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CHEMISTRY SS1 FIRST TERM LESSON PLAN SCHEME OF WORK

 

SUBJECT: CHEMISTRY                                                                       CLASS: SS1

SCHEME OF WORK

WEEK         TOPIC

1. Introduction to Chemistry: Meaning of chemistry, Career prospects tied to chemistry, application of chemistry, adverse effects of chemicals and, Scientific methods.

2. Particulate Nature of Matter: Physical and chemical changes, elements and their symbols, Atoms, molecules, atomicity and Dalton’s atomic theory and its Modifications.

3. Particulate Nature of Matter: Electronic configuration (K,L,M,N), Atomic number, mass number, Isotopy and Relative atomic mass based on C-12 isotope.

4. Valency, oxidation number, ions and Radicals: Valency of elements, oxidation number of elements in compounds, ions and radicals.

5. Formulae and Equations: Chemical formulae, Chemical equations, Empirical and Molecular formulae, Relative Molecular Mass, Molar mass and Percentage composition by mass of an element.

6. Laws of chemical combination: law of conservation of matters, law of constant composition, law of multiple proportions and Law of Reciprocal proportion

7. 7. Mid-Term Break and Holiday Assignment

8. Chemical Combination: Types of chemical bonds, IUPAC system of naming inorganic compounds.

9. Chemical industries: Types of chemical industries, importance of chemical industries and excursion to chemical industries.

10. Revision and preparation for examination.

11/12. Examination

REFERENCE. TEXTS:

1. Comprehensive certificate chemistry for senior secondary schools by G N C Ohia.et al

2. Chemistry for Senior Secondary Schools 1 by Magbagbeola O, et al; Melrose Books and Publishers.

3. New school chemistry for senior secondary schools by Osei yaw Ababio

4. Revised edition understanding chemistry for schools and colleges by Godwin O. Ojokuku.

 

 

 

WEEK 1

TOPIC: Introduction to Chemistry

CONTENT:

1. Meaning of chemistry

2. Career prospects tied to chemistry

3. Application (i) Hospital (ii) Military (iii) Teaching (iv) Chemical and petrochemical industries.

4. Adverse effects of chemicals, drug abuse, poisoning,

Corrosion and pollution.

5. Scientific methods.

PERIOD 1: MEANING OF CHEMISTRY

Chemistry is the study of matter: its structure, composition, properties and the changes it undergoes.

Chemistry is one of the three main branches of pure science, the other two being physics and biology. Chemistry which probes into the principles governing the changes that matter undergoes also deals with the composition, properties uses of matter. Some of the chemical changes which matter undergoes include; lighting a match, cooking, burning fire wood, making palm wine, rusting of nails, rotting of leaves.                                           Chemical changes are otherwise known as chemical reactions. The knowledge of chemistry helps us to subject some matter to chemical processes thereby producing some materials for our every day today use. Such materials include: soaps, detergents, hair cream, perfumes, oil, margarine and plastics among others.

There are three main branches of chemistry: inorganic, organic and physical chemistry.

Career prospects tied to chemistry

Career prospects tied to chemistry simply mean the job opportunities that are available for the students with knowledge of chemistry. Such students can be employed with private and public sectors which include: Teaching service, health service, food processing, petroleum and petrochemical industries, manufacturing industry, extractive industry, Agriculture and Forestry.

• Teaching services: Concern those who teach in primary, secondary schools, colleges of education and universities and even the laboratory assistants in schools and universities.

• Health service: Involves pharmacists, biochemists, chemists, nutritionists, dieticians, doctors, nurses, medical assistants, laboratory assistants and dispensers.

• Food processing: Food processing involves food technologists and research chemists.

• Petroleum and petrochemical industries –Involves application of the following people; research chemists, chemical engineers and laboratory assistants.

• Extractive industry- Involves chemists, mining engineers and geologists.

• Manufacturing Industry: This involves research chemists and chemical engineers in the wide variety of manufacturing industries such as iron and steel works and cement factories.

• Agriculture-Involves agricultural scientists, chemists, biochemists and physiologists who engaged in research to improve the quality and yield of crops and livestocks, and to advise farmers.

(viii)  Forestry: Scientists engaged in research to preserve and improve forests and forestry products.

EVALUATION

1. Define the term chemistry.

2. Mention five changes that matter undergoes.

3. Give the uses of chemistry in our day to day life.

4. List at least five career opportunities in chemistry

5. Explain any three of the career opportunities mentioned above.

PERIOD 2: APPLICATION/ USES OF CHEMISTRY

The knowledge of chemistry can be apply in the following areas; namely

1. Hospital: The knowledge of chemistry makes it possible for people to involve in chemical research and technology which lead to production of medicine that we use today.

2. Military: The duty of the military is defense, to defend the territorial integrity of a nation or state. Military cannot effectively do this without ammunition. Chemistry contributes to the discovery and description of the theoretical bases for the behavior of chemical substances such as explosives used by the military. The gun powder used in the earliest guns was made by mixing sulphur, charcoal and potassium trioxonitrates (v), compounded by early chemists. The manufacture of smokeless powder was based upon gun cotton, which is made from cotton fibers soaked in a strong mixture of HNO₃ and H₂SO₄.

3. Teaching- chemistry teachers and lecturers in secondary schools, polytechnics, colleges of education and universities.

4. Chemical and petrochemical industries: Application chemists, research chemists, chemical engineers and laboratory assistants.

5. Space science: chemistry is not out in space exploration. In our efforts to gain more knowledge of the other planets and outer space around us, special rockets called ‘space rocket’ are sent into space. The first rocket was sent into space on October 4, 1957 by Russia. In July, 1969, Apollo II astronauts Neil Armstrong and Edwin Aldrin landed on the moon. These are made possible by science and technology.

6. Agriculture: Agricultural scientists, chemists, biochemists and physiologists engaged in research to improve the quality and yield of crops and livestock, and to advise farmers.

EVALUATION

1. Enumerate and explain five application of chemistry you know.

PERIOD 3– ADVERSE EFFECTS OF CHEMICALS

The adverse effects of existence of chemistry

The existence of chemistry brought about the existence of chemicals. The adverse effects of chemicals include; drug abuse, poisoning, corrosion and pollution.

• Drug Abuse: simply involves wrong usage of drugs. Some of these drugs include heroin, cocaine and morphine which are used as addictive. Unscrupulous people produce and sell them at huge profits. Drug addiction is a major problem in our society, especially among young people. Many countries have imposed strict laws to control pollution and drug abuse. However, the most effective control measure is education. We must use what we learnt to improve our life and to control these abuses.

• Poisoning: This is where chemicals are used to poison the food we eat. This happens when the chemicals used as addictive probably as preservative are added more than required or expired in the food stuff where it was added, then instead of the food stuff bringing health to our body, it turns to poison.

• Corrosion: Corrosion of iron can also be called rusting and requires the presence of water and oxygen. Rusting can also be regarded as the slow deterioration of iron to iron (iii) oxide. This iron (iii) oxide is permeable to both air and water and cannot protect the iron from further corrosion of iron.

 This rusting can be prevented by four methods.

• Application of protective coating.

• Application of sacrificial metal.

• Cathodic protection.

• Pollution: Chemical industries through the action of production pollute our environment as the smoke enters into the air, and dirts of different kinds enter into the water thereby polluting the entire environment. Specifically chemical wastes from factories and oil refineries and radioactive wastes from nuclear plants pollute our environment. Oil spillage, exhaust from motor vehicles, pesticides, fertilizers and acid rain have made our environment unclean and endangered plant and animal life. Human health is also being threatened by environmental pollution. Presently, chemists are trying to come up with a fuel that will reduce the air pollution problem. They are also modifying chemical processes to recycle chemical wastes or change them to harmless products which can be safely discharged into the surrounding.

    PERIOD 4: SCIENTIFIC METHOD

This is the method the scientist used to produce different materials that exists as a result of chemistry. In the light of this, the scientists use their senses to observe what is happening around them. From a given set of observations, they see a certain pattern. This often leads to a problem which they try to solve. They put forward a reasonable explanation or hypothesis and carry out appropriate experiments to test it. Then, they carefully record their observations and the results of their experiments.

If the experiments support the hypothesis, they carry out further investigations. They discuss the hypothesis and results with other scientists in the field so that the hypothesis can be further tested. When a hypothesis has been tested and found to be correct within the limits of available evidence. It becomes a theory. A scientific law or principle is established only after the theory has been extensively tested and proven true without any exception. If the experiments give negative results, then the scientist goes back to his hypothesis and either modifies it or puts forward a new hypothesis. This way of studying a problem is known as the scientific method. It is the very foundation of all scientific discoveries.

EVALUATION

1. Mention five adverse effects of existence of chemistry in the world.

2. What do you understand by hypothesis?

3. Differentiate the terms hypothesis and theory

4. Explain fully what you understand by scientific method?

GENERAL EVALUATION

OBJECTIVE TEST:

1. Chemistry is defined as

2. a branch of knowledge which produces chemicals

3. the branch of science which deals with changes in matter

4. the oldest branch science

5. the branch of science which makes physics and biology career

6. Scientific approach to discoveries follows the order which includes:

7. Observation, hypothesis, and results

8. experiments, hypothesis and results

9. further experiments and problems solving

10. theory, negative and positive results and experiments

3. Chemical hypothesis is different from chemical law in that

4. hypothesis is a reasonable explanation to observations made while law is a statement from a scientist.

5. hypothesis is a reasonable explanation to observations while law is a statement which confirms the hypothesis after extensive tests.

C.hypothesis is not reasonable while law is reasonable.

1. none of the above

2. Chemical changes around us includes all except;

3. rusting of iron nails

4. sieving

5. fading of coloured cloth

6. decomposing of green leaves in a compost

7. One of these professions has no need for chemistry

8. Miners

9. Engineers

10. Philosophers

11. Geologists

ESSAY QUESTIONS

1. Give five reasons why chemistry is important in your life.

2. Explain in detail two of the reasons given above.

3. List three adverse effect of existence of chemistry in this world.

4. Explain two of those adverse effects mentioned above.

5. Explain the term scientific method full.

WEEKEND ASSIGNMENT:

PRE- READING ASSIGNMENT

Read about physical and chemical changes and differentiate them.

WEEKEND ACTIVITY

Explain fully what you understand by the following terms.

Atoms, Molecules, Constituents of atoms.

REFERENCE:

1. New school chemistry for senior secondary schools by Osei Yaw Ababio revised by L.E.S. Akpanisi Herbert Igwe.

WEEK 2

Topic: PARTICULATE NATURE OF MATTER

CONTENTS:

(1) Physical and chemical changes

(2) Elements and their symbols.

(3) Atoms, molecules, atomicity

(4) Dalton’s atomic theory

 

PERIOD 1: PHYSICAL AND CHEMICAL CHANGES

PHYSICAL CHANGES:

DEFINITION: A Physical change is one which is easily reversed and in which no new substances are formed.

Examples:

1. Melting of solids to liquids.

2. Freezing of liquids to solids.

iii. Vaporization of liquids to gases.

1. Liquefaction of gases to liquids.

2. Sublimation of solids to vapour.

CHEMICAL CHANGE:

DEFINITION: A chemical change is one which is not easily reversed andin which a new substance is formed.

Examples:

1. Burning of substances.

2. Dissolution of metals and limestone in acids.

iii. Chemical decomposition – like digestion of food.

1. Rusting of iron.

2. Charring of sugar.

3. Dissolution of metals in acids.

DIFFERENCES BETWEEN PHYSICAL AND CHEMICAL CHANGE

         PHYSICAL CHANGE                        CHEMICAL CHANGE

1. Easily reversible Not easily reversible

2. No new substance is formed New substance is formed

3. No change is mass. There is a noticeable change in mass.

4. Not accompanied by heat usually accompanied by heat change.

Change.

EVALUATION:

1. Mention three familiar process/changes which you know to be: (a) Physical changes (b) chemical changes.

2. List three differences between physical change and chemical change.

3. Classify each of the following as physical change or chemical change.

(a) Boiling of egg   (b) Burning of kerosene  (c) Melting of wax (d) Rusting of iron (e) Digestion of glucose (f) Dissolving iron in an acid.

4. State with a reason in each case whether each of the following is physical or chemical change.

• Dissolving common salt in water.

• Burning of petrol.

• Digestion of glucose.

 

PERIOD 2:  ELEMENTS AND THEIR SYMBOLS

An element is a substance that cannot be broken into simpler substances by any chemical methods. Examples of elements include: Iron, tin, aluminum etc.

There are about 118 known elements of which 92 are naturally exiting elements and the rest are artificially made.

Symbols are modern ways of representing atoms of elements by using abbreviations. The modern symbols were developed by Berzelius in 1814.

First, He used the first letter in the name of the element.

Examples

  ELEMENT                                              SYMBOL

Hydrogen                                                H

Boron                                                     B

Carbon                                                   C

Nitrogen                                                 N

Oxygen                                                   O

Fluorine                                                 F

Phosphorus                                            P

Sulphur                                                  S

Iodine                                                      I

The second principle uses the first two letters.

Examples:

ELEMENTS                                SYMBOL

Helium                                       He

Lithium                                      Li

Beryllium                                   Be

Neon                                          Ne

Aluminum                                  Al

Silicon                                        Si

Argon                                         Ar

Calcium                                     Ca

Bromine                                     Br

Barium                                       Ba

The third principle is when the first letter and another letter in the name are used.

Example:

ELEMENTS                                SYMBOL

Magnesium                                 Mg

Chlorine                                     Cl

Chromium                                  Cr

Manganese                                 Mn

Zinc                                           Zn

 

 

The fourth principle is the elements that derived symbols from their Latin names.

Example:

ELEMENT                   LATIN NAME             SYMBOL

Sodium                       Natrium                     Na

Potassium                   Kalium                       K

Iron                            Ferrum                      Fe

Copper                        Cuprum                     Cu

Silver                          Argentum                   Ag

Tin                              Stannum                    Sn

Gold                            Aurum                       Au

Mercury                      Hydrargyrum              Hg

Lead                           Plumbum                   Pb

 

 

PERIOD 3: ATOMS, MOLECULES AND ATOMICITY

ATOMS

DEFINITION: An atom is the smallest particle of an element which can take part in a chemical reaction.

STRUCTURE AND CONSITITUENTS OF AN ATOM

 An atom is made up of the three sub-particles known as protons, neutrons and electrons as shown in the diagram below. Their characteristics are also summarized in the table below:

 

                                                                          Electron

                                                                            Nucleus

CHARACTERISTICS OF THE SUB-PARTICLES

SUB-PARTICLE	LOCATION	RELATIVE CHARGE	RELATIVE MASS	SYMBOL
Proton	Nucleus	+	1	p
Electron	Outside nucleus	_	0.005	e–
Neutron	Nucleus	Zero	1	n

MOLECULES

DEFINITION: A molecule is the smallest particle of a substance that normally exist alone and still retain the chemical properties of that substance be it an element or a compound.

Some molecules can exist independently as single atoms e.g. He, Ne, Ar, Xe etc. Some molecules may be made up of atoms of the same element e.g. a molecule of hydrogen is H_2, that of chlorine is Cl₂, Oxygen is O_2, phosphorus is P₄, Sulphur is S_8. Some molecules may be made up of different elements e.g. a molecule of water is H₂O, Methane is CH₄, ammonia is NH₃, carbon (iv) oxide is CO₂ etc.

ATOMICITY: Atomicity is the number of atoms in each molecule of an element.

Atomicity of some molecules

Element	Formula of molecule	Atomicity
Hydrogen	H2	2
Oxygen	O2	2
Ozone	O3	3
Phosphorus	P4	4
Sulphur	S8	8
Chlorine	Cl2	2
Neon	Ne	1
Argon	Ar	1
Tetraoxosulphate(vi) acid	H2SO4	7
Amonium tetraoxosulphate(vi)	(NH4)2SO4	15

 

PERIOD 4: DALTONS ATOMIC THEORY

In 1808 John Dalton proposed the following Atomic theory.

1. All elements are made up of small indivisible particles called atoms.

2. Atoms can neither be created or destroyed

3. Atoms of the same element are alike in every aspect, and differ from atoms of all other elements.

4. When atoms combine with other atoms, they do so in simple ratios.

5. All chemical changes result from the combination or the separation of atoms.

      MODIFICATIONS OF DALTON’S ATOMIC THEORY

The following are the modifications to Dalton’s atomic theory.

1. All matter is made up of small particles, protons, neutrons and electrons.

2. An atom can be destroyed and created; when radioactive atoms disintegrate with the emission of particles, new atoms are produced.

3. The atoms of the same elements are not all alike, but may have different masses as proved by the phenomenon of isotopy.

4. In large organic molecules, such as proteins, fats and starch, the combining ratio are in large whole number.

 

EVALUATION:

1. What are the three fundamental units of all matter? Give their relative masses and charges.

2. Describe their relative positions to one another in an atom.

3. Name the two main part of an atom?

4. Mention the three subatomic particles in an atom.

5. Which particles are found in each part of the atom?

6. List three sub atomic particles with their corresponding charges.

7. State four Dalton’s atomic theory with their modifications.

GENERAL EVALUATION

OBJECTIVE TEST:

• The simplest unit of Matter that retains its properties is called.                          (a) an atom (b) an element (c) an hydroxide (c) a molecule

• Of the basic particles that make up an atom, the one with the smallest mass is? (a) a proton (b) a neutron (c) an x- particle (d) an electron

• The following are physical changes except: (a) melting of candle wax (b) Dissolving common salt in water (c) Freezing of water (d) Rotting of leaves.

• Which of the following is not a molecule of the same element. (a) O₂ (b) P₄ (c) S₈ (d)CO₂

• The atomicity of O₃ is (a) 1 (b) 2 (c) 3 (d )4

    ESSAY QUESTIONS

1. Write four examples in each case of (a) Physical change (b) Chemical change

2. Define the following giving two examples in each case. (a) Atom (b) Ion

3. Write the symbols for proton, electron and neutrons.

4. Define atomicity giving two examples.

5. Write four Dalton’s atomic theory.

WEEKEND ASSIGNMENT

Write the electronic configuration of the first twenty element using the concept of K,L,M,N and the sub-energy atomic level configuration i.e. s,p,d,f.

 

 

 

 

WEEK 3

TOPICS: PARTICULATE NATURE OF MATTER

CONTENTS:

1. Electronic configuration

2. Atomic number and mass number (nucleon number)

3. Relative atomic mass based on C-12 isotope

4. Isotopy of elements

PERIOD 1:  ELECTRONIC CONFIGURATION 

Electrons are found revolving around the nucleus of an atom in circular paths known as rings, orbits, energy levels or shells. Each shell contains electrons with similar energy. Those with the lowest energies being nearest to the nucleus.

3 (M shell)

                                                                                                 Nucleus

2(L shell)

1 (K shell)

Thus, the arrangement of electrons in the atom according to energy is called ELECTRONIC CONFIGURATION. Letters and figures are associated with these orbits or shells as shown above. The maximum possible number of electrons that can be accommodated in a shell is given by the formula:

N_max= 2n². Where N_max = Maximum no of electron. n= no, of shell.

Thus K- shell can contain 2 × 1² = 2 electrons.

L- Shell can contain 2 × 2²  = 8 electrons.

M- Shell can contain 2 × 3²= 18 electrons etc

The electron structures of the atoms of the first twenty elements are given in the table below.

Element	Symbol	Number of protons(or atomic number)	Number of electrons and their distribution in the shells.                                  K           L          M         N
Hydrogen	H	1	1
Helium	He	2	2
Lithium	Li	3	2            1
Beryllium	Be	4	2            2
Boron	B	5	2            3
Carbon	C	6	2            4
Nitrogen	N	7	2            5
Oxygen	O	8	2            6
Fluorine	F	9	2            7
Neon	Ne	10	2            8
Sodium	Na	11	2            8              1
Magnesium	Mg	12	2            8              2
Aluminium	Al	13	2            8               3
Silicon	Si	14	2            8               4
Phosphorus	P	15	2            8               5
Sulphur	S	16	2            8               6
Chlorine	Cl	17	2            8               7
Argon	Ar	18	2            8               8
Potassium	K	19	2            8               8        1
Calcium	Ca	20	2            8               8        2

The electronic configurations of some elements are shown below:

Hydrogen, H (atomic number 1)

                           Electronk₁

                                        Nucleus

Helium, He(atomic number 2)

                                             electrons              k₂

nucleus

Lithium, Li (atomic number 3).

K₂ L₁

Neon, Ne (atomic number 10)

 K₂ L₈

2,8

Sodium, Na (atomic number 11)

                                             K L M

                                       2  8 1

                   2, 8, 1

Argon, Ar (atomic number 18 )

                                          K L   M

                                          2   8    8

2,8,8

Potassium, K (atomic number 19)     K L M N

                                              2 8 8 1

2, 8, 8, 1

Calcium, Ca (atomic number 20)

                                            K   L   M N

                                        2   8   8   2

2,8,8,2

EVALUATION: Draw the electronic configuration of the following elements.

• Carbon (b) Fluorine   (c) Aluminium   (d) Nitrogen

 

PERIOD 2: ATOMIC NUMBER AND MASS NUMBER (NUCLEON NUMBER)

ATOMIC NUMBER:

DEFINITION:  Atomic number is the number of protons in an atom of an element.

The atomic number of an element is a whole number and is designated z. In a neutral atom the number of protons must be equal to the number of electrons (since protons are positively charged and electron are negatively charged).

 All the atoms of a particular element have the same number of protons in their nuclei (i.e. they have the same atomic number). NO two elements have the same number of protons in their atoms.

DEFINITION:

MASS NUMBER (NUCLEON NUMBER): The mass number is the sum of the protons and neutrons in an atom of an element.

 Mass number is represented by the letter A.

Mass number A = Number of protons + number of neutrons.

i.e. A =p + n. Where p=protons, n= neutrons.

Or number of neutrons n =A – Z.

An atom of an element can be described by writing its symbol together with its atomic number and mass number.

Examples: The atom of carbon, oxygen and sodium can be written as ¹²₆C, ¹⁶₈O and²³₁₁Na respectively.

EVALUATION:

 (1) Define the following:  (a) Atomic number        (b) Mass number.

(2) Describe the atoms of the following elements using their symbol, atomic number and mass number:  (a) Phosphorus (b) Silicon (c) Calcium

PERIODS 3 AND 4: ISOTOPY AND RELATIVE ATOMIC MASS

Definition: Isotopy is a phenomenon whereby atoms of an element exhibit different mass number but have the same atomic number.

Mass spectrometric studies show that the atoms of most elements exist in more than one form. This is due to the difference in number of neutrons present in these atoms. Such atoms are known as isotopes. Isotope of an element is represented by the original symbol of the element with the mass number and atomic numbers. For example ¹²₆C, ¹³₆C, ¹⁴₆C represent atoms of the isotopes of carbon. For each atom, the number of neutrons can be obtained by finding the difference between the mass number A and the atomic number Z i.e. A – Z. Each isotope of an element has its own mass known as isotopic mass.

Isotopes of an element have slightly different physical properties because neutrons contribute only to the mass of an atom and not its chemical behaviour. But isotopes of an element exhibit the same chemical properties because the number of valence electrons in an atom of an element determines its chemical behaviour (properties) and since isotopes have the same number of valence electrons they will be chemically alike.

NOTE:

 (i) An analysis of the chlorine isotopes.

                                       Isotope ³⁵₁₇Cl                       Isotope ³⁷₁₇Cl

Mass number, A                   35                                           37

Atomic number,Z                  17                                           17

Number of protons                17                                           17

Number of electrons              17                                           17

Number of neutrons (A-Z)      35 – 17=18                              37 – 17=20

Abundance in nature (%)        75                                         25

ISOTOPES OF THE SAME ELEMENTS.

Element	Carbon	Oxygen
ISOTOPES	126C 136C	168O  178O  188O
ABUNDANCE IN NATURE (%)	98.9  1.1	99.76   0.04   0.20

(ii) The names of the isotopic forms of hydrogen

 ¹₁H — Protium (or hydrogen)

²₁H— Deuterium (or heavy hydrogen or D)

³₁H— Tritium or T

(iii) The relative atomic mass, RAM of an element which exhibits isotopy is the average mass of its various isotopes as they occur naturally in any quantity of the element and they are not usually in whole numbers.

CALCULATION INVOLVING ISOTOPY.

WORKED EXAMPLE:

• Determine the relative atomic mass of element X from the data below

                              ISOTOPE           MASS         % ABUNDANCE

                                   24X              24              78.70

                                   25x              25              10.13

                                   ²⁶x               26              11.7

• An element X has two isotopes of ²⁰₁₀X and ²²₁₀X in the ratio 1:3. What is the relative atomic mass?

Add ratio of occurrence together.

1 + 3= 4

                                   X = 21.5

• Isotopes of an element X have isotopic masses 65 and 63 respectively. If the relative atomic mass of X is 63.60. Find the relative abundance of each isotope of the element.

Let the relative abundance of element X be y and Z respectively.

                              Z +Y =100

                               Z = 100 – y……. (i)

                                        65y + 63z = 63.60 × 100

                              65y + 63z = 6360 ……(ii)

                              65y +63(100 – y) = 6360

                              65y – 63y + 6300 = 6360

                                             2y = 60

                                              Y =  = 30

                                             Y= 30

                              Z = 100 – y= 100 – 30 = 70

                              Y = 30, Z = 70

The relative abundance of X = 30% 0f ⁶⁵X and 70% of ⁶³X

 

EVALUATION:

(a) How many neutrons are present on the isotopes of ⁴¹₁₉X (45%) and ⁴⁰₁₉x (55%)

(b)Calculate the relative atomic mass of X.

RELATIVE ATOMIC MASSES BASED ON C-12 ISOTOPE

Definition: The Relative Atomic Mass of an element is the number of times the average mass of an atom of the element is heavier than one-twelfth of the mass of one atom of carbon -12

RAM of an element=

Thus the atom of carbon -12 is adopted as the standard for defining the relative atomic mass of the other elements and is given a basic mass value of 12units.

The relative atomic mass of each element has been determined accurately with the aid of the mass spectrometer. This instrument measures the masses of the isotopes of the elements and their abundance and the relative atomic mass is calculated from the data.

Relative atomic masses of the first twenty elements in the periodic table

Element	Atomic number	Relative atomic mass
Hydrogen	1	1.008
Helium	2	4.0026
Lithium	3	6.939
Beryllium	4	9.0122
Boron	5	10.81
Carbon	6	12.011
Nitrogen	7	14.0067
Oxygen	8	15.9994
Fluorine	9	18.9884
Neon	10	20.183
Sodium	11	22.9898
Magnesium	12	24.312
Aluminum	13	26.9812
Silicon	14	28.086
phosphorus	15	30.9738
Sulphur	16	32.06
Chlorine	17	35.453
Argon	18	39.948
Potassium	19	39.102
Calcium	20	40.08

The relative atomic masses of the first twenty elements in the periodic table are given in the table below.

EVALUATION: From the complete periodic table of elements write out the relative atomic masses of (A) Magnesium (b) Oxygen (c) Chlorine (d) Carbon

GENERAL EVALAUATION

OBJECTIVES TEST :

• The maximum number of electrons that can be accommodated in the M-shell is. (a) 18 (b) 8 (c) 2 (d) 32

• The atomic number of chlorine is (a) 17 (b) 18 (c) 20 (d) 7

• Which of the following is an isotope of hydrogen?

(a)⁴₁H (b) ⁵₁H (c) ³₁H (d) ⁰₁H

ESSAY QUESTIONS

(1) Chlorine exists in two isotopic mixtures. The first has 17protons and 18 neutrons while the second isotope has 17 protons and 20 neutrons. If the two isotopes are present in ratio 3:1 respectively, calculate the relative atomic mass of chlorine.

(2) Show the electron structure of the following.

 (a) Calcium (b) Magnesium (c) Sodium (d) Oxygen

(3) If the numbers of charged and unchanged particles in the centre of an atom are 6 and 7 respectively, what is the mass number of the atom?

(4) Calculate the number of neutrons in

(a) ²³₁₁Na (b) ³⁷₁₇Cl

(5) (a)What is an ‘isotopy’?

(b) Explain briefly why the chemical properties of isotopes of an element are similar.

WEEKEND ASSIGNMENT: Read about the topic ‘’mass spectrometer’’

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