covalent bonding Flashcards
A covalent bond is formed between atoms by the sharing of a pair of electrons
The bond formed between the two atoms by mutual sharing of electrons so as to complete their octets or duplets.
Covalent bonds in terms of electrostatic attractions
In the case of a covalent bond, it is the electrostatic attraction between the bonding electrons and the two nuclei of the atoms bonded together. In the case of ionic bonding, it is the electrostatic attraction between the positive and negative ions.
Why substances with a simple molecular structures are gases or liquids, or solids with low melting and boiling points the term ‘intermolecular’ forces of attraction can be used to represent all forces
When simple molecular substances melt or boil, it is these weak intermolecular forces that are overcome. The covalent bonds are not broken. Very little energy is needed to overcome the intermolecular forces, so simple molecular substances usually have low melting and boiling points.
Why the melting and boiling points of substances with simple molecular structures increase, in general, with increasing relative molecular mass
The larger the molecules, the more surface area to form (weak) bonds with neighbouring molecules, and the more energy needed to make the molecules break free. So the melting and boiling points of simple covalent substances increase as the molecular mass increases.
Why substances with giant covalent structures are solids with high melting and boiling points
Substances with giant covalent structures are solids at room temperature. They have very high melting points and boiling points . This is because large amounts of energy are needed to overcome their strong covalent bonds to make them melt or boil.
How the structures of diamond, graphite and C60 fullerene influence their physical properties, including electrical conductivity and hardness
The rigid structure, held together by strong covalent bonds, makes diamond very hard. This physical property makes diamond useful for cutting tools, such as diamond-tipped glass cutters and oil rig drills.
The delocalised electrons are free to move through the structure, so graphite can conduct electricity. This makes graphite useful for electrodes in batteries and for electrolysis. The layers in graphite can slide over each other because the forces between them are weak.
The molecule has weak intermolecular forces of attraction between them which take little energy to overcome. Hence C60 fullerene has a low melting point, and it is soft. C60 fullerene cannot conduct electricity.
know that covalent compounds do not usually conduct electricity
Covalent compounds do not conduct electricity; this is because covalent compounds do not have charged particles capable of transporting electrons.
