Chapter-5 Science Extra question

Question 1.
Name two elements whose properties were predicted on the basis of their positions in Mendeleev’s periodic table.
Answer:
Gallium (Eka-aluminium) and germanium (Eka-silicon).

Question 2.
Write the formulae of chlorides of Eka-silicon and Eka-aluminium, the elements predicted by Mendeleev.  [NCERT Exemplar]
Answer:
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.

Question 3.
How many elements are there in period 2?
Answer:
Eight (8).

Question 4.
Name all the elements present in group-17 of the Modern Periodic Table.
Answer:
F, Cl, Br, I, At.

Question 5.
Name two elements whose atomic weight were corrected on the basis of their position in Mendeleev’s periodic table.
Answer:
Gold (Au) and platinum (Pt).

Question 6.
Arrange the following elements in the increasing order of their metallic character.
Mg, Ca, K, Ge, Ga     [NCERT Exemplar]
Answer:
Ge < Ga Mg < Ca < K.

Question 7.
Name the scientist who proposed the Modern Periodic Law.
Answer:
Henry Moseley, a scientist, proposed the Modern Periodic Law.

Question 8.
What is meant by a group in the periodic table?
Answer:
Groups are the vertical columns/vertical lines in the periodic table.

Question 9.
What is meant by a period in the periodic table?
Answer:
Periods are the horizontal rows in the periodic table.

Question 10.
Name the elements present in period 1 of the modern periodic table.
Answer:
Hydrogen (H) and Helium (He).

Question 11.
An element A is in group II (group 2) of the periodic table:
(а) What will be the formula of its chloride?
(b) What will be the formula of its oxide?
Answer:
(a) ACl2
(b) AO.

Question 12.
Why are the elements calcium, strontium and barium named as alkaline earths?
Answer:
These elements are called alkaline earths because their oxides are alkaline in nature and exist in the earth.

Question 13.
Give the name and electronic configuration of second alkali metal.
Answer:
The second alkali metal is sodium (Na). Its electronic configuration is 2, 8, 1.

Question 14.
What are Metalloids?
Answer:
Those elements which show some properties of both metals and non-metals are called metalloids. Examples: Boron, Silicon, Germanium, Arsenic, Antimony, Tellurium and Polonium.

Question 15.
Name three elements whose atomic masses were correct on the basis of their positions in Mendeleev’s periodic table.
Answer:

1. Beryllium (Be, group II A)
2. gold (Au, group II B)
3. platinum (Pt, group VIII).

Question 16.
Name three elements which behave as metalloids.
Answer:
The elements are:

1. arsenic (As)
2. antimony (Sb)
3. germanium (Ge).

Question 17.
Name the inert gas which has two electrons in its valence shell.
Answer:
Helium.

Question 18.
Name the most metallic and most non-metallic element in the Periodic Table.
Answer:
The most metallic elements is francium (group 1) and most non-metallic element is fluorine (group 17).

Question 19.
In the Modern Periodic Table, which are the metals among the first ten elements?
Answer:
Lithium (Li), Beryllium (Be) and Boron (B) are the metal elements among first ten elements in the Modern Periodic Table.

Question 20.
Two elements A and B belong to the same period. What is common in them?
Answer:
They have the same number of shells.

Question 21.
The electronic configuration of an element is 2, 8, 6. Identify the element and name of the family to which it belongs.
Answer:
The element with configuration 2, 8, 6 (Z = 16) is sulphur. It belongs to the oxygen family.

Question 22.
Calcium, Strontium and Barium form a Dobereiner’s triad. The atomic masses of calcium and Barium are 40 and 137 respectively. Predict the atomic mass of strontium.
Answer:
According to Dobereiner’s triad, atomic mass of strontium is the arithmetic means of Ca and Ba as strontium lies between Ca and Ba.
Atomic mass of Sr = 40+1372=1772=88.5

Question 23.
The formula of magnesium oxides is MgO. Write the formula of magnesium chloride.
Answer:
Oxygen is divalent in nature. The valency of magnesium in magnesium oxide is + 2. The formula of magnesium chloride is MgCl2 since chlorine has valency equal to one.

Question 24.
State whether the following statement is true or false?
The valency of an element of group 17 is 7.
Answer:
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.

Question 25.
Name two elements whose atomic weight were corrected on the basis of their position in Mendeleev periodic table.
Answer:

1. Gold (Au)
2. Platinum (Pt).

Question 26.
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?
Answer:
No, they should be placed in the same slot because the modern periodic table is based on the atomic number of the elements.

Question 27.
List any two properties of the elements belonging to the first group of the modem periodic table.   [Delhi 2014]
Answer:
Elements of first group have one valence electron each in their atoms. All the elements of group 1 have the same valency of 1.

Question 28.
What is the basic difference in the electronic configuration of the elements belonging to group 1 and group 2?
Answer:
All elements belonging to group 1 have one electron in the valence shell while all elements belonging to group 2 have two electrons in their valence shell.

Question 29.
Element ‘Y’ with atomic number 3 combines with element ‘A’ with atomic number 17. What will be the formula of the compound?
Answer:
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.

Question 30.
Name the property which remains unchanged on descending a group in the periodic table.
Answer:
Valence electrons.

Question 31.
An element X is in group 13 of the periodic table. What is the formula of its oxide?
Answer:
X2O3.

Question 32.
Elements ‘X’ and TP belong to groups 1 and 17 of the periodic table respectively. What will be the nature of the bond in the compound XY?
Answer:
Ionic bond.