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CHE1502 EXAM PACK 2023
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- University Of South Africa (Unisa)
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CHE1502 EXAM PACK2023
QUESTIONS AND ANSWERS
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, ASSIGNMENT 01
ANSWERS
TOPICS: Fundamental Concepts in Organic Chemistry, Alkanes and
Cycloalkanes, Stereochemistry and Alkyl Halides (Structure,
Properties, Nomenclature and Nucleophilic Substitution
Reactions)
1. Which of the following statements is INCORRECT?
(1) There are 3 distinct p orbitals in the second electron shell, where n = 2.
2 2 3
(2) The electron configuration of nitrogen is 1s 2s 2p
(3) The electron density of s orbitals has spherical symmetry.
(4) Hund's rule tells us that each orbital can hold a maximum of 2 electrons.
Correct Answer:
(4) Hund’s rule tells us that each orbital can hold a maximum of 2 electrons.
The above statement is INCORRECT. Hund’s rule tells us that that electrons in the same
energy level occupy as many available orbitals before pairs are formed in an orbital or
the electrons in singly occupied orbitals have the same spin.
2. Which of the following statements are INCORRECT?
(1) A carbon-hydrogen bond in methane, CH3, is nonpolar
(2) Electronegativity is the property of the atoms forming a given bond which
determines the polarity of the bond.
(3) Covalent bonds can only be polar.
(4) The electronegativity of elements on the periodic table increases going to the right
in each row.
Correct Answer:
(3) Covalent bonds can only be polar.
2
, CHE1502/001/0/2021
The above statement is INCORRECT because covalent bonds can be polar or non-polar,
depending on the electronegativity of atoms involved in the bond.
3. Which of the following statements represents the CORRECT type of bonding in the
following compounds?
(1) CH3OH ; ionic bonding
(2) CH3CH2CH2Br ; polar covalent bonding
(3) H-F ; ionic bonding
(4) CH3CH2OK ; covalent bonding
Correct Answer:
(2) CH3CH2CH2Br ; polar covalent bonding
The above statement is correct because the C-Br bond that is polar.
Covalent bonding: Within a bond, the electronegativity of an atom is the ability of an atom to
attract bonding electrons towards itself. Covalent bonding within the compound involves the
sharing of electrons between atoms involved in bond formation. A nonpolar covalent bond
exists between atoms having a very small or zero difference in electronegativity. A polar
covalent bond exists between atoms having a very small or zero difference in electronegativity.
A compound such as butane, CH3-CH2-CH2-CH3 is a non-polar compound and the compound
CH3CH2CH2Br is a polar compound.
Ionic Bonding: An ionic bond within a compound is formed by the electrostatic attraction
between a positive and negatively charged ions, i.e. when there is a big difference in
electronegativity of the atoms involved in bond formation.
The corrections to the other options are:
1) polar covalent bonding
3) polar covalent bonding
4) Rewrite the CH3CH2OK as CH3CH2O- K+. An ionic bond exists between the O- and K+
and covalent bonding exists between the atoms in the ethoxide ion, CH3CH2O-.
3
, 4. Which of the following Lewis structures is INCORRECT?
(1) nitric acid
O
H O N
O
(2) sulphuric acid
O
H O S O H
O
(3) methyl nitrite
CH3 O N O
(4) thionyl chloride
O
Cl S Cl
Correct Answer:
(4) thionyl chloride
O
Cl S Cl
The above Lewis structure is INCORRECT
The correct Lewis structure of thionyl chloride is:
4
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