CHAPTER 2:the structure of the atom

Mind Map - Structure Of Atom

A.MATTER

particulate nature of matter

• Matter is everything that occupies space and has mass
• The particle theory matter states that the matter is made up of a large number of tiny and discrete particles .

Particle theory of matter :

Matter is made up of a large number of tiny and discrete particles

Type of particles

1. Particles can exist as atoms , molecules or ions
2. Atom is the smallest , indivisible particle of an element .
3. Molecules are particles that made up of two or more atom
4. Ion are particles that carry charge .

                a) positive ion - cation
                b) negative ion - anion

                             

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Characteristics of Matter in Solid, Liquid and Gaseous State

Characteristics	Solid	Liquid	Gas
Arrangement of Particles	Particles are arranged inorderly 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	Follows the container
Heat Energy content	Lowest Energy Content	Moderate energy content.	Highest energy content
Shape	Fixed	Follows the container	Fills the whole container

Matter can divided into element and compound

ELEMENTS

An element is a substance that consists of only one type of atom.

Element can be either atoms or molecules.

EXAMPLES :

(Both the iron and oxygen are element because they consist of only one type of atoms)

COMPOUNDS

1. A compound is a substance composed of molecules made up of atoms of two or more elements.
2. A compound is made up of either molecules or ions

EXAMPLES:

(Both the sodium chloride and carbon dioxide are compound because they consist of more than one type of atoms) 

Change in Heat and Kinetic Energy of Particles

1. The change in temperature will influences the kinetic energy or the speed of the motion of the particles.
2. When a substance is heated, the kinetic energy of the particles in the substance increases. This causes the particles to move or vibrate faster.
3. 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.
4. The kinetic energy of the particles in a substance is directly proportional to the temperature of the substance.

Inter-conversion between States of Matter

 

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.
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.
Vaporizaon (Evaporation)	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 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 Humidity of the air. Temperature of the substance. Flow rate of air. 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. 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.
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
sublimation	Defintion 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.

Explanation on the heating process

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 still in solid state. Naphthalene molecules have received enough energy to overcome the forces of attraction between them. Some of the particles that gain enough energy begin to move freely. Naphthalene starts to melt and changes into a liquid.
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.

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How to read heating curve

Explanation on the cooling process

The graph above shows the cooling curve of a substance.

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.

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Cooling Process

Melting Point, Boiling Point and States of Matter

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B.THE ATOMIC STRUCTURE

History Of Development Of The Model Of Atom

Table below shows the scientists that contribute to the development of the Model of Atom.

John Dalton	Five main points of Dalton's Atomic Theory All matter is composed of extremely small particles called atoms. 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. Atoms cannot be created, divided into smaller particles, or destroyed. Different atoms combine in simple whole-number ratios to form compounds. 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.
J.J. Thomson	The electrons were positioned uniformly throughout the atom.
Ernest Rutherford	The atom is mostly empty space, Most of the atom's mass concentrated in a tiny center, the nucleus and electrons being held in orbit around it by electrostatic attraction. The nucleus was around 10-15 meters in diameter, in the centre of a 10-10 metre diameter atom. 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.
Neils Bohr	Electrons in an atom of an element are not randomly distributed around the atomic nucleus. Electrons move around the nucleus in fixed orbits. Each orbit forms a circle and has a fixed distance from the nucleus.
James 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

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Modern Atomic Model

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

The Subatomic Particles Of An Atom

1. Atoms are made up of tiny particles called subatomic particles.
2. An atom contains three types of subatomic particles: 
1. proton, 
2. neutron and 
3. electron, 
3. The proton and neutron form the nucleus at the centre of an atom. They are also called the nucleon of an atom.
4. The electron moves around the nucleus at a very high speed.
5. The nucleus is positively charged because of the presence of protons, which are positively charged. The neutrons are neutral.
6. 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

Proton Number And Nucleon Number

1. Proton number = the number of protons
2. Nucleon number = Number of protons + Number of neutrons

Proton Number

1. The proton number (Z) represent the number of protons found in the nucleus of an atom. 
2. Proton number = the number of protons
3. The proton number is also known as the atomic number.
4. In an atom of neutral charge, the number of electrons also equals the atomic number.
5. Hence, the proton number of an atom can also represent the number of electrons.

Nucleon Number

1. 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)
2. 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.

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

[Notes: In ion, the amount of protons IS NOT equal to the amount of electrons]

The Charge Of Particles

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

C.Isotopes

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 be defined as atoms of certain elements with the same proton numbers but with different 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	11H	1	1	1	0
	Deuterium	21H	1	12	1	1
	Tritium	31H	1	23	1	2
Oxygen	Oxygen-16	168O	8	16	8	8
	Oxygen-17	178O	8	17	8	9
	Oxygen-18	188O	8	18	8	10
Carbon	Carbon-12	126C	6	12	6	6
	Carbon-13	136C	6	13	6	7
	Carbon-14	146C	6	14	6	8
Chlorine	Chlorine-35	3517Cl	17	35	17	18
	Chlorine-37	3717Cl	17	37	17	20
Sodium	Sodium-23	2311Na	11	23	11	12
	Sodium-24	2411Na	11	24	11	13

D.THE ELECTRONIC STRUCTURE OF AN ATOM

Electron Arrangement In Atom

1. We have learnt that electrons occupy orbits with definite energy level of an atom, as suggested by Neils Bohr.
2. These orbits with definite energy level are known as the shell.
3. Every single shell is capable of holding up to certain amount of electrons.
4. The first shell can hold up to two electrons. This is called a duplet.
5. The second shell can hold up to eight electrons. This is called an octet. 
6. The third shell can hold up to eighteen electrons.
   
7. 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.
8. The way in which the electrons are distributed in the shells of an atom is called the electron arrangement of the atom
9. The examples below show the electron arrangement of some elements:

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

Table below shows the arrangement of electrons of the first 20 elements in the periodic table. We shall learn periodic table in chapter 4.

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

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Electron arrangement in an atom

Valence Electrons

Valence electrons are the electrons in the outermost shell.

1. The electrons in the outermost shell of an atom are called valence electrons.
2. The valence electrons have great significance in determining the chemical properties of an atom.
3. Elements with the same number of valence electron have the same chemical properties.

Example:
Given that a sodium atom has 11 protons 12 neutrons. Find the number of valence electron in a sodium atom.

Answer:

For an atom,

Number of electrons = number of protons = 11

Electron arrangement of sodium = 2.8.1

Therefore, sodium has 1 valence electron.