CHAPTER 2 : THE STRUCTUE OF AN ATOM

Nichole

LEARNING OBJECTIVES 2.1 Analyzing matter2.2 Synthesizing atomic structure2.3 Understanding isotopes and assessing their

importance2.4 Understanding the electronic structure of an atom2.5 Appreciate the orderliness and uniqueness of the

atomic structure

2.1 MATTER Matter is made up of tiny and discrete

particles. There are spaces between these particles.

Particles can be atom, molecules or ions.

Smallest Particle.Example: Metals Or

Non-metal

A group of two or more atoms which are

chemically bonded together.

positively-charged or negatively charged

particles.

CLASSIFICATION OF MATTER

Matter

Element

Atom

Gold, Au Argon Gas, Ar

Molecule

Oxygen Gas, O2

Sulphur, S8

Compound

Molecule

Water, H2O

Carbon Dioxide,

CO2

Ions

Sodium chloride, NaCl

Particles

CONT…. Particles in matter are in motion. Diffusion of substances

Particles of a substances move between the particles of another substances.

Rate of diffusion – depend on their mass (Lower molecular mass diffuse faster than higher molecular

masses) (Higher temperature – faster ) (Occur most rapidly in gases, slower in liquids and slowest in

solids)

THE KINETIC THEORY OF MATTER

CHANGES IN THE STATES OF MATTER

Used Heat Or Cool.

NH4Cl, dry ice (solid Carbon

dioxide)

Matter can either exist as an element or a compound. 

3. An element consists of only one type of atom and the particles can be either atoms or molecules.

A molecule is a neutral particle made up of either atoms of the same element or atoms of different elements.

An ion is a positively-charged or negatively-charged particles.

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

CHANGES IN STATES OF MATTER1. The changes in the states of matter are caused by heating

or cooling. For example, ice melts when it is heated and water changes into ice when it is frozen.

2. The kinetic theory of matter is used to explain the changes in states of matter.

MeltingWhen a solid is heated, the particles in the solid gain kinetic energy and vibrate more vigorously.

Melting• When a 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 gain is able to overcome the forces that hold them at their fixed positions.

• At this point, the solid becomes a liquid.• The temperature at which this happens is called the

melting point.• Melting point is the temperature at which a solid changes

into a liquid at a particular pressure.

Solid Liquid

Freezing• When a liquid is cooled, the particles in the liquid lose

energy and move slower.• As the temperature continues to drop, the particles continue

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

• Freezing point is the temperature at which a liquid changes into a solid at a particular pressure.

Boiling• When a liquid is heated, the particles of the liquid gain

kinetic energy and move faster as the temperature increases.

• Eventually, the particles have enough energy to completely break the forces holding them together.

• The particles are now able to move freely and far apart.• A gas is formed. • The temperature at which this happens is called the boiling

point.• Boiling point is the temperature at which a liquid changes into

a gas at a particular pressure.

Condensation• When a gas is cooled, the particles in the gas lose energy

and move slower.• As the temperature drops, the gas particles lose energy

and move more slowly.• Eventually, the movements of the particles become slow

enough for the gas to change into a liquid.• This change occurs at the boiling point of the substance.

SublimationSublimation is a process by which a solid changes directly into a gas without passing through the liquid state and vice versa.Examples of substances that undergo sublimation are iodine, ammonium chloride, NH4Cl and dry ice (solid carbon dioxide).

EXPERIMENT 1DIFFUSION OF BROMINE

Particles in matter are in motion. This has been confirmed by many experiments such as diffusion of bromine.

Diffusion occurs when particles of a substance move in between the particles of another substance.

Experiment 1 : To investigate the diffusion of particles in gases,

liquids and solids.

ProblemCan particles diffuse through the gaseous, liquid and solid

mediums? Hypothesis

During the diffusion of particles in two different media, the particles of one medium move to occupy the air spaces found in the other medium.

Variables(a) Manipulated : Air spaces of a particular medium (b) Responding : Movement of particles (c) Constant : Temperature

MaterialsLiquid bromine, potassium manganate(Vll) crystals,

copper(II) sulphate crystals, distilled water, jelly solution (5%)

Apparatus2 gas jars, boiling tube, beaker, retort stand, straw.

Procedure(I) Movement of particles in the gaseous medium

1. A drop of liquid bromine is added into a gas jar.2. It is then covered by tilting the second gas jar over it3. All observations are recorded.

(II) Movement of particles In the liquid medium1. A 500 cm3 beaker is filled until almost full.2. With the aid of a straw, 2-3 small crystals of potassium

manganate(VII), KMnO4, crystals are placed at the base of the beaker.

3. The apparatus is left aside for several hours. All observations are recorded.

(III) Movement of particles in the solid medium1. A boiling tube with hot jelly solution (5% concentration)

is filled up. Allow the jelly to cool (It will set and become a solid).

2. A copper(II) sulphate, CuSO4, crystal is placed on the jelly, the boiling tube is closed with a cork and set it up as shown in Figure 2.4(c).

3. It is then kept aside for two days. All observations are recorded.

RESULT

Medium Observations Inference

Gaseous Liquid vapourises into a brown gas which slowly fills up the first jar, before moving upwards into the second jar

Bromine gas diffuses into the air occupying the two gas jar

Liquid The purple colour of the KMnO4

crystals spread slowly until, after several hours, the whole solution turns purple

Diffusion of particles is slower in liquids than in gases

Solids The blue colour of the CuSO4 crystal spreads very slowly upwards through the jelly

Diffusion of particles is the slowest in solids

DISCUSSION

(I) In gases

1. Bromine gas (brown vapour) is composed of tiny and discrete molecules which are constantly and randomly moving in all directions.

2. The air in the two gas jars contains empty spaces among the air particles

3. Bromine molecules move from the bottom of the gas jar where they are highly concentrated, towards the top, where they are less concentrated. They do this by moving to occupy the empty spaces among the air particles until the bromine molecules are evenly distributed in the gas jars.

(II) In liquids1. Potassium manganate(VII) crystals is made up of tiny

and discrete particle move slowly into the spaces in between the water molecules.

2. Diffusion is slower because there are less empty spaces in liquids than in gases.

 (III) In solids1. Copper(II) sulphate crystals are made up of tiny, discrete

particles too.2. The particles move upwards and occupy the empty

spaces in between jelly particles.3. Diffusion is much slower in solids because solid

particles are arranged compactly with very little space between particles.

 (III) In solids4. The rates of diffusion of particles are highest in gases,

lower in liquids and lowest in solids.5. This is due to the different arrangement of particles in

solids, liquids and gases. The particles of a solid are packed closely together whereas the particles of a liquid are packed slightly loose. The particles of a gas are very far apart from each other and in a random arrangement.

CONCLUSIONGases, liquids and solids are made up of tiny and discrete particles, that are in in constant

motion.

EXPERIMENT 2: DIFFUSION 1. The rate of diffusion of gas particles

depends on their masses.2. The rate of diffusion is affected by the

temperature

The rate of diffusion of gas particles depends on their masses.a. Gases with low molecular masses diffuse faster than

those with high molecular masses.b. Figure shows the set-up of the apparatus used to compare

the rates of diffusion of ammonia gas, NH3 and hydrogen chloride gas, HCl.

c. A white solid ring formed nearer to the end with the hydrogen chloride. The white solid is ammonium chloride, NH4Cl, a compound produced from the reaction of ammonia gas and hydrogen chloride gas when they meet inside the glass tube.

d. This experiment shows that the ammonia molecules move faster than the hydrogen chloride molecules.

e. Ammonia gas diffuses faster than hydrogen chloride gas because the molecular mass of ammonia is less than that of hydrogen chloride.

The rate of diffusion is affected by the temperature. a. The higher the temperature, the faster the

particles move and so the faster the diffusion.b. For example, the colour of potassium

manganate(VII) spreads through the water much more quickly in hot water than in cold water.

EXPERIMENT 3: MELTING AND FREEZING POINTS OF

NAPHTHALENE.

To determine the melting and freezing points of naphthalene.

Aim: To determine the melting and freezing points of

naphthalene Materials

Naphthalene powder, water. Apparatus

Retort stand, beaker 250 cm3, boiling tube, a large conical flask, thermometer (0° -100°C), stop watch, wire gauze, Bunsen burner.

CHANGES IN STATES OF MATTER

PROCEDURES

CHANGES IN STATES OF MATTER Procedure

1. A boiling tube is filled with naphthalene to a depth of 3 cm and a thermometer is put into it.

2. The boiling tube is suspended in a beaker half-filled with water using a retort stand and a clamp as shown in Figure 2.10. The level of naphthalene in the boiling tube is ensured to be below the level of water in the beaker.

3. The water is heated and the naphthalene is stirred slowly with the thermometer.

4. When the temperature of the naphthalene reaches 60°C, the stopwatch is started. The temperature and the state(s) of the naphthalene are recorded at half-minute intervals until the temperature of the naphthalene reaches 90°C.

CHANGES IN STATES OF MATTER Procedure

5. The boiling tube in section A is removed from the water bath. The outer surface of the boiling tube is dried and immediately it is put in a conical flask, as shown in Figure 2.11. The naphthalene is stirred continuously.

6. The temperature and state(s) of the naphthalene are recorded at 30-seconds interval until it reaches 60°C.

RESULT

CHANGES IN STATES OF MATTER Results

DISCUSSION 1. The heating graph of naphthalene

2. The cooling graph of naphthalene

3. During the heating of naphthalene

4. During the cooling of naphthalene

CHANGES IN STATES OF MATTER Discussion

The heating graph of naphthalene1. Notice that there is a certain part of the curve where is no

change in temperature with time during heating. 2. Notice that there is a certain part of the curve where is no

change in temperature with time during cooling. At this temperature, both solid and liquid are present. It is the melting point of naphthalene. Hence, the melting point of naphthalene is 80.0°C.

CHANGES IN STATES OF MATTER (a) At point A, naphthalene exists as solid.

(b) When the solid is heated, heat energy is absorbed. This causes the particles to gain kinetic energy and vibrate faster. The temperature increases from point A to point B.

(c) At point B, solid naphthalene begins to melt. During the melting process, the temperature of naphthalene does not rise even though heating continues. The temperature remains constant because the heat energy absorbed by the particles is used to overcome the forces between particles so that the solid can turn into a liquid. At this temperature, both solid and liquid are present.

(d) At point C, all the solid naphthalene has melted.

(e) From point C to point D, the particles in liquid naphthalene absorb heat energy and move faster. The temperature increases from point C to point D.

Discussion:The cooling graph of naphthalene

1. Notice that there is a certain part of the curve where is no change in temperature with time during cooling.

2. Notice that there is a certain part of the curve where is no change in temperature with time during cooling. At this temperature, both solid and liquid are present. It is the freezing point of naphthalene. Hence, the freezing point of naphthalene is 80.0°C.

Discussion:a. At point M, naphthalene exists as liquid.b. When the liquid is cooled, the particles in the liquid lose

their kinetic energy. They move slower as the temperature decreases from point M to point N.

c. At point N, liquid naphthalene begins to freeze. During the freezing process, the temperature of naphthalene remains constant because the heat loss to the surroundings is balanced by the heat energy given off during freezing. At this temperature, both solid and liquid are present.

d. At point O, all the liquid naphthalene has frozen.e. From point O to point P, the particles in solid naphthalene

release heat energy and vibrate slower. The temperature decreases from point O to point P.

INTER-CONVERSION OF STATES OF MATTER AND KINETIC THEORY OF MATTER

3. Discussion• During the heating of naphthalene,

a. A water bath is used instead of direct heating with a Bunsen flame. This is to ensure that the naphthalene is heated evenly. Furthermore, the naphthalene is flammable.  

b. the naphthalene is stirred continuously to ensure an even heating.

Discussion4. During the cooling of naphthalene,

a. the boiling tube containing the liquid naphthalene is placed in a conical flask. The air trapped in the conical flask is a poor conductor of heat. This helps to minimize the heat loss to the surroundings which may affect the accuracy of the freezing point obtained.

b. the naphthalene is stirred continuously to avoid super cooling. Super cooling is a condition in which the temperature of a cooling liquid drops below its normal freezing point, without the appearance of a solid.

Discussion5. A water bath is used in this experiment because the

melting point of naphthalene is below 100°C, the maximum temperature that can be attained by the water bath. For solids with melting points above 100°C, a liquid with a higher boiling point than water such as oil must be used.

CONCLUSION

INTER-CONVERSION OF STATES OF MATTER AND KINETIC THEORY OF MATTER Conclusion The temperature of naphthalene increases when the

solid is heated and it decreases when liquid naphthalene is cooled down. The melting and freezing points are the same, that is 80°C.

SUMMARY

SUMMARY

2.2 THE ATOMIC STRUCTURE

HISTORY

DALTON’S ATOMIC MODEL

J.J.THOMSON(1856-1940)

ERNEST RUTHERFORD(1871-1937)

NEILS BOHR(1885-1962)

JAMES CHADWICK(1891-1974)

SUBATOMIC PARTICLES OF AN ATOM

Atoms are building blocks of elements Consist of 3 sub-atomic particles (smaller particles)

Protons, neutrons, electrons Elements are differentiated by the number of

proton

STRUCTURE OF AN ATOM

• An atom consists mostly of empty space.• Negatively charged electrons move around the nucleus in fixed

orbits or paths• When no. of proton = no. of electrons in an atom .It is electrically

neutral. It has no net charge• Proton and neutron are found in the nucleus of an atom while

electrons surround the nucleus.

A positively charged nucleus, densely concentrated in the centre.

The nucleus contains protons and neutrons, which are tightly packed

PROTON NUMBER AND NUCLEON NUMBER Proton number = the number of protons in an atom Also known atomic number No two different element have same proton number Atom are neutral. Proton number also tells us number of

electron. Nucleon number also known mass number Nucleon no. = proton no. + neutron number

SYMBOL OF ELEMENTS Most symbols are taken from the English name.

Some symbols are made up of two letters.

Some symbols are based on the Latin or Greek name

Complete symbols Contain the symbol of the element, the proton number

and the nucleon number.

X Protonnumber

NucleonnumberSubscript →

Superscript →

ISOTOPES AND THEIR IMPORTANCE

Same Different

Proton number Nucleon number

Number of protons in an atom Number of neutrons in an atom

Number of electron in an atom Physical properties – density, melting point. Electron arrangement

Chemical properties – same electron arrangement

Are atoms of the same element with the same proton no. but different nucleon no. or neutron no.

Isotopes of an element have same chemical properties but different physical properties

Example of isotopes Some isotopes are stable while the rest unstable

( radioactive isotopes)

ISOTOPES OF HYDROGENHydrogen :1

1

H

2

1

H

3

1

H

PROPERTIES OF ISOTOPES

Oxygen Isotopes

No of proton 16 16 16No of neutron 16 17 18

No of e- 16 16 16e- configuration 2.8.6 2.8.6 2.8.6Valence e- 6 6 6

16

8O

18

8O17

8O

CONCLUSION: Number of valence electron are same The chemical properties also same The physical properties might be same,

might be different

USES OF ISOTOPES Medicine

Cobalt-60 is a radioactive isotope of cobalt. It decays by giving out gamma radiation. In radiotherapy, maglinant cancer cells are killed by directing a beam of gamma rays towards cancer cells

Agriculture

radiation from radioisotopes is used to sterilise pests such as insects that destroy crops.

Industry

Gamma radiation is used to detect whether canned food or bottled drink is completely or partially filled

ELECTRONIC STRUCTURE OF AN ATOM The electron in atom are arranged in shell around its

nucleus Electron start to fill up the shells from the inner shells The first shell is the shell that nearest to nucleus and can

hold just 2 electrons Second shell can hold 8 electrons Third shell can hold 8 electrons All of this is called the electron arrangement or electronic

configuration of the atom Draw electronic arrangement if proton number is 4,5 and 6

Shell Maximum number of electrons1st 22nd 83rd 8 or 184th 36

The electrons in the last shell of an atom are known as valence electrons. They determine the chemical properties of the element.

Valence electron = 5 Valence electron = 1

ELECTRON ARRANGEMENT IN THE CARBON ATOM

C12

6

proton number = 6number of protons = 6number of electrons = 6

2 . 4

= electron

nucleus

Number of valence electrons = 4

VALENCE ELECTRONS Outermost shell of an atom is called the valence shell This shell should have electrons before it can be called a

valence shell The electrons in the valence shell are called the valence

electrons Elements with the same number of valence electrons have

the same chemical properties For example, chlorine and bromine, have 7 valence

electrons, will exhibit similar chemical properties.

2.8.7 2.8.18.7

Helium has a complete shell of 2 valence electrons or duplet condition. Similarly, neon and argon also have 8 valence electrons or the octet condition. These elements are monoatomic and are very stable gases.

The atomic structures of the first 20 elements in the Periodic Table of Elements are given in Table

Helium2

Neon2.8

Argon2.8.8

Element Proton number

Number of electrons

Number of elements in shell Electron arrangement

Number of valance electrons

1 2 3 4

Hydrogen 1 1 1 1 1Helium 2 2 2 2 2Lithium 3 3 2 1 2.1 1Beryllium 4 4 2 2 2.2 2Boron 5 5 2 3 2.3 3Carbon 6 6 2 4 2.4 4Nitrogen 7 7 2 5 2.5 5Oxygen 8 8 2 6 2.6 6Fluorine 9 9 2 7 2.7 7Neon 10 10 2 8 2.8 8Sodium 11 11 2 8 1 2.8.1 1Magnesium

12 12 2 8 2 2.8.2 2

Aluminium

13 13 2 8 3 2.8.3 3

Silicon 14 14 2 8 4 2.8.4 4

Element Proton number

Number of electrons

Number of elements in shell Electron arrangement

Number of valance electrons

1 2 3 4

Phosphorus

15 15 2 8 5 2.8.5 5

Sulphur 16 16 2 8 6 2.8.6 6Chlorine 17 17 2 8 7 2.8.7 7Argon 18 18 2 8 8 2.8.8 8Potassium

19 19 2 8 8 1 2.8.8.1 1

Calcium 20 20 2 8 8 2 2.8.8.2 2

The electron arrangement of an element, for example; Na is constructed by drawing 3 circles around the nucleus to represent each shell, as its electron configuration is 2.8.1. Thus we have

Table shows the electron arrangement of the first 20 elements in the Periodic Table.

2 8 1

Hydrogen(1)

Helium(2)

Lithium(2.1)

Beryllium(2.2)

Boron(2.3)

Carbon(2.4)

Nitrogen(2.5)

Oxygen(2.6)

Fluorine(2.7)

Neon(2.8)

Sodium(2.8.1)

Magnesium(2.8.2)

Aluminium(2.8.3)

Silicon(2.8.4)

Phosphorus(2.8.5)

Sulphur(2.8.6)

Chlorine(2.8.7)

Argon(2.8.8) Potassium

(2.8.8.1)Calcium(2.8.8.2)

Elements

ProtonNumber

NucleonNumber

Number of

NeutronsA 3 7B 6 12C 19 10D 16 16E 17 18F 40 20

Q1 Fill in the blanks

Elements

Number of

Neutron

Nucleon

Number

Number of

electrons

ElectronConfiguratio

n

A 5 9B 8 2.6C 19 2.7D 14 2.8.3E 32 16F 20 40

Q2 Fill in the blanks

QUESTIONS……..

1. What are the physical changes of matter according to the picture?

2. What is happen on the particles of the molecules during this process?

3. As the naphthalene melts, why does the temperature not increase?

The temperature is not increase because the heat energy in absorb to break the attractive forces between the molecule. The heat energy has not been used to raise the temperature of the naphthalene

R

Name the 3 subatomic particles? What is the relative charge of these particles? Name the particles located in the nucleus? What is the particle moving around the nucleus

called?

MCQQ: The three basic components of an atom

are:a. protons, neutrons, and ionsb. protons, neutrons, and electronsc. protons, neutrinos, and ionsd. protium, deuterium, and tritium

Q: An element is determined by the number of:

e. atomsf. electronsg. neutronsh. protons

Q: The nucleus of an atom consists of:i.  electronsj. neutronsk. protons and neutronsl. protons, neutrons, and electrons

Q: A single proton has what electrical charge?

a. no chargeb. positive chargec. negative charged. either a positive or negative charge

Q: Which particles have approximately the same size and mass as each other?

e. neutrons and electronsf. electrons and protonsg. protons and neutronsh. none - they are all very different in

size and mass

Q: Which two particles would be attracted to each other?

i. electrons and neutronsj. electrons and protonsk. protons and neutronsl. all particles are attracted to each

other