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NCERT · Class 10 · Science

Chapter 3: Metals and Non-metals

Practice each question, then open the answer or worked solution.

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In-text questions set 3

Textbook page 49 · 2 questions
Q1Written answer

(i) Write the electron-dot structures for sodium and oxygen.

(ii) Show the formation of Na2O and MgO by the transfer of electrons.

(iii) What are the ions present in these compounds?

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Worked solution

Solution: (i) Sodium:

Na

Oxygen:

o

(ii) Formation of Magnesium oxide:

When magnesium reacts with oxygen, the magnesium atom transfers its two outermost electrons to an oxygen atom. By losing two electrons, the magnesium atoms form a magnesium ion (Mg2+), and by gaining two electrons, the oxygen atom forms an oxide ion (O2-).

Mg:  +
o→ MgO

Formation of Sodium oxide:

Two sodium atoms transfer their 2 outermost electrons to an oxygen atom. By losing two electrons, the two sodium atoms form sodium ions (2Na+). And by gaining two electrons, the oxygen atom forms an oxide ion (O2-).

zz

(iii) The ions present in sodium oxide compound (Na2O) are sodium ions (2Na+) and oxide ions (O2-).

The ions present in Magnesium oxide compound (MgO) are magnesium ions Mg2+ and oxide ions (O2-).

Q2Written answer

Why do ionic compounds have high melting points?

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Worked solution

Solution: Ionic compounds are the ones which have both positive and negative charges. Hence, there will be strong force of attraction between them. This make expenditure of a lot of heat to break this force of attraction, hence ionic compounds have high melting points.