Transcript Atoms Template

Grade 10
Physical Science
Atoms
First ideas about atoms
• The ancient Greeks believed
that everything was made from
some combination of Earth,
Air, Fire and Water. Chemists
want more definite ideas and
tried to find the basic materials
that all things were made of.
Democritus
• 500BC – Democritus – Greek
philosopher. He thought that
everything was made up of tiny
particles, which were too small
to be broken into smaller parts,
atomos, meaning “uncuttable”.
Democritus’ ideas were not
widely believed because he
had no evidence to support this
hypothesis.
Antoine Lavoisier
• The French chemist, Antoine
Lavoisier recognised special
chemicals called elements.
Elements are very important
because they are pure
substances which cannot be
split up into simpler substances
by means of chemical
reactions.
Each element is made of only
one type of atom.
Law of Conservation of Mass
• In 1774, Antoine Lavoisier used a
new chemical balance to weigh the
chemicals he used in his
experiments. He found that if the
reactions take place in a sealed
container, then the mass of the
chemicals that were there before
the reaction took place was exactly
the same as the mass of the
products of the reaction after it was
finished. He called this discovery
the Law of Conservation of Mass.
Question 1
• Antoine Lavoisier is famous
for:
• A naming the atom
• B recognising elements
• C weighing atoms
Answer 1
B
recognising elements
Joseph Proust
• Joseph Proust, also a French
scientist, had seen that no
matter how you prepared a
chemical compound, it always
contains the same elements,
joined in the same proportions
by weight.
• If you heat copper (Cu) in
oxygen (O2) the compound
formed is copper oxide (CuO).
• If you heat copper carbonate
(CuCO3), the new compound is
also copper oxide.
Law of Constant
Proportions
• Proust found that in both
cases, the copper and the
oxygen are always there in the
ratio of 64:16 or 4:1. In 1799,
Proust stated these findings in
the Law of Constant
Proportions.
• 2Cu + O2  2CuO
• CuCO3  CuO + CO2
John Dalton
• John Dalton published a book
called A System of Chemical
Philosophy in 1808. He
suggested that the French
chemists’ laws and other
chemical behaviour could be
explained by the idea of tiny,
indestructible, solid particles,
which he called atoms.
Dalton’s atomic theory
Dalton’s atomic theory proposed
that:
•All matter consists of tiny particles
called atoms, which cannot be broken
up.
•All the atoms of a particular element
have the same mass and the same
behaviour, but are different to the
atoms of other elements.
•When atoms combine, they do so in
proportions of small whole numbers
to form ‘compound atoms’ (what we
call ‘molecules’). Atoms cannot be
created or destroyed in a chemical
reaction.
Question 2
Dalton's Atomic Theory states the
following:
1. matter is made up of tiny,
indestructible particles called atoms
2. the atoms of one element are all
identical
3. that atoms of different elements
have the same mass
A
B
C
D
Statement 1 is true
Statement 2 is true
Statement 3 is true
Statements 1, 2 and 3 are true
Answer 2
D Statements 1, 2 and 3 are true
Joseph Thomson
• Joseph Thomson (1856 –
1940), a British physicist, did
many experiments to find out
what happened when an
electric field acted on gases.
Thomson discovered that there
were negatively charged
particles present, which he
called electrons.
Thomson’s
plum pudding
model
• Since atoms have no overall
charge, Thomson proposed
that the atom was made up of
uniform positive charge with
the negative electrons stuck
into positive matter, like
currants in a currant bun.
“Plum pudding theory.”
Models and facts
• A model like Thomson’s atomic
model uses a simple idea to
help other people to
understand the way a scientist
is thinking. A model should fit
some of the known facts, but
need not fit all of them.
Thomson’s model is a good
illustration of this.
Here are some atomic
facts so far:
• All atoms contain electrons.
• All atoms contain positive
charges.
• The mass of an atom is much
more than the mass of the
electrons.
• Different atoms have different
sizes.
Question 3
Which of the following is the best
definition of a scientific model?
A any visual representation of
scientific experimental findings
B a 3D object used to demonstrate
key scientific theories and data
C a visual, verbal, or mathematical
explanation of experimental data
D an explanation of any scientific
idea, theory, or experimental
results
Answer 3
C a visual, verbal, or
mathematical explanation of
experimental data
Question 4
Thompson’s Plum Pudding model
allowed scientists studying the atom
to do which of the following:
A analyze and test Thompson’s
findings.
B create an image that could be
used in schools.
C increase interest and funding in
atomic theory.
D disperse the information more
quickly to the public.
Answer 4
A analyze and test
Thompson’s findings.
Marie Curie
In France, Marie Curie
discovered radioactivity. She
showed that a new kind of
radiation was given off by
uranium, polonium and radium.
These radiations could penetrate
paper and caused their
compounds to glow in the dark.
Sadly, unknown to her, they also
caused leukemia, from which
she died.
Ernest Rutherford
Rutherford realised that what
was happening with radioactivity
was that the atoms were splitting
and releasing energy in the form
of three kinds of radiation:
alpha (α) particles
beta (β) particles
gamma (γ) rays
Alpha, beta and gamma
• Beta particles turned out to be
electrons.
• Gamma rays were high energy
x-rays.
• Alpha particles had a charge of
+2 equal and opposite to the
charge on two electrons.
(helium atom)
Rutherford chose alpha particles
to explore the inside of atoms.
As a matter of interest
Rutherford’s scattering
experiment
In 1911, Rutherford started
testing Thomson’s model of the
atom. He placed very thin gold
foil in the path of alpha particles.
Most alpha particles deflected
1° to 4°, which would be
expected with the plum pudding
model.
The surprise!
Then, to the surprise of his two
assistants, T. Marsden and Hans
Geiger (who designed the Geiger
counter for radioactive studies),
some of the alpha particles were
being deflected by much greater
angles and one out of every
20 000 hit something and
bounced back!
Cannonball & loo roll
This didn’t fit Thomson’s model.
He said: ‘It was about as
incredible as if you fired a 375
mm shell at a piece of toilet
paper and it came back and hit
you!
Rutherford had to come up with
a new model.
Rutherford’s conclusion
Rutherford concluded that over
99,9% of the mass of an atom
and all its positive charge was
squeezed into a tiny nucleus at
its centre. The rest of the atom’s
volume was taken up by circling
electrons which moved around
the nucleus like planets circling
around the Sun.
Rutherford’s model
Rutherford found that the
nucleus was very small, one
10 000th the size of the atom
itself. Atoms have diameters of
2 to 3 × 10−10 m and nuclei
around 1 × 10−14 m. Imagine a
marble at the centre of the
Greenpoint stadium!
Question 5
Imagine a circle with a diameter
of 2 km. If this represents an
atom, which answer would best
represent the nucleus? (Figures
in brackets represent the
diameters).
A
A table tennis ball (2 cm)
B
A tennis ball (7 cm)
C
A volley ball (20 cm)
D
A soccer ball (25 cm)