Chapter 2The Structure of the Atom

2.1 MatterMatter: Anything that occupies

space and has massBased on theory: Matter is made up

of tiny and discrete particles. There are spaces between these particles

Types of particle: Atoms Molecules Ions

Atom: The smallest particle of an element that can participate in a chemical reaction

Molecule: A group of two or more atoms which are chemically bonded together

Ion: A positively-charged or negatively-charged particle

Diffusion: Occurs when particles of a substance move in between the particles of another substance

Diffusion of matter occurs most rapidly in gases, slower in liquids and slowest in solids → due to the different arrangement and movement of particles

Observe this video

Kinetic Theory of MatterTypes of matter:

Solid

Liquid

Gas

The arrangement and movement of particles in solid, liquid and gas are described in the kinetic theory of matter.

The Change in The State of Matter

Sublimation

Sublimation

Condensation

Boiling /Evaporation

Melting

Freezing

When solid is heated;The particles in the solid gain kinetic

energy and vibrate more vigorously.The particles vibrate faster as the

temperature increases until the energy they gained is able to overcome the forces that hold them at their fixed positions.

At this point, the solid becomes a liquid.This process called melting.The temperature at which this happens

is called melting point.

When liquid is heated;The particles in the liquid gain kinetic

energy and move faster.The particles move faster as the

temperature increases until the energy they gained is able to overcome the forces that hold them.

At this point, the liquid becomes a gas.This process is called boiling.The temperature at which this

happens is called boiling point.

When liquid is cooled;The particles in the liquid lose energy

and move slower.As the temperature decreases, the

particles lose more energy until they did not have enough energy to move freely.

At this point, the liquid changes into a solid.

This process is called freezing.The temperature at which this happens

is called freezing point.

Definition:Melting point

The temperature at which a solid changes into a liquid at a particular pressure.

Freezing pointThe temperature at which a liquid changes into a solid at a particular pressure.

The heating curve

Temperature (°C)

Time (min)

Melting point

A

B C

D

solid

begin to

melt liquid

solid-liquid

The temperature remains constant because:The heat energy absorbed is used to overcome the force attraction between particles so that solid can change into liquid

Heat energy is absorbed.Particles in solid gain kinetic energy and vibrate faster

Heat energy is absorbed.Particles in liquid gain kinetic energy and move faster

The cooling curve

Temperature (°C)

Time (min)

Freezing point

E

F G

H

liquid

solid

liquid-solid

The temperature remains constant because:The heat loss to the surrounding is equal to the heat energy formed during particles attraction to form a solid

Heat energy is released.Particles in liquid lose kinetic energy and move slower

Heat energy is released.Particles in solid lose kinetic energy and vibrate slower

2.2 The Atomic Structure

Historical development of atomic modelsModel Structure Characteristic

Dalton’s atomic model proposed by John Dalton in 1805

The atom was imagined as a small indivisible ball similar to a very tiny ball.

Thomson’s atomic model proposed by J.J. Thomson in 1897

J.J Thomson discovered electron, a negatively-charged particle.The atom was described as a sphere of positive charge embedded with electrons.

Model Structure Characteristic

Rutherford’s atomic model proposed by Ernest Rutherford in 1911

Ernest Rutherford discovered proton, a positively-charged particle in an atom.The central region of atom has a very small positively-charged nucleus, which contains almost all the mass of the atom.

Bohr’s atomic model proposed by Neils Bohr in 1913

The electrons in an atom move in shells around the nucleus which contains protons.

Model Structure Characteristic

Chadwick’s atomic model proposed by James Chadwick in 1932

Chadwick proved the existence of neutrons, the neutral particle in the nucleus.The nucleus of the atom contains protons & neutrons, and the nucleus is surrounded by electrons.

Subatomic particles in atom

Proton Neutron Electron

Subatomic particles

Relative electric charge: +1Relative mass: 1

Relative electric charge: 0Relative mass: 1

Properties of subatomic particles

Nucleus

Proton, p

Neutron, n

Relative electric charge: -1Relative mass: ≈ 0.0005

Electron, e

Proton number and nucleon number Proton number:

The number of proton in its atom** also shows the number of electrons in the atom

Nucleon number:The total number of protons and neutrons in its atom ** also known as mass number

What is the relationship??

Nucleon number

Proton number

Number of neutrons

= +

Nucleon number

Number of protons

Number of neutrons

= +

OR

Reminder!!!

Proton number

Nucleon number

Neutron number

√

√

XNumber of

neutron

Symbol of elements

XA

Z

Nucleon number

Proton number

Symbol of element

2.3 Isotopes and Their ImportanceIsotopes: Atoms of the same element with

same number of proton but different number of neutrons.OR

Atoms of the same element with same proton number but different nucleon number.

Example of elements with isotopes:

Hydrogen

H1

1 H2

1 H3

1

Hydrogen-1 Hydrogen-3Hydrogen-2

Chlorine

Cl35

17 Cl37

17

Chlorine-35 Chlorine-37

Uses of isotopes in our daily livesIn the medical field:Cobalt-60

Used in radiotherapy for the treatment of cancer

Iodine-131Treatment of thyroid gland

In the argiculture field:Phosphorus-32

Study the metabolism of phosphorus in plantsGamma ray of cobalt-60

Used to destroy bacteria in food

Uses of isotopes in our daily livesin industrial field:Sodium-24

Used detect leakages in pipesIn archeology field:Carbon-14

To estimate the age of fossils and artifacts

2.4 The Electronic Structure of an Atom

The first shell : 2 electrons

The second shell : 8 electrons

The third shell : 8 electrons

Nucleus

Example:

Chlorine atomProton number of 17Hence, chlorine atom has 17

electronsElectron arrangement:

2.8.7

Valence electronsThe electrons in the outermost

occupied shell

Outermost occupied shell

Valence electron