Bonding

Question 1

Describe the effect of lone pairs on the shape of molecule

Answer 1

Lone pairs have greater charge density which then means greater repulsion which pushes the bonded pairs closer together by 2.5/

Question 2

What are lone pairs

Answer 2

They are the electrons which are not bonded /shared to another atom in a covalent bond.
Can go up to two lone pairs (reduces by 5 degrees)

Question 3

How to work out shapes

Answer 3

1.) find group of central atom
2.) workout how many atoms are bonded to central number
3.) if there is a positive charge you take away ,if there is a negative you aff
4.) add that all together the divide by two
3.)compare to bonded atoms by taking away the pairs to find lone pairs

Question 4

What are the 6 shapes for molecules

Answer 4

Linear — 2 electron clouds

Trigonometry planar -3 electron clouds

Tetrahedral -4 electron clouds

Trigonal bipyramidal —5 electron clouds

Octahedral —6 electron clouds

Question 5

What the bond angles for all the shape

Answer 5

*pyramidal has -107
*For trigonal planar — 120 degrees
*For tetrahedral - 109.5 degrees
*For trigonal bipyramid -90 degrees and 120 degrees
*For octahedral - 90 degrees

Question 6

Describe the pyramidal shape

Answer 6

Molecules that would usually be a tetrahedral shape ,
when the have 3 bonded pair and one lone pair
107 degrees

Question 7

Describe v shape molecule

Answer 7

V shaped molecules have 2 bonding pairs
With 2 lone pairs
Bond angle of 104.5 degrees

Question 8

Describe a macro molecular structure

Answer 8

They are covalently bonded into a giant lattice structure
Each atom has a covalent bond
Giving high melting point
The strength makes macro molecule rigid

Question 9

Describe simple molecular structures

Answer 9

Covalently bonded molecules
With weak van set walls forces of attraction between them

Due to weak van der wals forces ,the molecule has low melting and boiling points

Question 10

The melting point of XeF4 is higher than the melting point of PF3
Explain why the melting points of these two compounds are different.

Answer 10

xef4 has a square planar shape with two lone pairs

whilst pf4 has a pyramidal shape
where electrons repel as far as possible

Xe has van der waals forces whilst PF4 has dipole dipole forces which are stronger than van der waals forces.
meaning more energy is required to break the forces of attraction between molecules.

Question 11

Explain why a fluoride ion is larger than a sodium ion.

Answer 11

Fluoride ion has (two) fewer protons/lower nuclear charge

Weaker attraction between nucleus and (outer) electrons

Question 12

Name the type of bond formed when HF reacts with H+
Explain how this bond is formed.

Answer 12

Coordinate bond
A (lone) pair of electrons is donated from F

Question 13

Explain, in terms of structure and bonding, why the melting point of sodium
fluoride is high.

Answer 13

(Electrostatic) forces of attraction between
oppositely charged ions/Na+ and F

Lots of energy needed to overcome/break forces

Question 14

What is simple molecular bonding

Answer 14

-Strong covalent bonds ,weak van der waals forces of attraction

-no lone pairs involved

Question 15

Do simple molecular structures have high or low boiling points

Answer 15

Low- weak van der waals forces of attraction between molecules

Doesn’t require as much energy to over come these forces

Question 16

Describe the structure of graphite

Answer 16

Each carbon is covalently bonded to three others

Van der waals forces of attraction between layers so can slide over each other

One electron from each carbon is delocalised and can carry charge

Question 17

define electronegativity

Answer 17

Electronegativity is the relative tendency of an atom in a covalent bond
in a molecule to attract electrons in a covalent bond

Question 18

describe permanent dipole-dipole forces

Answer 18

*Permanent dipole-dipole forces occurs between polar molecules
*It is stronger than Van der Waals and so the compounds have higher boiling points
*Polar molecules have a permanent dipole. (commonly compounds with C-Cl, C-F, C-Br H-Cl, C=O bonds)
*Polar molecules are asymmetrical and have a bond where there is a significant difference in
electronegativity between the atoms

Question 19

what is the main factor effecting van der waals forces

Answer 19

The more electrons there are in the molecule the higher the chance that temporary dipoles will form. This
makes the Van der Waals stronger between the molecules and so boiling points will be greater.

Question 20

when does hydrogen bonding occur

Answer 20

It occurs in compounds that have a hydrogen atom attached to one of the three most
electronegative atoms of nitrogen, oxygen and fluorine, which must have an available lone pair of
electrons.

Question 21

describe when a polar bond occurs

Answer 21

A polar covalent bond forms when the elements in the bond have different
electronegativities . (Of around 0.3 to 1.7)
When a bond is a polar covalent bond it has an unequal distribution of
electrons in the bond and produces a charge separation, (dipole)

Question 22

simple molecular lattice

Answer 22

a three dimensional structure of molecules held together by intermolecular forces