Biology Chapter 2: Life's Chemical Basis
radioisotope
Isotope with an unstable nucleus; decays into predictable daughter elements at a predictable rate
temperature
Measure of molecular motion
shell model
Model of electron distribution in an atom; orbitals are shown as nested circles, electrons as dots; 2-8-8-18
electron
Negatively charged subatomic particle that occupies orbitals around the atomic nucleus
atom
Particle that is a fundamental building block of matter; consists of varying numbers of electrons, protons, and neutrons
proton
Positively charged subatomic particle in the nucleus of all atoms. The number of protons (the atomic number) defines the element
radioactive decay
Process by which atoms of a radioisotope spontaneously emit energy and subatomic particles when their nucleus disintegrates
buffer system
Set of chemicals that can keep the pH of a solution stable by alternately donating and accepting ions that contribute to pH
solvent
Substance, typically a liquid, that can dissolve other substances; e.g., water
cohesion
Tendency of molecules to stick together under tension; a property of liquid water
atomic number
The number of protons in the nucleus of atoms of a given element
nucleus
The positively charged dense center of an atom
mass number
Total number of protons an neutrons in the nucleus of an element's atoms
evaporation
Transition of a liquid to a gas; requires energy input
mixture
Two or more types of molecules intermingled in proportions that vary
ionic bond
Type of chemical bond; strong mutual attraction between ions of opposite charge
compounds
Type of molecule that has atoms of more than one element
neutron
Uncharged subatomic particle in the atomic nucleus
hydrogen ions (H+)
an atom of hydrogen that has lost its electron. they are the key to the reactions of acids
PET scan
positron emission tomography scan; a visual display of brain activity that detects where a radioactive form of glucose goes while the brain performs a given task
hydroxide ions (-OH)
released from bases when added to water
isotopes
Forms of an element that differ in the number of neutrons their atoms carry
molecule
Group of two or more atoms joined by chemical bonds
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 the bonding electrons are shared equally by the bonded atoms, resulting in a balanced distribution of electrical charge
solute
A dissolved substance
electronegativity
A measure of an atom's ability to pull electrons away from other atoms
pH
A measure of the number of hydrogen ions in a solution
tracer
A molecule with a detectable label attached; researchers can track it after delivering it into a cell or other system
bases, basic
A substance that accepts hydrogen ions as it dissolves in water
elements
A substance that consists only of atoms with the same number of protons
orbital
A three-dimensional region around the nucleus that indicates the probable location of an electron
triple covalent bond
A type of covalent bond in which three pairs of electrons are shared by two atoms
double covalent bond
A type of covalent bond in which two atoms share two pairs of electrons; symbolized by a pair of lines between the bonded atoms
free radical
An atom or group of atoms with at least one unpaired electron
chemical bond
An attractive force that arises between two atoms when their electrons interact
polarity
Any separation of charge into distinct positive and negative regions
acids, acidic
Any substance that releases hydrogen ions in water
ion
Atom that carries a charge because of an unequal number of protons and electrons
hydrogen bond
Attraction that forms between a covalently bonded hydrogen atom and an electronegative atom taking part in a separate covalent bond
covalent bond
Chemical bond in which two atoms share a pair of electrons
salt
Compound that dissolves easily in water and releases ions other than H+ and OH-
hydrophilic
Describes a substance that dissolves easily in water; e.g., a salt Having a strong affinity for water
hydrophobic
Describes a substance that resists dissolving in water; e.g., an oil Lacking affinity for water