Page 22 - Fpgee Question And Answer 2024 Edition

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391. (c) The ionic bond was first described by with each of three hydrogen atoms; both atoms can
Walther Kossel. According to him, the maximum complete their shell. After sharing electrons with
number of electrons that can be present in each hydrogen, nitrogen now has total eight electrons
shell should be two in the first shell, eight in the (octet) in its outer shell, whereas each hydrogen
second shell, eight or eighteen in the third shell and atom has two electrons.
so on. The molecule that has the full outer shell will
express the greatest stability, e.g. noble gases such 393.(c) The region in space where an electron is
as N 2, O 2, Cl 2, etc. likely to be found is called an orbital. There are
different kinds of orbitals with different sizes and
shapes. The orbital at the lowest energy level is
defined as a 1s orbital. It is a sphere with its center
at the nucleus of the atom. The next higher energy
level is called a 2s orbital. It is larger than a 1s
orbital. Since it has a higher energy level, it has
lower stability compared to the 1s orbital. This is
because the average distance between the nucleus
and electrons in 2s orbital is greater than the
For example, in the formation of lithium fluoride, a average distance between the nucleus and
lithium atom has only one electron in its outer or electrons in 1s orbital. The next three orbitals are of
valence shell; the loss of one electron will make the equal energy, known as 2p orbitals. They are
full outer shell of lithium with two electrons. dumbbell-shaped. They are further differentiated
by the names 2px, 2py, and 2pz, where the x, y, and
In the case of fluorine atoms, fluorine has seven z refer to the corresponding axes.
electrons in its outer shell; therefore if it gains one
electron it will make fluorine with a full outer shell 394.(c) The Pauli Exclusion Principle is the most
of eight electrons. fundamental rule in organic chemistry. It was first
proposed by Wolfgang Pauli. According to Pauli,
Lithium fluoride is formed by the transfer of one only two electrons can occupy any atomic orbital at
electron from lithium to fluorine. Lithium now bears any given time, and to do so these two electrons
a positive charge due to the loss of electron must have an opposite spins.
whereas fluorine bears the negative charge by
gaining the electron. The electrostatic attraction 395.(a) The correct electronic configuration for
between the oppositely charged atoms helps Nitrogen (N) should be:
forming the bond. The type of bond where the bond
forms due to the transfer of electron is defined as
an ionic bond.
1S 2S 2Px 2Py 2Pz
392.(b) An NH 3 molecule is an example of a
covalent bond since bond formation is possible due In organic chemistry, an orbital becomes occupied
to the sharing of electrons by two atoms. only if the orbitals of lower energy are filled (e.g. 2s
after 1s, 2p after 2s). Also, an orbital is not occupied
by a pair of electrons until other orbitals of equal
energy are each occupied by one electron (e.g. 2px,
2py, 2pz). Nitrogen has seven electrons. On this
In the above example, the outer shell of nitrogen basis, a 1s orbital will be filled first with a pair of
has three single electrons. By sharing one electron electrons since this orbital has the lowest energy.

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