(page 313)
• smallest part of an element that has all the properties of the element.

• nucleus (page 316) – tiny, extremely dense, positively charged, center of the atom
• electron cloud (page 317) – regions where electrons are likely to be found

• See Figure 7 on page 316.

Particle Symbol Location Charge proton p + neutron n o electron e -

Particle Symbol Location Charge proton p + nucleus neutron n o nucleus electron e electron cloud

Particle Symbol Location Charge proton p + nucleus 1+ neutron n o nucleus none (0) electron e electron cloud
1-

• Number of protons
• = number of electrons
• Identifies the element.
• Locate on the periodic table.
(Page 768-769)

1) How many protons does carbon have?
2) How many electrons does carbon have?
3) How many protons does chlorine have?
4) How many electrons does aluminum have?
5) What element has 20 protons?
6) What element has 16 electrons?

Answers
1) How many protons does carbon have? (6)
2) How many electrons does carbon have? (6)
3) How many protons does chlorine have? (17)
4) How many electrons does aluminum have? (13)
5) What element has 20 protons?
(calcium)
6) What element has 16 electrons?
(sulfur)

Atomic Theory Model
Bohr’s
Model
Copper
(Cu) atom
These energy levels or shells follow a very predictable pattern. The closest shell to the nucleus can have up to 2 electrons. The second shell from the nucleus can have up to 8 electrons. The third shell can have up to 18 electrons. The fourth shell can have up to 32 electrons.

• 1 st energy level = 2
• 2 nd energy level = 8
• 3 rd energy level = 18
• 4 th energy level = 32

• See the number of electrons for each energy level.

atomic mass unit (amu,

)
= unit for mass on the atomic scale

Mass of subatomic particles
• proton ~ 1 amu
• neutron ~ 1 amu
• electron is tiny
(Who cares?)

• Number of protons + number of neutrons

• Aka: average atomic mass
• The weighted average of the masses of the naturally occurring isotopes of an element
• The other number on the periodic table (unit = amu)

for the most common kind of atom of that element.

Calculate number of neutrons
• Example: bromine (#35)
• Mass number = 80
• Atomic number = 35 = protons
• Neutrons = 80 - 35 = 45

Calculate number of neutrons
• Example: strontium (#38)
• Mass number = 88
• Atomic number = 38 = protons
• Neutrons = 88 - 38 = 50

Assignment Example
• Bromine
• symbol = Br
• Mass number = 80
• Atomic number = 35
• Number of protons = 35
• Number of neutrons =
80 – 35 = 45

Assignment Example
• Bromine continued
• Number of energy levels = 4
• Skip period and group columns today.