Week 5 - Physical Properties and Intermolecular Forces

Question 1

Carbon is an interesting and versatile element. There are over twenty million known compounds containing carbon,
encompassed in the growing field of organic chemistry. The element itself can exist in two major forms. Diamond
is a form of carbon that is extremely hard and is one of the few materials that can scratch glass. The other form
of carbon is graphite, a very soft material that we find in “lead” pencils. The two forms differ mainly in how the
carbon atoms are connected to one another. The differences in the arrangement of atoms affect the properties of the
material.

Answer 1

R

Question 2

The physical state and properties of a particular compound depend in large part on the type of chemical bonding it
displays.

Answer 2

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Question 3

Molecular compounds, sometimes called covalent compounds, display a wide range of physical properties
due to the different types of intermolecular attractions such as different kinds of polar interactions. The melting and
boiling points of molecular compounds are generally quite low compared to those of ionic compounds. This is
because the energy required to disrupt the intermolecular forces between molecules is far less than the energy
required to break the ionic bonds in a crystalline ionic compound.

Answer 3

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Question 4

Since molecular compounds are composed of
neutral molecules, their electrical conductivity is generally quite poor, whether in the solid or liquid state. Ionic compounds do not conduct electricity in the solid state because of their rigid structure, but conduct well when either
molten or dissolved into a solution. The water solubility of molecular compounds is variable and depends primarily
on the type of intermolecular forces involved. Substances that exhibit hydrogen bonding or dipole-dipole forces are
generally water soluble, whereas those that exhibit only London dispersion forces are generally insoluble. Most, but
not all, ionic compounds are quite soluble in water. Table 1.1 summarizes some of the differences between ionic
and molecular compounds

Answer 4

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Question 5

One type of molecular compound behaves quite differently than that described so far. A covalent network solid is a
compound in which all of the atoms are connected to one another by covalent bonds. Diamond is composed entirely
of carbon atoms, each bonded to four other carbon atoms in a tetrahedral geometry. Melting a covalent network
solid is not accomplished by overcoming the relatively weak intermolecular forces. Rather, all of the covalent bonds
must be broken, a process that requires extremely high temperatures. Before it was believed that its impossible for
diamond to melt as it only vaporizes at temperature higher than 3500 but recent innovations and research makes it
possible

Answer 5

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Question 6

The physical properties of a material are affected by the intermolecular forces holding the molecules together.

Answer 6

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Question 7

Forces between molecules

Answer 7

Intermolecular forces

Question 8

Ionic bonds composed in a lattice structure

Answer 8

Ionic compound

Question 9

Display a wide range of physical properties due to the different types of intermolecular
attractions such as different kinds of polar interactions.

Answer 9

Molecular compound