bonding + structure

Question 1

what is a covalent bond?

Answer 1

the strong electrostatic attraction between a shared pari of electrons and the nuclei of the bonded atoms

Question 2

what is an ionic bond?

Answer 2

the electrostatic attraction between positive and negative ions

Question 3

what is a dative covalent bond?

Answer 3

a covalent bond in which the shared pair of electrons have been provided by one atom only

Question 4

what is the octet rule?

Answer 4

the maximum number of electrons that can pair up is equivalent to the number of electrons in the outer shell and unpaired electrons pair up

Question 5

what is the electron repulsion theory?

Answer 5

the shape of a molecule is determined by the number pf electron pairs in the outer shell. these electron pairs repel each other and arrange themselves as far apart as possible

Question 6

what structure does 2 outer shell electron pairs give?

Answer 6

linear. 180 degree bond angle.

eg. BeCl2

Question 7

what structure does 3 outer shell electron pairs give?

Answer 7

trigonal planar. 120 degree bond angle.

eg BF3

Question 8

what structure does 4 outer shell electron pairs give?

Answer 8

tetrahedral. 109.5 degree bond angle.

eg. CH4

Question 9

what shape does 5 outer shell electron pairs give?

Answer 9

trigonal bi-pyramid. 120 degree horizontal bond angle and 90 degree vertical bond angle.
eg. PCl5

Question 10

what structure does 6 outer shell electron pairs give?

Answer 10

octahedral. 90 degree bond angle

eg. SF6

Question 11

lone pairs:

Answer 11

don’t take part in bonding, but do participate in electron repulsion. each lone pair reduces bond angles between bonded atoms by 2.5 degree.

Question 12

order of electron repulsion:

Answer 12

LP-LP > LP-BP > BP-BP

Question 13

structure of 3 outer shell electron pairs + 1 lone pair =

Answer 13

pyramidal. each angle 117.5 degrees

eg. PH3

Question 14

structure of 4 outer shell electron pairs + 2 lone pairs =

Answer 14

square planar. 90 degree bond angle

eg. XeF4

Question 15

what is electronegavity?

Answer 15

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

Question 16

what is a dipole?

Answer 16

a separation of charge across a distance (a difference in charge)

Question 17

what is a polar covalent molecule?

Answer 17

a molecule that has an overall dipole when you take into account any dipoles across the bonds

Question 18

what is a non polar covalent molecule?

Answer 18

a molecule that has no overall dipole when you take into account any dipoles across the bonds

Question 19

what is a polar covalent bond?

Answer 19

a covalent bond in which the bonding atoms have a difference in electronegavity and so has a permanent dipole.

Question 20

what is a non polar covalent bond?

Answer 20

a covalent bond in which the bonding atoms have the same electronegativity and so there is no permanent dipole

Question 21

the bonding atom with the higher electronegativity takes which delta?

Answer 21

the negative one as it acquires a partial negative charge

Question 22

the bonding atom with the lower electronegativity takes which delta?

Answer 22

the positive one as it acquires a partial positive charge

Question 23

what is a permanent dipole?

Answer 23

a small charge difference across a bond that results from a difference in the electronegativites of the bonded atoms.

Question 24

name the 3 types of intermolecular forces

Answer 24

permanent dipole-dipole forces
London forces
hydrogen bonds

Question 25

how do permanent dipole-dipole forces arise?

Answer 25

if the atoms involved in a bond have different electronegativities, the bond will be polar and the molecule will have a permanent dipole. these are then attracted to neighbouring molecules, positive - negative

Question 26

how do London forces arise?

Answer 26

1. at any moment, oscillations in an atom produce an instantaneous dipole - with more electrons in one area of the outer shell than another
2. these dipoles induce further dipoles in neighbouring molecules
3. induced dipoles attract one another

Question 27

how do hydrogen bonds arise?

Answer 27

an electron deficient Hydrogen atom attracts a lone pair of electrons on a highly electronegative atom (oxygen, nitrogen or fluorine) bonded within a different molecule

Question 28

what is a hydrogen bond?

Answer 28

a strond dipole - dipole attraction between an electron deficient H atom in one molecule and a lone pair of electrons on a different, highly electronegative atom such as oxygen, fluorine or nitrogen.

Question 29

order of strength of bond forces:

Answer 29

ionic + covalent > hydrogen bonds > dipole-dipole forces > London forces

Question 30

special properties of water due to hydrogen bonds:

Answer 30

ice is less dense than water

water has higher than expected melting and boiling points

Question 31

why is ice less dense than water?

Answer 31

in ice, water molecules are in an orderly pattern in an open lattice held apart by rigid hydrogen bonds. when ice melts some of these hydrogen bonds collapse and so molecules can move closer together, becoming more dense.

Question 32

why does water have higher boiling + melting points than expected?

Answer 32

hydrogen bonds are stronger than other molecular forces, the extra strength of which has to be overcome when melting/boiling, therefore requires more energy and has higher melting/boiling points