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Transcript of S.MORRIS 2006. Where did it all begin? The word “atom” comes from the Greek word “atomos”...
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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 ATOMHISTORY OF THE ATOM
460 BC Democritus develops the idea of atoms
he pounded up materials in his pestle and
mortar until he had reduced them to
smaller and smaller particles which he
called
ATOMAATOMA
(greek for indivisible)
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HISTORY OF THE ATOMHISTORY OF THE ATOM
1803 John Dalton
suggested that all matter was made up of
tiny spheres that were able to bounce
around with perfect elasticity and called
them
ATOMSATOMS
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Dalton’s Atomic Theory (1808)1. Elements are composed of extremely small particles
called atoms.
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
2. All atoms of a given element are identical. The atoms of one element are different from those of any other element
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8 X2Y16 X 8 Y+
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
2.1
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HISTORY OF THE ATOMHISTORY OF THE ATOM
1898 Joseph John Thompson
found that atoms could sometimes eject a
far smaller negative particle which he
called an
ELECTRONELECTRON
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HISTORY OF THE ATOMHISTORY OF THE ATOM
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
1890
like plums surrounded by pudding.
PLUM PUDDING
MODEL
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HISTORYHISTORY OF THE ATOMOF 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
1910
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1. atoms positive charge is concentrated in the nucleus2. proton (p) has opposite (+) charge of electron3. mass of p is 1840 x mass of e- (1.67 x 10-24 g)
particle velocity ~ 1.4 x 107 m/s(~5% speed of light)
(1908 Nobel Prize in Chemistry)
2.2
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atomic radius ~ 100 pm = 1 x 10-10 m
nuclear radius ~ 5 x 10-3 pm = 5 x 10-15 m
Rutherford’s Model of the Atom
2.2
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HISTORY OF THE ATOMHISTORY OF THE ATOM
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.
helium nuclei
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HISTORY OF THE ATOMHISTORY 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.
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HISTORY OF THE ATOMHISTORY 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.
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Chadwick’s Experiment (1932)
H atoms - 1 p; He atoms - 2 p
mass He/mass H should = 2
measured mass He/mass H = 4
+ 9Be 1n + 12C + energy
neutron (n) is neutral (charge = 0)
n mass ~ p mass = 1.67 x 10-24 g2.2
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Subatomic Particles
Particle Mass
(g) Charge
(Coulombs) Charge (units)
Electron (e-) 9.1 x 10-28 -1.6 x 10-19 -1
Proton (p) 1.67 x 10-24 +1.6 x 10-19 +1
Neutron (n) 1.67 x 10-24 0 0
mass p = mass n = 1840 x mass e-
2.2
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Bohr’s 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
+N
N
+-
-
proton
electron
neutron
Shell
What do these particles consist of?
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ATOMIC STRUCTUREATOMIC STRUCTURE
All About Atoms
Particle
Proton
Neutron
electron
Charge
+ charge
- charge
No charge
1amu
1 amu1/1836
Mass
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ATOMIC STRUCTUREATOMIC STRUCTURE
Represents the number of protons in an atom
Never changes
P+ equal to the number of e-
the number of protons and neutrons in an atomNeutrons equal mass # - atomic #
HeHe22
44 Mass Number
Atomic number
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
Na 11 protons11 electrons Na+ 11 protons
10 electrons
Cl 17 protons17 electrons Cl-
17 protons18 electrons
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 element’s naturally occurring isotopes
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2.3
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How many protons, neutrons, and electrons are in C146 ?
How many protons, neutrons, and electrons are in C116 ?
6 protons, 8 (14 - 6) neutrons, 6 electrons
6 protons, 5 (11 - 6) neutrons, 6 electrons
Do You Understand Isotopes?Isotope Maker
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
XAZ
H11 H (D)2
1 H (T)31
U23592 U238
92
Mass Number
Atomic NumberElement Symbol
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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Period
Group
Alkali M
etal
Noble G
as
Halogen
Alkali E
arth Metal
2.4
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ATOMIC STRUCTUREATOMIC 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 STRUCTUREATOMIC 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 CONFIGURATIONELECTRONIC CONFIGURATION
With electronic configuration elements are
represented numerically by the number of
electrons in their shells and number of shells. For
example;
N
Nitrogen
14
7
2 in 1st shell
5 in 2nd shell
configuration = 2 , 5
2 + 5 = 7
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ELECTRONIC CONFIGURATIONELECTRONIC CONFIGURATION
Write the electronic configuration for the following elements;
Ca O
Cl Si
Na20
40
11
23
8
17
16
35
14
28B
11
5
a) b) c)
d) e) f)
2,8,8,2 2,8,1
2,8,7 2,8,4 2,3
2,6
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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 DIAGRAMSDOT & 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;
Nitrogen N XX X
X
XX
X
N7
14
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DOT & CROSS DIAGRAMSDOT & CROSS DIAGRAMS
Draw the Dot & Cross diagrams for the following elements;
O Cl8 17
16 35a) b)
O
X
XX
X
X
X
X
X
Cl
X
X
X
X X
X
XX
X
X
X
X
X
XX
X
X
X
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SUMMARYSUMMARY
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.