Download Atomic structure

S.MORRIS 2006
Learning Outcomes
•
•
•
•
Define atom and element
Get an idea of the size of an atom
Basic structure of the atom
Types, numbers of, and properties of
subatomic particles in an atom
2
Atomic Theory
 Atoms are building blocks of elements = Atom is
the smallest particle of matter that can exist by itself
 Similar atoms in each element
 Different from atoms of other elements
 Two or more different atoms bond in simple
ratios to form compounds
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3
HISTORY OF THE ATOM
1808
John Dalton
suggested that all matter was made up of
tiny spheres that were able to bounce around
with perfect elasticity and called them
ATOMS
HISTORY OF THE ATOM
1898
Joseph John Thompson
found that atoms could sometimes eject a far
smaller negative particle which he called an
ELECTRON
HISTORY OF THE ATOM
1904
Thompson develops the idea that an atom was made up of
electrons scattered unevenly within an elastic sphere surrounded
by a soup of positive charge to balance the electron's charge
like plums surrounded by pudding.
PLUM PUDDING
MODEL
HISTORY OF THE ATOM
1910
Ernest Rutherford
oversaw Geiger and Marsden carrying out his
famous experiment.
they fired Helium nuclei at a piece of gold foil
which was only a few atoms thick.
they found that although most of them
passed through. About 1 in 10,000 hit
HISTORY OF THE ATOM
helium nuclei
gold foil
helium nuclei
They found that while most of the helium nuclei passed
through the foil, a small number were deflected and, to their
surprise, some helium nuclei bounced straight back.
HISTORY OF THE ATOM
Rutherford’s new evidence allowed him to propose a more
detailed model with a central nucleus.
He suggested that the positive charge was all in a central
nucleus. With this holding the electrons in place by electrical
attraction
However, this was not the end of the story.
HISTORY OF THE ATOM
1913
Niels Bohr
studied under Rutherford at the Victoria
University in Manchester.
Bohr refined Rutherford's idea by adding
that the electrons were in orbits. Rather
like planets orbiting the sun. With each
orbit only able to contain a set number of
electrons.
Bohr’s Atom
electrons in orbits
nucleus
Structure of the atom
Nucleus
Electrons orbiting the
nucleus
12
HELIUM ATOM
Shell
proton
+
-
N
N
+
electron
-
neutron
What do these particles consist of?
https://www.youtube.com/watch?v=lP57gEWcisY
ATOMIC STRUCTURE
Particle
Charge
Mass
proton
+ ve charge
1
neutron
No charge
1
electron
-ve charge
nil
Location of Subatomic Particles
10-13 cm
electrons
protons
nucleus
10-8 cm
LecturePLUS Timberlake
neutrons
15
Atomic Number
Counts the number
of
protons
in an atom
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16
Periodic Table
 Represents physical and chemical behaviour
of elements
 Arranges elements by increasing atomic
number
 Repeats similar properties in columns known
as chemical families or groups
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17
Periodic Table
1
2
3
4
5
6
7
8
11
Na
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18
Atomic Number on the Periodic
Table
Atomic Number
Symbol
11
Na
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19
All atoms of an element have
the same number of protons
11 protons
Sodium
11
Na
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20
Learning Check AT 1
State the number of protons for atoms of
each of the following:
A. Nitrogen
1) 5 protons
2) 7 protons 3) 14 protons
B. Sulfur
1) 32 protons
2) 16 protons
3) 6 protons
C. Barium
1) 137 protons 2) 81 protons
LecturePLUS Timberlake
3) 56 protons
21
Solution AT 1
State the number of protons for atoms of each
of the following:
A. Nitrogen
2) 7 protons
B. Sulfur
2) 16 protons
C. Barium
3) 56 protons
LecturePLUS Timberlake
22
Number of Electrons
 An atom is neutral
 The net charge is zero
 Number of protons = Number of electrons
 Atomic number = Number of electrons
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23
Mass Number
Counts the number
of
protons and neutrons
in an atom
LecturePLUS Timberlake
24
Atomic Symbols
 Show the mass number and atomic number
 Give the symbol of the element
mass number
23 Na
atomic number
sodium-23
11
LecturePLUS Timberlake
25
More Atomic Symbols
16
O
31
P
65
8
15
30
p+
n
e-
p+
n
eLecturePLUS Timberlake
Zn
p+
n
e26
Learning Objectives
• Bohr Structure
• Electronic Configuration
• Drawing structure of atoms
ATOMIC STRUCTURE
Electrons are arranged in Energy Levels or
Shells around the nucleus of an atom.
•
first shell
a maximum of 2 electrons
•
second shell
a maximum of 8 electrons
•
third shell
a maximum of 8 electrons
ATOMIC STRUCTURE
There are two ways to represent the atomic
structure of an element or compound;
1.
2.
Electronic Configuration
Dot & Cross Diagrams
ELECTRONIC CONFIGURATION
With electronic configuration elements are represented
numerically by the number of electrons in their shells
and number of shells. For example;
Nitrogen
2 in 1st shell
5 in
2nd
shell
configuration = 2 , 5
2
+
5 = 7
N
7
14
ELECTRONIC CONFIGURATION
Write the electronic configuration for the following
elements;
a)
Ca
20
b)
Na
40
2,8,8,2
d)
Cl
17
35
2,8,7
11
23
c)
2,8,1
e)
Si
14
28
2,8,4
O
8
16
2,6
f)
B
5
11
2,3
DOT & CROSS DIAGRAMS
With Dot & Cross diagrams elements and compounds
are represented by Dots or Crosses to show electrons,
and circles to show the shells. For example;
X
Nitrogen
X X
N
XX
X X
N
7
14
DOT & CROSS DIAGRAMS
Draw the Dot & Cross diagrams for the following
elements;
X
8
17
X
a) O
b)
Cl 35 X
16
X
X
X
X
X
X
X X X Cl X X
X
X
X
O
X
X
X
X
X
X
X
X
X
SUMMARY
1. The Atomic Number of an atom = number of
protons in the nucleus.
2. The Atomic Mass of an atom = number of
Protons + Neutrons in the nucleus.
3.
The number of Protons = Number of Electrons.
4.
Electrons orbit the nucleus in shells.
5.
Each shell can only carry a set number of electrons.
When an atom loses an electron it gets a
positive charge.
When an atom gains an electron it gets a
negative charge.
• How many neutrons and
electrons are there in the
ion
45 Sc +3
21