Physical: Shapes of molecules + Forces Arised Flashcards
explain e- pair repulsion theory
electrons are -vely charged so e- will repel each other, in a molecule a bonding pair of e- will repel other e- around the central atom causing a shape and bond angle and pairs will take up as much space and be as far away as possible
give the angle for linear
180
give the angle for triganol planar
120
give the angle for v shaped
104.5
contains two lone pairs
give the angle for pyramidal
107
contains a lone pair
give the angle for tetrahedral
109.5
give the trigonal bi pyramid
120 + 90
give the angle for octahedral
90
explain the process in calculating the bond angle of a molecule
-use trimethylamine
amine= nitrogen = group 5 so 5 valence e-
tri= 3 carbons= 3 bond pairs
5+3= 8
8/2= 4
4-3= 1 lone pair = pyramidal 107.
what is the most electronegative element in the periodic table
Fluorine= 4.0
explain trend in e-vity down a group
it decreases due to increase in atomic radii and and shielding so further away the outer most e- so less attractions between nucleus and e- so less able to attract pairs of electrons
explain trend in e-vity across a period
it increases as shielding stats about the same but atomic radii decreases due to increase in nuclear charge/ proton number so a stronger attraction between nucleus and outer most electron
what is difference between Intramolecular force and intermolecular forces
Intramolecular forces are forces within a molecule, whereas intermolecular forces are forces between a molecule.
Molecules contain weaker intermolecular force between the molecules:
Induced dipole – dipole forces also called van der Waals or London dispersion forces
Permanent dipole – dipole forces are the attractive forces between two neighbouring molecules with a permanent dipole
Hydrogen Bonding are a special type of permanent dipole - permanent dipole forces
Intramolecular forces are stronger than intermolecular forces
For example, a hydrogen bond is about one tenth the strength of a covalent bond
give the order of strength between forces that arise within molecules
covalent
hydrogen
permanent dipole-dipole
induces dipole- dipole (VdW)
what is non polar
When two atoms in a covalent bond have the same electronegativity the covalent bond is nonpolar
explain how polarity occurs
two atoms in a covalent bond have different electronegativities the covalent bond is polar and the electrons will be drawn towards the more electronegative atom
As a result of this:
The negative charge centre and positive charge centre do not coincide with each other
This means that the electron distribution is asymmetric
The less electronegative atom gets a partial charge of δ+ (delta positive)
The more electronegative atom gets a partial charge of δ- (delta negative)
explain how permanent dipole- dipole come about
polar molecules have permanent dipoles and the molecule will always have +ve and -ve ends, so with its neighbouring molecule will be attracted that already are polar
explain how induced dipole dipole occur
induced dipole - dipole forces exist between all atoms or molecules
They are also known as van der Waals forces
electron charge randomly shifts (since constantly moving) causing one end to be more -ve, forming temporary dipole, this induces neighbouring molecules
explain hydrogen bonding
it is the strongest type of bond between molecules only contains N,O,F since very electronegativity ,hydrogen is covalently bonded to an O, N or F, the bond becomes highly polarised
(bonds only to lone pairs) dotted lines must be shown
explain the trend in bp between hydrogen bonding and group 6 elements
H2O highest enthalpy due to h bonding which requires most energy to overcome but this is not present in other hydrides
H2S is immediately lower and increases H2Se and H2Te due to the number of electron number increases
this increases the number of van der walls forces/ induces d-d forces as the molecule becomes larger
