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Atomic Structure
 Atomic Number = # Protons
 Mass Number= Protons + Neutrons
 If atom is neutral (a charge of zero),
electrons = protons
Atomic Structure
 Nucleus is full of protons & neutrons.
 Nucleus contains nearly all the mass of
the atom
 Electrons are very small relative to the
protons and neutrons.
Protons have a positive charge +
Neutrons have no charge. 0
 Electrons have a negative charge


Reading the Periodic Table
Atomic Number
# proton+
Element Symbol
Element Name
Atomic Mass
Average mass of all of the
isotopes of an element.
3
Li
Lithium
6.941
Mass Number/ Atomic Mass
Mass # = protons + + neutons0
p+
n0
e-
Mass #
8
8
8
16
Arsenic
33
42
33
75
Phosphorus
15
16
15
31
Copper
29
35
29
64
Neon
10
10
10
Element
Oxygen
20
Practice Sheet
Atomic Structure
 Where are the electrons?
 What are electron shells?
 How many electrons per shell?
Electrons are in shells that circles
the nucleus at light speed.
Electron Shells
The letter n, represents the electron shell.
Number of electrons
that can fit in a shell:
2n2
2e
Electron Shell 1 can hold:
Electron Shell 2 can hold: 8eElectron Shell 3 can hold: 18e-
Electron Shell 4 can hold: 32e-
Energy Level 1 can hold:2eEnergy Level 2 can hold:8e-
Energy Level 3 can hold:18eEnergy Level 4 can hold:32eThings to remember:
•The element’s period # = the # of electron
shells
•There can only be 2 e- in the first energy
level
All atoms want to have 8 electrons on their
outer shells
Valence Electrons
 Valence electrons – Electrons on
highest energy level / highest
electron shell.
COOL FACT about atoms!
 Most of the volume (space) of an
atom is made up of electrons
 Electrons have very little mass and
take up very little space
 SO, atoms are mainly empty space
 We are made of atoms SO we are
empty mainly made up of Empty
Space
Sulfur
# Neutrons:
# Protons:
# Electrons:
Nucleus
Chlorine
# Neutrons:
# Protons:
# Electrons:
Nucleus