case /data -based (4 Marks)

Question 14 Marks

Read the following and answer any three questions from (i) to (iv).
The distance between the centre of the nucleus and the outermost shell of electrons is known as atomic radius. On moving from left to right along a period, atomic radii decrease because effective nuclear charge increases. For example, the atomic size decreases regularly from Li to F in the second period and from Na to Cl in the third period. It may, however, be noted that in any period, the noble gas has the largest size. On moving down in a group, atomic radii increase.

Write the maximum atomic radius?
Which element is the smallest size in group 13?
why the atomic radius decreases as we move across a period?

OR
A) ln the third period of the periodic table, Which element has the smallest size?
b) define atomic radius?

Answer

Explanation:
ln general, the atomic radii decrease along a period and increase down a group

Atom	12Mg	13AI	14Si	15P
Radius (pm)	160	143	118	110

Thus, Mg has maximum atomic radius.

(d) Boron.

Explanation:
Boron is the first element of group 13, hence it is smallest in size.

Explanation:
Effective nuclear charge increases along a period and due to addition of electrons in the same shell it causes the incoming electron to experience more force of attraction by the nucleus. Therefore, the size of the atom decreases.

Explanation:
Atomic size decreases across the period. Cl has smaller size than Ar. Argon has larger atomic size as compared to Cl due to the inert nature (it has completely filled outer shell).

(a) F, O, C, Cl, Br

Explanation:
Atomic size decreases from left to right in a period and increases from top to bottom in a group. Thus, the order is F < 0 < C < Cl < Br

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Question 24 Marks

Read the following and answer any three questions from (i) to (iv).After the discovery of large number of elements it became necessary to classify them and arrange them in a regular manner in order of their periodic properties. ln 1817, Johann Wolfgang Dobereiner tried to arrange the elements with similar properties into groups. He identified some groups of three elements having similar physical and chemical properties, known as Dobereiner's triads.
ln 1865, John Newlands arranged all known elements in the order of increasing atomic masses and found that the properties of every eighth element are similar to the properties of the first element.

If Cl, Br, I is a Dobereiner's triad and the atomic masses of Cl and I are 35.5 and 127 respectively, then what is the atomic mass of Br?
give examples of Dobereiner's triad?
a) A and B are two elements having similar properties which obey Newlands' law of octaves. How many elements are there in between A and B?

b) According to the Newlands' law of octaves, the properties of magnesium are similar to whom?

OR
On what basis the elements are arranged in Dobereiner's triad explain in brief.

Answer

Explanation:

ln a triad, the atomic mass of the central atom is near average of the atomic masses of the other two atoms. ln the triad, Cl, Br, I, the mass of Br will be the average mass of Cl and I.

Atomic mass of bromine $=\frac{35.5+127}{2}=81.25$

(b) Li, Na, K

Explanation:

Li, Na, K is a Dobereiner's triad. The atomic mass of middle element is approximately the arithmetic mean of the atomic masses of other two elements of the triad.

(d) 6

(a) Beryllium.

Explanation:

Properties of magnesium are similar to those of beryllium because magnesium is eighth element starting from beryllium.

(b) Atomic mass.

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Question 34 Marks

Read the following and answer any three questions from (i) to (iv)."Properties of elements are the periodic function of their atomic numbers." This is known as modern periodic law. It means that the properties of elements depend on their atomic numbers, and the elements are given positions in the periodic table on the basis of their increasing atomic number. Atomic number determines the distribution of electrons in the orbit, and electrons of the outermost orbit determine the properties of an element. There are 18 groups (vertical columns) and 7 periods (horizontal lines) in modem form of the periodic table. The number of the period is equal to the number of shells in the atoms of the elements belonging to that period.

What is the atomic number of elements of period 3 and group 17?
What is modern periodic law?
An element has a mass number of 40 and contains 20 neutrons in its atom. To which period and group of the periodic table does it belong?

OR
A) An element 'X' has an atomic number of 16. which of the elements will it show similarly?

B) Write the characteristics of the modern periodic table.

Answer

Explanation:

The element is chlorine (Z = 17).

(a) 3, 2

Explanation:

The element (sulphur) belongs to third period and its valency is 2.

Explanation:

Atomic number of the element= 40- 20 = 20 Electronic configuration of the element is 2, 8, 8, 2; i.e., the element is calcium which belongs to 4th period and 2nd group of the periodic table.

Explanation:

The element is sulphur. Sulphur and oxygen belong to group 16.

(d) All of these.

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Question 44 Marks

Read the following and answer any three questions from (i) to (iv).All the elements on the left side and in the middle of the periodic table (except hydrogen) are metallic elements or metals. Also, majority of elements in periodic table are metals. ln the modern periodic table, the metals are separated from non-metals by a zig-zag line. Some non-metals are gases, some are liquids and rest are solids at room temperature. They generally differ from metals in appearance and in other physical properties. Some elements, that lie along the zig-zag line that separates metals from non-metals, have properties that fall between those of metals and non-metals. These elements are regarded as semi-metals or metalloids.

Define metals and non -metals?
state the groups contains metals, non-metals and metalloids?
what is a metalloids? give example.

OR
A) Why Silicon is a metalloids?

B) Which is the lightest metal?

Answer

Explanation:

S, P, N are non-metals while Mg, Al, K and Na are metals.

Explanation:

Group-14

(b) Sb

(a) Li

Explanation:

Li is the lightest metal.

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Question 54 Marks

Read the following and answer any three questions from (i) to (iv).ln 1913, Henry Moseley showed that the atomic number of an element is the more fundamental property than its atomic mass. Accordingly, Mendeleev's periodic law was modified and atomic number was adopted as the basis of modem periodic table.
ln this periodic table, the elements are arranged in increasing order of their atomic numbers.
There are 18 vertical columns in the periodic table which constitute 18 groups or families. The groups are numbered as 1, 2, 3, ... upto 18. All the members of a particular group have similar outer shell electronic configuration. There are seven horizontal rows of the periodic table, which are known as periods.

According to modern periodic law, the properties of elements are the periodic function of their __________
All the elements in a period in the periodic table have the same_____________.
a) Write the combinations of elements that belong to the same group?
b) The atoms of elements belonging to the same group of periodic table have same number of__________.

OR
ln the periodic table, the element with atomic numbers 16, 24, and 35 will be respectively placed in the which group.

Answer

Explanation:

According to modern periodic law, the properties of elements are the periodic function of their atomic numbers.

(d) Valence shell.

Explanation:

All the elements in a period have the same valence shell.

(a) N, P, As.

Explanation:

N, P and As belong to the same group (group 15).

(d) Electrons in outermost shell.

(b) Sixteen.

Explanation:

Element with atomic number 16 has electronic configuration 2, 8, 6. Hence, it will be placed in 10 + 6 = 16th group.

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Question 64 Marks

Read the following and answer any three questions from (i) to (iv).Mendeleev arranged the 63 elements known at that time in order of their ascending atomic masses and prepared a periodic table. Mendeleev's periodic table contains vertical columns called 'groups' and horizontal rows called 'periods'. Elements with similar properties were placed in same groups.
The basis of Mendeleev's classification is his periodic law, which states that:

Atomic mass is the fundamental property of elements.
The physical and chemical properties of elements are periodic function of their atomic masses.

Which metals are not placed in the eighth group of Mendeleev's periodic table?
ln Mendeleev's periodic table, gaps were left for the elements to be discovered later. Which of the elements found a place in the periodic table later?
What is mandeleev's periodic table?

OR
What is difference between mendeleev and modern periodic table?

Answer

(b) Na

(b) Eleventh.

(d) Germanium.

Explanation:

Scandium - eka-boron

Gallium - eka-aluminium

Germanium - eka-silicon

(b) Group Vlll like groups I-VII has been divided into two sub-groups A and B.

Explanation:

Group Vlll consists of three triads such as Fe, Co, Ni; Ru, Rh, Pd and Os, Ir, Pt arranged in 4th, 5th and 6th periods respectively.

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Question 74 Marks

The picture shows a part of the periodic table.

8. Which element has the highest metallic property?
A. F
B. Al
C. K
D. Fe
9. Which element shows the properties of both metals and non-metals?
A. H
B. Ne
C. Mg
D. As
10. Which of these oxides is acidic in nature?
A. So₂
B. CaO
C. Al₂O₃
D. Fe₂O₃

Answer

8. C. K
9. D. As
10. A. So2

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Question 84 Marks

The picture shows an incomplete periodic table.
Arrow 1 and arrow 2 indicate increase or decrease in chemical properties.

7. What do arrow 1 and arrow 2 represent?

	Arrow 1	Arrow 2
A.	Decrease in atomic mass	Increase in atomic radius
B.	Increase in atomic radius	Increase in electronegativity
C.	Increase in electronegativity	Decrease in atomic radius
D.	Decrease in atomic radius	Decrease in atomic mass

Answer

7. B. Increase in atomic radius/Increase in electronegativity

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Question 94 Marks

The picture shows the modern periodic table.

3. What do the columns (X) and rows (Y) stand for in the periodic table?
X =
Y =
4.Which of these columns in the periodic table contains chemically inert elements?
A. X1
B. X2
C. X13
D. X18
5. What is the order of arrangement of elements in the periodic table?
A. Increase in valency
B. Decrease in atomic mass
C. Increase in atomic number
D. Decrease in the number of atomic shells
6. What does the position of an element in the periodic table indicate?
Circle ‘Yes’ or ‘No’ for the correct response.

Does the position of an element in the periodic table show this?	Yes or No
How reactive the element is?	Yes/No
What is the boiling point of the element?	Yes/No
What is the number of atomic shells in the element?	Yes/No

Answer

3. Mentions X as Groups and Y as Periods.
4. C. Dmitri Ivanovich Mendeléev
5. C. Increase in atomic number
6. Mentions all three responses correctly.
Yes
No
Yes

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Question 104 Marks

2. The Law of Octaves stated that – “when the elements are arranged in the order of increasing atomic masses, every eighth element had properties similar to that of the first”.
Why was the Law of Octaves not applicable to all elements?

Answer

2. Mentions that Law of Octaves does not hold true for heavier elements.

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Question 114 Marks

1. Which scientist first proposed the periodic table of elements?
A. Niels Bohr
B. John Newlands
C. Dmitri Ivanovich Mendeleev
D. Johann Wolfgang Dobereiner

Answer

1. C. Dmitri Ivanovich Mendeléev

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Science case /data -based (4 Marks)

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