CHEMISTRY CHAPTHER 1 AND 2

CHAPTHER ONE

1. INTRODUCTION TO CHEMISTRY

-Chemistry is the study of the composition, structure, properties and interactions of matter.

2.THE IMPORTANCE OF CHEMISTRY

Chemistry Related Careers

1. Aquaculturist
2. Bacteriologist
3. Biochemist
4. Chemical engineer
5. Cosmetic scientist
6. Doctor
7. Environmental scientist
8. Food technologist
9. Forensic scientist
10. Geologist
11. Horticulturalist
12. Laboratory technician
13. Nutritionist
14. Pathologist
15. Pharmacist

3. Steps in the Scientific Method

Making observation An investigation usually begins with an observation on a phenomenon. Observation is to observe and gather the information about the phenomenon. Making Inference After gathering sufficient information, we make an inference, or early conclusion, based on what has been observed. The inference may or may not be true and need to be proven true or false with further investigation. Identifying problem Asking question based on the inference made to identify the problem related to the observation. Making a hypothesis A hypothesis is a proposed explanation for a phenomenon. Normally, it is a general statement about the relationship between the manipulated variable and a responding variable in order to explain the question ask. Identifying variables A variable is a factor that affects other factors in an experiment. In a scientific investigation, we need to identify all related variables. There are three types of variable, namely Manipulated variable — the factor that is purposely changed in an experiment Responding variable — the factor that changes with the manipulated variable Fixed variables — the factors that are kept constant throughout an experiment. This is to ensure that other factors do not affect the results of the experiment. Controlling variables Deciding how to repeat the experiment several times by using different values of the manipulated variable. This step is to test the consistency in the experiment and also to relate the manipulated variable to the responding variable. Designing the experiment Deciding how to carry out the experiment, including determine the material, apparatus, experiment sets out and the procedure to take. Always keep in mind that the main purpose of the experiment is to o test the hypothesis. Carrying Out the Experiment After the planning of the experiment is done, you will need to carry out the experiment according to the procedure. Collecting data Make observations in the experiment by watching and measuring. Measure the quantities accurately using suitable measuring instruments and units. All data are collected and recorded in a proposed table. Analysing and interpreting data After collecting the data, you will need to analyse the results of the experiment. Data analysis is the step to studies information by breaking it down into smaller parts. The results can be presented in various forms, such as a table, graph or chart. Making a conclusion Draw conclusions based on the observations and results. State whether the hypothesis is true or false. Writing the report A report is written after an experiment is performed. The format of the report is arranged based on the scientific investigation method which is performed systematically; starting from the problems identified to the last stage. State any precautions taken to overcome problems in the experiment. A simple diagram of the experiment set-up would sometime be useful.

4. Scientific Investigation

Scientific Method

1. The scientific method or scientific process is fundamental to scientific investigation and to the acquisition of new knowledge based upon physical evidence by the scientific community.
2. Scientists use observations and reasoning to propose tentative explanations for natural phenomena, termed hypotheses.
3. The scientific method is a systematic approach to research. It consists of the following steps:

Steps in the Scientific Method

1. Making observation
1. An investigation usually begins with an observation on a phenomenon.
2. Observation is to observe and gather the information about the phenomenon.




2. Making an Inference

After gathering sufficient information, we make an inference, or early conclusion, based on what has been observed. The inference may or may not be true and need to be proven true or false with further investigation.



3. Identifying problem

Asking question based on the inference made to identify the problem related to the observation.



4. Making a hypothesis
1. A hypothesis is a proposed explanation for a phenomenon.
2. Normally, it is a general statement about the relationship between the manipulated variable and a responding variable in order to explain the question ask.




5. Identifying variables
1. A variable is a factor that affects other factors in an experiment.
2. In a scientific investigation, we need to identify all related variables.
3. There are three types of variable, namely
1. Manipulated variable — the factor that is purposely changed in an experiment
2. Responding variable — the factor that changes with the manipulated variable
3. Fixed variables — the factors that are kept constant throughout an experiment. This is to ensure that other factors do not affect the results of the experiment.




6. Controlling variables
1. Deciding how to repeat the experiment several times by using different values of the manipulated variable.
2. This step is to test the consistency in the experiment and also to relate the manipulated variable to the responding variable.




7. Designing the experiment
1. Deciding how to carry out the experiment, including determine the material, apparatus, experiment sets out and the procedure to take.
2. Always keep in mind that the main purpose of the experiment is to o test the hypothesis.




8. Carrying Out the Experiment

After the planning of the experiment is done, you will need to carry out the experiment according to the procedure.



9. Collecting data
1. Make observations in the experiment by watching and measuring.
2. Measure the quantities accurately using suitable measuring instruments and units.
3. All data are collected and recorded in a proposed table.




10. Analysing and interpreting data
1. After collecting the data, you will need to analyse the results of the experiment.
2. Data analysis is the step to studies information by breaking it down into smaller parts.
3. The results can be presented in various forms, such as a table, graph or chart.




11. Making a conclusion
1. Draw conclusions based on the observations and results.
2. State whether the hypothesis is true or false.




12. Writing the report
1. A report is written after an experiment is performed.
2. The format of the report is arranged based on the scientific investigation method which is performed systematically; starting from the problems identified to the last stage.
3. State any precautions taken to overcome problems in the experiment.
4. A simple diagram of the experiment set-up would sometime be useful.

CHAPTHER TWO

THE STRUCTURE OF THE ATOM

Matter

Matter is anything that occupies space and has mass.

[edit]Atom, Molecule and Ion

The particles can be atoms, molecules or ions.

Atom	Molecule	Ion
The atom is the smallest, indivisible particle of an element. Atoms of the same element are exactly alike and are different from the atoms of all other elements.	Molecules are the smallest particles of an element or compound that are made up of two or more atoms. Ions are particles that are charged due to loss or gain of electrons.	Ions which are positively charged are called cations. Ions which are negatively charged are called anions.
Example	Example	Example

Characteristic of Matter in Solid, Liquid and Gaseous State

Characteristic	Solid	Liquid	Gas
Image
Arrangement of Particles	Particles are arranged in an orderly manner and close to one another.	Particles are not arranged in order.	The space between particles is moderately large. The particles are very far apart and randomly arrange.
Movement of Particles	Particles vibrate at fixed positions.	Particles move randomly and slowly and sometimes will collide against each other.	The particles move randomly in all directions at great speed.
Force of Attraction between particles	very strong	Strong but weaker than in the solid state.	very weak
Ability to be compressed	Very difficult to be compressed because the particles are packed closely.	Not easily compressed because the particles are packed quite closely.	Easily compressed because the particles are very far apart.
Volume	Fixed	Fixed	Varied
Heat Energy content	Lowest Energy Content	Moderate energy content.	Highest energy content
Shape	Fixed	Follows the container	Fills the whole container

The changes in the state of matter

[edit]Melting

Definition Melting is the process where a solid changes to its liquid state at a certain temperature (called the melting point) and pressure when it is heated.

Notes

• When a solid is heated, the particles obtain energy and vibrate at a faster rate.
• As the temperature increases, the vibration of the particles increases until they reach the melting point where the particles obtain enough energy to overcome the forces that hold them in their fixed positions.The solid then changes into a liquid.
• During melting, the temperature remains constant. This is because the heat energy is taken in by the particles to overcome forces between them instead of being used to raise the temperature.
• The freezing and melting points of a pure substance are the same.

[edit]Freezing

Definition Freezing is the process where a liquid changes to its solid state at a certain temperature (called freezing point) and pressure when it is cooled.

Notes

• When a liquid is cooled, the temperature drops as heat energy is released to the surroundings.
• As heat energy is released, the kinetic energy of the particles in the liquid decreases, causing a slower movement of particles.
• The particles lose their energy and are pulled closer by the strong forces between the particles.
• As the temperature keep on dropping until it reach the freezing point, the liquid start changing into solid.
• The temperature stays constant while the liquid freezes because heat energy is released when the particles slow down to take up fixed and orderly positions in the solid.

[edit]Vaporization

Definition Vaporization, also called evaporation is the process whereby atoms or molecules in a liquid state gain sufficient energy to enter the gaseous state.

Boiling is the rapid vaporization of a liquid at a certain temperature (the boiling point) and pressure when heat is applied to it.

Notes

[edit]Evaporation

• Evaporation occurs below the boiling point of the liquid.
• The particles escape from the surface of the liquid to form gas.
• Evaporation differs from boiling in that it only takes place at the surface of the liquid and it is very slow.
• On the other hand, boiling takes place throughout the liquid and is very fast.
• Factors influencing rate of evaporation

1. Humidity of the air.
2. Temperature of the substance.
3. Flow rate of air.
4. Inter-molecular forces. The stronger the forces keeping the molecules together in the liquid or solid state the more energy that must be input in order to evaporate them.

• If conditions allow the formation of vapour bubbles within a liquid, the vaporization process is called boiling.

[edit]Boiling

• When a liquid is heated, the particles gain energy and move faster.
• As heat energy is keep on supplying to the liquid, the particles will eventually obtain enough energy to completely break the forces in between molecule.
• The liquid then changes into a gas and particles are now able to move freely and are far apart.
• The temperature at which this happens is called the boiling point.

The temperature remains constant during boiling because heat energy that is absorbed by the particles is used to break the forces holding them together.

[edit]condensation

Definition Condensation is the process by which a gas or vapor changes to liquid state at certain temperature and pressure when it is cooled.

Notes

• When a gas is cooled, the particles lose kinetic energy.
• As a result they move slower and this will cause the forces between them grow stronger.
• At this point, the gas changes into liquid.
• During condensation, heat is given out to the surroundings.
• Condensation can occur at or below the boiling point of the substance

[edit]sublimation

Definition Sublimation is a process of conversion of a substance from the solid to the vapour state without its becoming liquid.

Notes

• Some solids change directly into gas without becoming a liquid.
• This process is called sublimation.
• When heated, the particles of the solid gain enough energy to break the forces between them and move freely as a gas.
• When cooled, the gas changes straight back to solid.
• Examples of substances which sublime are solid carbon dioxide (dry ice), ammonium chloride and iodine.

Melting Point, Freezing Point and Boiling Point

[edit]Melting Point

Melting Point Melting Point is the temperature at which the solid and liquid forms of a pure substance can exist in equilibrium.

[edit]Freezing Point

Freezing Point Freezing Point is the temperature at which a liquid becomes a solid.

[edit]Boiling Point

Boiling Point is the temperature at which the pressure exerted by the surroundings upon a liquid is equalled by the pressure exerted by the vapour of the liquid. Under this condition, addition of heat results in the transformation of the liquid into its vapour without raising the temperature.

[edit]Physical State and Temperature

The physical state of a substance at a certain temperature and pressure depends on the values of its melting and boiling points.

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

Change in heat and kinetic energy of particles

• The change in temperature will influences the kinetic energy or the speed of the motion of the particles.
• When a substance is heated, the kinetic energy of the particles in the substance increases. This causes the particles to move or vibrate faster.
• Likewise, when a substance is cooled, the kinetic energy of the particles in the substance decreases. This causes the particles to move or vibrate slower.
• The kinetic energy of the particles in a substance is directly proportional to the temperature of the substance.

[edit]The Graph of the Heating Process

Heating Curve of Naphthalene

The graph above shows the heating curve of naphthalene.

A	Naphthalene is in solid state at any temperature below its melting point. The particles are very closely packed together in an orderly manner. The forces between the particles are very strong. The particles can only vibrate at a fixed position.
A-B	As the naphthalene is heated, heat energy is converted to kinetic energy. Kinetic energy increases and the molecules vibrate faster about their fixed positions and the temperature increases.
B	Naphthalene is in solid state at any temperature below its melting point. The particles are very closely packed together in an orderly manner. The forces between the particles are very strong. The particles can only vibrate at a fixed position.
B-C	Naphthalene exists in both solid and liquid states. The temperature remains constant because the heat that supplied to naphthalene is used to overcome the forces of attraction that hold the particles together. The constant temperature is called the melting point. The heat energy that absorbed to overcome the intermolecular forces is named as the latent heat of fusion.
C	All the naphthalene has completely melted. Solid naphthalene has turned into liquid.
C-D	Naphthalene is in liquid state. As the liquid naphthalene is heated, the molecules gain more heat energy and the temperature continues to increase. The particles move faster and faster because their kinetic energy is increasing.
D	Naphthalene still exists in liquid state. Naphthalene molecules have received enough energy to overcome the forces of attraction between the particles in the liquid. Some of the naphthalene molecules start to move freely and liquid naphthalene begin to change into gas.
D-E	Naphthalene exists in both liquid and gaseous states. The temperature remains unchanged. The is because the heat energy absorbed is used to overcome the intermolecular forces between the particles of the liquid rather than increase the temperature of the liquid. This constant temperature is the boiling point.
E	All the naphthalene has turn into gas.
E-F	The gas particles continue to absorb more energy and move faster. The temperature increases as heating continues.

[edit]The Graph of the Cooling Process

P	The substance exists in gaseous state. The particles have very high energy and are moving randomly. The intermolecular forces between the particles are very weak and can be ignored.
P-Q	The substance is in gaseous state. The particles lose kinetic energy during cooling, the particles getting closer to each other and the temperature drops.
Q	The substance still exists as a gas. As the molecules are close enough, stronger forces of attraction result in forming of intermolecular bonds. The gas begins to condense and become liquid.
Q-R	The process of condensation going on. Stronger bonds form as gas changes into liquid. The substance exists in both gaseous and liquid states. The temperature remains unchanged. This is because the energy produced during the formation of bonds is equal to the heat energy released to the surroundings during cooling. This constant temperature is the boiling point. The heat energy that releases during this condensation process is called the latent heat of vaporization.
R	The substance exists only in liquid state as all the gas particles have condensed into liquid.
R-S	The substance exists as a liquid. As the temperature falls, the naphthalene molecules lose heat energy. Their movement shows down and they move closer to each other.
S	The substance still in liquid state. The particles have very little energy and begin to move closer towards one another as it starts to freeze into solid.
S-T	The liquid is changing into solid form. Molecules rearrange to form the molecular arrangement of a solid. The substance exists as both liquid and solid. The temperature remains constant until all the liquid changes to solid. This is because the energy released is the same as the energy lost to the surroundings during cooling. This constant temperature is the freezing point. The heat energy that releases during this freezing process is called the latent heat of fusion.
T	All the liquid freezes into solid. The particles are now closely packed in an orderly manner.
T-U	Once all the liquid has become solid, the temperature falls once again until it reaches room temperature. The substance is in the solid state here.
U	The substance reaches room temperature and remain at this temperature as long as the room temperature remain the same.

[edit]Supercooling

Super-cooling is the cooling of a liquid to below its freezing point but keeping it in liquid state. Supercooling is possible because of the lack of solid particles around which crystals can form.

Atomic Structure

• In physics, atomic theory is a theory of the nature of matter. It states that all matter is composed of atoms.
• The word atom originally meant a smallest possible particle of matter, not further divisible.

History

[edit]Democritus

• The existence of atoms was proposed as early as in the 5th century BCE by the Greek philosophers Leucippus and his pupil Democritus, for which they were called atomists.
• Democritus, develop the idea of atoms. He asked this question: If you break a piece of matter in half, and then break it in half again, how many breaks will you have to make before you can break it no further?
• Democritus thought that it ended at some point, a smallest possible bit of matter. He called these basic matter particles, atoms.
• The word "atom" is derived from the Greek word "atomos", which means "indivisible".

[edit]John Dalton

Dalton's Model of Atom

John Dalton

• Five main points of Dalton's Atomic Theory

1. All matter is composed of extremely small particles called atoms.
2. All atoms of a given element are identical, having the same size, mass, and chemical properties. Atoms of a specific element are different from those of any other element.
3. Atoms cannot be created, divided into smaller particles, or destroyed.
4. Different atoms combine in simple whole-number ratios to form compounds.
5. In a chemical reaction, atoms are separated, combined, or rearranged.

Weakness

• Atoms consist of even smaller particles called electrons, protons and neutrons.
• Atoms can be created and destroyed in the nuclear reactions such as nuclear fusion and nuclear fission.
• Atoms of the same element can have different physical properties, for example, isotopes of hydrogen.

[edit]J.J. Thomson

JJ Thomson

• In physics, the Plum pudding model of the atom was made after the discovery of the electron and was proposed by the discoverer of the electron, J. J. Thomson.
• In it, the atom is envisioned as electrons surrounded by a soup of positive charge, like plums surrounded by pudding.
• The electrons were positioned uniformly throughout the atom.
• Instead of a soup, the model is also said to have had a cloud of positive charge.
• This model can be compared to a British treat called plum pudding, hence the name. It is also known as the chocolate chip cookie model.

[edit]Ernest Rutherford

[edit]Gold foil experiment

The gold foil experiment:Most of the alpha particles penetrated through the gold foil without deflection. The others were deflected at different angles. Small amount of the alpha particles were reflected back.

The Gold foil experiment, or Geiger-Marsden experiment was an experiment done by Hans Geiger and Ernest Marsden in 1909, under the direction of Ernest Rutherford at the Physical Laboratories of the University of Manchester which led to the downfall of the plum pudding model of the atom.

Expecting result base on plum pudding model

Actual result

• They measured the deflection of alpha particles directed normally onto a sheet of very thin gold foil.
• Under the prevailing plum pudding model, the alpha particles should all have been deflected by at most of a few degrees.
• However they observed that a very small percentage of particles were deflected through angles much larger than 90 degrees.
• From this Rutherford concluded that the atom contained a very small positive charge which could repel the alpha particles if they came close enough.

[edit]Rutherford Atom

Ernest Rutherford

• Early in 1911 Rutherford published a revised model of the atom, known as the Rutherford atom.
• He concluded that

1. the atom is mostly empty space,
2. most of the atom's mass concentrated in a tiny center, the nucleus and electrons being held in orbit around it by electrostatic attraction.
3. The nucleus was around 10-15 meters in diameter, in the centre of a 10-10 metre diameter atom.
4. Those alpha particles that had come into close proximity with the nucleus had been strongly deflected whereas the majority had passed at a relatively great distance to it.

[edit]Niels Bohr

Niels Bohr

• Niels Bohr improved on Rutherford's atomic model.
• Bohr model depicts the atom as a small, positively charged nucleus surrounded by electrons in orbit - similar in structure to the solar system, but with electrostatic forces providing attraction, rather than gravity.
• According to Bohr’s Model

1. Electrons in an atom of an element are not randomly distributed around the atomic nucleus.
2. Electrons move around the nucleus in fixed orbits.
3. Each orbit forms a circle and has a fixed distance from the nucleus.

[edit]James Chadwick

Chadwick

• Chadwick discovered the presence of neutrons in the nucleus.
• He concluded that the nucleus contains another tiny particle known as a neutron that has no charge.
• The neutron mass is almost similar to the proton mass.
• All nuclei contain protons and neutrons, except for the hydrogen which contains protons. only

[edit]Modern Atomic Model

• The atomic model in the present day is based on the contributions of the above scientists.
• According to the modern atomic model,

1. The central nucleus consists of protons and neutrons. It containing almost all the mass of the atom.
2. the nucleus of an atom is very small compared to the size of the atom
3. the electrons are orbiting outside the nucleus in the electron shells
4. the electrons are moving in electron shells at a very high speed and we cannot determine the position of the electrons at a particular time

[edit]The subatomic particles of an atom

• Atoms are made up of tiny particles called subatomic particles.
• An atom contains three types of subatomic particles:

1. proton,
2. neutron and
3. electron,

• The proton and neutron form the nucleus at the centre of an atom.
• The electron moves around the nucleus at a very high speed.
• The nucleus is positively charged because of the presence of protons, which are positively charged. The neutrons are neutral.
• The symbols, charge and relative masses of proton, neutron and electron are as below.

Particle	Symbol	Relative charge	Relative mass
Proton	p	+1	1
Neutron	n	0	1
Electron	e	-1	1/1840

[edit]The charge of particles

• A neutral atom contains the same number of electrons as the protons.
• The positive and negative charges of the protons and electrons respectively neutralise each other, for example, +4 + (-4) = 0
• If the number of protons is greater than the number of electron, the particle is positively charge.
• If the number of protons is greater than the number of electron, the particle is positively charge.

Example

Number of proton	Number of electron	Charge
3	3	0
5	2	+3
9	10	-1
11	10	+3
16	18	-2
17	18	-1
20	18	+3

[edit]Proton number and nucleon number

[edit]Proton Number

• The proton number (Z) represent the number of protons found in the nucleus of an atom.

Proton number = the number of protons

• The proton number is also known as the atomic number.
• In an atom of neutral charge, the number of electrons also equals the atomic number.
• Hence, the proton number of an atom can also represent the number of electrons.

[edit]Nucleon Number

• The nucleon number (A), also called atomic mass number or mass number, is the number of protons plus the number of neutrons in an atomic nucleus.
  

Nucleon number = Number of protons + Number of :neutrons

• The nucleon number of an atom is about the same as the mass of the atom because the mass of an electron is very small and can be ignored.

Example

Atom	Proton Number	Nucleon Number	Amount of Proton	Amount of electron	Amount of Neutron
Helium	2	4	2	2	2
Oxygen	8	16	8	8	8
Sodium	11	23	11	11	12
Chlorine	17	35	17	17	18

The structure of an atom can be written in symbol form, as shown in the figure below.

Symbol: X Proton Number: B Nucleon Number: A	Symbol: N Proton Number: 7 Nucleon Number: 14	Symbol: X Proton Number: B Nucleon Number: A

Isotope

• Isotopes are atoms of certain elements which have the same number of protons but different number of neutrons in the nucleus of the atoms.
• It can also can be defined as atoms of certain elements with the same proton numbers but with different nucleon numbers.

• Three important points to define isotopes.

1. Isotopes are different atoms of the same element.
2. Isotopes have the same number of protons or same proton numbers.
3. Isotopes have different numbers of neutrons or nucleon numbers.

Properties of Isotope

Number of proton	equal
Number of neutron	difference
Chemical properties	same
Physical properties	difference

Example

Element	Name	Symbol	Proton Number	Nucleon Number	Number of proton	Number of neutron
Hydrogen	Hydrogen		1	1	1	0
	Deuterium		1	12	1	1
	Tritium		1	23	1	2
Oxygen	Oxygen-16		8	16	8	8
	Oxygen-17		8	17	8	9
	Oxygen-18		8	18	8	10
Carbon	Carbon-12		6	12	6	6
	Carbon-13		6	13	6	7
	Carbon-14		6	14	6	8
Chlorine	Chlorine-35		17	35	17	18
	Chlorine-37		17	37	17	20
Sodium	Sodium-23		11	23	11	12
	Sodium-24		11	24	11	13

[edit]Uses of isotopes in our daily lives

• There are two types of isotopes, namely

1. the stable isotopes (non-radioactive)
2. the non-stable isotopes (radioactive).

• Unstable isotopes go through radioactive decay and emit radiation and they are known as radioisotopes.
• Radioisotopes have many applications in daily life.
• Several uses of radioisotopes in daily life are shown in Table below.

[edit]Medical

• Gamma rays of cobalt-60 are used to kill cancer cells without surgery in patients. This treatment is known as radiotherapy.
• Patients with skin cancer can be treated using beta rays from the isotopes phosphorus-32 and strontium-90
• Medical instruments such as surgical equipment, syringes and bandages can sterilize by using gamma rays.
• Radioisotopes are also used as tracers.

A small amount of sodium-24 is injected into the patient's body.

A radioactive detector is then used to detect accumulation of sodium-24 and therefore detect tumours and blood clots before they become dangerous.

• This tracing method is also used to investigate the thyroid glands by measuring the uptake of iodine-131.
• Plutonium-238 in a nuclear battery is used to produce small electric shocks in the heart pacemaker.

People with irregular heartbeats need to have a heart pacemaker implanted inside their chest.

The nuclear battery of the pacemaker provides a tiny electrical shock to ensure a steady heartbeat.

[edit]Agricultural

• Radio isotopes are used to cause mutation in insects so as to make them sterile or to cause death. These serve as pest control in agriculture.
• The metabolism of phosphorus by plants can be studied using phosphate fertilisers that contain phosphorus-32.

A small amount of phosphorus-32 is used in fertilisers.

The radiation produced by phosphorus-32decaying is detected by a Geiger-Miller counter.

This method can trace the passage of phosphate ions in plants..

• Carbon-14 is used to study the passage of carbon during photosynthesis in plants.

[edit]Industrial

• Isotope sodium-24 is used to detect leakage of underground pipes.
• Beta rays are used to control the thickness of plastic, paper and metal sheets in factory.
• Gamma rays are used to detect whether cans or bottles are filled up to the required amount.
• Sodium-24 is used to measure the wear out rate of engine in a vehicle.

[edit]Food Preservation

• The gamma rays from cobalt-60 are used to kill bacteria in food to make fresh vegetables and fruits last longer without any change in quality, flavour and texture of food.
• Gamma rays are used to inhibit budding in potatoes.

[edit]Archeology

• Radioisotope carbon-14 is used to study and estimate the age of ancient artifacts. This method is named as the radiocarbon dating.

[edit]Production of Energy

• Plutonium is used in nuclear reactors to produce electrical energy.

[edit]Danger of Radioactive

• Radioactive isotopes are very dangerous if it is misused.
• Short-term exposure to radioactive rays may

1. kill or destroy the cells in our body and cause organ damage
2. cause rashes and burns on the exposed skin

• Long-term exposure to radioactive rays may

1. ause mutation in our genes and abnormalities in newborn babies
2. disturb the growth and division of cells and consequently cause cancer

Electronic Structure

Electron Configuration in Atom

• We have learnt that electrons occupy orbits with definite energy level of an atom, as suggested by Neils Bohr.
• These orbits with definite energy level are known as the shell.
• Every single shell is capable of holding up to certain amount of electrons.
• The first shell can hold up to two electrons. This is called a duplet.
• The second shell can hold up to eight electrons. This is called an octet.
• The third shell can hold up to eighteen electrons.
• However, with the third shell, when eight electrons are present, extra stability is gained. The additional electrons go into the fourth shell before the third shell is completely filled.
• The way in which the electrons are distributed in the shells of an atom is called the electron arrangement or electron configuration of the atom.
• The examples below show the electron arrangement of some elements:

Example

Atom	Notes	Electrons Arrangement
	Lithium has 3 protons and 3 neutrons and three electrons as well. All the three electrons are arrange as follows: Two electrons are filled in the first shell. One electron is filled in the second shell. The electron arrangement of carbon is 2.1	2.1
	Chlorine has 17 protons and 18 neutrons and 17 electrons. All the three electrons are arrange as follows: Two electrons are filled in the first shell. Eight electrons are filled in the second shell. Seven electrons are filled in the third shell. The electron arrangement of chlorine is 2.8.7.	2.8.7
	Calcium has 20 protons and 20 neutrons and 20 electrons. All the three electrons are arrange as follows: Two electrons are filled in the first shell. Eight electrons are filled in the second shell. Eight electrons are filled in the third shell. Two electrons are filled in the forth shell. The electron arrangement of carbon is 2.8.8.2.	2.8.8.2

Element	Proton Number	Number of Electron	Number of electron in				Electron Arrangement
			1st shell	2nd shell	3rd shell	4th shell
Hydrogen	1	1	1	0	0	0	1
Helium	2	2	2	0	0	0	2
Lithium	3	3	2	1	0	0	2.1
Beryllium	4	4	2	2	0	0	2.2
Boron	5	5	2	3	0	0	2.3
Carbon	6	6	2	4	0	0	2.4
Nitrogen	7	7	2	5	0	0	2.5
Oxygen	8	8	2	6	0	0	2.6
Fluorine	9	9	2	7	0	0	2.7
Neon	10	10	2	8	0	0	2.8
Sodium	11	11	2	8	1	0	2.8.1
Magnesium	12	12	2	8	2	0	2.8.2
Aluminium	13	13	2	8	3	0	2.8.3
Silicon	14	14	2	8	4	0	2.8.4
Phosphorus	15	15	2	8	5	0	2.8.5
Sulphur	16	16	2	8	6	0	2.8.6
Chlorine	17	17	2	8	7	0	2.8.7
Argon	18	18	2	8	8	0	2.8.8
Potassium	19	19	2	8	8	1	2.8.8.1
Calcium	20	20	2	8	8	2	2.8.8.2

P/S : NOTES FROM www.one-schoolnet.com