Atoms

What are atoms?
 What’s in them?
 Why are they
important?
 Can you combine
them?
What is an atom?


An atom is the smallest particle of matter
An atom consists of a nucleus surrounded
by one or more electrons.
Atoms are made of smaller
particles





Protons
Neutrons
Electrons
Quarks
Leptons
The Nucleus

The nucleus is where
the protons and
neutrons are located.
 It accounts for 99.9%
of the mass.
What is the charge of each
particle?



Protons are positive
Neutrons are neutral
Electrons are negative
Quarks




Quarks make up protons and neutrons.
Six different quarks
Three quarks make up a proton.
Three quarks make up a neutron.
Where are the electrons?
They orbit around the nucleus and can be
lost, gained, or shared with another atom.
Electron Cloud

Space where the electrons are likely to be
found.
Energy Levels



Electrons are arranged in energy levels.
Electrons with the lowest energy can be
found in the energy level closest to the
nucleus.
Energy levels can hold 2, 8, 18
How are electrons arranged…

For eighth grade curriculum you only need
to teach the first three energy levels.
Valence Electrons


The electrons in an atom are not all the
same distance from the nucleus. Those
farthest away from the nucleus are called
valence electrons.
Valence electrons are involved in chemical
bonds.
Electron Dot Diagram



Used to represent the valence electrons of
an atom.
Elements can have between 1-8 valence
electrons.
During a chemical bond the element usually
ends up with either 0 or 8 valence electrons.
Chemical Bonds

Forms between two atoms when valence
electrons move between them. The valence
electrons may be transferred from one atom
to another, or they may be shared.
Atoms

Must have an equal
number of protons and
electrons.
 The overall charge of
an atom is neutral.

The number of
neutrons can change.
Atoms of the same
element with a
different number of
neutrons are called
isotopes.
Atomic Number

The atomic number is
the number of protons
in the nucleus of an
element.
 The atomic number
identifies the element.
Mass Number


The mass number of an atom is the sum of
the protons and the neutrons in its nucleus.
Mass Number = # protons + # neutrons
Atomic
Number
Atomic
Mass
Atomic Mass

The unit of measurement for the small mass
of an atom is an amu (atomic mass unit).
The mass of a proton or neutron is equal to
one amu.