5 periodic classification of elements

Periodic Classification of Elements

Which of the following statements is not a correct statement about the trends

when

a) Going from left to right across the periods of periodic Table

b) The elements

c) The number of valence electrons increases.

d) The atoms lose their electrons more easily.

e) The oxides become more acidic.

Solution:

As we move from left to right along a period in a periodic table, the elements

tend to be less metallic in nature, valence electrons increase gradually, the

oxides become more acidic in nature and the atoms gain electrons to attain

stable configuration. Hence, the incorrect statement is “The atoms lose their

electrons more easily”.

Become less metallic in nature.

Correct answer: C.

Element X forms a chloride with the formula XCl2, which is a solid with a high

Melting point. X would most likely be in the same group of the Periodic Table

as

(a) Na

(b) Mg

(c) AI

(d) Si

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Solution:

Mg forms MgCl2 with chlorine; hence, the element that forms XCl2, which is a

solid with a high melting point, belongs to the same group as Mg.

Correct Answer: B

Which element has?

a) Two shells, both of which are completely filled with electrons?

b) The electronic configuration 2, 8, 2?

c) A total of three shells, with four electrons in its valence shell?

d) A total of two shells, with three electrons in its valence shell?

e) Twice as many electrons in its second shell as in its first shell?

Solution:

a) The element with the first two shells completely filled is neon.

b) The element with the electronic configuration 2, 8, 2 is magnesium.

c) The element with 3 shells and 4 electrons in the valence shell is silicon.

d) The element with 2 shells and 3 electrons in the valence shell is boron.

e) The element with twice as many electrons in its second shell as in the first is

carbon.

a) What property do all elements in the same column of the Periodic Table as

boron have in common?

b) What property do all elements in the same column of the Periodic Table as

fluorine have in common?

Solution:

a) The elements belonging to the same column as boron in the Periodic Table

will have 3 valance electrons and a valency of 3.

b) All elements belonging to the same column as fluorine in the Periodic Table

will have same number of valance electrons and valency. They all have 7

valence electrons and their valency is 1.





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An atom has electronic configuration 2, 8, 7.

a) What is the atomic number of this element?

b) To which of the following elements would it be chemically similar?

(Atomic numbers are given in parentheses.)

N (7) F (9) P (15) Ar (18)

Solution:

a) The atomic number of the element with the electronic configuration 2, 8, 7

is 17.

b) The electronic configuration of N is 2, 5

F is 2, 7

P is 2, 8 , 5

Ar is 2, 8, 8

Hence, the elements with atomic number 17 will be chemically similar to F with

atomic number 9, since both have 7 electrons in their valence shell.

The position of three elements A, B and C in the Periodic Table are shown

below

Group 16 Group 17

- -

- A

- -

B C

a) State whether A is a metal or non-metal.

b) State whether C is more reactive or less reactive than A.

c) Will C is larger or smaller in size than B?

d) Which type of ion, cation or anion, will be formed by element A?





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Solution:

a) Non-metals lie on the right hand side of the Periodic Table, and group 17 is

also on the right hand side. Hence, A is a non-metal.

b) Group 17 has non-metals. The chemical reactivity of non-metals of decreases

down the group. Hence, C is less reactive than A.

c) The size of an atom decreases along a period. Hence, C will be smaller in size

than B

d) A is a non-metal. Non-metals gain electrons to form anions. Hence, A forums

an anion.

Nitrogen (atomic number 7) and phosphorus (atomic number 15) belong to

group 15 of the Periodic Table. Write the electronic configuration of these two

elements. Which of these will be more electronegative? Why?

Solution:

The electronic configuration of nitrogen is 2,5 and of phosphorous is 2, 8, 5.

Electro negativity decreases down a group. The nitrogen atom is smaller in size

compared to phosphorous, and has greater nuclear pull. Hence, it is more

electronegative than phosphorous.

How does the electronic configuration of an atom relate to its position in the

Modern Periodic Table?

Solution:

The electronic configuration of an element depicts its position in the periodic

table. The valence electrons represent the group, and the valence shell the

period. For example, X has an electronic configuration 2, 8, 5. X has 5 electrons

in the valance shell, and so belongs to the 5th group, and it has 3 shells, and

hence, belongs to the 3rd period.





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In the Modern Periodic Table, calcium (atomic number 20) is surrounded by

elements with atomic numbers 12, 19, 21 and 38. Which of these have physical

and chemical properties resembling calcium?

Solution:

The electronic configuration of calcium is 2, 8, 8, 2. The electronic

configuration of elements with atomic numbers

12 - 2, 8, 2

19 - 2, 8, 8, 1

21 - 2, 8, 8, 3 and

38 - 2, 8, 18, 8, 2

Thus, the elements with atomic number 12 and 38 will have chemical and

physical properties resembling calcium. This is because both have 2 electrons in

their valence shells, like calcium.

Compare and contrast the arrangement of elements in Mendeleev’s Periodic

Table and the Modern Periodic Table.

Solution:

Mendeleev's Periodic table Modern Periodic Table

Elements are arranged in increasing

order of atomic mass.

Elements are arranged in increasing

order of atomic number.

Has 8 vertical columns. Has 18 vertical columns.

No place for inert gases since they

were not discovered at that time.

Inert gases have a special place i.e,

group 18.

No place for isotopes. Isotopes are assigned the same place as

the respective elements since they

have the same atomic number.

Transitional elements are placed

arbitrarily in a group.

Transitional elements are placed in the

middle of the table.





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5 periodic classification of elements

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