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Atomic Theory. Click the links below to access the activities: Activity 1 Activity 2 Activity 3 Extension activity Activity 4. Activity 1: Conservation of mass. ?. If a piece of magnesium is burnt, will there be a gain or a loss in mass? . Video 1. Video 2. Your tasks…. Task 1

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Atomic Theory

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Atomic Theory

  • Click the links below to access the activities:

  • Activity 1

  • Activity 2

  • Activity 3

  • Extension activity

  • Activity 4


Activity 1: Conservation of mass

?


If a piece of magnesium is burnt, will there be a gain or a loss in mass?

Video 1

Video 2


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 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 3

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


What can you conclude from the above data?


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.’


People had no idea why the law was always true.


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.


Look at the results of the following reactions:

carbon + oxygen  carbon dioxide

carbon + oxygen  carbon monoxide

copper + oxygen  copper(II) oxide


What can you conclude from the data above?


‘A given chemical compound always contains the same proportions by mass of its constituent elements.’

Proposed by Joseph Louis Proust in 1797

The Law of Definite Proportions

Nobody could explain why elements behaved like this.


For elements, the particles are called atoms and they are indivisible and indestructible in chemical reactions.

Activity 3: Atomic theory

All matter is composed of very small discrete particles.


What is a law?

What is a theory?


What is a law?

What is a theory?

Laws are descriptions of relationships among phenomena in nature

Ideal Gas Law PV = nRT

Theories are the explanations of those relationships

Kinetic Theory


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


Law of Reflection

Incident light ray

Reflected light ray

Normal

θi

θr

Rebound

Steel Ball

Light

Reflection

Many light

particles in a light ray

Mirror

Another example

Explained by the “particle theory of light”


Law

Hierarchical relationship?

Theory

Hypothesis


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

Scientific theories and laws are different kinds of knowledge.


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!


Each atom of a given element has the same mass.

12C

isotopes

13C

For elements, the particles are called atoms and are indivisible and indestructible in chemical reactions.


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

Has this statement been revised?

Try to look up websites to answer this question!


Scientific knowledge is subject to change


(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.

Activity 4: Assessment

Question 1


Question 2

What would be left if all the atoms are removed?


Question 3

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


(b) Draw a picture to show what a piece of rusted iron would look like if you could see the atoms.


Before rusting

After rusting


crystals

Question 4

Compare the mass of the setup before and after CuSO4 crystals have grown. Explain your answer.

After a few days, crystals have grown.

CuSO4 solution in a closed system.


Question 5

Compare the masses of 355cm3 Diet Coketm and 355cm3regular 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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