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Download 7th Class General Science Notes (Unit-6) for Islamabad Model Schools & Colleges

Download 7th Class General Science Notes (Unit-6) for Islamabad Model Schools & Colleges

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Download 7th Class General Science Notes (Unit-6) for Islamabad Model Schools & Colleges


What is an atom? Name its sub atomic particles.
The smallest particle of an element that maintains its chemical identity is called an atom.

Define atomic number.
Atomic number is the number of protons in the nucleus of an atom. It is denoted by 'Z'.

What do you mean by the valency of an element?
The capacity of an element to combine with other atoms is called valency. It can be positive or negative. For example H+, O-2

Define a cation and an anion.
·         When an atom releases its one or more electrons from the outermost shell, the number of protons increases. It becoes a positve ion or cation.
·         When a atom acquire a negative charge and is called a negative ion or Anion.

Do all the isotopes have the same number of neutron?
No. All isotopes have not the same number of neutrons. For example in isotopes of hydrogen Protium, Deutrium and Tritium has 1,2 and 3 neutrons.


Describe the structure of an atom.
·         An atom has two major parts:
        i)      Nucleus present in the center of atom. Protons and neutrons are                        present in it.
        ii)      Electrons revolve in the shells or orbits around nucleus.
·         Electrons are positively charged particles.
·         Protons are positively charged particles.
·         Neutrons are neutral and have no charge.

Differentiate between atomic number and mass number. What are isotopes? What are their uses in medicine and agriculture?
Atomic Number:
The number of protons in the nucleus of an atom is called atomic number. It is denoted by Z.
Mass Number:
Total number of Protons and neutrons in the nucleus of an atom is called mass number. It is denoted by A.
Atoms having same atomic number but different mass number are called isotopes. For example hydrogen has 3 isotopes. Protium, Deutrium and Tritium.
Uses in Medicines:
·         Iodine-131 is used to treat cancer.
·         Phosphorus-32 is used to treat leukaemia.
·         Sodium-24 is used to study circulation of blood.
·         Iron-59 is used to study absorption of iron in body.
·         Chromium-51 is used to study red blood cells.
Uses in Agriculture:
·         Isotopes are used to produce high yielding and high protein containing crops.
·         They are used to produce disease resisting varieties.
·         They are used to locate water resources.
·         They are used to study photosynthesis.
·         Carbon-14 is used to calculate the age of plants.

Write formulae of the following:
Hydrogen fluoride                = HF
Silver Chloride            = AgCl
Magnesium Sulphide    = MgS
Sodium Oxide             = Na2O

State the law of constant composition. Explain it with the help of example.
The chemical composition of a compound is always the same regardless of how the compound was made or obtained.
·         Water is such a chemical compound which can be obtained from river, well, spring, sea and many other sources.
·         Water can also be prepared by chemical reactions in the laboratory.
·         The ratio between masses of hydrogen and oxygen present in it will always be 1:8.



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Download Class Notes: Download 7th Class General Science Notes (Unit-6) for Islamabad Model Schools & Colleges
Download 7th Class General Science Notes (Unit-6) for Islamabad Model Schools & Colleges
Download 7th Class General Science Notes (Unit-6) for Islamabad Model Schools & Colleges
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