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सी.आई.एस.सी.ई.आयसीएसई ICSE Class 7

Define Number - Chemistry

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प्रश्न

Define: Atomic number

व्याख्या
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उत्तर

Atomic number— Atomic number refers to the number of protons present in an atom. It is denoted by Z.

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पाठ 4: Atoms, Molecules and Radicals - Additional questions

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सेलिना Concise Chemistry [English] Class 7 ICSE
पाठ 4 Atoms, Molecules and Radicals
Additional questions | Q 1.3

संबंधित प्रश्‍न

Write down the name of a compound represented by the following formula:

Al2(SO4)3


Give the name of the element present in the following compound:

Quick lime


Calculate the number of molecules of sulphur (S8) present in 16 g of solid sulphur.


Define: Mass number : 


What is meant by atomicity ? Explain with two examples.


What is the atomicity of the following ?

  1. Oxygen
  2. Ozone
  3. Neon
  4. Sulphur
  5. Phosphorus
  6. Sodium

One of the forms of a naturally occurring solid compound P is usually used for making the floors of houses. On adding a few drops of dilute hydrochloric acid to P, brisk effervescence are produced. When 50 g of reactant P was heated strongly, than 22 g of a gas Q and 28 g of a solid R were produced as products. Gas Q is the same which produced brisk effervescence on adding dilute HCl to P. Gas Q is said to cause global warming whereas solid R is used for white-washing.

  1. What is (i) solid P (ii) gas Q, and (iii) solid R.
  2. What is the total mass of Q and R obtained from 50 g of P ?
  3. How does the total mass of Q and R formed compare with the mass of P taken ?
  4. What conclusion do you get from the comparison of masses of products and reactant ?
  5. Which law of chemical combination is illustrated by the example given in this problem ?

Work out the formula for magnesium hydrogencarbonate.


What are (i) ionic compounds, and (ii) molecular compounds ? Give two examples of each type of compounds.


The cation of an element has :


Molecular compounds are usually formed by the combination between :


An element A forms an oxide A2O5.

What is the valency of element A ?


An element X forms the following compounds with hydrogen, carbon and oxygen :

H2X, CX2, XO2, XO3

State the three valencies of element X which are illustrated by these compounds.


Why are the symbols and formulae of substances important?


Explain the term – molecules. Give three examples of atoms of the same element forming a molecule. State the atomicity of the same.


Give one example of a triatomic molecule


Give a reason why –

Helium is considered monoatomic, but hydrogen a diatomic molecule.


State the atomicity of the following:

Neon


State the atomicity of the following:

Oxygen


State the atomicity of the following:

Chlorine


State the atomicity of the following:

Sulphur


Classify the following molecules as the molecules of element or compound

1.  
2.  
3.  
4.  

Which of the following is a triatomic molecule?


The Atomicity of phosphorous is ______


Two elements sometimes can form more than one compound.


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