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Chapter 2
The Chemical Context of Life
42
Biology
12th Grade
12/01/2012

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Term
Matter
Definition
Anything that takes up space and has mass.
Term
Element
Definition
Any substance that cannot be broken down to any other substance by chemical reactions.
Term
Compound
Definition
A substance consisting of two or more different elements combined in a fixed ratio.
Term
Essential Elements
Definition
A chemical element required for an organism to grow, survive, and reproduce.
Term
Trace Elements
Definition
An element indispensable for life but required in extremely minute amouns.
Term
Atom
Definition
The smallest unit of matter that retains the properties of an element.
Term
Neutrons
Definition
A subatomic particle having no electrical charge (electrically neutral), with a mass of about 1.7x10-24 g, found in the nucleus of an atom.
Term
Protons
Definition
A subatomic particle with a single positive electrical charge, with a mass of about 1.7x10-24g, found in the nucleus of an atom.
Term
 Electron
Definition
A subatomic particle with a single negative electrical charge and a mass about 1/2000 that of a neutron or proton. One or more electrons move around the nucleus of an atom.
Term
Atomic Nucleus
Definition
An atom's dense central core, containing protons and neutrons.
Term
dalton
Definition
A measure of mass for atoms and subatomic particles; the same as the atomic mass unit, or amu.
Term
Atomic Number
Definition
The number of protons in the nucleus of an atom, unique for each element and designated by a subscript to the left of the elemental symbol.
Term
Mass Number
Definition
The sum of the number of protons and neutrons in an atom's nucleus.
Term
Atomic Mass
Definition
The total mass of an atom, which is the mass in grams of 1 mole of the atom.
Term
Isotope
Definition
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.
Term
Radioactive Isotope
Definition
An isotope (an atomic form of a chemical element) that is unstable; the nucleus decays spontaneously, giving off detectable particles and energy.
Term
Energy
Definition
The capacity to cause change, especially to do work (to move matter against an opposing force).
Term
Potential Energy
Definition
The energy that matter posseses as a result of its location or spatial arrangement (structure).
Term
Electron Shell
Definition
An energy level of electrons at a characteristic average distance from the nucleus of an atom.
Term
Valence Electron
Definition
An electron in the outermost electron shell.
Term
Valence Shell
Definition
The outermost energy shell of an atom, containing the valence electrons involved in the chemical reactions of that atom.
Term
Orbital
Definition
The three-dimensional space where an electron is found 90% of the time.
Term
Chemical Bond
Definition
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.
Term
Covalent Bond
Definition
A type of strong chemical bond in which two atoms share one or more pairs of valence electrons.
Term
Molecule
Definition
Two or more atoms held together by covalent bonds.
Term
Single Bond
Definition
A single covalent bond; the sharing of a pair of valence electrons by two atoms.
Term
Double Bond
Definition
A double covalent bond; the sharing of two pairs of valence electrons by two atoms.
Term
Valence
Definition
The bonding capacity of a given atom; usually equals the number of unpaired electrons required to complete the atom's outermost (valence) shell.
Term
Electronegativity
Definition
The attraction of a given atom for the electrons of a covalent bond.
Term
Nonpolar Covalent Bond
Definition
A type of covalent bond in which electrons are shared equally between two atoms of similar electronegativity.
Term
Polar Covalent Bond
Definition
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.
Term
Ion
Definition
An atom or group of atoms that has gained or lost one more electrons, thus aquiring a charge.
Term
Cation
Definition
A positively charged ion.
Term
Anion
Definition
A negatively charged ion.
Term
Ionic Compound
Definition
A compound resulting from the formation of an ionic bond; also called a salt.
Term
Salt
Definition
A compound resulting from the formation of an ionic bond; also called an ionic compound.
Term
Hydrogen Bond
Definition
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.
Term
van der Waals interactions
Definition
Weak attractions between molecules or parts of molecules that result from transient local partial charges.
Term
Chemical Reaction
Definition
The making and breaking of chemical bonds, leading to changes in the composition of matter.
Term
Reactant
Definition
A starting material in a chemical reaction.
Term
Product
Definition
A material resulting from a chemical reaction.
Term
Chemical Equilibrium
Definition
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.
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