Chapter 5 Periodic Classification of Elements Solutions
Question - 11 : - a) Lithium, sodium, potassium are all metals that react with water to liberate hydrogen gas. Is there any similarity in the atoms of these elements?
Answer - 11 : -
(b) Helium is an unreactive gas and neon is a gas of extremely low reactivity. What, if anything, do their atoms have in common?
Answer
They’ve one valence electron in their outermost shells and as a result of this, they are very unstable. So, they readily react with water to liberate hydrogen. They are also called alkali metals.
Their outermost shells are full leading to high stability. They react only in extreme circumstances and hence are called noble gases.
Question - 12 : - In the Modern Periodic Table, which are the metals among the first ten elements?
Answer - 12 : - Lithium and Beryllium are the metals among the first ten elements in Modern Periodic Table.
Question - 13 : - By considering their position in the Periodic Table, which one of the following elements -
Answer - 13 : - would you expect to have maximum metallic characteristic? Ga Ge As Se Be
Answer
Among the elements listed in the question. Be and Ga are expected to be most metallic. Out of Be and Ga, Ga is bigger in size and hence has a greater tendency to lose electrons than Be. Therefore, Ga is more metallic than Be.
Question - 14 : - Which of the following statements is not a correct statement about the trends when going from left to right across the periods of Periodic Table.
Answer - 14 : -
(a) The elements become less metallic in nature.
(b) The number of valence electrons increases.
(c) The atoms lose their electrons more easily.
(d) The oxides become more acidic
Answer
Correct answer is c . The atoms lose their electrons more easily.
The atoms lose their electrons more easily is a wrong statement because as we move from left to right across the periods of the periodic table, the non-metallic character increases.
Therefore, tendency to lose an electron decreases.
Question - 15 : - Element X forms a chloride with the formula XCl2, which is a solid with a high melting -
Answer - 15 : - point. X would most likely be in the same group of the Periodic Table as
(a) Na (b) Mg (c) AI (d) SiAnswer
(c) AI (d) Si
Also, Mg when combines chloride forms MgCl2.
Question - 16 : - Which element has?
Answer - 16 : -
(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?
Answer
a) Neon has two shells which are completely filled.
b) Magnesium has the electronic configuration 2, 8, 2
c) Silicon has a total of three shells, with four electrons in its valence shell
d) Boron a total of two shells, with three electrons in its valence shell
e) Magnesium has twice as many electrons in its second shell as in its first shell
Question - 17 : - (a) What property do all elements in the same column of the Periodic Table as boron have in common?
Answer - 17 : -
(b) What property do all elements in the same column of the Periodic Table as fluorine have in common?
Answer
(a) All the elements which lie in me same column as that of boron belong to group 13. Therefore, they have three electrons in their respective valence shells. Except, boron which is a non-metal, all other elements (i.e., aluminum, gallium, indium and thallium) in this group are metals.
(b) All elements in the same column of the Periodic Table as fluorine have in common three electrons in their valence shell and they all are belong to group thirteen.
Question - 18 : - An atom has electronic configuration 2, 8, 7.
Answer - 18 : -
(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)
Answer
(a)The element with electronic configuration (2+8+7) 17 is chlorine.
The no. of atomic number = no. of electrons
Therefore, atomic number is 17.
(b) An atom with electronic configuration 2, 8, 7 would be chemically similar to F (9)
Question - 19 : - The position of three elements A, B and C in the Periodic Table are shown below–
Group 16 Group 17
Answer - 19 : -
– –
– 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 be larger or smaller in size than B?
(d) Which type of ion, cation or anion, will be formed by element A?
Answer
1. Element A is a non-metal
2. Element C is less reactive than Element A
3. C is smaller in size than B
4. A will form anion
Question - 20 : - Nitrogen (atomic number 7) and phosphorus (atomic number 15) belong to group 15 of the Periodic Table.
Answer - 20 : - Write the electronic configuration of these two elements. Which of these will be more electronegative? Why?
Answer
Atomic number of Nitrogen is 7 hence Electronic configuration of Nitrogen is 1s2 2s2 2p3
Atomic number of Nitrogen is 15 hence Electronic configuration of Phosphorous is 1s2 2s2 2p6 3s2 3p3
On moving down a group in the periodic table, the number of shell increases. Due to this, valence electrons move away from the electrons and the effective nuclear charge decreases. This causes the decrease in the tendency to attract electron and hence electro negativity decreases. Because of all these reasons Nitrogen is more electronegative than phosphorus.