Elements

Question 1

Atom

Answer 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.

Question 2

Atomic Number

Answer 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.

Question 3

Electron

Answer 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

Question 4

Electron dot diagram

Answer 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

Question 5

Elements

Answer 5

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

Question 6

Energy Level

Answer 6

a particular region where electrons can orbit a nucleus

Question 7

Ion

Answer 7

an atom or molecule 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.

Question 8

Isotope

Answer 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.

Question 9

Mass Number

Answer 9

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

Question 10

Neutron

Answer 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.

Question 11

Nucleus

Answer 11

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

Question 12

Periodic table

Answer 12

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

Question 13

Proton

Answer 13

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

Question 14

Radioactive

Answer 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.

Question 15

Valance Electrons

Answer 15

electrons found in the outermost energy level of an atom