2: Water and Carbon: The Chemical Basis of Life Flashcards
chemical evolution
The theory that simple chemical compounds in the early atmosphere and ocean combined via chemical reactions to form larger, more complex substances, eventually leading to the origin or life and the start of biological evolution.
element
A substance, consisting of atoms with a specific number of protons. Elements preserve their identity in chemical reactions.
atomic number
The number of protons in the nucleus of an atom, giving the atom its identity as a particular chemical element.
mass number
The total number of protons and neutrons in an atom.
isotopes
Any of several forms of an element that have the same number of protons but differ in the number of neutrons.
atomic weight
The average mass of an element that is based on the relative proportions of all the naturally occurring isotopes.
radioactive isotope
A version of an element that has an unstable nucleus, which will release radiation energy as it decays to a more stable form. Decay often results in the radioisotope becoming a different element.
dalton
(Da) A unit of mass equal to 1/12 the mass of one carbon-12 atom; about the mass of 1 proton or 1 neutron.
orbitals
The region of space around an atomic nucleus in which an electron is present most of the time. Each orbitals can hold up to two electrons.
electron shells
A group of orbitals of electrons with similar energies. Electron shells are arranged in roughly concentric layers around the nucleus of an atom, and electrons in outer shells have more energy than those in inner shells. Electrons in the outermost shell, the valence shell, often are involved in chemical bonding.
valence shell
The outermost electron shell of an atom.
valence electrons
An electron in the outermost electron shell, the valence shell, of an atom. Valence electrons tend to be involved in chemical bonding.
valence
The number of unpaired electrons in the outermost electron shell of an atom; often determines how many covalent bonds the atom can form.
chemical bonds
An attractive force binding two atoms together. Covalent bonds, ionic bonds, and hydrogen bonds are types of chemical bonds.
covalent bond
A type of chemical bond in which two atoms share one or more pairs of electrons.
chemical reaction
Any process in which one compound or element is combined with others or is broken down; involves the making and/or breaking of chemical bonds.
molecules
A combination of two or more atoms held together by covalent bonds.
nonpolar covalent bond
A covalent bond in which electrons are equally shared between two atoms of the same or similar electronegativity.
polar covalent bond
A covalent bond in which electrons are shared unequally between atoms differing in electronegativity, resulting in the more electronegative atom having a partial negative charge and the other atom, a partial positive charge.
ion
An atom or a molecule that has lost or gained electrons and thus carries an electric charge, either positive(cation) or negative (anion), respectively.
cation
A positively charged ion.
anion
A negatively charged ion.
molecular formulas
A notation that indicates only the numbers and types of atoms in a molecule, such as H2O for the water molecule.
structural formulas
A two-dimensional notation in which the chemical symbols for the constituent atoms are joined by straight lines representing single, double, or triple covalent bonds.
ball-and-stick models
A representation of a molecule where atoms are shown as balls – colored and scaled to indicate the atom’s identity – and covalent bonds are shown as rods or sticks connecting the balls in the correct geometry.
space filling models
A representation of a molecule where atoms are shown as balls – color-coded and scaled to indicate the atom’s identify–attached to each other in the correct geometry.
electronegativity
A measure of the ability of an atom to attract electrons toward itself from an atom to which it is bonded. Left to right, increase in electronegativity. Top to bottom, decrease in electronegativity.
solvent
Any liquid in which one or more solids or gasses can dissolve.