Atomic Structure
• Atoms are composed
of three particles
• Protons
• Neutrons
• Electrons
• Particles can be
distinguished by their
charge, mass, and
location within the
atom
Atomic Structure
Particle
Symbol
Charge
Mass
Location
Proton
p+
+1
1
Nucleus
Neutron
n
0
1
Nucleus
Electron
e-
-1
1836
Around
nucleus
1/
Atomic Number = Element
• Each element has a
different number of
protons in its nucleus
• The number of
protons determines
which element it is
• The “atomic
number” of an
element is the
number of protons in
its nucleus
• Because atoms are
neutral, the number
of electrons is equal
to the atomic
number
Mass Number = Isotope
• The mass of an atom
depends on the
number of protons
plus the number of
neutrons (p+ + n)
• This is called the
“mass number”
• Isotopes are atoms of
the same element
(same number of
protons in nucleus)
that have different
numbers of neutrons
Electrons = Energy Levels
• Electrons are located
around the nucleus
only at certain radial
distances
• Different radial
distances correspond
to different levels of
electron energy
• Thus, the different
distances are called
energy levels
Electrons = Energy Levels
• There are 7 energy levels – each with room for
different numbers of electrons
• Starting closest to the nucleus
•
•
•
•
•
•
•
level 1 = 2 electrons
level 2 = 8 electrons
level 3 = 18 electrons
level 4 = 32 electrons
level 5 = 32 electrons
level 6 = 18 electrons (based on known elements)
level 7 = 8 electrons (based on known elements)
Bohr Diagrams
• The structure of a
given atom can be
represented in a
“Bohr Diagram”
which shows:
• the number of protons
and neutrons in the
nucleus
• the number of
electrons in each of
the 7 energy levels