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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 2Task 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.

Task 2Task 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.

Task 1Task 1

Measure the mass of 500 cm3 of your favourite drink. Then compare your body mass before and after drinking it.

Task 1Task 1

Measure the mass of 500 cm3 of your favourite drink. Then compare your body mass before and after drinking it.

Task 3Task 3

Dissolve 5 g table salt in 100 cm3 of water. Compare the masses of solute, solvent and the resulting solution

Task 3Task 3

Dissolve 5 g table salt in 100 cm3 of water. Compare the masses of solute, solvent and the resulting solution

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What can you conclude from the What can you conclude from the above data? above data?

What can you conclude from the What can you conclude from the above data? above data?

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The Law of Conservation of MassThe 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 What can you conclude from the conclude from the

data above? data above?

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The Law of Definite ProportionsThe Law of Definite Proportions

Nobody could explain why elements behaved like this.

‘A given chemical compound always contains the same proportions by mass

of its constituent elements.’

Proposed by Joseph Louis Proust in 1797

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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 law?

What is a What is a theory?theory?

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What is a law?

What is a theory?

Theories are the explanations of those relationships

Theories are the explanations of those relationships

Laws are descriptions of relationships among phenomena in nature

Laws are descriptions of relationships among phenomena in nature

Ideal Gas Law PV = nRT

Kinetic Theory

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Law and Theory

Kinetic Theory explains these behaviours i.e. the Ideal Gas Law.

The Ideal Gas Law describes the behaviours of ideal gases.

Kinetic model

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Another example

Explained by the “particle theory of light”

Law of Reflection

Incident light ray Reflected light ray

Normal

θi θr

Steel Ball Rebound

Light Reflection

MirrorMany light particles in a light ray

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Hypothesis

Theory

Law

Hierarchical relationship?

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A theory will not turn into a law or A theory will not turn into a law or vice versavice versa..

Scientific theories and laws are Scientific theories and laws are different different kindskinds of knowledge. of knowledge.

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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.

Each atom of a given element has the same mass. (ii) All atoms of 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.

Comment on Dalton’s Atomic Theory!

Comment on Dalton’s Atomic Theory!

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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.

12C13

C

isotopes

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“An atom is made of electrons, protons and neutrons.”

“An atom is made of electrons, protons and neutrons.”

Has this statement been

revised?

Try to look up websites to answer this question!

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Scientific knowledge Scientific knowledge is subject to changeis subject to change

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Activity 4: Assessment

(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.

Question 1

(c) When you heat a silver ring, it expands. This is because the silver atoms become bigger.

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What would be left if all the What would be left if all the

atoms are removed?atoms are removed?

Question 2

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(a) What will be the difference in masses of the iron, compared to the rusted iron?

(a) What will be the difference in masses of the iron, compared to the rusted iron?

Question 3

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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.

27Before rusting After rusting

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Compare the mass of the setup before Compare the mass of the setup before and after CuSOand after CuSO44 crystals have grown. crystals have grown.

Explain your answer.Explain your answer.

Question 4

CuSO4 solution in a closed system.

After a few days, crystals have grown.

crystals

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Question 5

Compare the masses of 355cmCompare the masses of 355cm33 Diet Coke Diet Coketmtm an and 355cmd 355cm33 regular Cokeregular Coketmtm after pouring them out after pouring them out of the cans. Discuss whether this is related to tof the cans. Discuss whether this is related to t

he Law of Conservation of Mass or not. he Law of Conservation of Mass or not.