Bonding Flashcards
Definition of Electronegativity
“the ability of an atom to attract the bonding electron pair in a covalent bond to itself.”
Ionic Bonding Definition
“an ionic bond is the electrostatic attraction between oppositely charged ions. It is formed by the transfer of electron(s).”
Metallic Bond definition
“attraction between the orderly arrangement of positive metal ions and the moving valence electrons.”
or
“lattice of positive metal ions embedded in a sea of valence electrons.”
Covalent Bond Definition
“consists of a shared pair of electrons with one electron being supplied by each atom either side.”
Hydrogen Bonding Definition
“hydrogen bonds occur when H is covalently bonded to the 3 most electronegative atoms (FON) - the dipole is so great that the strong attractions are set up to the lone pairs on F,O or N atoms on neighbouring molecules.”
London Dispersion Forces Definition
are the movement of electron clouds
an instantaneous dipole is created which then induces a dipole in the neighbouring molecules
Dipole Dipole Forces Definition
are an electrostatic attraction which is formed by the separation of charge (polar molecules)
Resonance Definition
“resonance occurs when there is two or more Lewis Structures to represent a particular molecule or ion. They occur when there is more than one possible position for a double bond in a molecule.”
Hybridisation Definition
“results from the mixing of atomic orbitals to form the same number of new equivalent hybrid orbitals that have the same mean energy as the contributing orbitals.”
Sigma Bond Definition
form by the direct head - on (end to end) overlap of atomic orbitals, resulting in electron density concentrated between the nuclei of bonding atoms.”
Pi Bonds Definition
formed by the sideways overlap of p atomic orbitals, resulting in electron density above and below the plane of the nuclei bonding atoms.
Delocalisation Definition
when a molecule or ion has more than two atoms, the pi electrons are spread over more than two nuclei, they are mobile and shared by a number of atoms.
This spreading out of electrons gives the species a lower potential energy making it more stable than if it were composed of a simple double and single bond.
What elements form ionic bonds?
elements with low electronegativity will form ionic bonds with elements of high electronegativity
What elements form covalent bonds?
elements with moderate to high electronegativity form covalent bonds with each other
(where the elements are different, the more EN one will carry the partial negative charge resulting in a polar covalent bond)
What elements metallic bond?
elements of low electronegativity (metals) form metallic bonds (alloys)
Rule of 1.7
Used to determine if a bond is ionic or covalent
ionic and covalent are not separate things but differences in degree
atoms that have EN dif. > 1.7 usually form ionic bonds
atoms that have EN dif. < 1.7 form polar covalent bonds
the smaller the EN dif. the less polar the bond will be
if the difference = 0 the bond is totally covalent
Properties of Ionic Compounds
very high mp - a large mount of energy must be put in to overcome the strong electrostatic attraction and separate the ions
very brittle - any dislocation leads to the layers moving and similar ions being adjacent, the repulsion splits the crystal
electrical conduction - doesn’t conduct when in solid form as the ions are held tightly in lattice, does conduct when molten or aqueous as ions become mobile
solubility- insoluble in non-polar solvents but soluble in water (polar)
MUST KNOW polyatomic ions
ethanoate ion = CH3COO-
hydroxide = OH-
sulfate ion = SO4 2-
ammonium ion = NH4+
hydrogen carbonate ion = HCO3-
Nitrate ion = NO3 -
Carbonate ion = CO3 2-
Phosphate ion = PO4 3-
Properties of Metals
excellent conductors of electricity - the electron cloud is very mobile, meaning electrons are free to move throughout structure
malleable - can be hammered into sheets
ductile - can be drawn into a wire
(both these are because the electron cloud is non-directional and continues to bind the ‘ions’ together when beaten into another shape)
mp/bp - smaller metals = higher, bigger metals = lower, more charge = higher, less charge = lower
Properties of Discrete Covalent Molecules
electrical - do not conduct electricity a they have no mobile ions or electrons
solubility - tend to be more soluble in organic solvents than in water
low bp - the intermolecular forces are weak, they increase as the molecules get more electrons
Molecular Dipole (dipole moment)
the polarity of a molecule can be measured. It is called the dipole moment and is a measure of how large the dipoles are
Physical properties of Polar Substances
- if an electrically charged object is placed near a streat of a polar liquid, the polar molecules will align themselves so that the oppositely charged end of the molecule is attracted to the rod
- polar molecular substances dissolve in polar solvents
- do not conduct electricity as they don’t have electrically charged particles that are free to move under the influence of an electric field
Formal Charge
is the charge an atom would have if all the atoms had the same electronegativity
FC = (number of valence electrons - 1/2 number of bonding electrons - number of electron lone pairs)
sp3 hybridisation
one of the 2s electrons is promoted into the vacant 2p orbital to produce an atom that has 4 unpaired electrons in its valence shell.
One of these is an s electron and the other 3 are p electrons, the s orbital and the p orbitals interact to form 4 identical sp3 hybrids that orientate in a tetrahedral arrangement
(all single bonds, hence forms sigma bonds, no pi)
sp2 hybridisation
the 2px and 2py orbitals combine with the 2s orbital to form the hybrid orbitals and the 2pz orbital remain unchanged
resulting in 3 orbitals with intermediate energy between 2s and 2p (sigma bonds)
and one p orbital (pi bond)
planar geometry - double bonds
sp hybridisation
the 2s orbital is mixed with only one 2p orbital to form the two sp hybrid orbitals
this process leaves an electron in each of the two unhybridised 2p orbitals
the 2sp hybrid orbitals form two sigma bonds
and the unhybridised orbitals form pi bonds
linear shape - triple bonds comprised of two pi bonds and one sigma bond
How do you determine hybridisation type?
- look at the electron domain geometry
- the shape of the molecule
- this will give the type of hybridisation
Diamond
sp3 hybridised
Tetrahedral shape
Bond angles 109.5 degrees
No mobile ē
Non-conductor of electricity
Good thermal conductor
Highly transparent
The hardest known natural substance
Brittle
Very high mp
Graphite
sp2 hybridised
Hexagon shape
Bond angles are 120 degrees
Has weak London Dispersion Forces
Delocalised ē
Good electrical conductor due to delocalised ē
Not a good thermal conductor
Slippery due to layers being able to slide over one another
Used as a dry lubricant
Fullerene C60
sp2 hybridised
spherical
12 pentagons 20 hexagons
NOT a giant covalent structure
Semiconductor
Light and strong
Low melting point in comparison to other allotropes (280)
Low thermal conductivity
Graphene
sp2 hybridised
Bond angles 120 degrees
2D material
Honeycomb
Single layer
Best conductor
1 delocalised ē per atom
Very thin but strong
Flexible
Very high mp
Founded recently
Silicon
identical structure to diamond
Silicon dioxide
each Si forms 4 covalent bonds
tetrahedral arrangement
same properties as diamond
(Giant lattice structure
sp3 hybridised
Strong
Insoluble
High mp
Non-conductor)
