Hssive-Xi-Chem-3. Classification of Elements Q & A
Hssive-Xi-Chem-3. Classification of Elements Q & A
Hssive-Xi-Chem-3. Classification of Elements Q & A
7. (a) Give the IUPAC name of the element with Atomic number 117. (1)
(b) In the modern periodic table elements in a given group have similar chemical properties. Give reason. (1)
Ans: (a) Ununseptium (Uus)
(b) Elements in a given group have same no. of valence electrons. So they have similar chemical properties.
8. Account for the following :
(a) The ionic radius of fluoride ion (F-) is 136 pm, while the atomic radius of fluorine (F) is only 64 pm. (1)
(b) The second ionization enthalpy of an element is always greater than that of the first ionization enthalpy. (1)
[July 2019]
Ans: (a) This is due to greater electronic repulsion and lesser effective nuclear charge in F –.
(b) This is because it is more difficult to remove an electron from a positively charged ion than from a neutral atom.
9. 'Chlorine has the most negative electron gain enthalpy'. Justify the statement. (2)
Ans: This is because, when an electron is added to F, it enters into the smaller 2nd shell. Due to the smaller size, the
electron suffers more repulsion from the other electrons. But for Cl, the incoming electron goes to the larger 3rd
shell. So the electronic repulsion is low and hence Cl adds electron more easily than F.
10. Identify the positions of Al (z=13) and S (z=16) in the periodic table with the help of their electronic configurations.
Predict the formula of the compound formed between them. (2) [March 2019]
2 1
Ans: 13Al – [Ne] 3s 3p , Period – 3, Group - 13
What conclusion can you derive from the graph regarding the first ionization enthalpies of alkali metals and
noble gases? Justify your answer. (2)
b) Aluminium forms [AlF6]3- whereas boron cannot form [BF6]3- but forms [BF4]- even though both belong to the
same group. Explain. (2) [October 2015]
Ans: a) In a period, the alkali metals have the least ionisation enthalpy and the noble gases have the most. This
is because after the removal of only one electron from the valence shell, alkali metals get the stable completely
filled electronic configuration. So they have low ionisation enthalpy. Noble gases have stable octet
configuration. So they have high ionisation enthalpy.
b) Due to the presence of vacant d orbitals in Al, Al can extend its covalency beyond 4. So it can form [AlF6]3-. But
in B, there is no vacant d-orbitals. So its maximum covalency is 4.
21. a) Transition elements were placed in groups 3 and group 12 of the periodic table. Give any two characteristics of
transition elements. (2)
b) Does the ionization enthalpy decrease along a group? Give reason. (2) [August 2014]
Ans: a) Transition metals are all metals. They form coloured compounds or ions. They show variable oxidation states
and valencies. Most of them are paramagnetic and show catalytic properties.
b) Yes, the ionization enthalpy decreases down a group due to increase in atomic size and shielding effect.
22. a) The first member of a group of elements in the s and p block differs from the rest of the family in chemical
behaviour. Write any one reason for this. (1)
b) Write the general electronic configuration of d-block elements. (1)
Ans: a) Due to decrease in atomic size and increase in nuclear charge across a period.
b) B and O have lower ionisation enthalpy than expected. This is because after the removal of one
electron, B gets the stable fully filled configuration and O gets the stable half filled configuration.
24. a) The IUPAC has made some recommendations to name elements with atomic numbers above 100. What would
be the name for the element with atomic number 104? (1)
b) Electro negativity is the ability of an element to attract shared pair of electrons. Name a numerical scale of
electro negativity of elements. (1)
c) Give reason for the following:
i) Phosphorus forms PCl5 while nitrogen cannot form NCl5. Why? (1)
ii) The first ionization enthalpy of oxygen is smaller compared to nitrogen. (1) [September 2013]
Ans: a) Unnilquadium (Unq)
b) Pauling’s electronegativity scale
c) i) Due to the absence of vacant d-orbitals in N
ii) Ref. qn. No. 6 (a)
25. a) Electron gain enthalpy is the amount of energy released when an isolated gaseous atom accepts an electron to
form a mono-valent anion.
The values of electron gain enthalpy with atomic number of halogens are given below:
Element At. No. ∆egH in kJ/mol
F 9 328
Cl 17 349
What do you observe from the graph? Give justification for your observation. (2) [March 2012]
Ans: a) The modern periodic law states that the properties of elements are the periodic functions of their atomic
numbers.
b) Unnilennium (Une)
c) Down a group, the ionisation enthalpy decreases. This is due to the increase in atomic size and shielding effect.
27. a) A graph showing the variation of atomic radius with atomic number for alkali metals is given below.
Comment on the variation of atomic radius with increase in atomic number in a group. Give reason. (2)
b) What is meant by isoelectronic species? (1)
c) Select the isoelectronic species from the following. N, O2-, F-, Mg2+, Al2+, Na+ (1) [October 2011]
Ans: a) Down a group, the atomic size increases due to increase in no. of shells and shielding effect.
b) They are species having same no. of electrons.
c) O2-, F-, Mg2+and Na+
28. A graph of atomic radius verses atomic number is given below:
CLASSIFICATION OF ELEMENTS - Prepared by ANIL KUMAR K L, GHSS ASHTAMUDI, KOLLAM Page 5