Covalent bonding Flashcards
What is a covalent bond?
Shared pair of electrons between two non-metals.
Pair of electrons in an atom not used up for covalent bonds are called what?
Lone pairs
What is an expansion of the Octet?
When an atom uses all the electrons in the 3d subshell form covalent bonds regardless of whether the atom ends up with a noble gas electronic configuration or not.
What is a dative/co-ordinate bond?
When a lone pair of electrons are used to form a covalent bond. The two electrons come from the same atom instead if different.
Dative/co-ordinate bond has the same what as covalent bonds?
- Length
2. Strength (average bond enthalapy)
The acceptor ion in a dative/co-ordinate bond must be what?
Electron deficient (have spaces for those electrons).
How do u show a dative/co-ordinate bond?
- ->
eg. NH3 –> H
Shapes of molecules are based on what fact?
Electron pairs repel each other and move as part apart from each other as possible in order to minimise replusion.
Give shape name and angle for 2 total pairs
Linear 180*
Give shape name and angle for 3 total pairs
Trigonal planar 120*
Give shape name and angle for 4 total pairs
Tetrahedron 109.5*
Give shape name and angle for 5 total pairs
Trigonal bipyramidal 90/120*
Give shape name and angle for 6 total pairs
Octahedral 90*
What effect does lone pair have on bond angles and why?
Lone pairs repel more strongly than bonding pairs so each pair reduces the bonding angle by 2.5
Overall how to do the shape of molecules: (3steps)
- Find the base shape according to the total no. of pairs.
- Reduce the angles according to lone pairs.
- Ignore the lone pairs and find a new name of shape with the modified angles.
What is electronegativity?
The ability of an atom to attract the pair of electrons to itself in a covalent bond.
Describe and explain the trends of electronegativity across and down a group.
- Increases across a period (as atomic radius decreases and nuclear charge increases).
- Decreases down a group (as shielding increases)
How is electronegativity measured?
Using a Pauling scale (1-4)
Different between pure covalent bond and polar covalent bond.
In pure covalent bonds, the shared pair of electrons lie midway between the two equally electronegative nuclei. Whereas, in polar covalent bonds, the pair of electrons are attracted more towards a more electronegative nuclei causing a separation of charge (dipole) and creating an overall polarity (dipole moment).
How is a polar bond shown.
S+ S-
S= small charge
–!–> points towards more electronegative element
Give/explain 4 properties of simple molecular substances
- Low MP (weak intermolecular forces)
- Soft and breaks easily
- Does not conduct electricity( no charged ions to carry charge).
- Non-polar soluble in non-polar solvent and polar in polar solvent.
Give 3 properties of diamond (macromolecular)
- Hard
- High MP/BP
- Does not conduct electricity (each C atom bonded to 4 other so no free charge).
Give 3 properties of graphite (macromolecular)
- Soft (layers can slide)
- High MP/BP
- Does conduct electricity (Each carbon bonded to 3 other- free electron to carry charge).
