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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
Neutrons
Protons
Electrons
Particles in an Atom Review
Particle
Mass
Charge
Location of
particle
Proton
1
1+
nucleus
Neutron
1
0
nucleus
Electron
0
1-
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 12
Oxygen 16
Iron 56
Calcium 40
Sodium 23
Zinc 65
3. Mass # = Protons + Neutrons
4. How many Neutrons on average are found
in the following elements?
Boron 6
Fluorine 10
Silicon 14
Copper 35
Silver 61
Gold 118
A. Def – An atom that has a different number of
neutrons.
1. Does not affect the element
This means
2. Only changes the weight of the element
the mass #
3. Ex: Boron-10 and Boron-11
5 protons
5 protons
ppppp
nnnnn
5 neutrons
Boron-10
ppppp
nnnnn
n
Boron-11
6 neutrons
4. How many neutrons do the following isotopes
have?
Oxygen-14 6
Titanium-50 28
Magnesium-22 10
Potassium-43 24
Aluminum-23 10
Iodine-130 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.
e-
e-
e- e- ee- e
e-
e-
e-
e-
18 electrons
eeeeee
e- eee- eee- eeee
ee- ee
e- eeeeeeee- e
e
32 electrons
e
e8 electrons
eeeee- e- eeeenucleus
ee- ee- e2 electrons
Energy Level
Maximum # of
Electrons
1
2
2
8
3
18
4
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?