Science Ch 4 Vocab

Front 1

atom

Back 1

the basic unit of matter
o An atom is the smallest particle of an element that still has all the properties of the element.
o Atoms are made up of smaller particles called protons, neutrons, and electrons. The smaller electrons orbit around a central nucleus of protons and neutrons.

Front 2

atomic number

Back 2

the number of protons in the nucleus of an atom.
o Elements are distinguished from one another by their atomic numbers.
o For example, any atom with two protons is an atom of helium.
o The symbol for the atomic number is Z.
o In an element symbol, the atomic number is shown at lower left.

Front 3

electron

Back 3

a negatively charged particle that moves around the nucleus.
o The mass of an electron is less than one thousandth of the mass of a proton.

Front 4

electron dot diagram

Back 4

– a diagram that shows the element symbol surrounded by dots representing valence electrons.
o For example, the electron dot diagram at right shows that neutral helium atoms have two valence electrons.

Front 5

element

Back 5

a pure substance that cannot be broken down into simpler substances by ordinary chemical means.
-Elements are made of one type of atom.
-Atoms of different elements are distinguished by the number of protons in the nucleus. For example, all carbon atoms have 6 protons.

Front 6

energy level

Back 6

a particular region where electrons can orbit a nucleus.

Front 7

ion

Back 7

– an atom that has an electrical charge because it has gained or lost electrons.
o An atom with more protons than electrons is a positively charged ion, or cation.
o An atom with more electrons than protons is a negatively charged ion, or anion.
o In an element symbol, the electric charge is shown at upper right.

Front 8

isotopes

Back 8

one of several forms of the same element.
o All isotopes of a given element have the same number of protons, but differ in the number of neutrons.
o Most isotopes are radioactive. Usually only one or two stable isotopes exist for a given element.

Front 9

mass number

Back 9

the number of protons plus neutrons in the nucleus of an atom.
o Electrons also contribute to the mass of an atom. But, because their mass is only one thousandth of the mass of a proton or neutron, they are not counted in the mass number.
o For example, the mass number of helium is 4 (2 protons and 2 neutrons).
o The symbol for the mass number is A.
o In an element symbol, the mass number is shown at upper left.

Front 10

neutron

Back 10

– a particle with no charge located in the nucleus of an atom.
o Neutrons have slightly more mass than protons.
o The number of neutrons is described by the neutron number, N.
o To find the number of neutrons, subtract the atomic number from the mass number.

Front 11

nucleus

Back 11

the positively charged, dense center of an atom.
-The nucleus contains protons and neutrons.

Front 12

periodic table

Back 12

a chart that organizes the chemical elements based on their properties.

Front 13

proton

Back 13

– a positively charged particle located in the nucleus of an atom.
o Protons have slightly less mass than neutrons.
-The number of protons determines the element

Front 14

radio active

Back 14

capable of releasing radiation.
o In a radioactive atom, the nucleus can spontaneously decay and emit particles and/or light. These emissions are called radiation.
o The energy released by radioactive substances can be harnessed to produce electricity in a nuclear power plant. This energy also can be used to create a massive explosion in a nuclear bomb.
o If the emissions change the number of protons in the nucleus, the atom becomes a different element.

Front 15

valence electrons

Back 15

electrons found in the outermost energy level of an atom.