Isotopes are atoms with the same number of protons but differing numbers of neutrons. In other words, isotopes have different atomic weights. Isotopes are different forms of a single element.

(b) The element copper has naturally occurring isotopes with mass numbers of 63 and 65. The relative abundance and atomic masses are 69.2% for a mass of 62.93 amu and 30.8% for a mass of 64.93 amu. What is the average atomic mass of copper?

Take the weighted average of the individual isotopes.

Explanation:

⁶³Cu has 69.2% abundance.

⁶⁵Cu has 30.8% abundance.

So, the weighted average is 62.93×69.2% + 64.93×30.8% = 63.55 amu.

If we look at the Periodic Table, copper metal (a mixture of isotopes but 63Cu and 65Cu predominate) has an approximate atomic mass of 63.55 g⋅mol−1,

The electronic configuration of ions A³⁺and B² are 2.8 and 2.8.8 respectively

Write the
Electronic arrangement of the atoms of elementA and B
Formulae of compound formed when A and B react.
Name the type of bond in a(ii)

Figure 2 is a section of the periodic table. Study it and answer the questions that follow. The letters do not represent the actual symbols of elements.

(i) Select elements which belong to the same chemical family.

K and J

(ii) Write the formulae of ions for elements in the same period. KL and M

(b) The First ionisation energies of two elements K and M at random are 577 kJ/mol and 494 kJ/mol

Write equations for the 1ˢᵗ ionisation energies for elements K and M and indicate their energies.
ii) Explain why the ionization energy for M is higher than that of K

Across the period ,sizes of atoms decreases and therefore more energy is required to remove an electron from an atom in its gaseous state hence the 1^st ionization energy for M will be greater than that of K

(iii) Write the formula of the compound formed when L and I react.

L₃I₂
(iv) Give one use of elemcnt V.

Being an inert gas ,V can be used in fluorescent tubes and bulbs

J is more reactive than K because of the increase in the atomic size . This is because the size of atoms increases as you go down the group and so does their reactivity
(d) (i) Elements L and M form chlorides.

Complete the following table by writing the formulae of each chloride and state the nature of the solutions.

Elements	Formula of chloride	Nature of chloride solution
L	LCl₂	Neutral
M	MC₃ or M₂Cl₆	Acidic

(ii) The chloride of element M vapourises easily while its oxide has a high melting point. Explain.

Chloride of M vaporizes easily because of its weak van der wall forces between its dimers , its oxides have high melting points because of its strong ionic bonds which are very difficult to break

Taking the symbol ¹⁶₈X to represent an atom of element X . determine

Atomic number

Mass number

Number of electrons

Number of neutrons

The electronic configuration for elements represented by letters W, X,Y and Z are 2.8.6,2.8.2,2.8.1 and 2.8.8 respectively .

Identify the elements which forms a :
Double charged anions

Wand X

Soluble carbonates

Determine the elements with the smallest atomic radius and give a reason

List two physical properties of alkali metals
The table below give information concerning elements A,B,C,D and E

*Element*	*Atomic number*	*Melting point*
A	11	*97.8*
B	13	*660*
C	14	*1410*
D	17	*-101*
E	19	*63.7*

Write the electronic arrangement for the ions formed by the elements B and D
Identify the element which is the most reactive :
Metal
Non metal

(c ) State the period and group in which element E belongs

Explain why :
Element E loses its outermost electrons more readily than A
Melting point of element B is higher than that of A
Draw an electronic diagram to show bonding between elements C and D
Write an equation for the reaction between A and H₂O
Describe how a solid mixture of the sulphate of element E and lead sulphate can be separated into solid sample

(a) Write an equation to show the effect of heat on the nitrate of:

(i)Potassium (ii)Silver

(b) The table below gives information about elements Ai, A2, A3, and A4

i) In which period of the periodic table is element A2? Give a reason.

Period 2, because it has two energy levels

(ii) Explain why the atomic radius of:
I. Ai is greater than that of A2;

A2 has greater atomic number than AI, it also has greater nuclear charge and more protons than A1, Therefore , you would expect a greater nuclear pull on A2 than on A1 hence a reduction in its atomic size

A4 is smaller than its ionic radius.

A4 gains electrons, this incoming electrons are usually repelled by existing electrons which causes them to move far away from the nucleaus hence the reason for their increased electron cloud

(iii) Select the element which is in the same group as A3.

A2
(iv) Using dots (•) and crosses(x) to represent outermost electrons, draw a diagramto show the bonding in the compound formed when Ai reacts with A4.

Define term ‘relative atomic mass’

The relative atomic mass of an element is defined as the weight in grams of the number of atoms of the element contained in 12.00 g of carbon-12. Every atom has its own unique relative atomic mass (RAM) based on a standard comparison or relative scale e.g. it has been based on hydrogen H = 1 amu and oxygen O = 16 amu in the past (amu = relative atomic mass unit).

The relative atomic mass of an element takes into account the different masses of the isotopes of that element and the abundance of the isotopes in the naturally occurring element (meaning the percentage of each isotope present).
Relative atomic mass is defined and explained below, and examples of how to calculate it from data.

The relative atomic mass scale is now based on an isotope of carbon, namely, carbon-12, nuclide symbol , which is given the arbitrary value of 12.0000 amu by international agreement.

To calculate the relative atomic mass of chlorine, the average mass of one atom of chlorine is found by considering 100 atoms of chlorine.

Calculating the relative atomic mass of bromine and

bromine consists of two isotopes, and , calculate the A_r of bromine from the mass numbers (top left numbers).
Think of the calculation in terms of ‘100 atoms’
A_r= [ (50 x 79) + (50 x 81) ] /100 = 80
So the relative atomic mass of bromine is 80 or RAM or A_r(Br) = 80
Note the full working shown. Yes, ok, you can do it in your head BUT many students ignore the %’s and just average all the isotopic masses (mass numbers) given, in this case bromine-79 and bromine-81.
The element bromine is the only case I know where averaging the isotopic masses actually works! so beware!
Calculating the relative atomic mass of chlorine based on the and isotopes
Chlorine consists of two isotopes, 75% chlorine-35 and25% chlorine-37, so using these two mass numbers …
… again think of the data based on 100 atoms, so 75 have a mass of 35 and 25 atoms have a mass of 37.
The average mass = [ (75 x 35) + (25 x 37) ] / 100 = 5
So the relative atomic mass of chlorine is 35.5 or RAM or A_r(Cl) = 5
Note: ³⁵Cland ³⁷Cl are the most common isotopes of chlorine, but, there are tiny percentages of other chlorine isotopes which are usually ignored at GCSE/IGCSE and Advanced GCE AS/A2 A level.

Why do elements potassium and sodium have similar chemical properties?

Both elements, sodium (Na) and potassium (K) lie in the Group 1 column of the Periodic Table , which contains the members of the Alkali Metals family. Members within a family, or column, of elements tend to have similar chemical properties.

Table below shows the melting point of three alkali metals

Alkali metal

Melting point (^oC)

Lithium

Sodium

Potassium

180

Explain the trend in the melting point of the tree metals

A 2.4g piece of magnesium ribbon was cleaned in steel wool and then completely burned in presence of oxygen . it produced a weight of 4g after cooling

Explain why
It was necessary to clean the ribbon

So as to remove any oxide film on it I. layer of magnesium oxide

What observation was made on the crucible after burning?

A white solid formed which is magnesium oxide

There was an increase in mass

The increase in mass was due to oxygen which combined with with magnesium

Write a
balanced reaction for this reaction

2Mg(s)+ O2 2MgO(s)

Word equation for this reaction

(c ) calculate the number of moles of oxygen used during the burning of the ribbon (O=16)

The product in (b) was dissolved in water and then filtered . the resulting solution was tested with both blue and red litmus paper . Explain the observation

The filtrate was magnesium hydroxide which is alkaline . the red litmus paper turned blue . there was no change in the blue litmus paper

The table below gives the information about particles A,B,C,D,E and F

Particle

proton

Neutron

Electron

Identify the letters that represent
Neutral atoms of a metal
Noble gas
Pair of isotope
Cation
Anion
(i) Write a balance equation for the reaction between C and D
Name the type of chemical bond formed in b(i)
Determine the mass number of particle B
Name the period and the group of periodic table to which particle D belongs
Write the spdf electronic configuration of particle E

Element A has atomic mass 23 and element B has atomic mass 7 and also have 12neutorns and 4 neutrons respectively.
1. Write the electronic arrangement of A and B

A= 2.8.1
B= 2.1

Which element has higher ionization energy? Explain

Strong attraction of the outermost energy level electron to the nucleus make it difficult to remove This is due to smaller atomic radius compared to A
Or – Outermost electrons are closer to the nucleus hence higher force of attraction

The table below shows the relative atomic masses and the percentage abundance of isotope M₁and M₂of element M.

	Relative atomic mass	% abundance
M₁	*62.93*	*69.09*
M₂	*64.93*	*30.91*

Calculate the relative atomic mass of element M

R.A.M = (62.93 x 69.09) + (64.93 x 3091)
100
= 4347.834 + 2006.99
100
= 63.5482
≈ 63.5

Element V has two isotopes. Two thirds of V and one third of V . What is the relative atomic mass of element V?

R.A.M = (33 x 2) + (30 x 1)
3
99 = 33
3

The following refers to element Y

*Isotope*	A	B	C
*Isotope mass*	54	56	57

Given that isotope C contains 31 neutrons in its nucleus find the number of protons in isotope B

Number of electrons of C = 57 − 31 = 26
Number of electrons of B is the same as for C = No. of Protons
B = 26 protons

The melting point of phosphorous trichloride is -91^oc while that of magnesium chloride is 715^o Explain the difference in their melting points

The table below shows the relative atomic masses and the percentage abundance of the isotopes L₁and L₂of element L.

	Relative atomic mass	% abundance
L₁ L₂	*62.93* *64.93*	*69.09* *30.91*

Calculate the relative atomic mass of element K.

69.09 x 62.93 + 30.91 x 64.93
100 100
43.4783 + 20.0698
= 63.548

An element M has two isotopes M and M . The relative atomic mass of the naturally occurring is 63.55. Calculate the percentage of each isotope

63 x + 65 (100 – x) = 63.55
100
63x + 6500 – 65x = 6355
2x = 6355 – 6500
2x = -145
x = 72.5
% abundance of ⁶³M = 72.5%
⁶⁵M = 27.5%

An oxide of element G has the formula as G₂O₃

State the valency of element G

Valency of G is 3

In which group f the periodic table is element G?

G is a group 3 element

The table below gives information about the ions T⁺and Z^2-

Ion	T⁺	Z^2-
Electron arrangement	2.8	2.8.8
Number of neutrons	12	16

How many protons are there in the nucleus of ?

Element T? 11 protons
Element Z? 16 protons

Determine the relative formula mass of the compound formed between T and Z

Formula of compound = T₂Z
Mass number of T = 11+ 12 = 23
Mass number of Z = 16+16 = 32
Formula Mass of T₂Z = ( 23×2) + 32 = 78

State two conditions under which the compound would conduct electricity

When molten
When in aqueous solution

Explain why

The is a general increase in the first ionization energies of elements in period 3 from the left to right

Across a period from left to right, the ionisation energy increases. This is due to the increase in nuclear charge having a greater pull on the electrons and therefore more energy is required to remove electrons.

Anhydrous aluminum chloride is soluble in organic solvents while anhydrous magnesium chloride is insoluble

Aluminium chloride is covalent hence soluble in organic solvents while magnesium being ionic is insoluble in organic solvents

Carbon and silicon belong to the same group of the periodic table, yet Carbon (IV) oxide is a gas while silicon (IV) oxide is a solid with a high melting point. Explain this difference

Silicon (IV) Oxide has giant atomic structure with strong covalent bond holding the atom together. These require a lot of energy to break, hence it has high melting point. Carbon (IV) Oxide has simple molecular structure with weakVan Der Waals forces holding the molecules together which require little energy to break, hence sublimes at low temperature and is a gas at room temperature and pressure

An ion of oxygen is larger than oxygen atom. Explain
The oxide ions has 2 extra electrons that causes greater electron repulsion than in oxygen atom
Explain why the ionic radius of non-metallic element is greater than its atomic radius

When a non metal gains electrons to become a negative ion the radius increases. The number of protons remains the same so the pull on the electrons is the same. However as the number of electrons increases with the extra electrons the average pull on the electrons is less. The decreased pull causes the distance from the nucleus to increase.

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