Covalent bonds

Question 1

A covalent molecular element

Answer 1

made up of molecules of the same element. The molecules may contain varying numbers of atoms. These include diatomic molecules, which are composed of two atoms that share electrons (e.g. Cl2).

Question 2

A covalent molecular compound

Answer 2

made up of atoms of different elements (e.g. CH4).

Question 3

how are covalent bonds produced

Answer 3

Covalent bonds are produced when non-metallic atoms react together(metal and non-metal are ionic bonds), sharing pairs of electrons so that each may get eight outer-shell electrons. These bonds are the result of the force of attraction between shared electrons and the nuclei of the non-metal atoms in the bond.

Question 4

the molecule shape is:

Answer 4

linear if the central atom has one bonding pair or one pair on either side (e.g. H2, CO2)

bent or V-shaped if the central atom has two bonding pairs and two lone pairs (e.g. H2O)

planar if the central atom has three bonding pairs and no lone pairs (e.g. C2H4)

pyramidal if the central atom has three bonding pairs and one lone pair (e.g. NH3)

tetrahedral if the central atom has four bonding pairs and no lone pairs (e.g. CH4).

Question 5

non-metallic properties

Answer 5

Non-metallic atoms have high electronegativities, which means that they have a strong attraction for the shared electrons in a covalent bond. Differing electronegativities cause electrons to be unequally shared and can affect the polarity of the bond.

Question 6

List three typical properties of covalent molecular substances.

Answer 6

Covalent molecular substances have low melting and boiling temperatures, do not conduct electricity and are soft.

Question 7

what is the central atom

Answer 7

The atom with the most bonding electrons is known as the central atom.

Question 8

Which of the following exhibits hydrogen bonding? Justify your response.

a. CF3H

b. CH3OCH3

c. NH3

d. HF

Answer 8

a and b do not exhibit hydrogen bonding because the hydrogen atoms are not bonded to highly electronegative atoms. In both, hydrogen is bonded to C.

c and d exhibit hydrogen bonding because hydrogen atoms are bonded to the highly electronegative atoms nitrogen and fluorine respectively.

Question 9

At room temperature, methane is a gas while tetrachloromethane is a liquid. Choose the statement that best explains this.

Answer 9

Both molecules are non-polar; the difference in boiling point is only due to the difference in molecular mass and the difference in dispersion forces that results.

Question 10

The boiling point of iodine is 184 °C, whereas fluorine has a boiling point of –188 °C. Explain this difference.

Answer 10

Iodine has more electrons and hence stronger dispersion forces.

Question 11

What states do fluorine and iodine assume at room temperature?

Answer 11

Fluorine is a gas at room temperature due to its weak dispersion forces. Iodine is a solid at room temperature because it has much stronger dispersion forces.

Question 12

Are the bonds in the molecule polar or non-polar?CO2(carbon dioxide)

Answer 12

The bonds are polar due to the electronegativity difference between carbon and oxygen atoms.

Question 13

Is the molecule polar or non-polar?CO2(carbon dioxide)

Answer 13

The dipoles present in the bonds cancel out due to the linear shape (the molecule is symmetrical).

Question 14

What type of interactions would you expect between the molecules in solid carbon dioxide?

Answer 14

Dispersion forces. The molecule is non-polar so can only have dispersion forces.

Question 15

Molecular substances properties

Answer 15

have low melting and boiling points due to weak intermolecular forces

are usually liquid or gaseous at room temperature due to weak intermolecular forces

do not conduct electricity because the molecules are electrically neutral

are soluble in water if polar, and soluble in non-polar solvents if non-polar (the like-dissolves-like rule) are soft.

Question 16

A covalent network lattice

Answer 16

is a three-dimensional network lattice where many atoms are covalently bonded to each other. Examples are diamond

Question 17

Covalent network lattices

Answer 17

exist as solids and have very high melting points due to the strong covalent bonds between atoms

do not conduct electricity because they have no free electrons

are good conductors of heat due to rigid connections and collision of particles

are hard and brittle

are chemically inert( a substance that is not chemically reactive.)

are insoluble in water.

Question 18

Graphite Properties

Answer 18

is solid with a high melting point due to strong covalent bonds

conducts both electricity and heat due to the presence and movement of delocalised electrons

is slippery to the touch because weak dispersion forces between layers allow the layers to slide over each other

has a metallic sheen due to the interaction between light and the delocalised electrons.

Question 19

Covalent layer lattices examples

Answer 19

Covalent layer lattices, such as graphite, are made up of many atoms held strongly in two-dimensional layers by covalent bonds. These layers are held together by weak dispersion forces.

Question 20

When diamond is heated to high temperature, it burns to form carbon dioxide. If oxygen is excluded, however, it changes to graphite, which then sublimes at about 3500 °C. Three other substances, silicon, a form of silicon carbide, SiC, called moissanite and germanium are also able to resist very high temperatures.
Question 1
a. Describe the type of bonding that you would expect in each of the substances mentioned.

b. Would you expect germanium to be hard or soft? Explain.

c.Samples of these four substances are labelled A, B, C and D. In an experiment, they are subjected to extreme heat in the absence of oxygen. It is observed that D melts before B. At the conclusion of the experiment it is noted that A has not melted and C has turned a dark grey colour. Identify which substance is which and explain your reasoning.

Answer 20

a)The type of bonding in each substance is covalent network bonding. because it is mention that it is similar to diomond.

b)Germanium would be expected to be hard. This is because the strong covalent bonds between its atoms are hard to disrupt.

c)C is diamond because the dark grey colour is consistent with it turning into graphite. Of the others, the melting temperature represents the increasing strength of their covalent bonds. This is caused by the bonds becoming shorter, due to the period on the periodic table to which each belongs. Therefore, D is Ge (longest and weakest bonds), B is silicon and A is silicon carbide (shortest bonds).

Question 21

Non metals=??

Answer 21

Covalent bonding

Question 22

Dispersion forces are effected by:

Answer 22

Number of electrons= more attraction/ stronger force
Shape of a molecule
Linear has stronger force
Tetrahedral not strong force

Question 23

Dipole dipole interactions

Answer 23

All polar must have dipoles

Question 24

Hydrogen bonding

Answer 24

When hydrogen bond to fluorine, oxygen and nitrogen(FON)

Question 25

How do you nonpolar molecules stick together?

Answer 25

They stick together, using dispersion forces