1. Which of the following statements is not a correct statement about the trends when going from left to right across the periods of Periodic Table.
(a) The elements become less metallic in nature.
(b) The number of valence electrons increases.
(c) The atoms lose their electrons more easily.
(d) The oxides become more acidic.
Answer:
(c) The atoms lose their electrons more easily.
2. Element X forms a
chloride with the formula XCl2, which is solid with a high melting
point. X would most likely to be in the same group of the periodic table as
(a) Na (b)
Mg (c) Al (d) Si
Answer:
(b) Mg
3. Which element has
a)
two shells, both
of which are completely filled with electrons?
b)
the electronic configuration
2, 8, 2?
c)
a total of three
shells, with four electrons in its valence shell?
d)
a total of two
shells with three electrons in its valence shell.
e)
twice as many
electrons in its second shell as in its first shell?
Answer:
(a) Neon (2, 8)
(b) Magnesium
(c) Silicon (2, 8, 4)
(d) Boron (2, 3)
(e) Carbon (2, 4)
4. (a) What property
do all elements in the same column of the Periodic Table as boron have in
common?
(b) What property do all elements in the same column of
the Periodic Table as fluorine have in common?
Answer:
a) Elements in the
same column as boron have valency of three and have three valence electrons.
b) Elements in the
same column as fluorine form acidic oxides and have seven electrons in their
outermost shells and have valency of one.
5. An atom has electronic
configuration 2, 8, 7.
a. What is the atomic
number of this element?
b. To which of the
following elements would it be chemically similar? (Atomic numbers are given in
parentheses.)
N (7) F (9) P (15) Ar
(18)
Answer:
a) The atomic number is 17 (2 + 8 + 7).
b)
Fluorine (F). Its electronic
configuration is 2, 7.
6. The positions of
three elements A, B and C in the periodic table are shown below:
|
Group 16 |
Group 17 |
|
– |
– |
|
– |
A |
|
– |
– |
|
B |
C |
a)
State whether A is
a metal or non-metal.
b)
State whether C is
more reactive or less reactive than A.
c)
Will C be larger
or smaller in size than B?
d)
Which type of ion,
cation or anion, will be formed by element A?
Answer:
a) A is a non-metal.
b) C is less reactive
than A because as we move down in a group, the reactivity of non-metals decreases.
c) C is smaller in
size than B because the atomic size decreases as we move from left to right in
a period.
d) A will form anion
because it is a non-metal.
7. Nitrogen (atomic
number 7) and phosphorus (atomic number 15) belong to group 15 of the periodic
table. Write the electronic configuration of these two elements. Which of these
will be more electronegative? Why?
Answer:
Electronic configuration of nitrogen= 2,5.
Electronic configuration of phosphorus = 2, 8, 5.
Nitrogen is more electronegative because outermost shell
is nearer to nucleus and therefore nucleus will attract electrons more
strongly. In a group, electron attracting tendency decreases as we move down.
8. How does the
electronic configuration of an atom relate to its position in the Modern
Periodic Table?
Answer:
Modern periodic table is based on the atomic number and
atomic number is related to the electronic configuration. We can find the group
number and period number of an element on the basis of electronic
configuration. E.g., if an element has 1 electron in its outermost shell, then
it belongs to group 1.
All the alkali metals have one electron in their outermost
shell, so they are placed in group 1. Thus, all the group 2 elements have 2
electrons in their outermost shell. In group 15 elements, there are 5 electrons
in their outermost shell.
The number of shells in an element indicates its period
number. E.g., electronic configuration of Mg is 2, 8, 2. Thus it is an element
of 3rd period.
9. In the Modern
Periodic Table, calcium (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?
Answer:
The electronic configuration of elements with:
Atomic number 12 = 2, 8, 2
Atomic number 19 = 2, 8, 8, 1
Atomic number 20 = 2, 8, 8, 2
Atomic number 21 = 2, 8, 9, 2
Atomic number 38 = 2, 8, 18, 8, 2
Elements with atomic number 12 (magnesium) and 38 (strontium)
will have similar physical and chemical properties as element with atomic numbers
20 (calcium).
10. Compare and
contrast the arrangement of elements in Mendeleev’s Periodic Table and the
Modern Periodic Table.
Answer:
|
Mendeleev’s
Periodic Table |
Modern Periodic
Table |
|
Elements are arranged in the
increasing order of atomic mass. |
Elements are arranged in the
increasing order of atomic number. |
|
There are nine groups. |
There are eighteen groups. |
|
There is no place for noble
gases. |
Noble gases are placed on
the right-hand side of the table. |
|
There is no place for
isotopes. |
Isotope are kept at the same
place. |
|
Transition elements are
placed together in group VIII. |
Transition elements are
placed in the middle of the long period (Group 3 to 12). |