Worksheet with Solutions: Classification of Elements and Periodicity in Properties | Chemistry Class 11 - NEET PDF Download

Answer: calcium

Answer: atomic masses

Answer: vertical columns

Answer: periods

Answer: nine

Ans: (b) groups
Explanation: The vertical columns in the periodic table are termed as groups.

Ans: (b) 8
Explanation: The valence shell configuration of Z=26 is [Ar] 3d⁶ 4s². That for the group of element is 6 + 2 = 8.

Ans: (a) halogens
Explanation: The elements of atomic numbers 9, 17, 35, 53, 85 are respectively F, Cl, Br, I, At etc are called halogen.

Ans: (b) 1s² 2s² 2p⁶ 3s¹
Explanation: Ionisation enthalpy is the amount of energy required when an electron is removed from the outermost orbit of an isolated gaseous atom. Electronic configuration of 1s² 2s² 2p⁶ 3s¹ has the lowest ionisation enthalpy.

Ans: (a) The Ionic radius of cation is always less than the atomic radius. 
Explanation: Cation is formed by the loss of electrons. So that the effective nuclear charge increases as a result ionic radius decreases.

Answer: (c) Assertion is correct, reason is incorrect
Exaplanation: The assertion is true because the second period of the periodic table contains 8 elements. However, the reason is incorrect. The correct statement should be: "The number of elements in each period is twice the number of atomic orbitals available in the energy level being filled." The second period corresponds to the filling of 2s and 2p orbitals, which gives 8 elements, not four times the number of orbitals.

Answer: (d) Assertion is incorrect, reason is correct.
Exaplanation: The assertion is not true as it talks about equal gaps in atomic masses, which is not a correct representation of triads. The reason is true and correct: In a triad, the middle element’s atomic mass is the average of the first and third elements' atomic masses. This is part of Döbereiner's triad law.

Answer: (c) Assertion is true but reason is false.
Exaplanation:  The assertion is correct because, in general, smaller atoms have greater electronegativity (due to the stronger attraction of electrons in smaller atoms). However, the reason is incorrect. Electronegativity refers to an atom's tendency to attract electrons in a bond, not to share electrons.

Answer: (d) Assertion is incorrect, reason is correct.
Exaplanation: The assertion is incorrect. Mendeleev's periodic table was based on atomic masses, not atomic numbers. The reason is correct as atomic number is indeed the number of protons in an atom, but it does not directly explain Mendeleev's theory.

Answer: (a) Assertion is correct, reason is correct; reason is a correct explanation for assertion.
Exaplanation: Both the assertion and the reason are correct. Ununbium (Uub) is the former name for element 112, and the prefix "un-" means "one" and "bi-" means "two" in Latin, which explains the naming convention for the element.

Answer: This is due to the small size of the fluorine atom. As a result of the strong interelectronic repulsions in fluorine’s relatively small 2p orbitals, the incoming electron does not experience much attraction.

Answer: All transition metals are d-block elements, but not all d-block elements are transition elements because all d-block elements that do not have completely filled d- orbitals are not counted as transition elements, making such elements exceptional. Zn, Cd, and Hg are a few examples.

Answer: For element having atomic number 119:

Group – 1, Valency – 1, Outermost electronic configuration – 8s¹ and the general formula of the oxide will be M₂O.

Answer: Among the elements, B, Al, C and Si

(i) The element that has the highest first ionisation enthalpy is C.

(ii) The element that has the most metallic character is Al.

Answer: The outermost electronic configuration of nitrogen is 2s² 2p_x¹, 2p_y¹, 2p_z¹ whereas that of oxygen is 2s² 2p_x², 2p_y¹, 2p_z¹. 
Since oxygen acquires a stable configuration, i.e., 2p³, by removing one electron from the 2p-orbital, it has a lower ionisation enthalpy than nitrogen. In the case of nitrogen, however, due to its stable configuration, it is difficult to remove one of the three 2p-electrons.

Answer: (i) S< P< O< N is the accurate, increasing order of the first ionisation enthalpy.

On going down the group, the ionisation enthalpy decreases, and as we move along the period, then it increases; however, in the case of oxygen and nitrogen, because of the half-filled stability of 2p orbitals of nitrogen, it has the higher ionisation enthalpy than oxygen.

(ii) P<S<N<O is the accurate, increasing order of non-metallic character.

Moving down the group, we will see non-metallic character decrease as the effective nuclear charge on the outermost shell decreases, which helps to gain an electron. The effective nuclear charge increases moving along the period, increasing the non-metallic character.

Answer: Mendeleev organised the components in his periodic table according to the order of their atomic weight. He organised the components in groups and periods according to the increment order of atomic weight. He placed the elements with equal properties in the same group.

So, he did not stick to this arrangement for long. He discovered that if the elements were organised according to their increasing atomic weights, thus some of the elements didn’t fit in with his classification scheme.

Thus, he ignored the order of atomic weights in some cases. For example, the atomic mass of the iodine is lower than the atomic mass of the tellurium.

Still, Mendeleev set tellurium (in the Group 6) ahead of iodine (in Group 7)  along with fluorine, chlorine, and bromine because of similarities in properties.

Answer: In the periodic table containing elements, a period shows the value of a principal quantum number (n) for the outermost shells. Every period starts with filling the principal quantum number (n). The value for n for the 6th period is equal to 6. then, for n = 6, the azimuthal quantum number (l) could have “0, 1, 2, 3, 4” values.

According to  Aufbau’s principle, electrons have been added to the various orbitals in order of their  increasing energies. Here, the 6d subshell has much higher energy than the energy of the 7s subshell.

In the sixth period, the electrons could fill in only  6s, 4f, 5d, and 6p subshells. 6s has only one orbital, 4f has seven orbitals, 5d has five orbitals, also 6p has three orbitals. Therefore, there are a sum of 16 (1 + 7 + 5 + 3 = 16) orbitals available. As per Pauli’s exclusion principle, each orbitals can accommodate a maximum of  2 electrons.

Hence, sixteen orbitals can accommodate a maximum of 32 electrons.

So, the 6th period of the periodic table should have 32 elements.