THE STRUCTURE OF THE ATOM

CHEMISTRY TERM MEANING (ENGLISH)

MEANING (MALAY)

Compound    

Diffusion    

Electron arrangement    

Forces of attraction    

Indivisible    

Outermost shell    

Particle    

Subatomic particles    

Valence electrons    

  

WORD GALLERY

Electron arrangements

Sub-atomic particles: proton, electron, neutron

Particles in matter: atom, molecule and ionDiffusion in a solid,

liquid and gasChanges in state of

matter

Atomic StructureKinetic theory of matter

MATTER

Isotopes

Determination of the melting point of naphthalene

Chapter 22.0 The Structure of The Atom 2.1              Matter

1. Definition : Anything that occupies space and has mass.

2. Exists in three states which are solid, liquid and gas.3. Examples of matter : air, water, soil, plants, animals,

human etc.4. Examples of non – matter : electricity5. Matter can either exist as an element or a compound.6. An element is a pure substance which cannot be

broken down into simpler substance physically or chemically.

7. A compound is usually made up of two or more elements which are chemically bonded together.

8. Figure 2.1 shows some examples of matter.

Matter

CompoundElement

MoleculeAtom Molecule Ion

Example: Iron Oxygen gas Water Sodium chloride

Sodium Hydrogen gas Carbon dioxide Lithium oxide

 

9. An atom is the smallest neutral particle of an element that can take part in a chemical reaction.

10. A molecule is a neutral particle made up of either atoms of the same element or atoms of different elements. Examples of molecules are oxygen, O2 (two atoms of the same elements) and carbon dioxide, CO2 (three atoms from two different elements).

11. An ion is a charged particle which consists of either one atom or atoms from different elements. Examples of ions are sodium ion, Na+, chloride ion, Cl- dan sulphate ion, SO4

2-.12. Matter is made up of tiny and discrete particles.13. These particles can either be atoms, molecules or ions.

2.2 Diffusion 1.      Diffusion occurs in gases, liquids and solids.2.      It occurs when the particles of a substance move

randomly in between the particles of another substance.3.      Brownian movement, an example of diffusion,

supports the kinetic theory of matter.4.      Examples of Brownian movement are(a)    movement of smoke particles in air(b)   movement of pollen grains in water(c)    pouring concentrated sugar solution into water(d) Diffusion proves that matter is made up of tiny particles.

2.3 Kinetic Theory of Matter 1. The kinetic theory of matter states that matter

consists of tiny, discrete particles that are constantly moving.

2. These particles move in a randomly motion and collide with one another.

3. When a substance is heated, the particles in it gain kinetic energy and move faster.

4. When a substance is cooled, the particles lose kinetic energy and move slower.

5. The arrangement and movement of particles in solid, liquids and gases are described in the kinetic theory of matter

  The particles are packed closely together in an orderly manner.

  There are strong forces between the particles.• The particles can only vibrate and rotate about

their fixed positions.

Solid

Liquid

 The particles are packed closely together but not in orderly arrangement.

  The particles are held together by strong forces but weaker than the forces in a solid.

• The particles can vibrate, rotate and move throughout the liquid. They collide against each other.

Gas

 The particles are very far apart from each other and in a random motion.

  There are weak forces between the particles.• The particles can vibrate, rotate and move

freely. The rate of collision is greater than the rate of collision in a liquid.

2.4 The Change in the State of Matter 1. Changes in the state of matter can occur through

heating or cooling processes. This is when the heat energy is absorbed or released from matter.

2. Figure 2.4 shows the changes in the state of matter.

Melting

Freezing

Boiling

Condensation

SublimationSublimation

Gas

Solid Liquid

 

Key : Heating Cooling

3. A substance is in solid state if it exists at a temperature below its melting point.

4. A substance is in liquid state if it exists at a temperature above its melting point but below its boiling point.

5. A substance that exists at a temperature higher than its boiling point will exist in gaseous state.

6. The kinetic theory of matter is used to explain the change in state of matter.

7.When a solid is heated, the particles gain kinetic energy and vibrate more vigorously

8. The particles vibrate faster as the temperature increase until the energy they gained is able to overcome the forces that hold them at their fixed positions.

9. At this point, the solid become liquid.

10. When a liquid is cooled, the particles in the liquid release energy and move slower

11. As the temperature decrease, the particles lose energy.

12. At this point, the liquid changes into a solid.13. Figure 2.5 shows the heating curve of

naphthalene. The curve shows the changes in temperature when solid naphthalene melts.

14. Figure 2.6 shows the cooling curve of naphthalene. The curve shows the changes in temperature when liquid naphthalene is cooled

The inter – conversion of the states of matter

Heating Curve

A

B C

D E

F

Temperature /0C

Boilingpoint

Meltingpoint

Time/minute

HEATING CURVE• A : The substance is in solid state. The particles are very

closely packed, therefore the forces between the particles are very strong.

• A – B : Heating causes the particles to absorb more energy and vibrate faster. The temperature of the substance and the kinetic energy increases.

• B : The heat energy absorbed by the particles is enough to overcome the forces of attraction between them. Bond begin to break and the solid begins to melt.

• B – C : The substance exists in both solid and liquid states. Continuous heating does not cause the temperature increase.

The energy absorbed is used to overcome the forces of attractionbetween the particles. This cause

the substance to change from solid to liquid.The constant temperature is called the melting point.

• C : The melting process ends here. Now the substance exists only in liquid state.

• C – D : The substance is in liquid state. The particles move faster and the kinetic energy increase.

• D : The substance exists only in liquid state. The energy absorbed by the substance now is enough to overcome the forces

of attraction between the particles. Bonds begin to break.

• D – E : The substance exists in both liquid and gaseous states. The heat energy absorbed is used to overcome the forces of attraction between the particles of the liquid. The temperature remain

unchanged. This constant temperature is the boiling point.

• E : The substance exists only in the gaseous state

• E – F : The gas particles continue to absorb more energy and move faster. The temperature increases as heating

continues.

Cooling Curve

A

B C

D E

F

Boiling point

Freezingpoint

Temperature/0C

Time/minute

Do you have any idea on how does the cooling curve works?

• D : The substance exists as a gas. The particles have very high energy and are moving randomly. The forces of attraction between particles are very weak.

• D-E : The particles lose kinetic energy during cooling and the temperature

drops.

• E : The substance still exists as a gas. The gas begins to condense and become liquid.

• E – F : The substance exists in both gaseous and liquid states. Stronger bonds form as gas changes into liquid. The energy produced during the formation of bonds is equal to the heat energy released to the surroundings during cooling. Thus, the temperature remains unchanged. This constant temperature is the boiling point.

• F : The substance exists only as a liquid as all the gas particles have condensed into liquid.

• F-G: The substance exists only as a liquid. Particles lose more kinetic energy, move slower and the temperature decreases.

• G : The substance still exists as a liquid. Have very little energy and to move closer towards one another as it starts

to freeze into a solid.

• D – E : The substance exists as both liquid and solid. The stronger bonds formed during

freezing release energy. This energy released is the same as the energy lost to the surroundings during cooling. Thus, temperature remains unchanged. This constant temperature is the freezing point.

• E : All the liquid freezes into solid. The particles are now closely packed in orderly

manner.

• E – F : The substance exists as a solid. The temperature decreases as cooling continues.

B. The Atomic Structure

• Please complete this section ( Pg 25 & 26) in group next time (Take this as your home work).

• Please make references to complete this task.

SUBATOMIC PARTICLES• Atom is made up of three subatomic particles :

proton, neutron and electron• The Proton & neutron form a nucleus at the

centre of an atom.• The electron moves around the nucleus at a

very high speed• The mass of the atom is concentrated at the

nucleus

electron

neutron

shell

proton

nucleus

SubatomicParticleProton

Neutron

Electron

Symbol

p

n

e

Mass (g)

1.672 x 10-24

1.675 x 10-24

9.11 x 10-28

Relativemass 1

1

1 / 1837

Charge

+1

0

-1

  2.7 Comparison between subatomic particles1. The atom of any element is neutral as the number of protons

and number of electrons in the atom is equal.

2. For neutral atom, the total positive charged in the nucleus is equal to the total negative charged of electrons around the nucleus.

2.7 Proton Number and Nucleon Number 1. Atoms of same element will have the same

number of protons.2. For example, a nucleus which has 1 proton is

hydrogen and a nucleus with 12 protons is magnesium.

3. Thus, the number of protons in an atom determines the type of element formed.

4. The proton number is the number of protons in the atom nucleus of an element.

Proton number = number of protons

5. For example, a sodium atom has 11 protons, thus the proton number of sodium is 11.

6. For a neutral atom, the proton number also refers to the number of electrons in the atom.

Proton number = number of protons = number of electrons

7. The nucleon number is the total number of protons and neutrons in the nucleus of an element’s atom.

8. For example, an oxygen atom has 8

protons and 8 neutrons, thus the nucleon number for an oxygen atom is 16.

Nucleon number = number of protons + number of neutrons

Number of neutrons = nucleon number - proton number

XA

ZProtonnumber

Nucleon number

Element

2.9 Symbol of element

Proton number

Nucleon number

Symbol of element for magnesium

24 Mg

12

Eg.

Number of proton = 12

Number of electrons = 12

Number of neutrons = 24 – 12 = 12

2.9 Isotopes and their Importance1. Isotopes are atoms of certain elements which have

the same number of protons/proton number but different number of neutrons /nucleon number in the nucleus of the atoms.

2. Isotopes for certain elements have similar chemical properties as they have the same electron arrangement.

3. Physical properties such as melting point, boiling point, density and mass of each isotope of certain element differ due to the different number of neutrons.

4. Hydrogen has three isotopes, as shown in figure 2.7

1p 1p1n 1p

2n

Hydrogen – 1 Hydrogen – 2 Hydrogen - 3

 

Field Isotope application

Medical         Gamma rays from cobalt – 60 are used to kill cancer cell without surgery in patients. This treatment is known as radiotherapy.        Medical instruments are sterilized using gamma rays.        Radioactive materials such as iodine – 131 are injected into patients to detect malfunction of thyroid glands.

Archeology   

Agricultural   

Industrial   

5. Isotopes has many application in daily life.6. Several uses of isotopes in daily life are shown in

Table 2.92

2.10 The Electronic Structure of an atom1.    Atoms are made up of nucleus and electrons.

This electrons move around the nucleus the atom.2.    Electrons are arranged in these shells.3.    Each shell is numbered 1, 2, 3, and so on.4. Figure 2.10.1 shows the arrangement of shell in

an atom.

First shell

electronSecond shell

nucleus

5.     Each shell can only consists of a certain number of electrons.

6.      Electron will fill in shell from the lowest energy level which is the one nearest to the nucleus.

7. Electrons arrangement can be drawn by putting the electrons into the shells without exceeding the maximum capacity of each shell as shown in Table 2.10.1

Shell Maximum number of electrons

1 2

2 8

3 8

4 8

8. For example, an atom of calcium has 20 electrons (20 protons). The electron arrangement for the atom can be shown in Figure 2.10.2.

The electron arrangement for a calcium atom is 2.8.8.2

2.11 Valence electrons 1.    Valence electrons are electrons in the

outermost shell of an atom.2.    The number of valence electrons is the number

of electrons in the outermost shell of an atom.3. For example, a magnesium atom has an

electron arrangement of 2.8.2. So, it has two valence electrons.

2.12 Quick Test 1.    Write the electron arrangement for the atoms

below : (i)  35 Cl17

  (ii) 27 Al

13

2.8.7

2.8.3

1.   Draw the atomic structure for the atoms below :

(i) 11 Na23

 

(ii)  8 O

16

Na O

END OF CHAPTER 2