Ch.
No. 1. SCHOOL OF ELEMENTS
Q1. A. Fill in the
blanks.
1.
The formula of chloride of metal M is
MCl2. The metal M belongs to group 2.
2.
18th group
in the periodic table contains elements that are all gases at room temperature.
3.
The arrangement of elements in a group
of three is known as traids.
4.
The law used by Newlands to arrange
elements is known as Newlands’ Octaves.
5.
The element eka – aluminum in
Mendeleev’s periodic table is known as Gallium in modern periodic table.
6.
Elements showing properties of both
metals and non – metals are known as metalloids.
Q1. B. Match the
columns.
|
Column I
|
Column II
|
|
1.
Sodium
2.
Cerium
3.
Sulphur
4.
Manganese
|
a.
Lanthanide
b.
Metalloid
c.
Transition metal
d.
Noble metal
e.
Metal
f.
Non – metal.
|
Ans.
|
Column I
|
Column II
|
|
1.
Sodium
2.
Cerium
3.
Sulphur
4.
Manganese
|
e.
Metal
a.
Lanthanide
f.
Non – metal
c.
Transition metal
b.
Metalloid
|
Q2. Give scientific
reasons.
1. Atomic
size increases down the group.
Ans.
i.
The atomic numbers of the elements
increase as we go down the group. Thus, the elements placed lower have more
electrons.
ii.
To accommodate these electrons new
shells are added to the atom.
iii.
These new shells take the outermost
electrons farther from the nucleus causing atomic size (radius) to increase as
we go down the group.
2. Metallic
character decreases from left to right in a period.
Ans.
i.
Atoms of metals tend to lose electrons,
whereas those of non – metals tend to gain them.
ii.
In a period, as we go from left to
right, atomic number increases, increasing the number of electrons and protons.
iii.
These additional electrons are placed in
the same outer shell and are strongly attracted towards the positively –
charged nucleus.
iv.
This strong attraction does not allow
loss of electrons, causing metallic character to decrease from left to right in
a period.
3. Elements
in the same group show the same valency.
Ans.
i.
Valency is the number of electrons
given, taken or shared by an atom to complete its outermost shell.
ii.
All the elements in the same group have
the same number of electrons in their outermost shells.
iii.
Thus, all these elements take, give or
share the same number of electrons.
iv.
Hence, elements in the same group show
the same valency.
Q3. Answer the
following
1. How
could the modern periodic table remove various anomalies of Mendeleev’s
periodic table?
Ans.
i.
Hydrogen was placed in group 1 and in group
17 as it resembles alkali metals as well as halogens. Therefore, no fixed
position could be given to hydrogen in Mendeleev’s periodic table. But in Modern periodic table it is placed in
group 1.
ii. Mendeleev
arranged the elements in their increasing order of atomic masses. But some
elements with higher atomic masses are placed before those having lower atomic
masses. E.g. Cobalt (Co) with atomic mass 58.93 is placed before Nickel (Ni)
having atomic mass 58.71. But in Modern periodic table the elements were
arranged on the basis of the atomic number of elements. Thus atomic number of
Co is 27 and that of Ni is 28. So Nickel is placed after Cobalt.
iii. Though
isotopes of the same elements have different atomic masses, they cannot be
placed separately in the periodic tale. Since isotopes are chemically similar,
they had to be given the same position in the periodic table. Isotopes occupy
the same position in the Modern periodic table.
iv. In
Modern periodic table elements are classified according to their electronic
configuration into different blocks. Thus, various anomalies (irregularity)
which were seen in Mendeleev’s table due to the arrangement according to atomic
masses were overcome by the Modern Periodic table.
2. In
modern periodic table, which are the metals, non metals and metalloids among
the first 20
elements?
Ans. In the
modern periodic table, among the first 20 elements, following are the metals,
non – metals and metalloids.
|
Metals
|
Non metals
|
Metalloids
|
|
Lithium (Li)
Beryllium (Be)
Sodium (Na)
Magnesium (Mg)
Aluminium (Al)
Potassium (K)
Calcium (Ca)
|
Hydrogen (H)
Helium (He)
Carbon (C)
Nitrogen (N)
Oxygen (O)
Fluorine (F)
Neon (Ne)
Phosphorus (P)
Sulphur (S)
Chlorine (Cl)
Argon (Ar)
|
Boron (B)
Silicon (Si)
|
3. What
are the demerits of Mendeleev’s periodic table?
Ans.
i.
Hydrogen was placed in group 1 and in
group 17 as it resembles alkali metals as well as halogens. Therefore, no fixed
position could be given to hydrogen in Mendeleev’s periodic table.
ii.
Though isotopes of the same elements
have different atomic masses, they cannot be placed separately in the periodic
table. Since isotopes are chemically similar, they had to be given the same
position in the periodic table.
iii.
Some elements with higher atomic masses
are placed before those having lower atomic masses, e.g. cobalt with atomic
mass 58.93 is placed before nickel having atomic mass 58.71.
iv.
Dissimilar elements were placed in the
same group. E.g. Mn (Manganese) was placed in the group of halogens which
totally differ in the properties.
4. Define
atomic size. How does it vary in a period and in a group?
Ans.
i.
Atomic size is determined by using
atomic radius.
ii.
For an isolated atom, its atomic radius
is the distance between the centre of the atom (i.e. centre of its nucleus) and
its outermost shell.
iii.
In a period, atomic radius generally
decreases from left to right. This is because the electrons are added to same
shell and experience greater pull from the nucleus.
iv.
Atomic radius increases in a group from
top to bottom as new shells are added bringing outermost electrons farther from
the nucleus.
Q. 4. Name
1. Three
elements having a single electrons in their outermost shell.
Ans. Hydrogen, Lithium, Sodium, Potassium.
2. Three
elements with filled outermost shell.
Ans.
Helium, Neon, Argon, Krypton, Xenon.
3. Three
elements having 7 electrons in their outermost shell.
Ans.
Fluorine, Chlorine, Bromine, Iodine.
