2. Periodic Classification Of Elements

Question 1

What is total number of elements

Answer 1

118

Question 2

Information of Dobereiner’s Triads

Answer 2

In the year 1817 a German scientist Dobereiner made groups of three elements each, having similar chemical properties and called them triads.He arranged the three elements in a triad in an increasing order of atomic mass and showed that the atomic mass of the middle element was approximately equal to the mean of the atomic masses of the other two elements. However, all the known elements could not be classified into the Dobereiner’s triads.

Question 3

Definition of Triads

Answer 3

In the year 1817 a German scientist Dobereiner made groups of three elements each, having similar chemical properties and called them triads.

Question 4

Give examples of Triads

Answer 4

1. Li, Na K (Lithium,Sodium,Potassium) = 23.0
2. Ca, Sr, Ba (Calcium,Strontium, Barium) = 88.7
3. Cl, Br, I (Chlorine,Bromine,Iodine) = 81.2

Question 5

Actual mass of Na (Sodium)

Answer 5

23.0

Question 6

full name of Na

Answer 6

Sodium

Question 7

Full name of Sr

Answer 7

Strontium

Question 8

Full name of Br

Answer 8

Bromine

Question 9

Actual mass of Sr

Answer 9

87.6

Question 10

Mean of Dobereiner’s triads = ?

Answer 10

a+c/2

Question 11

H

Answer 11

Hydrogen

Question 12

Li

Answer 12

Lithium

Question 13

Be

Answer 13

Beryllium

Question 14

Na

Answer 14

Sodium

Question 15

Mg

Answer 15

Magnesium

Question 16

He

Answer 16

Helium

Question 17

B

Answer 17

Boron

Question 18

C

Answer 18

Carbon

Question 19

N

Answer 19

Nitrogen

Question 20

O

Answer 20

Oxygen

Question 21

F

Answer 21

Fluorine

Question 22

Ne

Answer 22

Neon

Question 23

Al

Answer 23

Aluminum

Question 24

Si

Answer 24

Silicon

Question 25

P

Answer 25

Phosphorus

Question 26

S

Answer 26

Sulphur

Question 27

Cl

Answer 27

Chlorine

Question 28

Ar

Answer 28

Argon

Question 29

K

Answer 29

Pottasium

Question 30

Ca

Answer 30

Calcium

Question 31

Sc

Answer 31

Scandium

Question 32

Merits of mendeleev’s periodic table

Answer 32

1. Atomic masses of some elements were revised so as to give them proper place in the Periodic Table in accordance with their properties ex. Atomic mass of beryllium, 14.09 was changed to the correct value 9.4 and beryllium was placed before boron.
2. Mendeleev kept vacant places in the Periodic Table for elements not discovered till yet. Three unknown elements were given names : eka-boron, eka-aluminium and eka-silicon.
3. Mendeleev created the ‘zero’ group without disturbing the original Periodic Table in which the noble gases were fitted very well

Question 33

Demerits of Mendeleev’a Periodic Table

Answer 33

1. The whole number atomic mass of the elements cobalt (Co) and Nickel (Ni) is the same. Therefore there was an ambiguity regarding their sequence in mendeleev’s period table.
2. As isotopes have the same chemical properties but different atomic masses, a challenge was posed in placing them in mendeleev’s Periodic Table
3. When elements are arranged in an increasing order atomic masses, the rise in atomic mass does not appear to be uniform.
4. Position of hydrogen : hydrogen shows similarities with halogens (group VII) and also with the alkali metals (group I). On considering the above properties it can not be decided whether the correct position of hydrogen is in the group of alkali metals (GROUP I) or in the group of halogens (GROUP VII).

Question 34

What is modern Periodic law?

Answer 34

‘Properties of elements are a Periodic function of their atomic numbers.’

Question 35

Who made the modern Periodic table?

Answer 35

An English scientist ‘Henry Moseley’ in the A.D. 1913 with the help of experiments done using X-ray tube

Question 36

The long form of Periodic table is called what?

Answer 36

The modern Periodic table

Question 37

Drawback of modern Periodic table

Answer 37

The ambiguity about the position of hydrogen is not removed even in the modern Periodic table

Question 38

The total number of electrons in an atomic is same as the _____________________

Question 39

How many periods does modern Periodic table contain?

Answer 39

7

Question 40

What are horizontal rows called in the modern Periodic table?

Answer 40

The periods

Question 41

What are vertical columns are called in the modern Periodic table?

Answer 41

The groups

Question 42

What are called lanthanide and actinic series in the modern Periodic table?

Answer 42

Apart from the seven periods, two rows are shown separately at the bottom of the Periodic Table. There are called lanthanide and actinide series.

Question 43

Name the four blocks in the modern Periodic table

Answer 43

S-block, p-block, d-block and f-block

Question 44

What are d-block elements called?

Answer 44

Transition elements

Question 45

As we go down a group, the number of shells goes on __________

Answer 45

Increasing

Question 46

Uranium has atomic number _____

Answer 46

92

Question 47

What is called as valency?

Answer 47

The valency of an element is determined by the number of electrons present in the outermost shell of its atoms, that is, the valence electrons.