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Download 9th Class Chemistry Notes (Unit # 3) for Federal Board (FBISE) Islamabad

Download 9th Class Chemistry Notes (Unit # 3) for Federal Board (FBISE) Islamabad

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Download 9th Class Chemistry Notes (Unit # 3) for Federal Board (FBISE) Islamabad

Write the valence shell electronic configuration of an element present in the 3rd period and Group III-A.
Aluminum (Al):
K      =      1s2
L       =      2s2, 2p6
M      =      3s2, 2p1 (Valence Shell)

Write two ways in which isotopes of an element differ.
·        The number of neutrons in the nucleus.
·        The atomic mass.
·        Physical properties and the nuclear stability.

Which atom has higher shielding effect, Li or Na?
·        The valence-shell electron of 11Na experience less attraction from the nucleus due to the presence of 10 inner-shell electrons as compares to 3Li having 2 inner shell-electrons.
·        Na atoms will have greater shielding effect due to greater number of inner shell electrons as compare to Li.

Explain why, Na has higher ionization energy than K?
·        Ionization energy decreases from top to bottom in a group.
·        The size of sodium (3 shells) is smaller than potassium (4 shells).
·        Therefore Na has higher ionization energy than K (group I-A elements)

Alkali metals belong to s-block in the periodic table, why?
Groups I-A on the left side of the table, constitute s-Block because outer shell valence electrons of these elements are present in s-orbitals/sub shell.

Arrange the elements in each of the following groups in order of increasing ionization energy:
Li, Na, K
Ionization energy of Li > Ionization energy of Na > Ionization energy of K
(Group I-A Elements)
CI, Br, I
Ionization energy of CI > Ionization energy of Br > Ionization energy of I
(Group VII-A Elements)

Arrange the elements in each of the following in order of decreasing shielding effect
Li, Na, K
Shielding effect of Li < Shielding effect of Na < Shielding effect of K
CI, Br, I
Shielding effect of CI < Shielding effect of Br < Shielding effect of I
CI, Br
Shielding effect of CI < Shielding effect of Br

Specify which of the following elements you would expect to, have the greatest electron affinity. S, P, Cl
As we move from left to right across a period, the electron affinity generally increases. This is due to increase in nuclear charge and decrease in atomic radius, which binds the extra electron more tightly to the nucleus. Therefore Cl has greatest electron affinity as compared to S and P.

For normal elements, the number of valence electrons of an element is equal to the group number. Find the group number of the following elements.
(Note: This is not the answer, but method to find the group number of any element)
  • Do Electronic Configuration
  • Guess No. of Electrons in Valance Shell
  • That will be the Group Number

Write the valence shell electronic configuration for the following groups
Alkali Metals:
ns1,
Alkaline Earth Metals:
ns1,
Halogens:
Ns2, np5,
Noble Gases:
Ns2, np6,

Imagine you are standing on the top of Neon-20 nucleus. How many kinds of sub- atomic particles you would see looking down into the nucleus and those you would see looking out from the nucleus.
Sub atomic particles present inside the nucleus of Neon-20 are:
Number of protons       =      10
Number of neutrons     =      A - Z                 = 20 - 10 = 10

Sub atomic particles present outside the nucleus of Neon-20 are:
Number of electrons    =      10

What types of elements have the highest ionization energies and what types of elements have the lowest ionization energies.
Noble gases (group VIII-A) have the highest ionization energies because they have complete outer most shells (follows octet or duplet rule). Therefore it is difficult to remove an electron from their outer most shell.
On the other hand Alkali metals (group I-A) have greater size, therefore Alkali metals have lowest ionization energy.

Two atoms have electronic configuration 1s2, 2s2, 2p6 and 1s2, 2s2, 2p6, 3s1. The ionization energy of one is 20801KJ/mole and that of the other is 496 KJ/mole. Match each ionization energy with one of the given electronic configuration. Give reason for your choice.
  • Noble gases (group VIII-A) have the highest ionization energies because they have complete outer most shells (follows octet or duplet rule). Therefore it is difficult to remove an electron from their outer most shell. Therefore in this case the value of ionization energy will be 20801 KJ/mol.

  • The electronic configuration 2s2, 2p6, 3s1 (Na) shows the alkali metals (Group I-A). Alkali metals (group I-A) have greater size, therefore Alkali metals have lowest ionization energy. Therefore in this case the value of ionization energy will be 496 KJ/mol

Use the second member of each group from Group I-A, II-A and VII-A to show that the number of valence electron on an atom of the element is the same as its group number.
i)      Second member of group I-A is (Li). Valance shell configuration of lithium is 2S1. Here valance electron of Lithium is 1 therefore its group number is also I-A.
ii)     Second member of group II-A is (Mg). Valance shell configuration of magnesium is 3S2. Here valance electrons of magnesium are 2 therefore its group number is also II-A.
iii)    Second member of group VII-A is (Cl). Valance shell configuration of chlorine is 3s2, 3p5 Here valance electrons of chlorine are 2+5=7 therefore its group number is also VII-A.

In what region of the periodic table you will find elements with relatively a) High ionization energies, b) Low ionization energies:
a)      High ionization energies:
Noble gases (group VIII-A) have the highest ionization energies because they have complete outer most shells (follows octet or duplet rule), therefore it is difficult to remove an electron from their outer most shell. Therefore, elements in the upper right of the periodic table have the highest ionization energy, (Noble gases, p-block)

b)      Low ionization energies:
On the other hand Alkali metals (group I-A) have greater size, therefore Alkali metals have lowest ionization energy. Therefore, elements in the upper left of the periodic table have the lowest ionization energy, (Alkalis metals, s-block).

Define periodic table. What is the basis of the classification of elements in the modern periodic table?
A table showing systematic arrangement of elements is called periodic table. It is based on the Periodic law that states if the elements are arranged in the order of their increasing atomic numbers, their properties are repeated in a periodic manner.

Today how much elements are listed in the periodic table?
By the end of 18th century, 23 elements are known, by 1870, 65 by 1925, 88, today there are 109.

Give the significance/advantages of periodic table?
·        The periodic table is one of the most important tools in chemistry.
·        It is very useful for understanding and predicting the properties of the elements.
·        For instance if you known physical and chemical properties of one element in a group, you can predict about the physical and chemical properties of any other element present in the same group.
·        We can use periodic table to relate trends in the reactivity of elements with their atomic structure.
·        We can also predict which elements can form ionic or covalent bonds.

Define period. How many periods are there in the long form of periodic table?
·        The horizontal rows of the periodic table are called periods. There are seven periods.
·        First three periods are called short periods and the remaining periods are called long periods.
What do you mean by group or family in the periodic table?
·        Elements that have similar properties lie in the same column in the periodic table.
·        Each vertical column of elements in the periodic table is called a group or family.

What are the representative and transition elements?
Normal elements:
·        Group A elements are called normal or representative elements. They are also called main group elements
·        All s-block and p-block elements excluding the noble gases are called representative or main group elements.
Transition elements:
·        The d-block elements are called transition elements or outer transition elements.
·        These elements occupy group 3 to 12 of the periodic table and lie in between the s- and p-block elements.
·        The f-block elements are called inner-transition elements.

What was the concept of John Newland.
·        In 1864, John Newland an English chemist arranged 24 element in order of increasing atomic masses.
·        He noticed that every eighth element starting from any point has similar properties.
·        His scheme however, failed because many elements were found out of place in his arrangement

What was concept of Mendeleev?
·        In 1869, Mendeleev a Russian chemist developed a classification scheme of elements.
·        He recognized that if elements were placed in order of increasing atomic masses, the properties of elements repeated at regular intervals.
·        He arranged 65 elements in periods and groups.
What is meant by the periodicity of properties?
·        The electronic configuration of the elements shows a periodic variation with the increasing atomic number.
·        Therefore, the elements also show periodic variation in their physical and chemical properties.
·        Elements having similar valence shell electronic configuration have been placed in the same group, one below the other.
Periodicity in Chemical properties:
·        Chemical properties depend on the valence shell electronic configuration.
·        Because all the elements of a particular group have similar valence shell electronic configuration, they possess similar chemical characteristics.
Periodicity in Physical properties:
·        Physical properties depend on the sizes of atoms.
·        Since sizes of atoms change gradually from top to bottom in a group.
·        Therefore, elements show gradation in physical properties in the same group.
·        In a period of periodic table the number of electrons present in the valance shell increase gradually from left to right.
·        Their chemical and physical properties also show variation in the same manner.

How does the shielding effect influence the atomic size, ionization energy and electron affinity? Justify that shielding effect increases down the group, and remains constant in a period from left to the right.
Variation of shielding effect in a group:
·        As we move from top to bottom in a group the number of electronic shells increase.
·        So the number of electrons in the inner shell also increase.
·        As a result shielding effect increases. . '
Variation of shielding effect in a period:
·        When we travel from left to the right in the periodic table in a period then number of shells remain the same.
·        So the shielding effect does not change in a period.
Influence of shielding effect on atomic size:
·        Greater is the atomic size, greater will be the shielding effect.
·        As the force of attraction between the nucleus and outer electron decreases with the increases in distance.
·        The electron can be removed more easily with less energy.
·        Moreover the force of attraction also decreases with the increasing shielding effect of the intervening electron.
Influence of shielding effect on ionization energy:
·        Shielding effect depends upon the inner shell electrons.
·        If the inner shell electrons are greater, shielding effect will be high and force of attraction between valence shell and nucleus will be low.
·        In a group, number of shells increases from top to bottom and shielding effect also increases.
·        The atoms with high shielding effect have low ionization energies.

Influence of shielding effect on electron affinity:
·        In groups, the atomic radius increases with the increase in the proton number due to successive increase of electronic shell which also exert a shielding effect on the force of attraction between the nucleus and the valence electrons.
·        Thus, the electron affinities usually decrease from top to bottom.
·        There are, of course, exceptions to this generalization e.g. fluorine has electron affinity less than that of chlorine because it has a smaller atomic size than that of chlorine.

Define electro negativity. Name the most electronegative element and discuss its variation in groups and periods.
Electro negativity is the ability of an atom to attract the electrons towards itself in a chemical bond. The American chemist Linus Pauling devised a method for calculating relative electro negativities of elements.
Most electronegative element:
·        Pauling assigned maximum value of 4.0 to the electro negativity of fluorine (F).
·        The least electronegative element is cesium (Cs) and its electronegative value is 0.7
Variation in a group:
·        Electron negativity of elements decreases from top to bottom in a group.
·        This is because an increase in the atomic size decreases the tendency to attract the shared pair of electrons.
Variation in a period:
·        The electro negativity increases from left to right in a period.
·        The nuclear charge increases from left to right while the electrons enter the same shell.
·        The electrons in the same shell cannot shield each other effectively from the attractive force of the nucleus. Hence, the increased nuclear charge attracts the shared pair of electrons more strongly.

·        This results in higher electro negativity.

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Download Class Notes: Download 9th Class Chemistry Notes (Unit # 3) for Federal Board (FBISE) Islamabad
Download 9th Class Chemistry Notes (Unit # 3) for Federal Board (FBISE) Islamabad
Download 9th Class Chemistry Notes (Unit # 3) for Federal Board (FBISE) Islamabad
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