Since students are mostly on the internet these days, it is also necessary to take our classrooms to the internet too. So I have decided to start up this thread for JAMB candidates who are science inclined to discuss chemistry. Ask your questions, get answers and join the discussion.

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lets begin with this:

-PVC-

PolyChloroEthene also know as PolyVinyl Chloride or PVC is a polymer manufactured from either ethene or ethyne. Ethene is first chlorinated to form chloroethene (vinyl chloride), CH2=CHCl, which is the starting monomer. Chloroethene (vinyl chloride) is polymerized at about 55 degree celsius under pressure in the presence of hydrogen peroxide as catalyst to give PolyChloroEthene (PolyVinyl Chloride).

QUESTION:
PolyVinyl Chloride is used in the production of

A. Glass
B. Alloy
C. Plastic Pipes
D. Ceramic

Lets read this and give the answer:

In the laboratory preparation of gases, we often hear statements like; gases are collected by upward delivery, downward delivery, upward displacement of air, downward displacement of air. Which of the option below is correct.

A. Upward delivery and downward displacement of air are the same
B. Downward delivery and downward displacement of air are the same
C. Upward delivery and upward displacement of air are the same
D. Downward delivery and upward displacement of air are not the same.

WHAT YOU SHOULD KNOW ABOUT THE PERIODIC TABLE

The periodic table of elements is one of the most basic subjects of study in chemistry. The periodic table contains all the known elements, placed in order by their atomic number, which is the number of protons in an atom of that element. The rows of the periodic table are known as periods, while the columns are known as groups. The periodic table helps reveal patterns for many of the chemical properties of the elements.

Elements in the same group tend to resemble one another in their chemical behavior, WHY??

Reason is because they have same valence electron and as such elements in the same group tend to have the same chemical property.

Isomers are compounds with the same molecular formula but different molecular structures.

Isomers with the same molecular formula and belonging to the same homologous series tend to have similar chemical properties. WHY?

Reason: Because they have the same functional group, which determines the chemical properties.

ISOTOPY AND RELATIVE ATOMIC MASS (R.A.M)

Isotopy: This could be defined as a situation where by atoms of an element have the same atomic number but different mass numbers. The difference in the mass number is due to the difference in the number of neutrons. ISOTOPES have the same chemical properties due to the same atomic number which also determine their chemical reactivity and position of the element in the periodic table. However, they have different physical properties.

RELATIVE ATOMIC MASS(R.A.M): This is the mass of an atom measured in relative to the mass of an atom which serves as a standard. The standard used presently is based on carbon-12 scale.
The RELATIVE ATOMIC MASS of an element is the number of times the average mass of one atom of that element is heavier than one-twelfth the mass of one atom of carbon-12.
The R.A.M of all elements have been determined successfully using their isotopes and abundance by an instrument called mass spectrometer. Using an instrument called mass spectrometer, the isotope and abundance of various elements have been determined. By this method, the mass ratio of an element to carbon-12 is measured and such measurement provides data for obtaining the relative atomic mass of that element. Most elements are represented by their relative atomic masses which is the mean of the weighed atomic masses of the isotopes of the atoms of the elements. This is why they are not usually whole numbers. The relative atomic mass can be calculated provided that the mass numbers and the occurrence or abundance of the isotopes of an element are known, using this formula;
R.A.M=(mass of one isotope X its abundance) + (mass of one isotope X its abundance)
note: abundance can be in percentage or in ratio.

EXAMPLE:
What is the relative atomic mass of chlorine if it has two isotopes with mass numbers 35 and 37 with abundance of 75% and 25% respectively?

SOLUTION:
Method 1:
R.A.M=(mass of one isotope X its abundance) + (mass of one isotope X its abundance)
R.A.M= (35 X (75/100)) + (37 X (25/100))
=35.5
note: 75% = 75/100 and 25% = 25/100

Method 2:
The ratio of their abundance is 75:25 = 3:1 for isotopes 35 and 37 respectively.
Therefore, isotope 35 whose abundance is 3 contributed 35 X 3 = 105.
Isotope 37 whose abundance is 1 contributed 37 X 1 = 37.
Total contribution = 105 + 37
= 142
total number of atoms making contribution is 3 + 1 = 4
The weighed mean = 142/4
= 35.5
therefore, relative atomic mass = 35.5

RELATIONSHIP BETWEEN ELECTRONIC CONFIGURATION AND PERIODIC TABLE.

The place of an element in a periodic table can be obtained from its electronic configuration. Take for instance this electronic configuration 1s2, 2s2, 2p2; the figures in front of the letters, s and p indicates the PERIOD in the periodic table. The letters indicates the block of the periodic table, if it is the main group, transition or inner transition. The s and p represent the main group block, d represents the transition block and f represents the inner transition block. The figures after the letters which are normally written as superscript indicates the particular GROUP in the block. However to locate the place of an element in the periodic table using its electronic configuration, we only consider what the electronic configuration ended with. Taking the electronic configuration we used previously; 1s2, 2s2, 2p2. It ended with 2p2 meaning that the element that has it belongs to PERIOD 2 and the second GROUP in the p block. The second group in p block is GROUP 4.


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TYPES OF BONDS.

Atoms may attain a stable electronic configuration in three different ways: by losing electrons, by gaining electrons, or by sharing electrons.

Elements may be divided into:
1. Electropositive elements, whose atoms give up one or more electrons fairly readily.
2. Electronegative elements, which will accept electrons.
3. Elements which have little tendency to lose or gain electrons.

Three different types of bond may be formed depending on the electropositive or electronegative character of the atoms involved.

When an electropositive element combines with an electronegative element, an IONIC BOND is formed.

When an electronegative element combines with an electronegative element, a COVALENT BOND is formed.

When an electropositive element combines with an electropositive element, a METALLIC BOND is formed.

Ionic bonding involves the complete transfer of one or more electrons from one atom to another. Covalent bonding involves the sharing of a pair of electrons between two atoms, and in metallic bonding the valence electrons are free to move throughout the whole crystal.

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