Chapter1: Lets us answer these (Page 18)

Q1. What name has been given to the horizontal arrangement of elements in the periodic table? Is there any gradation in the properties of elements across these rows? Give two examples to illustrate.
Ans: Periods.

         Yes, there is gradation of properties in rows.

          

        Example: In a period, the atomic number increases as the number of protons increases from left to right. The electrons are added at the same shell while the charge on the nucleus increases steadily. This should result in a greater degree of attraction between the nucleus and the electrons. Hence, the size of atoms decrease as move from left to right in a period.

2. How do the properties of group 1 elements differ from those of group 17 elements? Illustrate the difference in at least two points.

Ans:-

Elements of Group -1 Elements of Group -17

1. Valence electron = 1

2. They are metals.

3. They are electropositive. 1. Valence electron = 7

2. They are non-metals.

3. They are electronegative.

3. From the standpoint of electronic configuration, determine which element will be the first and which will be the last in a period of the periodic table?

Ans:- In each period, elements having valence electron 1 will be in the first while elements having 2/8 valence electrons will be in the last.

Example: In 2nd period, Li, Be, B, C, N, O, F, Ne, etc.

Electronic configuration of Li= 2, 1

Electronic configuration of Ne= 2, 8.

4. Accommodation of isotopic form of the same element was an upset in Mendeleev's periodic table. How could the Modern Periodic Table revolve the anomaly?

Ans:- The anomaly was remedied by replacing "atomic mass" by "atomic number".

5. Name two elements you would expect to show chemical reactions similar to lithium. What is the basis of your choice?

Ans:- Similar chemical reactions with Li are Na and K.

Reason: Li, Na and K are in the same group of periodic table.

6. Name:

(i). three elements having one electron in their outermost shells.

Ans:- Li, Na and K.

(ii). two elements having four electrons in their outermost shells.

Ans:- Ca, Si and Ge.

(iii). three elements with completely filled shells.

Ans:- Elements in group zero i.e H, Ne, Ar, Kr.

7. Fluorine, chlorine and bromine belongs to group 17 of the periodic table. What similarity is there in the atoms of these elements?

Ans:- All of them have 7 valence electrons each.

8. By considering their position in the periodic table, which of the following elements is expected to have maximum metallic character? In, Sn, Sb, Te, I.

Ans:- All of them in the 5th period of the periodic table but different groups.

In group 13, Sn group 14, Sb group 15, Te group 16 and I group 17.

   Therefore, the element in the leftmost i.e Indium will have maximum metallic character.

9. How would be the tendency to gain electrons change as we go from left to right across a period?

Ans:- As we go from left to right across a period, the tendency to gain electrons increases.

10. How would be the tendency to gain electrons change as we go down a group?

Ans:- As we go down a group, the tendency to gain electrons decreases.

11. Why is non-metals are found on the right hand side of the periodic table towards the top?

Ans:- As the non-metallic character of elements increases as

   i. from left to right along a period, and

ii. from down to upwards along a group.

So, non-metals are found on right hand side towards top of the periodic table increases non-metallic character.

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