Transcript Atomic Theory - University of Hong Kong

Atomic Theory
Click the links below to access the
activities:
- Activity 1
- Activity 2
- Activity 3
- Extension activity
- Activity 4
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Activity 1: Conservation of mass
?
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If a piece of magnesium is burnt, will there be a gain
or a loss in mass?
Video 1
Video 2
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Your tasks…
Task 1
Measure the mass of 500 cm3 of
your favourite drink. Then
compare your body mass before
and after drinking it.
Task 3
Dissolve 5 g table salt in 100 cm3
of water. Compare the masses of
solute, solvent and the resulting
solution
Task 2
Compare the mass of sodium
hydroxide (NaOH) solution and
copper(II) sulphate (CuSO4)
solution with the mass of the
mixture where we can see some
precipitate of Cu(OH) 2.
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What can you conclude from the
above data?
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The Law of Conservation of Mass
‘In a chemical reaction, the mass of the
products is equal to the mass of the
reactants.’
‘Matter can neither be created nor
destroyed in any physical or chemical
change.’
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People had no idea why the law was
always true.
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Activity 2: The Law of Definite
Proportions
End of 1700s
Some chemists tried to mix different
elements to see how they reacted with
each other.
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Look at the results of the following
reactions:
carbon + oxygen  carbon dioxide
carbon + oxygen  carbon monoxide
copper + oxygen  copper(II) oxide
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What can you
conclude from the
data above?
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The Law of Definite Proportions
Nobody could explain why elements
behaved like this.
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Activity 3: Atomic theory
All matter is composed of very
small discrete particles.
For elements, the particles
are called atoms and they
are indivisible and
indestructible in chemical
reactions.
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What is a law?
What is a theory?
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What is a law?
Laws are descriptions of relationships
among phenomena in nature
Ideal Gas Law PV = nRT
What is a theory?
Theories are the explanations of those
relationships
Kinetic Theory
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Law and Theory
The Ideal Gas Law describes the
behaviours of ideal gases.
Kinetic Theory explains these
behaviours i.e. the Ideal Gas Law.
Kinetic model
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Another example
Law of Reflection
Incident light ray
Reflected light ray
Normal
θi
θr
Steel Ball
Rebound
Explained by the “particle theory of
light”
Light
Many light
particles in a light ray
Mirror
Reflection
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Law
Theory
Hierarchical
relationship?
Hypothesis
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Scientific theories and laws are different
kinds of knowledge.
A theory will not turn into a law or
vice versa.
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Extension
Atomic Theory
All matter is composed of very small discrete particles.
For elements, the particles are called atoms and are indivisible
and indestructible in chemical reactions.
Comment on Dalton’s Atomic
Each atom of a given element
has the same mass. (ii) All atoms of
Theory!
a given element are identical. (iii) The masses of atoms of different
elements are different.
A chemical compound is formed from its elements by the
combination of the different atoms in a fixed ratio for that
compound.
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For elements, the particles are called atoms and are indivisible
and indestructible in chemical reactions.
Each atom of a given element has the same mass.
12C
13C
isotopes
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“An atom is made of electrons,
protons and neutrons.”
Try to look up websites to answer this question!
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Scientific knowledge
is subject to change
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Activity 4: Assessment
Question 1
(a) The mass of an iron atom in a hammer is greater
than the mass of an iron atom in a nail.
(b) When you change a piece of solid copper into
the liquid state, the mass of each copper atom
decreases.
(c) When you heat a silver ring, it expands. This is because
the silver atoms become bigger.
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Question 2
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Question 3
(a) What will be the
difference in masses of
the iron, compared to
the rusted iron?
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(b) Draw a picture to show what a
piece of rusted iron would look like
if you could see the atoms.
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Before rusting
After rusting
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Question 4
Compare the mass of the setup before
and after CuSO4 crystals have grown.
Explain your answer.
crystals
After a few days, crystals
have grown.
CuSO4 solution in a closed
system.
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Question 5
Compare the masses of 355cm3 Diet Coketm
and 355cm3 regular Coketm after pouring them
out of the cans. Discuss whether this is related
to the Law of Conservation of Mass or not.
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