or loss of one or more electrons
ionic bond
a bond resulting from two ions with opposite charges attracting each other
salt
ionic compound, sodium chloride
hydrogen bond
a bond found on a hydrogen atom
chemical reaction
the breaking and making of chemical bonds that leads to changes in the composition of matter
reactants
the starting materials in a chemical reaction
product
material resulting from a chemical reaction
cohesion
the tendency of molecules of the same kind to stick together
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
heat
the amount of energy associated with the movement of atoms and molecules in a body of matter
temperature
measures the intensity of heat, the average speed of molecules
evaporative cooling
when a substance evaporates and the remaining surface of the liquid cools down
solution
a liquid consisting of a uniform mixture of two or more substances
solvent
the dissolving agent
solute
the substance that is dissolved
aqueous solution
a solution in which water is the solvent
acid
a compound that donates hydrogen ions to solutions
base
a compound that accepts hydrogen ions and removes them from solution
pH scale
used to describe how acidic or basic a solution is
buffers
substances that minimize changes to pH
acid precipitation
rain, snow or fog with a pH lower than 5.2
ocean acidification
Co2 dissolving in seawater lowers ocean pH