Science Chapter 4 Form 4 3x1t1a

Chapter 4 MATTER AND SUBSTANCES. 4.1 Changes in The States of Matter. Kinetic theory of matter • the properties of matter can be explained by using the kinetic theory of matter. • the kinetic theory matter tries to explain the three states of matter : solid, liquid, gas : based on the following assumptions : (a) matter is made up of a very fine and discrete particles. (b) the particles of matter constantly move or vibrate. (c) the particles constantly collide against one another and the walls of the container. (d) forces of attraction exist among the particles in matter, the forces of attraction become stronger when the particles are packed closely together. (e) the higher the temperature , the higher the kinetic energy of the particles. • among the examples which the kinetic theory of matter is the diffusion process. • diffusion is the movement particles in matter from an area of high concentration to an area of low concentration until both area have the same concentration. • example – if a little bit of perfume is sprayed in area A, we can smell it in are B three metres away because the process of diffusion has occurred – this is because the particles of the perfume have moved into the empty spaces between air particles. • the particles of liquid and gas move randomly and collide against one another. (Brownian movement) • temperature influences the kinetic energy content of matter. • the higher the temperature, the higher the kinetic energy content of the particles.

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Properties of matter Properties of matter Arrangement of particles

Solid Arranged closely, compactly and orderly in fixed positions. There is very little empty space between one particle and another.

Liquid Liquid particles neatly nor closely arranged. There are empty spaces among the particles. Most of the particles keep with one another.

Movement of particles

Particles do not move freely and only vibrate at their fixed positions. Very strong

Particles move Particles move slowly in a fast in a random random manner. manner and in all directions. Not very strong

Very weak

Very low Fixed

Moderate Following the shape of the container Fixed Very difficult to compress

Very high Fills up the whole container

Forces of attraction between particles Energy content Shape Volume Compression

Fixed Not compressible

Gas Gas particles are not neatly arranged and are further apart from one another.

Not fixed Easily compressed

Changes in the state of matter. • heat is the energy that determine the movement particles in matter. • if the temperature of matter increases, particles will get higher kinetic energy to move faster. • consequently, changes in the state of matter occur through the process of heating or cooling, i.e. when heat energy is absorbed or releases from the matter. • when heat is supplied, the state of matter will change from solid to liquid, and finally to gas.

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• • • •

take changes in the state of matter which take place when heat is supplied are – melting, boiling, sublimation when heat is released the state of matter will change from gas to liquid and finally to solid. the changes in the state of matter which take place when heat is released are – freezing, condensation, sublimation. sublimation occurs when the state of matter changes from solid to gas or vice versa without going through the liquid stage.

Melting

 when a solid is heated, heat is absorbed by its particles.  particles possesses more kinetic energy and vibrate faster.  at melting point, particles in the solid have enough energy to overcome the forces of attraction between particles and to move freely.  the solid melts and changes to become liquid. Boiling

 when liquid is heated, heat energy is absorbed by its particles.  the liquid particles have more kinetic energy and move faster.  at boiling point, the energy possessed enable the particles to overcome the forces of attraction between the particles and they released as gas. Sublimation

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 when a solid is heated, its particles gain more energy and move faster.  the particles in solid separate from solid lattice and release as gas into the air. Freezing

 when liquid is cooled, its particles lose energy and are held together by strong forces of attraction between particles.  this cause liquid particles not able to move freely and they only vibrate in their positions  the liquid freezes to become solid. Condensation

 when gas is cooled, its particles lose energy and are held together by forces of attraction between particles.  this causes the particles to moves slowly.  the distance between gas particles becomes closer.  the gas changes to liquid. Sublimation

 when gas is cooled, its particles lose energy and are held together by strong forces of attraction between particles.  this cause the particles to move very slowly.  the distance between gas particles becomes closer.

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 the gas changes to solid.

Changes in the state of matter involving heat change↓ Solid sublimation (heat released)

sublimation (heat absorbed)

melting (heat absorbed)

freezing (heat released)

condensation (heat released) Gas

Liquid boiling (heat absorbed)

4.2 Structure of Atoms. Atoms • all matter consists of tiny units called atoms. • atom is a basic unit of all matter. • atoms cannot be seen with an ordinary microscope because they are so tiny. • an atom consists of a nucleus in the centre surrounded by electrons. • electrons move around the nucleus following a certain orbit. orbit nucleus

electron structure of an atom Subatomic particles • an atom is made up of particles that are even smaller called subatomic particles.

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•

• • •

there are three types of subatomic particles :  protons  neutrons  electrons protons and neutrons from the nucleus in the centre of an atom. electrons move around the nucleus at high speed. the mass of an atom is concentrated in its nucleus. electron (-)

nucleus

proton (+)

neutron

subatomic particles in an atom Comparison between subatomic particles Subatomic particle

Symbol

Proton Neutron Electron

p n e

Position in atom

Nucleus Nucleus Moves around nucleus

Relative charge

Relative mass

Mass in gram

+1 0 -1

1 1 1/1840

1.672 x 10-24 1.675 x 10-24 9.107 x 10-28

comparison between subatomic particles • •

atoms of any element are neutral because the number of electrons in an atom are the same. in a neutral atom, the total positive charges in the nucleus are the same as the total negative charges from the electrons which orbit around the nucleus. Atom

Hydrogen Helium Carbon Sodium • •

Number of protons

Number of electrons

Number of neutrons

1 1 2 2 6 6 11 11 number of subatomic particles in different atoms

0 2 6 12

ions are atoms or particles which have charge. ions are produced when the number of protons (positive charge) and the number of electrons (negative charge) are not balanced.

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• •

positive ions are particles that are positively charged. positive ions are produced when the number of protons is more than the number of electrons. • negative ions are particles that are negatively charged • negative ions are produced when the number of electrons is more than the number of protons. 4.3 Proton Number and Nucleon Number in Atoms of Elements. Proton number and nucleon number • proton number is the number of protons in an atom of an element. • elements can be differentiated by referring to their proton number. • in a neutral atom, the proton number also refers to the number of electrons in that atom. proton number = number of protons = number of electrons in a neutral atom •

nucleon number is the total number of protons and neutrons in an atom of an element. nucleon number = number of protons + number of neutrons = proton number + number of neutrons

•

the number of neutrons in an atom can be calculated if its proton number and nucleon number are known. number of neutrons = nucleon number – proton number = nucleon number – number of protons

•

in a neutral atom : a) nucleon number = number of electrons + number of neutrons b) number of neutron = nucleon number + number of electrons

•

table below shows that atoms of different element possesses different numbers of protons and electrons.

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Element

Number of protons

Number of electrons

Number of neutrons

Proton number

Nucleon Number

Hydrogen 1 1 0 1 1 Helium 2 2 2 2 4 Lithium 3 3 4 3 7 Beryllium 4 4 5 4 9 Boron 5 5 6 5 11 Carbon 6 6 6 6 12 Nitrogen 7 7 7 7 14 Oxygen 8 8 8 8 16 Fluorine 9 9 10 9 19 Neon 10 10 10 10 20 • atoms of certain elements can represented by the following symbol : nucleon number

14

proton number

N 7

symbol of element

number of neutron = 14 – 7 = 7 Isotopes • are atoms of the same element that possesses the same number of protons but different number of neutrons. • can also be defined as atoms of the same element with the same proton number but different nucleon number. • isotopes of the same element possess the same chemical properties. • the physical properties of isotopes are different. Element Hydrogen Oxygen Carbon

Isotope Hydrogen-1 Hydrogen-2 Hydrogen-3 Oxygen-16 Oxygen-17 Oxygen-18 Carbon-12 Carbon-13 Carbon-14

Nucleon number

Proton number

1 2 3 16 17 18 12 13 14

1 1 1 8 8 8 6 6 6

examples of isotopes

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Number of protons 1 1 1 8 8 8 6 6 6

Number of neutrons 0 1 2 8 9 10 6 7 8

Number of electrons 1 1 1 8 8 8 6 6 6

4.4 Classification of Elements in Periodic Table. GROUP

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

1

P E R I O D

2 3 4 5 6 7

The classification of elements. • in the periodic table, the element are arranged in order of increasing proton number. • the proton number increases from left to right and from top to bottom in the periodic table. • each vertical column is called a group. • elements in the same group have similar chemical properties. • each horizontal row is called a period.

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• • • • • •

the chemical and physical properties of the elements are gradually changed when crossing periods. in the periodic table, there are 18 groups numbered from 1 to 18 and 7 periods numbered from 1 to 7. group 1 (alkali metals) and group 2 (earth alkali metals) consist of very reactive metals. the elements in group 17 are non-metals halogens. group 18 consists of noble (inert) gases which are chemically stable and unreactive. the elements located between groups 2 and 13 are transition elements.

Importance of the periodic table. • the importance of element classification in the periodic table is as follows : (a) helps us to study elements in an orderly and systematic approach. (b) helps us to know the properties elements easily because the elements with similar properties are located in the same group. (c) helps us to predict the properties and uses of an element by referring to the element’s location in the periodic table. 4.5 Properties of substances based on their particle content. • there are three types of particles. • atoms are the tiniest particles in an element. • molecules are groups of atoms ed together. • a molecule consists of two or more atoms • ions are particles which carry positive or negative charges. Atomic substances. • are substances that consist of only atoms. • all metals are atomic substances. (ex : iron, lead, sodium) • the atoms are in atomic substances are packed closely, compactly and arranged orderly in fixed positions. • the atoms in atomic substances are held together by a strong chemical bond. atom

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arrangement of atoms in metal Molecular substances. • molecules are the simplest particles found in molecular substances. • nitrogen, sulphur dioxide and iodine are examples of molecular substances. • molecular substances are made up of molecules which have two or more atoms of the same type. • for example, two oxygen atoms combine to form one oxygen molecule. • molecular substances can also be made up of two or more atoms of different types. • for example, one nitrogen atom combines with three hydrogen atoms to form one ammonia molecule.

H

N H

H

ammonia molecule consists of one nitrogen atom and three hydrogen atoms. • •

molecules are made up of non-metal atoms held together by a strong covalent bond. however, the forces of attraction between molecules in a molecular substance are relatively weak . the weak forces between molecules in molecular substance are called Van der Waals forces.

Ionic substances. • are formed when atoms of metals combine with atoms of non-metal through chemical bonding to form compounds. • sodium chloride, lead (II) bromide and magnesium oxide are examples of ionic compounds. • positive ion and negative ion attract one another. • forces of attraction between ions of opposite charge are called electrostatic attraction force. sodium ion (+) chloride ion (-)

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Physical properties of atomic, molecular and ionic substances. Physical property Physical state at room temperature

Atomic Substance Solid except mercury

Ionic Substances Solid

Very strong

Molecular Substance Solid : Iodine Liquid : Water Gas : Oxygen Solid : Packed Liquid : Not packed Gas : Far apart Weak

Arrangement of particles

Packed very closely

Forces of attraction between particles Melting point and boiling point Electrical conductivity

High

Low

High

All metals and carbon (graphite)

Does not conduct electricity

Does not dissolve in anything

Most of them dissolve in organic solvent

Conducts electricity in molten state Most of them dissolve in water

Solubility

Packed very closely Very strong

4.6 Properties and Uses of Metals and Non-Metals. Metals and Non-Metals. • elements can be classified into metals and non-metals. • ex : iron, aluminium, zinc, copper, lead, tin ,and gold. • carbon, iodine, bromine, sulphur, phosphorus, and chlorine are examples of non-metals. • all metals exist in a solid state at room temperature except mercury.(liquid) • non-metals exist in a solid, liquid, or, gaseous state at room temperature. Physical properties of Metals and Non-Metals. Metals Have shiny surfaces Ductile Easily rolled or hammered into foils or thin sheets High Good conductor of electricity Good conductor of heat High High Solid (except mercury in liquid state)

Differences Luminosity Ductility Malleability Tensile strength Electrical conductivity Heat conductivity Melting point and boiling point Density State of matter at room temperature

Uses of Metals and Non-Metals in daily life. Page 12

Non-metals Have dull surfaces Not ductile Cannot be forged Low Do not conduct electricity except carbon Poor conductor of heat Low Low Solid, liquid, or gas

Metal Iron

Physical Property High tensile strength

Aluminium

Light, good conductor of electricity and heat Ductile and malleable, good conductor of electricity and heat Do not rust Does not rust and is shiny Ductile, malleable

Copper Tin Gold Lead

Non-metal Carbon (graphite)

Physical Property Soft and smooth, good conductor of electricity

Carbon (diamond) Neon gas and krypton Chlorine

Hard Poor conductor of heat Acidic

Use Railway tracks and framework for bridges Kitchen utensils and electric cables Electrical wires Electroplating of food cans Jewellery Cable casing

Use Lead of pencils, used as the electrodes in electrolysis and in dry cell Drill bits for cutting stone Lights used for billboards Used to kill germs in drinking water

4.7 Methods of Substance Purification. Characteristics of pure substances. • pure substances do not contain any impurities. • pure substances always have specific melting (freezing) point and boiling point. • for example : pure water boils at 100oC and ice melts or freezes at 0oC at normal atmospheric pressure. pure iron melts at 1540 oC and boils at 2800oC at normal atmospheric pressure. • any impurities added to a pure substance will increase the boiling point or lower the freezing (or melting) point of that substance. • for example : water that is added with salt will boil at a temperature higher than 100oC and will freeze at a temperature lower than 0 oC. Method of substance purification. • impurities can be separated from pure substances. • the process of separating impurities form a substance is called purification. • there are two methods of purification : Page 13

 

distillation crystallisation

Distillation

• •

is used to obtain pure liquid from a solution which contains impurities. this method is used to separate two liquids (liquid mixture) that : 1. dissolve one another 2. do not react 3. possess different boiling points

•

distillation involves the process of heating liquid until it becomes vapour (gas) this vapour is then condenses to become pure liquid.

•

Liquid • • •

boiling

Gas

condensation

Liquid

distillation can be conduced to separate mixtures of substances such as purifying alcohol from a mixture of alcohol and water and also purifying water from a mixture of water and salt. the substance with a lower boiling point boils and vaporises earlier. then the gas (vapour) will go through condensation to form the pure product of distillation.

Crystallisation • crystallisation is a purification method carried out to obtain pure crystals from a saturated solution of the substances. • example : purification of salt from its saturated solution. • saturated solution is a solution containing maximum quantity of solute. Application of Purification Method. • distillation and crystallisation are often used to obtain pure substances. Page 14

• •

•

these purification methods have produced many substances for our daily needs. examples of the application of distillation : (a) breaking crude petroleum into its fractions such as petrol, kerosene and diesel to produce fuels and to make various kinds of plastic material. (b) production of pure water or distilled water for the preparation of chemical solution, medicine, as well as food and beverages. (c) obtaining pure ethanol from fermentation of sugar solution and yeast. examples of the application of crystallisation : (a) production of salt from seawater. (b) preparation of white sugar crystals from sugarcane juice.

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