Connect your learning
Draw and label an atom
of carbon – include as
much information as you
can
Start Timer
3 Minutes
3
2
Extension:
What are
carbon- 12 and
carbon-14?
1
0
Connect your learning
How did you do?
Labelled the protons, neutrons and electrons (1)
Protons and neutrons in the nucleus (1)
Electrons in shells orbiting the nucleus (1)
Correct charges on protons + (1) and mass 1 (1)
Correct charges on neutrons 0 (1) and mass 1(1)
Correct charges on electrons -(1) and mass 0 (1)
6 protons (1)
6 electrons (1)
6 neutrons (1)
2 electrons in 1st shell and 4 electrons in outer shell (1)
Learning outcomes
State how the model of the atom has changed
over the years and how it continues to do so
(D)
Describe some of the experiments conducted and how
they contributed to the model of the atom (C/B)
Describe some of the strengths and weaknesses of
these model and theories that were propsed (A/A*)
Sharing new info
Early ideas
It’s all Greek to me.
• Early Greek philosophers like Democritus thought
that everything was made up of tiny particles that
could not be divided.
• These particles were called ‘atoms’ , a word derived
from the Greek atomos which means “indivisible”.
• Democritus also thought that these ‘atoms’ were held
together by tiny hooks.
Sharing new info
Research task
• In pairs or threes, you need to produce
a ‘famous atomic scientist’ factsheet
• You need to include
–
–
–
–
When they made their discovery
What their discovery was
How they made their discovery
Their model of the atom
• Each group will be assigned a scientist from;
– John Dalton (1766 – 1844)
– JJ Thomson (1856 – 1940)
– Ernest Rutherford(1871 – 1937) with Geiger and
Marsden
– Niels Bohr (1885 – 1962)
• Try and summarise their discovery into bullet
points
• You will be using this information to teach the
rest of the class so make sure it contains the
key relevant information
• You have 20 minutes!
Homework
• Read up on each of the scientists that
the groups have covered today.
• Use the factsheets as a starting point
but find out your own information.
• Once you have done this complete the
class notes worksheet handed out to you
http://rossettes.wikispaces.com/Lesson+1+The+cha
nging+atom
John Dalton
In 1807 an English chemist, John Dalton put
forward his atomic theory.
He suggested that:
• Atoms are tiny particles that make up elements
• Atoms cannot be divided
• All atoms of a given element are the same
• Atoms of one element are different from those of every other
element
• Dalton developed his own
symbols to represent
atoms of different
elements.
• Dalton’s theory is still
considered to be strong
as most of his
predictions hold true
today.
JJ Thomson
• Joseph John (JJ) Thomson carried out a
series of experiments using cathode rays
• Cathode rays had been recently discovered
but no-one knew what they were.
• Cathode rays are emitted from the negative
electrode inside cathode ray tubes.
Cathode ray tube
• For information only!!!!!!
Properties of cathode rays
• Thomson discovered that cathode rays
were a stream of particles. Each
particle had the following properties:
• It had a negative charge
• It could be deflected by both a magnet and
an electric field
• It had a very, very small mass.
• Cathode rays are, in fact, electrons.
• Thomson concluded they must have come from
the within the atoms of the electrodes
themselves.
• He disproved the idea that the atom could not
be split any further.
• Thomson proposed that an atom should be
thought of being made of negative charges
moving in a ‘sea’ of positive charge
• The overall negative charge is the same as
the overall positive charges, therefore the
atom is neutral
Thomson’s model
• ‘the plum pudding model’
• Positive and negative charges balance to
make the atom neutral
• Mass of the atom is due to the nucleus
• The mass of the electron was 1/1840
the mass of hydrogen the lightest
element
• There were 1840 electrons in an atom
of hydrogen
Plum Pudding Model 1904
“the atoms of the elements consist of a number of
negatively electrified corpuscles enclosed in a sphere
of uniform positive electrification”
Rutherford’s gold-leaf experiment
• 1909 began work that
disproved the ‘plumpudding’ model
• They fired alpha (α)
particles towards
some thin gold foil and
measured any
deflection.
• Rutherford calculated
that the plum-pudding
atom would hardly
deflect the αparticles at all.
• The results of their experiment surprised
them. They found:
– Most of the particles were not deflected at all
– A very small percentage of particles were
deflected through large angles
– A very few particles were deflected back towards
the source.
• From these observations, Rutherford
calculated that an atom’s positive charge must
be concentrated into a space smaller than the
atom itself
Rutherford’s model
• The atom consists mainly of space
• The mass is concentrated in the nucleus,
which is a small core at the centre of
the atom
• The nucleus has positive charges
• Electrons move around the nucleus
• The atom is neutral
Niels Bohr
• Niels Bohr (1885 – 1962)
• Worked with Rutherford at Cambridge
• He applied Max Planck’s idea that
energy came in little packets called
‘quanta’.
• This meant that electrons could only
follow certain paths
Bohr’s model
• Most of the mass of an atom is in the central
nucleus that contains protons
• The electrons are arranged in definite shells
or energy levels and orbit the nucleus
• The electron shells are a long way from the
nucleus
• When one shell is full a new shell is started
(electronic configuration)
• Atoms with full shells are not very reactive
• Electrons determine the reactivity of an atom
James Chadwick
• Discovered the neutron and this is
added to the atom
• It is the same mass as a proton but has
no charge
I proposed my model of atomic
structure in the early 1800s
I stated that once an electron shell
is full another shell is started
My experiments fired alpha
particles at some thin gold foil
and measured deflection
I disproved the idea that atoms
could not be split further
I stated electrons are arranged in
definite shells or energy levels –
orbittng the nucleus
I put forward the “plum pudding
model” sphere of positive charge
with negative electrons dotted
throughout
I discovered the neutron
I suggested that tiny particles
make up atom
My work started to dis prove the
plum pudding model
My ideas were strong as many of
them still hold true today
I suggested that atoms cannot be
divided
I stated that atoms mainly consist
of space
I stated that neutrons are the
same mass as protons but they
don’t have a charge
I stated that most of the mass is in
the central nucleus that contains
protons
I stated that the electrons move
around the nucleus
I stated that electrons determine
the reactivity of atoms
I stated the nucleus of an atom
has a positive charge and this is
where the mass of an atom is
concentrated
I suggested atoms of the same
atom are all the same
I stated that atoms with full shells
are not very reactive
‘I stated that in an atom the
positive and negative charges
equal out – so an atom is neutral
over all
I carried out experiments using
cathode rays