Chemistry Vocabulary Chapter 3

Front 1

The number that represents the average
atomic mass of the element’s isotopes weighted by
percentage abundance.

Back 1

Atomic weight

Front 2

Matter is neither lost nor
gained during a chemical reaction

Back 2

Law of conservation of matter

Front 3

In a compound, the constituent
elements are always present in a definite proportion by
weight

Back 3

Law of definite proportions

Front 4

Small central core of the atom; contains the
protons and neutrons

Back 4

Nucleus

Front 5

Negatively charged subatomic particles found in
the space around the nucleus

Back 5

Electrons

Front 6

Positively charged subatomic particles found in the
nucleus

Back 6

Protons

Front 7

Electrically neutral subatomic particles found in
the nucleus

Back 7

Neutrons

Front 8

Spontaneous decomposition of unstable
atomic nuclei; produces alpha, beta, and gamma
radiation

Back 8

Radioactivity

Front 9

Positively charged particles identical to
helium-4 nuclei; emitted by certain radioactive isotopes

Back 9

Alpha particles

Front 10

Electrons ejected at high speeds from certain
radioactive isotopes

Back 10

Beta particles

Front 11

High-energy electromagnetic radiation emitted
from radioactive isotopes

Back 11

Gamma rays

Front 12

The number of protons in the nuclei of
the atoms of an element

Back 12

Atomic number

Front 13

Number of neutrons plus number of protons
in the nucleus of an atom

Back 13

Mass number

Front 14

Atoms of the same element having different mass
numbers

Back 14

Isotopes

Front 15

The unit for relative atomic masses
of the elements; 1 amu 5 1/12 the mass of the carbon-12
isotope. 1 amu 5 1.6605 3 10224 g

Back 15

Atomic mass unit (amu)

Front 16

The number that represents the average
atomic mass of the element’s isotopes weighted by
percentage abundance.

Back 16

Atomic weight