Covalent bonds Flashcards
A covalent molecular element
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).
A covalent molecular compound
made up of atoms of different elements (e.g. CH4).
how are covalent bonds produced
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.
the molecule shape is:
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).
non-metallic properties
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.
List three typical properties of covalent molecular substances.
Covalent molecular substances have low melting and boiling temperatures, do not conduct electricity and are soft.
what is the central atom
The atom with the most bonding electrons is known as the central atom.
Which of the following exhibits hydrogen bonding? Justify your response.
a. CF3H
b. CH3OCH3
c. NH3
d. HF
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.
At room temperature, methane is a gas while tetrachloromethane is a liquid. Choose the statement that best explains this.
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.
The boiling point of iodine is 184 °C, whereas fluorine has a boiling point of –188 °C. Explain this difference.
Iodine has more electrons and hence stronger dispersion forces.
What states do fluorine and iodine assume at room temperature?
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.
Are the bonds in the molecule polar or non-polar?CO2(carbon dioxide)
The bonds are polar due to the electronegativity difference between carbon and oxygen atoms.
Is the molecule polar or non-polar?CO2(carbon dioxide)
The dipoles present in the bonds cancel out due to the linear shape (the molecule is symmetrical).
What type of interactions would you expect between the molecules in solid carbon dioxide?
Dispersion forces. The molecule is non-polar so can only have dispersion forces.
Molecular substances properties
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.
A covalent network lattice
is a three-dimensional network lattice where many atoms are covalently bonded to each other. Examples are diamond
Covalent network lattices
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.
Graphite Properties
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.
Covalent layer lattices examples
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.
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.
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).
Non metals=??
Covalent bonding
Dispersion forces are effected by:
Number of electrons= more attraction/ stronger force
Shape of a molecule
Linear has stronger force
Tetrahedral not strong force
Dipole dipole interactions
All polar must have dipoles
Hydrogen bonding
When hydrogen bond to fluorine, oxygen and nitrogen(FON)
How do you nonpolar molecules stick together?
They stick together, using dispersion forces 
