Bonding

Question 1

Why is ice less dense than water ?

Answer 1

ice molecules arrange themselves in a rigid tetrahedral structure ( hexagonal rings) which causes big gaps in their bonding. on the other hand water molecules remain in linear bonding form so molecules are held a lot closer together ( by hydrogen bonds)

Question 2

How does ion charge affect melting point

Answer 2

the greater the charge on the ion the greater the electrostatic attraction ( stronger ionic bond) so more energy is needed to break the bonds. hence a higher melting point.

Question 3

Which has the highest medium and lowest mp out of sodium, magnesium and potassium ?

Answer 3

Mg has the highest mp because it forms a 2+ charge unlike the other two group 1 metals. Then sodium because it is in period 2 and so has a higher charge density due to less shells ( more positive charge concentrated on fewer electron shells) and finally potassium which has a lower charge density because it is in period 3 and has more shells

Question 4

What is a coordinate/ dative bond ?

Answer 4

a normal covalent bond, but one molecule supplies both electrons. on a displayed formula a dative bond is shown by an arrow

acceptor atom receiving eelctrons must be electron deficient for dative bond to form

Question 5

What is an ionic bond ?

Answer 5

• the force of electrostatic attraction, not the transfer of electrons ( that is how ionic bond is formed)

Question 6

What is electronegativity

Answer 6

ability of an atom to attract the electron pair in s covalent bond to itself

Question 7

What is a polar bond vs a non polar bond

Answer 7

• different atoms with different electronegativities, one will pull on electron pair more, so will have a slight neg charge, other slightly pos charge. Dipole formed and bond is said to be polar

non polar - similar atoms have the same electronegativity so will both pull on electrons to the same extent meaning they are equally shared.

Question 8

What is Pauling scale

Answer 8

a scale for measuring electronegativity. 4 will have the highest electrnegativity

Question 9

What is a permanent dipole

Answer 9

• regions of partial positive and negative charge within same molecule

Question 10

How can dipoles interact

Answer 10

• attract the opposite charges on neighbouring molecules
• slight positive reg would attract slight negative reg on neighbour molecule

Question 11

What is a hydrogen bond ?

Answer 11

• attraction between slight positive charge on one atom of molecule and lone pair of electrons
• very strong
• hydrogen must be directly bonded to electronegative element ie oxy, fluorine and there must be a lone pair of electrons not bonded present

Question 12

how are temporary dipoles formed?

Answer 12

• when two atoms come towards each other electrons repel each other
• causes sudden displacement of electrons to one side, causing atom to have a temp dipole
• side where electrons have moved to would have slight neg charge and other side would have a slight pos charge.
• this is known as an instantaneous dipole
• this atom can now repel another atom and cause a shift in its electrons to one side, thus inducing a dipole ( not the same as an instantaneous dipole)

Question 13

What are the three types of intermolecular forces and which are the strongest and weakest

Answer 13

permanent dipoles, hydrogen bonding and induced dipole

strongest is hydrogen bonding and weakest is induced dipole

Question 14

How does electronegativity progress accross a period

Answer 14

• across period from left to right electronegativity of atoms increases due to them having a greater number of protons to more strongly attract electrons in the covalent bond

Question 15

How does electronegativity progress down a group ?

Answer 15

• decreases because atoms have more energy levels and so shielding effect is increased, therefore harder to pull attract electrons in covalent bond

Question 16

A molecule may be non polar even if it has polar bonds. How is this determined?

Answer 16

• if molecule is symmetrical will usually be non polar because dipoles do cancel out

Question 17

Where are temporary dipoles also known as London forces found ?

Answer 17

all molecules

Question 18

How does hydrogen bonding affect water properties

Answer 18

• high boiling point of water due to strong hydrogen bonds
• ice less dense than water due to water molecules being further apart than in liquid water. In ice water molecules are arranged in a ordered structure stabilised by network of hydrogen bonds

Question 19

What are simple molecules

Answer 19

• small molecules with a fixed number of atoms

Question 20

What does the solid line tell you in a compound? ( the solid lines representing the bonds)

Answer 20

tells you that the two bonds lie on the plane of the screen or the page

Question 21

What does the solid wedge shape tell you ?

Answer 21

Bond is coming out of the plane of the page

Question 22

What does a dotted wedge tell you?

Answer 22

bond is projecting back behind the plane of the page

Question 23

What does electron pair repulsion theory state?

Answer 23

The shape of the molecule is determined by the electron pairs surrounding the central atom. only refers to the outer shells in this case because pairs of electrons repel all of the other electron pairs.

Question 24

What does the repulsion of the electrons cause ?

Answer 24

Move as far apart as possible to minimise repulsion, and assume a shape that most minimises this.

Question 25

If you have BeCl2 what would the shape look like?

Answer 25

would be linear because there are two pairs of electrons ( covalent bonds) surrounding the central atom. So they will push as far away from each other as possible the furthest they can get is 180 degrees.

Question 26

When looking at double or triple bonds how do you treat the bonding area?

Answer 26

You treat it as a single bonding area and so therefore even if there is a double or triple bond this doesn’t affect the shape of the molecule

Question 27

If you have BF3 what does the shape of the molecule look like?

Answer 27

Central boron atom bonded to three fluorine atoms, in a trigonal planar shape which has a bond angle of 120 degrees.

Question 28

When will you have a trigonal planar compared to a linear shape of a molecule?

Answer 28

• If you have a central atom bonded to three pairs of electrons you will have a trigonal planar shape while otherwise if you have two pairs of electrons you will have a linear shape. ( 180 degrees) if no lone pairs

Question 29

What are the bond angles in a tetrahedral molecule ?

Answer 29

109.5 degrees

Question 30

What if the central atom has 5 pairs of electrons

Answer 30

Two of the bonding pairs move to opposite sides of the molecule to minimize repulsion. The other three bonding pairs now take up a central position lying on the same plane, and spread themselves out as far as they can.

Question 31

What are the bond angles if the central atom has 5 pairs of electrons?

Answer 31

two bond angles to consider, one of which is 90 degrees and the other one of 120 degrees. the shape is trigonal bipyramidal because the base is a triangle and two pyramids are formed between the other atoms, one above and one below the plane.

Question 32

What is the shape of a molecule with 6 electron pairs around the central atom?

Answer 32

octahedral shape, bonding pair above and below the central plane, and 4 bonding pairs lying on the central plane. Bonds pointing up and down at 9-0 degrees to CP angle between bonds lying on CP also 90 in this case.

Question 33

Do dative bonds have an effect on the shape of a molecule?

Answer 33

No they don’t

Question 34

What can be said about lone pairs compared to bonding pairs?

Answer 34

Lone pairs repel more strongly, extra repulsion decreases bond angles by 2.5 degrees.

Question 35

What is the shape of H20 ( water) taking into account lone pairs of electrons?

Answer 35

oxygen has two lone pairs of electrons because has 6 valence electrons and only 2 used up in bonding. One lone pair reduces the bond angle by 2.5 degrees, so all together would be reduced by 5 degrees so the bond angle is reduced to 104.5 degrees instead of 109 degrees. shape is tetrahedral because there are 4 bonding areas ( 4 pairs of electrons)

Question 36

What is the difference between tetrahedral and square planar shape

Answer 36

• square planar is basically the same, only difference is that with sq planar shape there are two lone pairs on central atom.

Question 37

hydrogen bonding occurs when ?

Answer 37

between hydrogen and either fluorine, nitrogen or oxygen