Chapter 2 - Atoms, Molecules, and Ions

atoms

smallest units of an element that have all the properties of that element

element

composed entirely of one type of atomc

compound

contains atoms of two or more different elements

law of constant composition

all samples of a pure substance contain the same elements in the same proportion by mass

law of multiple proportions

when the same elements form more than one compound, the mass of one element that combines with a fixed mass of a second element are in a ratio of small whole numbers

law of conservation of mass

there is no detectable change in mass when a chemical reaction occurs

atomic number

the number of protons in the nucleus of an atom

mass number

the sum of the numbers of protons and neutrons in the nucleus

isotopes

atoms of an element whose nuclei contain different numbers of neutrons

isotopic mass

the mass of a particular isotope of an element

atomic mass

the weighted average mass of the naturally occurring isotopes of the element

period

horizontal row of the periodic table

group

vertical column of the periodic table

metal

an element that is shiny and is good electrical conductor

nonmetal

an element that is typically a nonconductor

metalloid

an element that has properties of both metals and nonmetals

molecule

a combination of atoms joined so strongly that they behave as a single particle

molecular formula

gives the number of every type of atom in the molecule

structural formula

shows how the atoms are connected in the molecule

molecular mass

the sum of the atomic masses of all atoms presents in the molecular formula

empirical formula

formular of an ionic compound that uses the smallest whole number subscripts to express the relative numbers of ions

polyatomic ion

a group of atoms with a net charge that behaves as a single particle

formula mass

the sum of the atomic masses of all atoms in the empirical formula of an ionic compound

chemical nomenclature

the organized system for naming compounds

acid

a compound that produces hydrogen cations when dissolved in water

hydrocarbons

organic compounds that contain only the elements hydrogen and carbon

electrolyte

a substance that forms ions in water solution

nonelectrolytes

water and compounds that dissolve in water as neutral molecules and don’t conduct electrical current