3.1.3.2 Nature of covalent and dative covalent bonds Flashcards
What are covalent bonds?
The electrostatic attraction between positive nuclei and the shared pair of electrons
(usually between metal/non-metal)
What is the bonding pair of electrons?
The shared pairs of electrons present between the bonded atoms.
What are lone pairs of electrons?
Electron pairs that do not participate in bonding
What is a co-ordinate bond?
A covalent bond in which a shared pair of electrons comes from one atom.
For this to happen, one atom must have a lone pair of electrons, and the other has the be electron deficient
What is an example of a co-ordinate bond?
NH4+
What are the two types of covalent substances?
Simple covalent structures (lattice)
Giant (macromolecular) covalent structures (lattice)
What are the properties of simple covalent compounds?
Low mp/bp
Usually gasses/ liquids at room temp.
Cannot conduct electricity
Some soluble
Why do simple covalent compounds have low mp/bp?
Simple molecules have weak forces between molecules so less energy to overcome forces
Why are simple covalent molecules gasses/liquids at room temp?
Low mp/bp
Why don’t simple covalent molecules conduct electricity?
No delocalised electrons to move
When do simple covalent molecules dissolve in water?
Depends on polarity of molecules. Polar ones dissolve in polar solvents, non-polar ones dissolve in non-polar solvents
What are examples of giant covalent structures?
Diamond
Graphite
Silicon dioxide (sand)
Describe the structure of diamond
Each C atom is covalently bonded to 4 other C atoms, so its a crystal lattice structure because of the many strong covalent bonds. It has a tetrahedral shape.
What are the properties of diamond?
High m.p./b.p.
Hard
Non-conductor
Why does diamond have a high boiling point?
Giant covalent structure with strong covalent bonds so lots of energy needed to break bonds
Why is diamond hard?
3D/rigid/not layered structure
Why does diamond not conduct electricity?
No free electrons to move
Describe the structure of graphite
C atoms arranged in sheets of flat hexagons covalently bonded with 3 other C atoms. The 4th electron of each C atom is delocalised
What are the properties of graphite?
High mp/bp
Good conductor of electricity
Soft and slippery
Low density
Insoluble in any solvents
Why does graphite have a high boiling point?
Giant covalent structure with strong covalent bonds so lots of energy to break bonds
Why does graphite conduct electricity?
Free electrons that can move
Why is graphite soft and slippery?
Layers can slide over each other due to weak Van der Waal’s forces between layers
What is graphite used for?
To make strong light weight sports equipment
(and pencils)
Describe the structure of silicon dioxide
One Si atom bonded to 4 O atoms
One O atom bonded to 2 Si atoms
Tetrahedral shape
