Chapter 3 (Atoms: The Building Blocks of Matter) Vocabulary

Law of Conservation of Mass

Mass is neither created nor destroyed during ordinary chemical or physical reactions.

Law of Definite Proportions

A chemical compound contains the same elements in exactly the same proportions by mass regardless of the size of the sample or the source of the compound.

Law of Multiple Proportions

If two or more different compounds are composed of the same two elements, then the ratio of the masses of the second element combined with a certain mass of the first element is always a ratio of small whole numbers.

Atoms

The smallest unit of an element that maintains the properties of that element.

Avogardo's Number

6.022 1367 x 10^23: the number of particles in exactly one mole of a pure substance.

Nuclear Forces

A short-range proton-neutron, proton-proton, neutron-neutron force that holds the nuclear particles together.

Isotopes

Atoms of the same element that have different masses.

Atomic Mass Unit

A unit of mass that is exactly 1/12 the mass of a carbon-12 atom, or 1.660 540 x 10^-27 kg.

Mass Number

The total number of protons and neutrons in the nucleus of an isotope.

Atomic Number

The number of protons in the nucleus of each atom of an element.

Molar Mass

The mass of one mole of a pure substance.

Mole

The amount of a substance that contains as many particles as there are atoms in exactly 12g of carbon-12.

Average Atomic Mass

The weighted average of the atomic masses of the naturally occurring isotopes of an element.

Nuclide

The general form for any isotope of an element.