Transcript Atomic Theory

Atomic Theory
The Movers and Shakers
of the Subatomic World.
Democritus
• 440 B.C.E
• All matter is made up of atoms, which
are indivisible
• 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)
Dalton
• In the early 1800’s, the
English chemist John Dalton
did a number of experiments
that eventually led to the
acceptance of the idea of
atoms.
Dalton’s Atomic Theory
• All elements are composed of
atoms. Atoms are solid small
spheres and indivisible
particles.
continued...
• Atoms of the same element
are exactly alike.
H
H
continued...
• Atoms of different elements
are different.
O
H
continued...
• Compounds are formed by the
joining of atoms of two or
more elements.
H
H
O
Questions...
• What were the four parts
of the Dalton’s atomic
theory?
• Say it again...
Was he right?
• Dalton’s atomic theory of
matter became one of the
foundations of chemistry.
• BUT it needed work…other
scientists had to modify the
theory.
Thomson
• In 1897, the work of an
English scientist J. J.
Thompson provided the first
hint that atoms were made up
of even smaller particles
• Atoms are divisible…Dalton
was wrong!
Thompson’s Model
• He stated that atoms are
made up of positively (+)
and negatively (-) charged
particles
And...
• He thought the positive (+)
and negative (-) particles were
s p r e a d o u t in atoms like
ppuldudmisn
• (plums in puddin’)
Questions...
• What kind of particles did
Thompson find in atoms?
• What did his idea of an
atom look like?
Was Thomson Right?
• Not really…there are
positively (+) and
negatively (-) charged
particles inside atoms.
•BUT...
Rutherford’s Model
• In 1908, Rutherford
discovered the nucleus.
• He stated that atoms have a
small, dense, positively (+)
charged ce
nucleus.
nter called a
The Nuclear Atom
Alpha Particle Scattering
06/04/2016
.
Alpha Source
An atom
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Next
The Nuclear Atom
06/04/2016
Rutherford’s Model
He suggested that all of the atom’s positive
charge, together with most of its mass, is
concentrated
in the centre.
+
Alpha particles which travel close to the
nucleus are strongly deflected. The degree
of deflection depends on how close it
approaches.
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Next
The Nuclear Atom
Rutherford’s Model
06/04/2016
The nucleus must be very small in comparison
to the atom.
This will account for the vast majority making it
through unaffected.
Back
Next
Questions...
• What did Rutherford find
inside the atom?
• What did Rutherford’s
atom look like?
So...
• Particles are not spread out
like plums in pudding…
• Positive particles (protons)
are in the center (nucleus).
• Where are the negative
particles (electrons)?
Bohr’s Model
• In 1913, Niels Bohr proposed
an improvement to
Rutherford’s Model:
• Electron’s move in definite
orbits around the nucleus, like
planets around the sun.
+
Back
Next
Questions...
• What did Bohr propose?
• Where were the particles
in Bohr’s model of an atom?
• What did it look like?
• What was special about the
electrons in Bohr’s model?
Are we there yet?
• Bohr’s model was used for a
long time…
•BUT...
Modern Atomic Model
• An atom has a small, positively
charged nucleus surrounded
large region
by a
in
which there are enough
electrons (-) to make the
atom neutral (0).
E
E
E
E
E
PPP
P PP P P
PP P P
E
E
E
E
E
E
E
Questions...
• Do electrons have specific
orbits in the modern
model?
• What does the atom look
like in the new model?
Make Your Timeline
• After the sheet is passed out:
– write your name on it!
– Fill out the timeline according
to date, scientist, notes, and
picture (if there is one) for
each scientist we went over.
– Neatness counts!!!!!
– HAVE FUN
Bohr’s Atom
electrons in orbits
nucleus
HELIUM ATOM
Shell
proton
+
-
N
N
+
electron
What do these particles consist of?
-
neutron
ATOMIC STRUCTURE
Particle
Charge
Mass
proton
+ ve charge
1
neutron
No charge
1
electron
-ve charge
nil
ATOMIC STRUCTURE
2
He
Helium
4
Atomic number
the number of protons in an atom
Chemical Symbol
Chemical Name
Atomic mass
the number of protons and
neutrons in an atom
number of electrons = number of protons
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
•
forth shell
a maximum of 8 electrons
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
7
N
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
Bohr Rutherford Diagrams
With Bohr Rutherford diagrams, elements and
compounds are represented by Dots to show electrons,
and circles to show the shells. For example;
O
Nitrogen
O O
N
OO
O O
N
7
14
Bohr Rutherford Diagrams
Draw the Bohr Rutherford Diagrams for the following
elements;
O
8
17
O
a) O
b)
Cl 35 O
16
O
O
O
O
O
O
O O O Cl O O
O
O
O
O
O
O
O
O
O
O
O
O
O
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.
References
• Investigating Science Pearson 9
• Dercho