Atomic Structure

 Democritus and Aristotle
◦ Democritus thought all matter consisted of
extremely tiny particles that could not be divided.
(Cut aluminum foil in half)
◦ Also thought matter in liquids was round and
smooth; in solids rough and prickly
◦ Aristotle thought there was no limit to the number
of times matter could be divided.

 Developed a theory to explain why the
elements in a compound always behave in the
same way.
 Main Points
◦ 1) All elements are composed of atoms.
◦ 2) All atoms of the same element have the same
mass, and atoms of different elements have
different masses.
◦ 3) Compounds contain atoms of more than one
element.
◦ 4) In a compound, atoms of different elements
always combine in the same way.

 Used a cathode ray tube to show evidence for
subatomic, charged particles.

 Plum pudding model (chocolate chip ice
cream.
 Negatively charged particles evenly spaced
throughout a solid mass of positive charge.

 The Gold Foil Experiment – Evidence for a
nucleus.

“Structure of the Atom”

A. An atom
1. smallest part of matter
2. Ripping paper example
B. Areas of an atom
1. Nucleus – center of an atom
-holds protons and neutrons
a. Protons (P) – positively charged
particle found in the nucleus.
-has a mass of 1
-has a charge of 1+

b. Neutrons (N) – non-charged particle found
in the nucleus.
-has a mass of 1
-has no charge “0”
2. Electron Cloud – area around the nucleus
which contains electrons
a. Electrons (e) – negatively charged particle
found outside of the nucleus
-has a mass of 0
-has a charge of 1-
-moves around the outside of the
nucleus

Protons
Electrons
Neutrons

Particle Mass Charge Location of
particle
Particles in an Atom Review
Proton
Neutron
Electron
1
1
0
1+
0
1-
nucleus
nucleus
Electron cloud

A. Def – the # of protons in an atom’s nucleus.
1. Every carbon atom has 6 protons…
2. Every neon atom has 10 protons…
B. On P.T. – located right above the chemical
symbol
*Protons dictate the type of element we have*
*Electrons always equal the # of protons*

A. Def – The sum of protons and neutrons in the
nucleus of an atom.
1. On P.T. – bottom number
-round up/down
2. Ex: What is the mass number of the following
elements?
Carbon Oxygen
Iron Calcium
Sodium Zinc
12
56
23
16
40
65

3. Mass # = Protons + Neutrons
4. How many Neutrons on average are found
in the following elements?
Boron Fluorine
Silicon Copper
Silver Gold 118
14
6
61
10
35

A. Def – An atom that has a different number of
neutrons.
1. Does not affect the element
2. Only changes the weight of the element
3. Ex: Boron-10 and Boron-11
p p p p p p p p p p
n n n n n
n n n n n
n
5 protons 5 protons
5 neutrons 6 neutrons
This means
the mass #
Boron-10 Boron-11

4. How many neutrons do the following isotopes
have?
Oxygen-14
Titanium-50
Magnesium-22
Potassium-43
Aluminum-23
Iodine-130
6
28
10
24
10
77

A. Def – average mass of all isotopes of one
element combined.
1. Found on P.T. underneath chemical symbol.
2. Ex: Carbon = 12.011
“Carbon has 3 known isotopes.
Carbon-12, 13, and 14. Carbon-12 makes up 99%
of all carbon on earth. Carbon-13 and 14 make
up 1%.”

“Modern Atomic Theory”
Chemistry Timeline…pg. 114-115

A. Def – a specific area where an electron is
likely to be.
nucleus
2 electrons
8 electrons
18 electrons
32 electrons
e- e-
e-
e-
e-
e-
e-
e-
e-
e-
e- e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
e- e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
e-

Energy Level Maximum # of
Electrons
1
2
3
4
2
8
18
32

1. Draw a picture of the following atoms with the
correct number of e’s, p’s, and n’s…
a. Na d. He
b. Al e. C
c. K f. S
2. Assign: Read pg. 118 and 119
3. What is the difference between a ground state
and an excited state?