Download C2.1 Key Terms Atomic number: The number of protons in the

Atomic number:
The number of protons in the nucleus of an
atom.
Atoms:
The smallest part of an element that can
take part in chemical reactions.
Electronic configuration:
The arrangement of electrons in shells
around the nucleus of an atom.
Electrons:
Negative particles of negligible mass and
charge -1 (relative to a proton).
Energy levels:
In chemistry, space around a nucleus that
can be occupied by electrons, usually
drawn as a circle. Also referred to as
shells.
Groups:
Columns in the periodic table, containing
elements with similar properties.
Isotopes:
Atoms of an element with the same
number of protons and electrons but with
a different number of neutrons.
Mass number:
The total number of protons and neutrons
in the nucleus of an atom.
Neutrons:
Particles found in the nucleus, having zero
charge and mass of 1 (relative to a
proton).
Nucleus:
In chemistry, the positively charged centre
of an atom.
Periodic table:
Chart in which the chemical elements are
arranged in order of increasing atomic
number.
Periods:
Rows in the periodic table in which the
atomic number increases by one from one
element to the next.
Protons:
Positive particles found in the nucleus,
having a charge of +1 and a mass of 1.
Relative abundance:
The number of objects of a particular kind
in a sample shown as a percentage of the
total number of objects in the sample.
Relative atomic mass:
The mean mass of an atom relevant to the
mass of an atom of carbon-12, which is
assigned a mass of 12.
Relative charge:
The electrical charge of a subatomic
particle compared to the electrical charge
of a proton.
Shells:
In chemistry, space around a nucleus that
can be occupied by electrons, usually
drawn as a circle. Also referred to as
energy levels.