2 Regions of the Atom
 3 Subatomic particles
Electron
Cloud (-)
 electrons
Nucleus (+)
 Protons
 neutrons
Nucleus – dense core that carries a positive charge and
composed of 2 types of subatomic particles
(protons & neutrons)
Electron Cloud – a cloud of negative charge that
surrounds the nucleus composed of 1 type of subatomic
particle (electrons). The cloud is very large compared
to the nucleus
Region 1 – The Nucleus
+
+
 carries a positive
0
+
(+) charge
0
 dense and tiny
+
compared to the entire
atom
 contains protons and
neutrons which only come in
whole numbers (can’t have ½ proton)

Protons (abbv. P or +)
 postively charged (gives nucleus its
positive charge)
 mass of 1 P = 1 amu (1.673 x 10-24 g)
 Atomic # = # of P
 # of P gives the element its identity
 all atoms of the same element have the
same # of P atoms of different elements
have different # of P

Neutrons (N or 0)
 particle in the nucleus that has no charge
 neutral
 mass of 1 N = 1 amu (about the same as
a P)
 The number of N in an element can vary
Region 2 – The
Electron Cloud
e- cloud density decreases
 probability
e- energy increases
cloud
 contains
electrons (e-)
 density of the
↑ density
cloud
↓ e- energy
 most
dense at
↓ density
↑ e- energy
the center
 least dense
toward the outside
 electron energy
 e- energy is greatest toward the outside
 e- energy is least at the center

Electron
 negatively charged particle that moves
around the nucleus forming a cloud of
negative charge
 mass of 1 e- = 0 amu
 1800 times smaller than a Proton (9.10953 x
10-28 g)
 # e- = # P in a neutral (uncombined) atom
Energy Levels
 not circular orbits
 not all e- have the same energy
 each e- has different energy levels it can occupy in the electron
cloud
Energy Level Capacities
1st Energy Level
s
 closest to the nucleus
 1 spherical in shape (s orbital)
 holds a maximum of 2 ep
2nd Energy Level
 holds a maximum of 8 electrons
o 1 spherical shape (s – orbital holds
2 e -)
o 3 sets of 2 teardrop shapes (p – orbitals
holds 2 e- each)
3rd Energy Level
 can hold up to 18 eo s orbital (2 e-)
o p orbital with 3 - suborbitals (2 e- each)
o d orbital with 5 - suborbitals (2 e- each)
4th Energy Level
 can hold up to 32 eo s orbital (2 e-)
o p orbital (6 e-)
o d orbital (10 e-)
o f orbital with 7 suborbitals (2 e- each)
p
s
p
p
p
p
Electron Cloud - Energy Levels continued
 Lowest energy level fills first, then second
 Atoms seek a stable number of e- in their outer energy
level
o the most stable e- arrangement in an outer energy
level is an octet
 8 e- in the outer energy level
o 2e- in the outer energy level or a filled outer
energy level are the next most stable arrangements
+
 8 outer e most stable
condition
 won’t react
+
 2 outer e somewhat stable
 will react but
usually slowly or
needs energy