Shapes and IMFs.

Question 1

Electron-pair repulsion theory.

Answer 1

Arranged around central atom and determine shape
Pairs repel each other as far apart as possible
Arrangement of pairs minimises repulsion, holding atom in determined shape

Question 2

Tetrahedral shape.

Answer 2

4 electron pairs
109.5 degree angles
Wedges used to show 3 dimensions(line=paper plane, dotted=into paper plane, solid=comes out of paper plane)

Question 3

Lone pairs in terms of repulsion.

Answer 3

Slightly closer to atom at centre
Takes up more space
Repels more strongly than bonded pair
Repel bonded pairs slightly closer together
Decreases bond angle between bonded pairs
-2.5 degrees for each lone pair.

Question 4

Bond angles and shapes names.

Answer 4

Linear:
2 regions, 180 degrees
Trigonal planar:
3 regions, 120 degrees
Tetrahedral:
4 regions, 109.5 degrees
Octahedral:
6 regions, 90 degrees
Practice w/ diagrams of each shape.
Non-linear:
104.5 degrees
Pyramidal:
107 degrees

Question 5

Shape of ions.

Answer 5

NH4+=4 bonded pairs, 109.5, tetrahedral
CO32-,NO3-=3 regions, trigonal planar, 120
SO42-=4 regions, tetrahedral, 109.5

Question 6

Electronegativity definition.

Answer 6

The ability of an atom to attract the bonding electrons in a covalent bond.

Question 7

Pauling electronegativity scale trends/values.

Answer 7

Across table:
nuclear charge increases
atomic radius decreases
electronegativity increases
-Increases up the table too
Fluorine=highest
Lithium=lowest

Question 8

Determination of bond types from pauling scale.

Answer 8

Electronegativity difference:
0=covalent
0 to 1.8=polar covalent
1.8 or more=ionic.
Larger electronegativity value=negative delta.

Question 9

Properties of non-polar bonds.

Answer 9

Bonded pair shared equally between bonded atoms
Bonded atoms are the same or
Bonded atoms have the same/similar electronegativity.

Question 10

Properties of polar bonds.

Answer 10

Bonded electron pair shared unequally between bonded atoms
Bonded atoms are different
Have different electronegativity values

Question 11

Permanent dipole meaning and formation.

Answer 11

Can be polarised by delta +charge on lower electronegative atom
and delta - on more electronegative atom
separates opposite charges=dipole
Dipole in polar covalent bond does not change=permanent dipole.

Question 12

Predictions for polarity.

Answer 12

Tend to be polar if:
-symetrical molecule/shape
-has asymmetrical polar bonds
-OH,H or N at end
Non-polar tend to be:
-contain carbon(not always)
-diatomic elements with two of the same atom
-has no polar bonds
-has symmetrical polar bonds

Question 13

When is a molecule polar?

Answer 13

-When a permanent dipole(polar bond) act in the same direction
-Dont cancel the charges out

Question 14

What is bond polarity?

Answer 14

-the distribution of electric charge across a chemical bond between two atoms.
-if the bond is non-polar, the charge is evenly distributed across the bond.
-If the bond is polar, one end of the bond will have a slightly positive charge and the other end will have a slightly negative charge

Question 15

Explanation of H2O polarity.

Answer 15

-2 O-H bonds have permanent dipole
-act in diff directions but do not oppose each other
-O end has minus and H end has +

Question 16

Explanation of CO2 non-polarity.

Answer 16

2 C=O bonds have permanent dipoles
-act in opposite directions and directly oppose each other
-Dipoles cancel so overall dipole is 0

Question 17

Explanation for solubility of polar solvents.

Answer 17

The water molecules attract the negative and positively charged ions in the compound
The ionic lattice breaks down
Which means water molecules then surround the ions in the polar solvent
Cations attracted to delta -
Anions attracted to delta+

Question 18

General intermolecular forces definition.

Answer 18

Weak interactions between dipoles of different molecules.

Question 19

3 types of IMFs.

Answer 19

Induced dipole-dipole interactions(london forces)
Permanent dipole-dipole interactions
Hydrogen bonding.

Question 20

London forces origin/formation.

Answer 20

-Electron movement produces a changing dipole
-At any time, an instantaneous dipole will exist, but position is constantly shifting
-instantaneous dipole induces dipole on neighbouring molecule
-Induced dipole induced further dipoles on neighbouring molecules
-then attracts another
Temporary.

Question 21

The strength of london forces.

Answer 21

More electrons in a molecule:
-larger instantaneous and induced dipoles
-greater induced dipole-dipole interactions
-stronger attractive forces between molecules
-Higher boiling point as more energy needed to overcome IMFs

Question 22

Formation of permanent dipole-dipole interactions.

Answer 22

Act between permanent dipoles in different polar molecules

Question 23

What IMFs do polar molecules contain vs non polar?(effect on bp)

Answer 23

Polar have London forces and permanent dipole-dipole interactions
Non-polar only have London forces
Therefore boiling point of Polar molecules is higher than non-polar.

Question 24

Structure of simple molecular lattices.

Answer 24

-Covalently bonded molecules(strongly between molecules)
-Held in place/attracted by weak intermolecular forces between atoms.

Question 25

Boiling point and explanation of simple molecular substances.

Answer 25

Low melting and boiling point:
-Weak intermolecular forces can be broken by low temperatures
-Only weak intermolecular forces break when melting
-the covalent bonds are strong and do not break.

Question 26

Solubility and explanation of non-polar simple molecular substances.

Answer 26

In non-polar solvent are soluble:
-IMFs form between molecules and the solvent.
-These interactions weaken the IMFs in the simple molecular substance
-IMFs forces break and compound dissolves.
In polar solvent are insoluble:
-little ineraction between molecules in lattice and solvent molecules
-IM bonding in polar solvent too strong to break.

Question 27

Solubility and explanation of polar simple molecular substances.

Answer 27

Soluble in polar solvents:
-can form IMFs w/ other polar molecules
-because of perm dipole-dipole or H bonding
Insoluble in non-polar solvents:
-cant form as strong IMFs or not at all

Question 28

Electrical conductivity and explanation of simple molecular substances.

Answer 28

Non-conductors in solid or liquid:
-No mobile charged particles
-Cannot carry an electrical charge/complete and electrical circuit
-No ions or delocalised electrons.

Question 29

Hydrogen bonding definition.

Answer 29

Permanent dipole dipole interactions between molecules with:
-an electronegative atom w/ a lone pair of electrons(O, N or F)
-a hydrogen atom attached to an electronegative atom(H-O, H-N or H-F)

Question 30

Properties in the hydrogen bond.

Answer 30

Act between lone pair of electronegative atom in one molecule and H atom of another molecule.
Strongest type of IMF.
Shape around bond=linear.

Question 31

Explanation of density of ice.

Answer 31

Solid ice is less dense than water:
-Hydrogen bonds hold water molecules apart in an open lattice structure
-Water molecules in ice are further apart than in water
-Floats in water.
-Each water molecule can form 4 hydrogen bonds
-bonds extend outwards, holding molecules further apart in terahedral open lattice w/ holes
-180 degree bond angle
-holes decreases density
-when melts move closer again as lattice collapses.

Question 32

Explanation of boiling and melting point.

Answer 32

Relatively high:
-has london forces
-H bonds=extra forces over and above these
-more energy needed to break the H bonds
-so higher bp than just london forces
-H bonds break completely when boiled
-when ice melted only arrangement of h bonds in ice is broken.

Question 33

Other anomalous properties of H2O due to H bonding.

Answer 33

-high surface tension and viscosity(fluids resistance to flow)
-Detergents reduce surface tension=wetter water.