Chapter 2: The Chemical Context of Life Flashcards
Valence shell
The outermost energy shell of an atom, containing the valence electrons involved in the chemical reactions of that atom.
Cation
A positively charged ion.
Trace elements
An element indispensable for life but required in extremely minute amounts.
Ionic compounds
A compound resulting from the formation of an ionic bond; also called a salt.
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.)
Van der Waals interactions
Weak attractions between molecules or parts of molecules that result from transient local partial charges.
Protons
A subatomic particle with a single positive electrical charge, with a mass of about 1.7 times 10 to the negative 24 g, 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.
Reactants
A starting material in a chemical reaction.
Anion
A negatively charged ion.
Element
Any substance that cannot be broken down to any other substance by chemical reactions.
Valence electrons
An electron in the outermost electron shell.
Salts
A compound resulting from the formation of an ionic bond; also called an ionic compound.
Potential energy
The energy that matter possesses as a result of its location or spatial arrangement (structure).
Energy
The capacity to cause change, especially to do work (to move matter against an opposing force).
Molecule
Two or more atoms held together by covalent bonds.
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.
Ionic bond
A chemical bond resulting from the attraction between oppositely charged ions.
Chemical bonds
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.
Ions
An atom or group of atoms that has gained or lost one or more electrons, thus acquiring a charge.
Products
A material resulting from a chemical reaction.
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.
Atomic number
The number of protons in the nucleus of an atom, unique for each element and designated by a subscript.
Neutrons
A subatomic particle having no electrical charge (electrically neutral), with a mass of about 1.7 times 10 to the negative 24 g, found in the nucleus of an atom.
Orbital
The three-dimensional space where an electron is found 90 percent of the time.
Chemical reactions
The making and breaking of chemical bonds, leading to changes in the composition of matter.
Single bond
A single covalent bond; the sharing of a pair of valence electrons by two atoms.
Atom
The smallest unit of matter that retains the properties of an element.
Dalton
A measure of mass for atoms and subatomic particles; the same as the atomic mass unit, or amu.
Electron shells
An energy level of electrons at a characteristic average distance from the nucleus of an atom.
Half-life
The amount of time it takes for 50 percent of a sample of a radioactive isotope to decay.
Mass number
The total number of protons and neutrons in an atom’s nucleus.
Covalent bond
A type of strong chemical bond in which two atoms share one or more pairs of valence electrons.
Compound
A substance consisting of two or more different elements combined in a fixed ratio.
Electronegativity
The attraction of a given atom for the electrons of a covalent bond.
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.
Essential elements
A chemical element required for an organism to survive, grow, and reproduce.
Nonpolar covalent bond
A type of covalent bond in which electrons are shared equally between two atoms of similar electronegativity.
Double bond
A double covalent bond; the sharing of two pairs of valence electrons by two atoms.
Isotopes
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.
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.
Electrons
A subatomic particle with a single negative electrical charge and a mass about 1 two-thousandths that of a neutron or proton. One or more electrons move around the nucleus of an atom.
Radiometric dating
A method for determining the absolute age of rocks and fossils, based on the half-life of radioactive isotopes.
Matter
Anything that takes up space and has mass.
Atomic nucleus
An atom’s dense central core, containing protons and neutrons.
