Chapter 2 The Chemical Context of Life Flashcards
anion
a negatively charged ion
atom
The smallest unit of matter that retains the properties of an element.
atomic mass
The total mass of an atom, numerically equivalent to the mass in grams of 1 mole of the atom. (For an element with more than one isotope, the atomic mass is the average mass of the naturally occurring isotopes, weighted by their abundance.)
atomic nucleus
An atom’s dense central core, containing protons and neutrons.
atomic number
The number of protons in the nucleus of an atom, unique for each element and designated by a subscript.
cation
a positively charged ion
chemical bond
An attraction between two atoms, resulting from a sharing of outer-shell electrons or the presence of opposite charges on the atoms. The bonded atoms gain complete outer electron shells.
chemical equilibrium
In a chemical reaction, the state in which the rate of the forward reaction equals the rate of the reverse reaction, so that the relative concentrations of the reactants and products do not change with time.
chemical reaction
The making and breaking of chemical bonds, leading to changes in the composition of matter.
compound
A substance consisting of two or more different elements combined in a fixed ratio.
covalent bond
A type of strong chemical bond in which two atoms share one or more pairs of valence electrons.
dalton
A measure of mass for atoms and subatomic particles; the same as the atomic mass unit, or amu.
double bond
A double covalent bond; the sharing of two pairs of valence electrons by two atoms.
electron
A subatomic particle with a single negative electrical charge and a mass about 1/2,000 that of a neutron or proton. One or more electrons move around the nucleus of an atom.
electron shell
An energy level of electrons at a characteristic average distance from the nucleus of an atom.
electronegativity
The attraction of a given atom for the electrons of a covalent bond.
element
Any substance that cannot be broken down to any other substance by chemical reactions.
energy
The capacity to cause change, especially to do work (to move matter against an opposing force).
essential element
A chemical element required for an organism to survive, grow, and reproduce.
half-life
The amount of time it takes for 50% of a sample of a radioactive isotope to decay.
hydrogen bond
A type of weak chemical bond that is formed when the slightly positive hydrogen atom of a polar covalent bond in one molecule is attracted to the slightly negative atom of a polar covalent bond in another molecule or in another region of the same molecule.
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.
Ionic compound
A compound resulting from the formation of an ionic bond; also called a salt.
Isotope
One of several atomic forms of an element, each with the same number of protons but a different number of neutrons, thus differing in atomic mass.
mass number
The total number of protons and neutrons in an atom’s nucleus.
Matter
Anything that takes up space and has mass.
Molecule
Two or more atoms held together by covalent bonds.
neutron
A subatomic particle having no electrical charge (electrically neutral), with a mass of about 1.7×10–24g, found in the nucleus of an atom.
nonpolar covalent bond
A type of covalent bond in which electrons are shared equally between two atoms of similar electronegativity.
Orbital
The three-dimensional space where an electron is found 90% of the time.
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.
potential energy
The energy that matter possesses as a result of its location or spatial arrangement (structure).
product
A material resulting from a chemical reaction.
Proton
A subatomic particle with a single positive electrical charge, with a mass of about 1.7×10−24g, found in the nucleus of an atom.
radioactive isotope
An isotope (an atomic form of a chemical element) that is unstable; the nucleus decays spontaneously, giving off detectable particles and energy.
radiometric dating
A method for determining the absolute age of rocks and fossils, based on the half-life of radioactive isotopes.
reactant
A starting material in a chemical reaction.
Salt
A compound resulting from the formation of an ionic bond; also called an ionic compound.
single bond
A single covalent bond; the sharing of a pair of valence electrons by two atoms.
trace element
An element indispensable for life but required in extremely minute amounts.
Valence
The bonding capacity of a given atom; the number of covalent bonds that an atom can form, which usually equals the number of unpaired electrons in its outermost (valence) shell.
valence electron
An electron in the outermost electron shell.
valence shell
The outermost energy shell of an atom, containing the valence electrons involved in the chemical reactions of that atom.
van der Waals interactions
Weak attractions between molecules or parts of molecules that result from transient local partial charges.
