2.1 The Building Blocks: Atoms, Isotopes, Ions, and Molecules

anion

negative ion that is formed by an atom gaining one or more electrons

atom

the smallest unit of matter that retains all of the chemical properties of an element

atomic mass

calculated mean of the mass number for an element’s isotopes

atomic number

total number of protons in an atom

balanced chemical equation

statement of a chemical reaction with the number of each type of atom equalized for both the products and reactants

cation

positive ion that is formed by an atom losing one or more electrons

chemical bond

interaction between two or more of the same or different atoms that results in forming molecules

chemical reaction

process leading to rearranging atoms in molecules

chemical reactivity

the ability to combine and to chemically bond with each other

compound

substance composed of molecules consisting of atoms of at least two different elements

covalent bond

type of strong bond formed between two atoms of the same or different elements; forms when electrons are shared between atoms

electrolyte

ion necessary for nerve impulse conduction, muscle contractions, and water balance

electron

negatively charged subatomic particle that resides outside of the nucleus in the electron orbital; lacks functional mass and has a negative charge of –1 unit

electron configuration

arrangement of electrons in an atom's electron shell (for example, 1s22s22p6)

electron orbital

how electrons are spatially distributed surrounding the nucleus; the area where we are most likely to find an electron

electron transfer

movement of electrons from one element to another; important in creating ionic bonds

electronegativity

ability of some elements to attract electrons (often of hydrogen atoms), acquiring partial negative charges in molecules and creating partial positive charges on the hydrogen atoms

element

one of 118 unique substances that cannot break down into smaller substances; each element has unique properties and a specified number of protons

equilibrium

steady state of relative reactant and product concentration in reversible chemical reactions in a closed system

hydrogen bond

weak bond between slightly positively charged hydrogen atoms and slightly negatively charged atoms in other molecules

dipole

a separation of positive and negative charges in a bond; a bond or molecule whose ends have opposite charges

inert gas

element with filled outer electron shell that is unreactive with other atoms (also, noble gas)

ion

atom or chemical group that does not contain equal numbers of protons and electrons

ionic bond

chemical bond that forms between ions with opposite charges (cations and anions)

irreversible chemical reaction

chemical reaction where reactants proceed unidirectionally to form products

isotope

one or more forms of an element that have different numbers of neutrons

law of mass action

chemical law stating that the rate of a reaction is proportional to the concentration of the reacting substances

mass number

total number of protons and neutrons in an atom

matter

anything that has mass and occupies space

molecule

chemical structure consisting of at least two atoms held together by one or more chemical bonds

neutron

uncharged particle that resides in an atom’s nucleus; has a mass of one unified atomic mass unit (u)

noble gas

see inert gas

nonpolar covalent bond

type of covalent bond that forms between atoms when electrons are shared equally between them

nucleus

core of an atom; contains protons and neutrons

octet rule

rule that atoms are most stable when they hold eight electrons in their outermost shells

orbital

region surrounding the nucleus; contains electrons

periodic table

organizational chart of elements indicating each element’s atomic number and atomic mass; provides key information about the elements’ properties

polar covalent bond

type of covalent bond that forms as a result of unequal electron sharing, creating slightly positive and negative charged molecule regions

product

molecule that is a result of a chemical reaction

proton

positively charged particle that resides in the atom’s nucleus; has a mass of one unified atomic mass unit (u) and a charge of +1

radioisotope

isotope that emits radiation comprised of subatomic particles to form more stable elements

reactant

molecule that takes part in a chemical reaction

reversible chemical reaction

chemical reaction that functions bidirectionally, where products may turn into reactants if their concentration is great enough

valence shell

outermost shell of an atom

van der Waals interaction

very weak interaction between molecules due to temporary charges attracting atoms that are very close together