Q 1 – Upto which element the law of octaves was found to be applicable.?
(a) oxygen
(b) Carbon
(c) cobalt
(d) potassium
New lands law of octaves was applicable only to lighter elements having atomic masses up to 40 u i.e., up to calcium. Every eighth element did not possess properties similar to that of the first element.
Q 2 – Which of the following is the outermost shell for elements of the period.?
(a) K shell
(b) L shell
(c) M shell
(d) N shell
The elements of the 2nd period involve the filling of the 2nd shell i.e., L shell. Because in period 2 there are two shells JK and l.
Q 3 – What type of oxide would Eka – aluminum From?
(a) EO3
(b) E3O2
(c) E2O3
(d) EO
Gallium has a valiancy of 3. Hence it forms an oxide having molecular formula E2O3 in other options, valiancy of E is not 3.
Q 4 – Which of the following set of elements is written in order of their increasing metallic charter?
(a) Be, Mg, Ca
(b) Na, Li, K
(c) Mg, Al, Si
(d) C,O, N
Metallic Charter increases down a group and decreases along a period. Thus metallic charter increases in the order Are, Mg, Ca as they Belong to the same group.
Q 5 – According to Mendeleev’s Periodic law, the elements were arranged in the periodic table in the order of
(a) increasing atomic number (b) decreasing atomic numbers
(c) increasing atomic masses (d) decreasing atomic masses
According to Mendeleev’s periodic law, the elements were arranged in the periodic table in the order of increasing atomic masses.
Q 6 – Which of the following gives the correct increasing order of the atomic radii of 0, F, and N?
(a) O,F, N (b) N,F,O (c) O,N,F (d) F,O, N
As we move from left to right in a period, the atomic number of each succeeding element increases by 1. So, the electrons are attracted close to the nucleus, and hence, the atomic size decreases, along a period from left to right.
Therefore the increasing order of radii is F, O, N as the atomic numbers of F, O, and 9,8 and 7 respectively. Due to which F belongs to 17th group O belongs to 16th group and N belongs to 15th group.
Q 7 – Three elements B, Si and Ge are
(a) Metals
(b) Non-metals
(c) metalloids
(d) Metal, Non-metal, and metalloid respectively
The elements boron (B) silicon (Si) and germanium (Ge) are metalloids. In the periodic table, metals have been separated from non-metals by some elements called ‘metalloids’ which are placed diagonally in the periodic table. These metalloids are B. Si, Ge, As (arsenic), Sb (antimony), Te (tellurium), and Po polonium.
Q 8 – Which group of elements could be placed in Mendeleev’s periodic table without disturbing the original order? Give reason.
The noble gases could be placed in a new group without disturbing the existing order because they were inert and present in extremely low concentrations in our atmosphere.
When Mendeleev grave his periodic table at that time noble gases such as helium (He), neon(Ne) argon (Ar), Krypton (Kr) xenon (Xe), and radon (Rn) were not known when these gases were discovered much later, these were placed in a new group called the Zero group.
Q 9 – On Moving from left to right in a period in the periodic table, the size of the atom?
(a) increases
(b) decreases
(c) dose does not change appreciably
(d) first, decrease and then increases
Due to the large positive charge on the nucleus, the electrons are pulled in closely to the nucleus, and the size of the atom decreases. However, the size of an atom of inert gas is bigger than that of the preceding halogen atom the greater size of the inert gas atom in a period is due to the structural stability of its outermost shell consisting of an octet of electrons.
Q 10 – IF an element X is placed in group 14 what will be the formula and the nature of bonding of its chloride.?
Element X is Placed in group 14. Therefore its electronic configuration is 2,8,4
∴ Number of valence electrons is 4.
Further, Since it is difficult to lose all the four valence electrons or gain four more electrons.
Therefore, it prefers to share these four electrons to acquire the stable electronic configuration of the nearest inert gas.
Thus, the nature of the chloride of element X is covalent. Its chloride will be XCI4
Q 11 – Which of the following statements about the modern periodic table is correct?
(a) It has 18 horizontal rows known as periods
(b) It has 7 vertical columns rows known as periods
(c) It has 18 vertical columns known as groups
(d) It has 7 horizontal rows known as groups
The modern periodic table has 18 vertical columns, known as groups, and 7 horizontal rows known as periods.
Q 12 – Name two elements whose properties were predicted on the basis of their positions in Mendeleev’s periodic table.
Gallium (Eka-aluminium) and germanium (Eka-silicon).
Q 13 – Write the formulae of chlorides of Eka-silicon and Eka-aluminium, the elements predicted by Mendeleev.
Ans. Eka-aluminium represents gallium (Ga) with valency three and Eka-silicon is for germanium (Ge) with valency four. The formulae of their respective chlorides are GaCl3 and GeCl4.
Q 14 – How many elements are there in period 2?
Eight (8).
Q 15 – Name all the elements present in group-17 of the Modern Periodic Table
F, Cl, Br, I, At.
Q 16 – Why are the elements calcium, strontium, and barium named as alkaline earth?
. These elements are called alkaline earth because their oxides are alkaline in nature and exist in the earth.
Q 17 – Give the name and electronic configuration of the second alkali metal.
The second alkali metal is sodium (Na). Its electronic configuration is 2, 8, 1.
Q 18– What are Metalloids?
Those elements which show some properties of both metals and non-metals are called metalloids. Examples: Boron, Silicon, Germanium, Arsenic, Antimony, Tellurium, and Polonium.
Q 19 – In the Modern Periodic Table, which are the metals among the first ten elements?
Lithium (Li), Beryllium (Be), and Boron (B) are the metal elements among the first ten elements in the Modern Periodic Table.
Q 20 – The formula of magnesium oxides is MgO. Write the formula of magnesium chloride.
Oxygen is divalent in nature. The valency of magnesium in magnesium oxide is + 2. The formula of magnesium chloride is MgCl2 since chlorine has a valency equal to one.
Q 21 – State whether the following statement is true or false?
The valency of an element of group 17 is 7.
This statement is wrong. The number of valence electrons in an element of group 17 = 17 – 10 = 7.
Therefore, the valency of the element = 8 – 7 = 1.
Q 22 – The two isotopes of chlorine have atomic mass 35.4 and 37.4. Should they be placed in separate slots in the modern periodic table?
No, they should be placed in the same slot because the modern periodic table is based on the atomic number of the elements.
Q 23 – Element ‘Y’ with atomic number 3 combines with element ‘A’ with atomic number 17. What will be the formula of the compound?
The electronic distribution in elements ‘A’ and ‘Y’ are 2, 1 and 2, 8, 7 respectively. Both have valency equal to 1. The formula of the compound is AY.
Q 24 – The three elements A, B, and C with similar properties have atomic masses X, Y, and Z respectively. The mass of Y is approximately equal to the average mass of X and Z. What is such an arrangement of elements called? Give one example of such a set of elements.
The arrangement of these elements is known as the Dobereiner triad. For Example, Lithium, sodium, and Potassium.
Q 25 – In group, I of the periodic table, three elements X, Y, and Z have atomic radii 1.33 A, 0.95 A, and 0.60 A respectively. Arrange the elements (X, Y, and Z) in the increasing order of atomic number and mention a suitable reason for it.
In a given group, the atomic radii increase on moving down the group. Therefore, the arrangement of the given elements in the increasing order of their atomic numbers is as follows: Z, Y, X.
Q 26 – If an element X is placed in group 14, what will be the formula and the nature of bonding of its chloride?
Since element “X’ is placed in group 14, therefore, its valency is 14 – 10 = 4. Further, since it is difficult to either lose all the four valence electrons or gain four more electrons, therefore, it prefers to share these four electrons to acquire the stable electronic configuration of the nearest inert gas. Its formula will be XCl4. Thus, the nature of the chloride of element ‘X’ is covalent.
Q 27 – Explain clearly, why an atomic number of an element is most important to the chemist than its relative atomic mass.
The atomic number corresponds to the number of electrons in an atom or it reflects the electronic configuration of the element. The elements having similar electronic configurations can then be placed together in the same group, it helps in the systematic classification of elements.
Q 28 – Write two reasons responsible for the late discovery of noble gases.
- Noble gas elements were not present in earth crust as minerals like other elements and were present in air to a very small extent.
- Their atoms have stable electronic configuration of their outermost shells also called valence shells. (2 in case of He and 8 for other elements). They do not combine with atoms of other elements.
Q 30 – Na, Mg, and Al are the elements of the same period of Modern Periodic Table having one, two and three valence electrons respectively. Which of these elements (i) has the largest atomic radius, (ii) is least reactive? Justify your answer stating the reason for each case.
(1) Na has the largest atomic radius because on moving from left to right in the periodic table, the atomic radius decreases due to an increase in positive charge on the nucleus which pulls the outermost electrons close to the nucleus, and the size of the atom decreases.
(2) Al is least reactive because on moving from left to right in the periodic table the nuclear charge increases and the valence electrons are pulled in closely to the nucleus. Therefore, the tendency to lose electrons decreases, and hence reactivity decreases.