Atomic Theory Modern Model

atom (page 313)

• smallest part of an element that has all the properties of the element.

Two parts• nucleus (page 316) – tiny,

extremely dense, positively charged, center of the atom

• electron cloud (page 317) – regions where electrons are likely to be found

The atom is mostly empty space.

• See Figure 7 on page 316.

Subatomic particlesParticle Symbol Location Charge

proton p+

neutron no

electron e-

Particle Symbol Location Charge

proton p+ nucleus

neutron no nucleus

electron e- electroncloud

Particle Symbol Location Charge

proton p+ nucleus 1+

neutron no nucleus none (0)

electron e- electroncloud

1-

atomic number

• Number of protons• = number of electrons• Identifies the element.• Locate on the periodic table.

(Page 768-769)

Study Buddies1) 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?

Answers1) 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

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.

Bohr’s Model

Copper (Cu) atom

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

Periodic Table• See the number of

electrons for each energy level.

Size of atomatomic 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?)

mass number

• Number of protons + number of neutrons

atomic weight• 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)

Atomic weight is close to the mass number

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.