Science and Technology - Unit Test 1
School of Elements
Answer Paper
Time: 1 Hr. 30 min.----------------------------------------------------------------------------------------------------------Max. Marks: 40
Note 1). All questions are compulsory.
Note 2). Draw diagrams wherever necessary.
Q. 1. A. Answer the following.
(5 marks)
i. Match the pairs. (2 marks)
Question :
Column A
Column B
Group 1
Halogens
Group 2
Alkali metals
Group 17
Metalloids
Group 18
Alkaline earth metals
Noble gases
Answer :
Column A
Column B
Group 1
Alkali metals
Group 2
Alkaline earth metals
Group 17
Halogens
Group 18
Noble gases
ii. Name the following : (3 marks)
1. An element having a single electron in the outermost shell
An element having a single electron in the outermost shell : Li, Na, K, Rb, Cs, Fr
2. An element with filled outermost shell
An element with filled outermost shell : He, Ne, Ar, Kr, Xe, Rn
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3. An element having 7 electrons in the outermost shell
An element having 7 electrons in the outermost shell : F, Cl, Br, I, At
Q. 1. B. Rewrite the following statement by choosing the correct alternative.
(5 marks)
1. Outermost shell of halogens contains . . . . . . .
(a) 3 electrons
(b) 1 electron
(c) 7 electrons
(d) 5 electrons
Outermost shell of halogens contains 7 electrons.
2. The element eka-silicon in Mendeleev’s periodic table is known as . . . . . . in the modern periodic table.
(a) scandium
(b) gallium
(c) beryllium
(d) germanium
The element eka-silicon in Mendeleev’s periodic table is known as germanium in the modern periodic table.
3. The third row elements have . . . . . . shells.
(a) 3
(b) 7
(c) 0
(d) different number of
The third row elements have 3 shells.
4. The elements belonging to lanthanides and actinides are . . . . . . .
(a) noble gases
(b) normal elements
(c) inner transition elements
(d) transition elements
The elements belonging to lanthanides and actinides are inner transition elements.
5. The electronic configuration of aluminium is . . . . . . .
(a) (2,8,3)
(b) (2,8,8,3)
(c) (2,3)
(d) (2,8,7)
The electronic configuration of aluminium is (2,8,3).
Q. 2. Answer the following. (Any 5)
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(10 marks)
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1. Give scientific reason : Atomic size increases down the group.
Atomic size is determined using atomic radius. For an isolated atom, atomic radius is the distance between the centre
of atom and the outermost shell.
Down the group, new shells are added bringing outermost electrons farther from the nucleus. Thus, atomic radius
increases.
Hence, atomic size increases in a group from top to bottom.
2. Give scientific reason : Molecular formulae of chlorides of sodium and potassium are similar,while those of
sodium and magnesium are different.
Both sodium and potassium belong to the same group IA. As a result, they have the same number of valence electrons
and therefore similar chemical properties. Hence, molecular formulae of chlorides of sodium and potassium are similar
namely NaCl and KCl.
Sodium and magnesium belong to the same period but different group. Therefore the number of valence electrons in
each case is different and hence molecular formulae of chlorides of sodium and magnesium are different, namely NaCl
and MgCl2.
3. Complete the following table.
Element
Lithium Li
......
Potassium K
Atomic Mass
6.9
......
39
Element
Chlorine Cl
......
Iodine I
Atomic Mass
35.5
......
126.9
Element
Lithium Li
Sodium Na
Potassium K
Atomic Mass
6.9
23
39
Element
Chlorine Cl
Bromine Br
Iodine I
Atomic Mass
35.5
79.9
126.9
4. Give scientific reason : Valency varies gradually along a period.
As we go from left to right along a period , the atomic number goes on increasing. The electronic configuration
therefore varies as we go along the period.
The first element in a period has one electron in the outermost shell while the last element has outmost shell
completely filled.
Since the number of valence electrons varies along a period, the valency also varies gradually along a period.
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5. What is a metalloid ? Give two examples.
The element which shows the properties of metals as well as of nonmetals is called a metalloid. Metalloids lie on the
boundary between metals and non-metals.
Boron, Silicon and Germanium are examples of metalloids.
6. How were the positions of the isotopes of various elements decided in the modern periodic table? Explain
with an example.
Hydrogen has three isotopes - Hydrogen, Duterium, Tritium having atomic number 1 and atomic mass 1, 2, 3 resp. But
modern periodic table deals with only atomic number and not atomic mass. Hence, the position of isotopes is same as
hydrogen. Similarly in case of oxygen and chlorine, the position of isotopes is same as the element.
Q. 3. Answer the following. (Any 5)
(15 marks)
1. What were the limitations of Newlands’ octaves?
Limitations of Newlands’ octaves :
i. Newland could arrange elements only upto calcium out of total 56 elements known at that time.
ii. After calcium, every eighth element did not possess properties similar to that of the first.
iii. Later on, several new elements were discovered, whose properties did not fit into the Law of Octaves.
iv. In order to fit elements into his Table, Newlands adjusted two elements in the same slot, but also put some unlike
elements under the same note. Cobalt and nickel are in the same slot and these are placed in the same column as
fluorine, chlorine and bromine which have very different properties than these elements. Iron, which resembles cobalt
and nickel in properties, has been placed far away from these elements.
v. This periodic table did not include inert (noble) gases because they were not discovered.
2. Name two elements you would expect to show chemical reactions similar to magnesium. What is the basis
of your answer?
Elements in the modern periodic table are arranged in increasing order of atomic numbers. Elements having same
number of valence electrons or having same outer electronic configuration are present in the same group. Elements
present in the same group show similar chemical properties.
Be(Berillium), Ca(Calcium), Sr(stroncium) are the elements showing similar chemical properties of element Mg
because they belong to the same group.
3. Compare and contrast the arrangement of elements in Mendeleev’s periodic table and modern periodic
table.
Point of
Mendeleev’s periodic table
Modern periodic table
difference
Principle
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Properties of elements are the periodic
Properties of the element are the
function of their atomic weight.
periodic function of their atomic
number.
Arrangement of
Cobalt (atomic mass 58.9) is placed
Atomic number of cobalt and nickel are
elements
before Nickel (atomic mass 58.7). This
27 and 28 respectively. Therefore
is the demerit.
cobalt will come first and then Nickel,
although its atomic mass is greater.
Empty spaces
Mendeleev had left some empty
These places were filled up by the
spaces for the elements not known at
elements : germanium, gallium and
that time.
scandanium
4. There are two elements with atomic number 13 and 20. State the period and group of these elements with
reasons.
The element has 13 electrons. Hence, its electronic configuration would be (2,8,3).
It has three shells of electrons which indicates that the element belongs to period 3. Since it has three electrons in the
outermost shell the element belongs to group 3. Therefore, the element belongs to Period 3 and Group 3.
The element has 20 electrons. Hence, its electronic configuration would be (2,8,8,2).
It has four shells of electrons which indicates that the element belongs to period 4. Since it has two electrons in the
outermost shell the element belongs to group 2. Therefore, the element belongs to Period 4 and Group 2 .
5. Write name,symbol and atomic number of any two elements starting from C.
Atomic
Name
Symbol
Carbon
C
6
Chlorine
Cl
17
Calcium
Ca
20
number
6. Write symbol and atomic number of elements X,Y,Z shown in figure given below.
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Element X is Be with atomic number 4.
Element Y is He with atomic number 2.
Element Z is Al with atomic number 13.
Q. 4. Answer the following questions. (Any 1)
(5 marks)
1. In the modern periodic table Ca(atomic number 20) is surrounded by elements with atomic number 12, 19, 21
and 38 which of these have physical and chemical properties resembling calcium?
Electronic configuration of Ca is 2, 8, 8, 2. It has four orbits with 2 electrons in the outermost orbit.
Electronic configuration of element having atomic no. 12 – 2, 8, 2
Electronic configuration of element having atomic no. 19 – 2, 8, 8, 1
Electronic configuration of element having atomic no. 21 – 2, 8, 8, 3
Electronic configuration of element having atomic no. 38 – 2, 8, 18, 8, 2
Elements having same number of valence electrons or having same outer electronic configuration are present in the
same group. Elements present in the same group show similar chemical properties.
Elements having atomic number 12 and 38 resemble calcium with similar physical and chemical property.
2. Describe the four blocks of the periodic table based on the electronic configuration of elements.
i. The modern periodic table is divided into four blocks namely s-block, p-block, d-block and f-block based on the
electronic configuration of elements.
ii. The groups IA and IIA (groups 1 and 2) together with hydrogen form s-block elements.
iii. The groups IIIA - VIIA (groups 13 to 17) together with group zero (group 18) constitute p-block elements.
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iv. The elements of s-block and p-block together (except inert elements) are called normal elements .
v. Group 3 to group 12 elements together are called d-block elements. They are all transition elements having their last
two shells incompletely filled.
vi. The lanthanide and actinide series at the bottom of the periodic table together form f-block elements. They are inner
transition elements having their last three shells incompletely filled.
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