Atomic structure

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ATOMIC STRUCTURE
S.MORRIS 2006
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Where did it all begin?

• The word atom comes from the Greek word
  atomos which means indivisible.
• The idea that all matter is made up of atoms
  was first proposed by the Greek philosopher
  Democritus in the 5th century B.C.

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HISTORY OF THE ATOM
Democritus develops the idea of atoms
460 BC
he pounded up materials in his pestle and mortar
until he had reduced them to smaller and smaller
particles which he called
ATOMA (greek for indivisible)
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HISTORY OF THE ATOM
John Dalton
1803
suggested that all matter was made up of tiny
spheres that were able to bounce around with
perfect elasticity and called them
ATOMS
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Daltons Atomic Theory (1808)
1. Elements are composed of extremely small
particles called atoms.
2. All atoms of a given element are identical.
The atoms of one element are different from
those of any other element
3. Atoms of different elements can combine in
simple whole number ratios to form compounds.
4. Chemical reactions only involve the
rearrangement of atoms. Atoms are not created or
destroyed in chemical reactions.
2.1
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8 X2Y
Law of Conservation of Mass
2.1
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Law of Definite Proportions

• The ratio of mass of elements in a compound is
  always the same
• Every Water molecule will contain 16g of oxygen
  and 2 g of hydrogen

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2
Law of Multiple Proportions
2.1
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HISTORY OF THE ATOM
Joseph John Thompson
1898
found that atoms could sometimes eject a far
smaller negative particle which he called an
ELECTRON
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HISTORY OF THE ATOM
1890
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
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HISTORY OF THE ATOM
Ernest Rutherford
1910
1910
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
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(1908 Nobel Prize in Chemistry)

• particle velocity 1.4 x 107 m/s
• (5 speed of light)

• atoms positive charge is concentrated in the
  nucleus
• proton (p) has opposite () charge of electron
• mass of p is 1840 x mass of e- (1.67 x 10-24 g)

2.2
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Rutherfords Model of the Atom
atomic radius 100 pm 1 x 10-10
m nuclear radius 5 x 10-3 pm 5 x 10-15 m
If the atom is the Ralph Wilson Stadium Then the
nucleus is a marble on the 50 yard line
2.2
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HISTORY OF THE ATOM
gold foil
helium nuclei
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.
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HISTORY OF THE ATOM
Rutherfords 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.
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HISTORY OF THE ATOM
Niels Bohr
1913
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.
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Chadwicks Experiment (1932)
H atoms - 1 p He atoms - 2 p mass He/mass H
should 2 measured mass He/mass H 4
neutron (n) is neutral (charge 0) n mass p
mass 1.67 x 10-24 g
2.2
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Subatomic Particles
mass p mass n 1840 x mass e-
2.2
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Bohrs Atom
electrons in orbits
nucleus
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Atoms

• of protons neutrons
• The basic unit of Matter
• The smallest particle of an element that retains
  the properties of that element.

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HELIUM ATOM
Shell
proton
N

-

N
-
neutron
electron
What do these particles consist of?
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ATOMIC STRUCTURE All About Atoms
Particle
Charge
Mass
Proton
charge
1amu
Neutron
No charge
1 amu
electron
- charge
1/1836
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ATOMIC STRUCTURE
He
2
Atomic number
Represents the number of protons in an atom Never
changes P equal to the number of e-
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Mass Number
the number of protons and neutrons in an
atom Neutrons equal mass - atomic
number of electrons number of protons
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Ions Charged particles due to the loss or gain
of electrons
2) Atoms that are called cations lose e- thus
becoming positive
1) Atoms that are called anions gain e- thus
become negative
2.5
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Isotopes

• Atoms with the same atomic number but different
  mass number
• Atoms having the same number of protons but
  different numbers of neutrons
• Average Atomic Mass of an element is the weighted
  average of an elements naturally occurring
  isotopes

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2.3
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Do You Understand Isotopes? Isotope Maker
6 protons, 8 (14 - 6) neutrons, 6 electrons
6 protons, 5 (11 - 6) neutrons, 6 electrons
2.3
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Atomic number (Z) number of protons in nucleus
Mass number (A) number of protons number of
neutrons
atomic number (Z) number of neutrons OF
NEUTRONS mass number atomic number
2.3
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Bohr Model of the Atom

• Electrons travel around the nucleus in one of
  several orbits/shells/ nrg levels
• Principal energy level is designated by a quantum
  number (n)
• Quantum number is the same as period on the
  periodic table

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2.4
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ATOMIC STRUCTURE
Electrons are arranged in Energy Levels or Shells
around the nucleus of an atom.

• first shell maximum of 2
  electrons
• second shell maximum of 8 electrons
• third shell max of 18
  electrons
• fourth shell max of 32 electrons

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ATOMIC STRUCTURE
There are two ways to represent the atomic
structure of an element or compound
1. Electronic Configuration
2. Electron dot diagrams
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ELECTRONIC CONFIGURATION
With electronic configuration elements are
represented numerically by the number of
electrons in their shells and number of shells.
For example
Nitrogen
configuration 2 , 5
14
2 in 1st shell 5 in 2nd shell
N
7
2 5 7
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ELECTRONIC CONFIGURATION
Write the electronic configuration for the
following elements
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11
8
O
Na
Ca
a)
b)
c)
16
23
40
2,8,8,2
2,8,1
2,6
14
Si
17
5
Cl
B
d)
e)
f)
11
35
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2,8,7
2,8,4
2,3
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Valence

• Valence shell is outermost occupied energy level
  and is the same as the period number in the
  periodic table
• Valence electrons are the electrons in the outer
  energy level of an atom

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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
N
7
N
X
X
X
X
14
X
X
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DOT CROSS DIAGRAMS
Draw the Dot Cross diagrams for the following
elements
X
8
17
X
O
Cl
a)
b)
X
35
X
16
X
X
X
X
X
Cl
X
X
X
X
X
X
O
X
X
X
X
X
X
X
X
X
X
X
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SUMMARY

• The Atomic Number of an atom number of
• protons in the nucleus.
• The Atomic Mass of an atom number of
• Protons Neutrons in the nucleus.
• The number of Protons Number of Electrons.
• Electrons orbit the nucleus in shells.
• Each shell can only carry a set number of
  electrons.