Chapter 7: Covalent molecules, networks and layers
7.1 Three Different forms of Carbon
The chemical composition of __________ , _____________ and __________ is ‘ ___’ .
Charcoal, diamond and graphite are different physical forms, ___________, of carbon.
Graphite (C):






The physical properties of a substance reflect the nature of the particles present the
strength of the bonding between particles. Substances with very high melting points
generally have strong bonding throughout the substance. Consists of a layer of carbon. It
has very strong bonds within the layers though very weak bonds between the layers.
Diamond (C): consists of carbon atoms bonded very strongly to other carbon atoms in a
3D lattice.
Charcoal (C): its structure is subject of research. It appears to be made up of
fragments of buckyballs (groups of 60 carbon atoms).
Compounds of Carbon
Carbon readily forms many compounds with other non-metals.
Carbon dioxide: ______________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
Covalent bonding: involves the sharing of electrons.
COVALENT BONDING = NON-METAL + NON-METAL….
7.2 Bonding model for Covalent Molecular Substances
When a covalent molecular substance melts, the molecules separate from each other yet
the atoms within the molecules remain bound to one another. Therefore, our bonding
model for molecular substances must describe the two kinds of forces.
 The strong forces of attraction, which hold atoms together within molecules
(intramolecular).
 The weak forces of attraction between molecules (intermolecular).
Covalent bonding within molecules
Non-metals share electrons to form a stable outershell.
Some small molecules with single covalent bonds
Hydrogen (H2)
Is the simplest molecule is that formed with hydrogen atoms bond. The hydrogen
molecule is _________ (H2). Solid hydrogen melts at _______ therefore ________
forces ___________ hydrogen molecules. Though a large amount of energy is needed to
break the atoms apart, indicating that the attraction between the two hydrogen atoms is
very strong.
Chlorine (Cl2)
Electronic configuration: ________________
The two chlorine atoms are held together by the electrostatic force of attraction
between the nuclei of the two chlorine atoms and one shared pair of electrons.
Summarising (Cl2):




Hydrogen Chloride (HCl)





Molecules with more than two atoms
Water (H2O)






Ammonia (NH3)






Simple Hydrocarbons
Methane (CH4)
Ethane (C2H6)
Propane (C3H8)
Some small molecules with double or triple bonds
Oxygen ( ___ ): ________ covalent bond
Nitrogen ( ___ ): __________ covalent bond
Ethene ( _____ )
Representing Molecules
Chemists commonly use two types of diagrams to represent molecules__________________ and _________________ (structural).
Example:
QUESTIONS: 1, 2, 3, 4, 5 & 6.
7.3 Shapes of molecules
Shapes of molecules
Hydrogen (H2) or hydrogen Chloride (HCl), the shape is linear.
Eg. carbon dioxide
Methane: the central carbon atom is surrounded by four pairs of electrons, single
covalent bonds with hydrogen. These electron pairs are negatively charged and so repel
each other.
The molecule is most stable when the electron pairs are as fas apart as possible. Shape:
tetrahedral.
Eg. methane
Water: the structural formulae for water, oxygen atom has four pairs of electrons
around it, these adopt the same tetrahedral arrangement as above. When describing the
shape, it’s important to notice the positions of the atoms. The water molecule is said to
be angular or V-shaped.
Eg. water / hydrogen sulfide
Although the lone pairs help to determine the shape of a molecule, they are not
included in the description of that shape. Shape describes the positions of the
atoms only.
Ammonia: pyramidal in shape.
Eg. ammonia
QUESTIONS: 7, 8 & 9ace.