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Atomic
Structure
+ +
A Helium atom
©2010 - Doug Gilliland
The Physical Science Series
Atomic Structure Menu
Protons, Neutrons & Electrons
Isotopes
Bohr Model
Menu
Over the past century
scientist have discovered
that the atom is composed
of 3 subatomic particles:
+
Protons
Neutrons
Electrons
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+
The Proton
1) Symbol = P +
• Relative Mass = 1 Atomic Mass Unit (AMU).
Actual mass = 1.674 x 10 -24 g
• Location: Inside the nucleus
• Electrical charge: Positive.
• Importance: The atomic number which is the
identity of the element.
• Discovered by: Ernest Rutherford in 1909
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The Electron
1) Symbol = e• Relative Mass = 1 /1836 Atomic Mass Unit.
Actual mass = 9.11 x 10 -28 g
• Location: Energy level outside the nucleus
• Electrical charge: Negative.
• Importance: The number of electrons located
in the last energy level determine
the chemical activity of the element.
• Discovered by: J.J.Thomson in 1897
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The Neutron
1) Symbol = N0
• Relative Mass = 1 Atomic Mass Unit (AMU).
Actual mass = 1.675 x 10 -24 g
• Location: Inside the nucleus
• Electrical charge: Neutral.
• Importance: Is responsible for isotopes
(atoms of the same element with different
numbers of neutrons).
• Discovered by: James Chadwick in 1932
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An element's Square on the Periodic Table
Atomic Number
# of protons =
# of electrons
3
Li
6.941
3 protons
3 electrons
4 neutrons
Atomic Mass
When rounded to a whole number it is the
total number of protons & neutrons
added together.
nucleus
+
+
+
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Fill in the table of p+, n0 and e-.
Element
Protons
Neutrons Electrons Element
Silver
47
61
47
Zinc
30
35
30
Potassium
19
20
19
Uranium
92
146
92
Neon
10
10
10
Gold
79
118
79
Hydrogen
1
0
1
Fluorine
9
10
9
Sulfur
16
16
16
Cesium
55
78
55
Protons
Neutrons Electrons
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Isotopes
•Isotopes are atoms of the same element
that have different masses due to having
different numbers of neutrons.
•The atomic mass (weight) on the periodic
table is the average of the abundance of all
the isotopes of an element.
Isotope:
+
proton
neutron
electron
H-1
H-2
H-3
+
+
+
0.014%
0.001%
Abundance: 99.985%
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Isotopes and Atomic Mass
Isotope:
+
proton
neutron
electron
H-1
H-2
H-3
+
+
+
0.014%
2 amu
0.001%
3 amu
Abundance: 99.985%
Atomic Mass 1 amu
(approx.)
Average(numerical) = (1+2+3)/3 = 2 amu
Average(abundance) = [1(0.99985)+2(0.00014)+3(0.00001)]
3
= 1.00016 amu
Isotopes
QuickTime™ and a
H.263 decompressor
are needed to see this picture.
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1
H
2
1.0079
Chemical Symbols
He
4.002
A chemical symbol is a short-hand way of writing
the name of an element.
Chemical symbols consists of either one or two
letters.
The first letter is always uppercase (capitalized). If
there is a second letter, it is lowercased and half
the size of the first letter.
Correct : Mg, He, Li, Be, Ca, Au, Fe
Incorrect: HE, he, HE, He
Where did the chemical
symbols come from?
Most symbols came from first one or two letters in
the English name of the element.
Examples: H = hydrogen, He = helium,
Ne = neon, Al = aluminum, S = sulfur
Others come from the first one or two letters in the
Latin words for the element.
Examples: Pb = lead (plumbum),
Sn = tin (stannum), Cu = copper (cuprum)
Fe = iron (ferrum), Ag = silver (agrum)
Where did the chemical
names come from?
The elements names came from:
Planets: Neptunium, Plutonium, Mercury...
People: Einsteinium, Curium, Nobelium...
Places: Gallium (France), Europium, Polonium...
Color: Chlorine (yellow-green in Latin),
Indium (Indigo), Iodine ( violet in Greek)
Myth: Thorium (Norse war god), Titanium (Titan)...
Minerals: Calcium (chalk), Boron (borax)...
The only thing you cannot name an element after is
a living human.
Mendeleev’s
Table
187
2
186
9
Mendeleev’s Table (1871)
While it was the first periodic table, Mendeleev had very
different elements, such as the very reactive potassium and
the very stable copper, in the same family. Forty years later
Henry Moseley rearranged the elements by their atomic
number which gave the table better periodicity.
Dimitri
Mendeleev
Henry Moseley
In 1915 Moseley rearranged
the elements by their
atomic number. This gave
elements better periodicity.
Short form of the Table
These elements are
placed here to make the
table less wide.
Long form of the Table
The Chinese Periodic Table
Russian Periodic
Table
Most Abundant Elements:
All stars create
energy by
converting
hydrogen to
helium.
The Bohr Model of the Atom
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So what does an atom “look” like?
Bohr Model
11p
+
- electrons travel in fixed circular orbits around
12Nthe nucleus in
0
discrete energy states
- electrons occupy the lowest energy level (ground state) until
they absorb energy and move to a farther orbit level (excited
state)
Quantum-mechanical model
- electrons do not travel in fixed orbits
- the energy of an atom occurs in discrete levels
- accounts for wave and particle nature of matter and energy
- exact location of an electron is impossible to know
The Bohr Model of the Atom
The Bohr Model places protons
and neutrons in the nucleus and
electrons in energy levels around
the nucleus.
These energy levels help explain
the organization of the Periodic
Table of Elements.
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Periods and Families
Pe
r
i
od
s
1
2
3
4
5
6
7
Groups
Families)
the table.
table.
Periods (aka
1-7 run
acrossrun
thedown
periodic
Members
of anumber
group (with
exception
of He)energy
have the
same
The period
is thethe
number
of electron
levels.
number
electrons
their
outside
energy
All elements
of aof
period
haveinthe
same
number
of e- level.
energy levels.
These e- are called valence electrons.
IA
IIA
Groups (Families)
VIIIA
IIIA IVA VA VIA VIIA
Iodine would have 5 e- energy
levels and 7 valence e-.
6
7
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The Importance of
Valence Electrons
In the early 1900's, scientists
discovered that it was the
valence electrons of an atom
(the electrons in the last energy level)
that determined how elements reacted with
each other.
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Fill in the table with e- energy levels & valence e-.
element
e- energy
levels
valence e-
element
e- energy
levels
valence e-
Ca
4
2
C
2
4
F
2
7
P
3
5
Al
3
3
Rn
6
8
K
4
1
H
1
1
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Through experimentation
Neils Bohr was able to
determine the
Maximum
number
of electrons
This is the
largest number
of
electrons
in each each energy level can hold.
Therelevel:
can be less than this
energy
number but not more.
energy level
maximum
number of
electrons
1st
(s)
2nd
(p)
3rd
(d)
4th
(f)
5th 6th 7th
2 8 18 32 18 8 2
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Step
Drawing a Bohr Model
1 of a Strontium atom
Draw a circle to represent the nucleus
and write in the number of protons and
neutrons.
Number of 88 = p+ + n0
Protons
+
-38
=
p
+
38
p
38
50 n0
50 n0
S
87.62
r
Menu
StepDrawing a Bohr Model of a
2
Strontium atom
Draw the correct number of e- energy levels in
the atom (Period #). Draw only a section of the
circle to represent the energy level.
S
5
87.62
r
Period
38
Draw only part of
the e- energy level.
38 p+
0
50 n
Menu
StepDrawing a Bohr Model of a
3
Strontium atom
Fill in the last energy level with the correct
number of electrons (group A number).
You always do the last e- energy level first!
Group
IIA
S
5
87.62
r
Period
38
38 p+
0
50 n
2
Menu
StepDrawing a Bohr Model of a
4
Strontium atom
Go to the first e- energy level and fill it
with the maximum number of electrons.
Do this with the other energy levels until
you get to the 2nd to the last energy level.
S
87.62
r
38
38 p+
0
50 n
2 8 18
2
Menu
StepDrawing a Bohr Model of a
5
Strontium atom
Add up the number of e- you have and subtract it
from the total number of e(atomic number). Place those
e- in that 2nd to the last energy level.
38 p+
0
50 n
38 e2 + 8+18 8
+ 2= 30 e8 e-
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Draw a Bohr Model of:
Aluminum 13 p+
14 n 0
2 8 3
Bromine
35 p+
0
45 n
2 8 18 7
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Periods and Families
IA
1
2
3
4
5
6
7
IIA
6
7
Periods run horizontally.
All elements of a period
VIIIA
have the same number of
electron energyIIIAlevels.
IVA VA VIA VIIA
All the elements from
rubidium to xenon have
5 electron energy levels.
Families (aka Groups)
run vertically.
All elements of a family
have the same number of
valence electrons - which
determine an element’s
chemical & physical
properties
Alkali Metals, Group 1-A
Lithium, Sodium, Potassium,
Rubidium, Cesium & Francium
IA
VIIIA
IIA
IIIA IVA VA VIA VIIA
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Alkali Metals: Chemical Activity
Li
Na
K
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H.264 decompressor
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Rb
Cs
Fr
As you go down the Alkali Metal Family
the radii of the atoms becomes greater
and their hold on the valence electron becomes weaker.
Weak hold on valence electron =
greater chemical activity.
Alkaline Earth Metals, Group 2-A
Less reactive than the alkali
metals
but more reactive than the
other metals.
IA
VIIIA
IIA
IIIA IVA VA VIA VIIA
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Radium glows in the
dark and is radioactive.
Transition Metals
Generally stable metals such as
iron, gold, silver, copper, zinc, &
nickel.
IA
IIA
QuickTime™ and a
Sorenson
H.263
Video
decompressor
decompressor
are needed to see this picture.
VIIIA
IIIA IVA VA VIA VIIA
Properties of the Elements:
Metals, Nonmetals & Metalloids
20
Nonmetals
82
Metals
7
Metalloids
Boron
Family,
3-A
Two hundred years ago
Aluminum
was the
most expensive Gallium,
Boron,
Aluminum,
metal on earth.
and
Napoleon’s Indium
favorite guests
were Thallium.
served
IA
on aluminum plates - his second
IIA
favorite
ate off gold plates.
VIIIA
IIIA IVA VA VIA VIIA
Carbon Family, 4-A
Contain a wide variety of elements
from 1 nonmetal (C), 2 metalloids (Si &
Ge) and 2 metals (Pb & Sn). VIIIA
IA
IIA
IIIA IVA VA VIA VIIA
Nitrogen Family, 5-A
Nitrogen, Phosphorus, Arsenic,
Antimony & Bismuth.
IA
VIIIA
IIA
IIIA IVA VA VIA VIIA
QuickTime™ and a
Sorenson
H.263
Video
decompressor
decompressor
are needed to see this picture.
IA
Oxygen Family, 6-A
Oxygen, Sulfur, Selenium,
Tellurium & Polonium.
VIIIA
IIA
IIIA IVA VA VIA VIIA
Halogens, Group 7-A
The most reactive nonmetals:
Fluorine, Chlorine, Bromine,
Iodine & Astatine.
IA
IIA
IIIA IVA VA VIA VIIA
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Sorenson Video decompressor
are needed to see this picture.
VIIIA
Noble Gases, Group 8-A
The inert (non-reactive) gases:
Helium, Neon, Argon, Krypton, Xenon & Radon.
IA
VIIIA
IIA
IIIA IVA VA VIA VIIA
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H.263 decompressor
are needed to see this picture.
General Properties of Metals
• Silver in color and have luster.
• Solid @ Room Temperature.
• Have high densities.
• Are malleable & ductile.
• Are good conductors of heat & electricity.
• Atoms have between 1-3 valence electrons.
• Atoms have a loose hold on their valence
electrons - they give them up easily.
• Corrode (rust) in the presence of oxygen.
Periodic Trends:
Periods and Metallic Properties
M
o
r
e
M
e
t
a
l
l
i
c
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Sorenson Video decompressor
are needed to see this picture.
Less Metallic
Periodic Trends:
Atomic Radii
Atomic
Radius
valence e-
nucleus
Atom
Two variable determine the atomic radius of a atom:
the number of protons in the nucleus
the number of electron energy levels in the atom.
The number protons and radius are inversely proportional.
As protons increase, the radius decreases.
The number of energy levels and radius are proportional.
As energy levels increase, the radius also increases.
Li
m
o
r
e
Na
a
c
t
i
v
e
K
Reactivity
of
Alkali
Metals
Metals lose their valence
152
Radius in
186
Angstroms (Å)
227
electrons in a chemical
reaction.
The easier it is to lose the
electron the more
chemically active the
element.
The further the valence
electron is from the
nucleus, the weaker the
hold on the electron and
the easier it is lost to a
nonmetal.
Atomic Radii & Protons
As you go across a period, the atoms gain protons while
the number of electron energy levels remain the same.
Positive protons and negative electrons attract each other.
This increase in the number of protons causes a greater
attraction between the nucleus and the electrons in the atom.
As protons are added, electrons are pulled closer the nucleus
giving the atom a smaller radius as you go across a period.
+
+
++
++
k
e
y
+ proton
electron
Force of
Attraction
Atomic Radii
The number protons and atomic radii are inversely proportional.
As protons increase across a period, the radius decreases.
The number of energy levels and atomic radii are proportional.
As energy levels increase down a family, the radius also
increases.
Atomic Radii of the Elements
IA
Atomic
Radii
increases
due to
an
increase
in the
number
of eenergy
levels.
H
VIIIA
IIA
IIIA
IVA
VA
VIA
VIIA
Mg
Al
Si
P
S
Cl
Li
Na
Ar
K
Rb
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Sorenson Video decompressor
are needed to see this picture.
Cs
Atomic Radii decreases due to the increase in the number of protons.
Ionization Energy of the Elements
Ionization energy is the energy required to
remove a valence electron from an atom.
IA
Ionization
Energy
decreases
as the
valence
electrons
are
located
farther
from the
nucleus.
VIIIA
H
IIA
IIIA
IVA
VA
VIA
VIIA
Mg
Al
Si
P
S
Cl
Li
Na
Ar
K
Rb
Cs
Ionization Energy increase due to increasing # of protons.
The Periodic Table
M
e
t
a
l
l
i
c
p
r
o
p
e
r
t
i
e
s
i
n
c
r
e
a
s
e
Summing
Up
Periodic
Trends
I
o
n
i
z
a
t
i
o
n
e
n
e
r
g
y
d
e
c
r
e
a
s
e
s
A
t
om
i
c
R
a
d
i
i
i
n
c
r
e
a
s
e
s
This table is called a Periodic Table
because periodic trends occur as you go
down
families and across periods.
Atomic Radii decreases
Valence electrons increase
Metallic properties decrease
Ionization Energy increases
We will use these periodic trends to
understand how elements combine to form
compounds in the next chapter.
Graphing
Periodic
Trends
Please take out your lab and the
Bohr Model of the Atom
program sheet so you can look
at the models you drew on the
back.
The atomic radii decreases
because more protons are
added to the nucleus.
This causes the electrons
to be pulled closer
to the nucleus.
The energy required
to remove an electron
becomes greater because
there are more protons
in the atom
(greater attraction).
As you go across a
period, the valence
electrons in the A-groups
increase by one.
As you go down the
As youelectrons
go down get
the Alakali
Alkali Metals, the valence
Metals and
family,
number of efurther from the nucleus
arethe
easier
energy
to remove from
the levels
atom. increases. This
causes their
atomic radii to
The lower the ionization
energy
increase.
the higher the chemical activity.
As you go down the
Halogen family,
the valence
get the Halogen
Aselectrons
you go down
further fromfamily,
the nucleus
and of e- energy
the number
are easier
remove This causes the
levelstoincreases.
from theatomic
atom. radii to increase.