Bonding Flashcards
Ionic Bond
Electrostatic attraction between oppositely charged ions.
Melting point for ionic compounds
High - strong electrostatic attraction between oppositely charged ions
Ionic bonding is stronger when…
Ions are smaller and/or have higher charges. (A higher charge density)
Covalent Bond
Shared pair of electrons
Dative covalent bond
When the shared pair of electrons both come from one of the bonding atoms. Also called co-ordinate bonding.
Metallic bonding
electrostatic force of attraction between cations and a sea of delocalised electrons
Factors that affect strength of metallic bond
Number of protons (more = stronger), number of delocalised electrons (more = stronger), size of ion (smaller = stronger)
4 crystal structures are…
ionic, simple molecular, macromolecular and metallic
conductivity of ionic compounds
poor when solid - ions can’t move. Higher when molten or dissolved - ions free to move
boiling points of molecular compounds
low - weak intermolecular forces between molecules (Van der Waals)
melting point of macromolecular compounds
high - many strong covalent bonds to break
melting point of metallic substances
high - strong electrostatic forces of attraction between cations and delocalised electrons
Conductivity of molecular substances
Poor - no charged particles
Conductivity of macromolecular
Diamond and silica - poor. Not electrons or ions.
Graphite - good as delocalised electrons able to move between layers
Conductivity of metals
Good - delocalised electrons able to move
Shape of molecule with 2 bp, 0 lp
linear 180 angles
Shape of molecule with 3 bp, 0 lp
trigonal planar, 120 angles
Shape of molecule with 4 bp, 0 lp
tetrahedral, 109.5 angles
Shape of molecule with 3 bp, 1 lp
trigonal pyramidal, 107 angles
Shape of molecule with 2 bp, 2 lp
V shape or bent. 104.5 angles
Shape of molecule with 5 bp, 0 lp
trigonal bypyramidal, 120 and 90 angles
Shape of molecule with 5 bp, 1 lp
See-saw
Shape of molecule with 6 bp, 0 lp
Octahedral 90 angles
How to explain shape
- State number of bonding pairs and lone pairs.
- State that electron pairs repel to get as far apart as possible
3a. If no lone pairs state that electron pairs repel equally
3b. If there are lone pairs state that lone pairs repel more than bonding pairs - State shape and bond angle
Shape of molecule with 4 bp, 2 lp
Square planar 90 angles
Shape of molecule with 5 bp, 1 lp
Square based pyramid
How to calculate number of electron pairs
Group of central atom + number of electrons from bonding atoms +/- electrons from charge = total number of electrons. Divide by 2 = number of pairs. Work out whether they are bonding or lone pairs
Shape CO2
linear 180 angles
Shape CS2
linear 180 angles
Shape HCN
linear 180 angles
Shape BeF2
linear 180 angles
Shape BF3
Trigonal planar, 120 angles
AlCl3
Trigonal planar, 120 angles
SO3
Trigonal planar, 120 angles
NO3 -
Trigonal planar, 120 angles
CO3 2-
Trigonal planar, 120 angles
SiCl4
Tetrahedral, 109.5 angles
CH4
Tetrahedral, 109.5 angles
NH4+
Tetrahedral, 109.5 angles
PF3
Trigonal planar, 107 angles
NH3
Trigonal planar, 107 angles
H30 +
Trigonal planar, 107 angles
H2O
Bent/ V-shape 104.5
OCl2
Bent/ V-shape 104.5
H2S
Bent/ V-shape 104.5
OF2
Bent/ V-shape 104.5
SCl2
Bent/ V-shape 104.5
PF5
Trigonal bypyramidal, 120 & 90
PCl5
Trigonal bypyramidal, 120 & 90
SF6
octahedral, 90
XeF4
Square planar, 90
BrF5
Square pyramid, 89
I3 -
Linear, 180
ClF3
T shape, 89
SF4
see saw, 119 & 89
IF4 +
see saw, 119 & 89
Electronegativity
Ability of an atom to attract a pair of electrons in a covalent bond
How electronegativity changes across a period
increases - more protons, same number of shells and shielding so easier to attract incoming pair of electrons
How electronegativity changes down a group
decreases - more protons but greater distance to outer shell so less easy to attract an incoming pair of electrons
Effect of large electronegativity difference between elements
perfect ionic compound
Effect of small difference in electronegativity between elements
purely covalent compound
Effect of some difference in electronegativity between elements
Polar bond or ionic bond with covalent character
Polar bond
covalent bond with an unequal distribution of electrons in the bond. This causes a dipole with partially charged atoms
Non-polar molecule
A symmetric molecule with all identical bonds and no lone pairs. Individual dipoles cancel out.
Polar molecules
Asymmetric molecules with at least one polar bond
3 types of intermolecular force in order of strength
weakest: van der Waals’ forces,
permanent dipole-dipole,
strongest: hydrogen bond
How Van der Waals’ forces form
Electrons move constantly and randomly in any molecule. A temporary, instantaneous dipole can occur. This induces a dipole in a neighbouring molecule forming an attraction
Main factors affecting the size of Van der Waals.
More electrons and larger surface area of a molecule increases the VdWs so boiling points are higher
Trend in bp down group 7
Larger molecules with more electrons so greater temporary and induced dipoles therefore stronger attraction between molecules so higher bp
Trend in bp in alkanes
Longer alkanes have more electrons so have greater VdWs between molecules. Less branched alkanes have a greater surface area of contact between molecules so also have stronger VdWs between molecules and so have higher bps
Cause of permanent dipole-dipole forces
Occur between polar molecules with a dipole. Stronger than VdWs so compounds have a higher bp
Explanation of hydrogen bonding
Occurs in compounds with a H atom attached to very electronegative F, O or N. The large difference of electronegativity creates a partial charge difference with d+ H and d- FON. An attraction is formed between the H and a lone pair on the FON
3 marks for drawing a hydrogen bond
Partial charges shown,
All lone pairs shown
Attraction shown between lone pair on FON and H attached to a FON
Requirements for hydrogen bonding
Hydrogen atom attached to a F,O or N. and a FON on another molecule
Trend in bp of group 4 hydrides - CH4, SiH4, GeH4, SnH4
Increases down group as molecules become larger so have more electrons and stronger VdWs between molecules
Trend in bp of group 5,6 and 7 hydrides
Generally increases down the group as molecules become larger and have stronger VdWs. HF, H2O and NH3 have unexpectedly high bp because they can form H bonds as well as VdWs
What is unusual about ice?
It is less dense than liquid water. The H bonding between molecules holds them further apart from each other in a regular arrangement
Diagram of iodine
herringbone structure of I2 molecules