bonding and structure: content

Question 1

what is an ionic bond in terms of electronegativity

Answer 1

when the difference between electronegativities is greater than 2.1 and the electron is transferred from the [metal] to the [nonmetal]

Question 2

structure of ionic substances

Answer 2

ALWAYS giant ionic
strong

Question 3

physical properties of ionic compuonds

Answer 3

high melting and boiling points
do not conduct in the solid state (no mobile charge carriers)
conduct when aqueous or molten (mobile ions)
most are soluble (polar substances dissolve in polar substances [water])

Question 4

what factors influence the strength of ionic bonding

Answer 4

the greater the ionic charge
the smaller the ionic radius
the greater the difference in electronegativity

Question 5

octet rule

Answer 5

atoms want a noble gas electron configuration (eight valence electrons) in order to become stable

Question 6

**exceptions to the octet rule! **
molecules where the central atom is stable with <8 outer shell electrons

Answer 6

BF₃: boron trifluoride
- boron has six valence electrons

AlCl₃: aluminium chloride
- aluminium has six valence electrons

Question 7

when can you expand the octet

Answer 7

when the central atom is in group three or higher (max no. of e⁻ in a shell = 2n²)

Question 8

**exceptions to the octet rule! **
molecules where the central atom is stable with >8 outer shell electrons

Answer 8

PCl₅: phosphorus pentachloride
- phosphorus has 10 valence electrons

SF₆: sulphur hexafluoride
- sulphur has 12 valence electrons

Question 9

criteria for a dative covalent bond

Answer 9

the atom donating must have a lone pair
the atom receiving must have a vacant orbital

Question 10

how are dative covalent bonds represented

Answer 10

donor species → receiving species

Question 11

order or electron pair repulsion

Answer 11

LEAST REPULSION
bonding region - bonding region
lone pair - bonding region
lone pair - lone pair
MOST REPULSION

Question 12

VSEPR structure: bond going into the page

Answer 12

Question 13

VSEPR structure: bond coming out of the page

Answer 13

Question 14

2 bonding regions
0 lone pairs

Answer 14

linear 180°

Question 15

2 bonding regions
1 lone pair

Answer 15

nonlinear 117.5

Question 16

3 bonding regions
0 lone pairs

Answer 16

trigonal planar 120°

Question 17

4 bonding regions
0 lone pairs

Answer 17

tetrahedral 109.5°

Question 18

3 bonding regions
1 lone pair

Answer 18

trigonal pyramid/pyramidal 107°

Question 19

2 bonding regions
2 lone pairs

Answer 19

nonlinear 104.5°

Question 20

6 bonding regions
0 lone pairs

Answer 20

octahedral 90°

Question 21

4 bonding regions
2 lone pairs

Answer 21

square planar 90°

Question 22

effect of each lone pair present on the bond angle

Answer 22

reduces the bond angle by roughly 2.5°

Question 23

methods for identifying molecular shapes/bond angles

Answer 23

• dot and cross diagram
• count e⁻ pairs
• any remaining e⁻ (from group no. of central atom) will be lone pairs
• group no. of central atom
• add one for each bond made
• divide by two for the number of e⁻ pairs

Question 24

effect of double/triple bonds on bond angles

Answer 24

none: all bonding regions have equal repulsion regardless of bond strength

Question 25

electron structure of diatoms

Answer 25

nuclei are identical so attraction to electrons is equal ** electron density is distributed equally** : nonpolar both atoms have the same electronegativity

Question 26

factors affecting electronegativity

Answer 26

- atomic radius of the atom - nuclear charge (no. of protons) - number of principal energy levels

Question 27

how does atomic radius impact electronegativity

Answer 27

smaller radius → electrons can get closer to nucleus → greater attractive force → more electronegative

Question 28

how does nuclear charge impact electronegativity

Answer 28

more protons → stronger attractive forces between nucleus and attracted e- pair → more electronegative

Question 29

how does the number of principal energy levels impact electronegativity

Answer 29

more energy shells → more shielding → weaker attractive forces → less electronegative

Question 30

most electronegative atoms

Answer 30

FLUORINE, oxygen, nitrogen, chlorine

Question 31

electron distribution within a polar bond

Answer 31

electronegativities are not equal electron attraction is not equal electron density distribution is not equal one side is slightly more positive than the other: opposite sides create a dipole

Question 32

polarity of C-H bonds

Answer 32

nonpolar

Question 33

difference between polar molecules and polar bonds

Answer 33

polar molecules have overall [partial] charges polar bonds have dipoles but these may cancel out within a nonpolar molecule

Question 34

when will polar bonds form part of a nonpolar molecule

Answer 34

when the molecule is symmetrical equal pull on the central atom in [horizontal and vertical] components all non-central atoms have equal polarity and electronegativity

Question 35

what holds simple molecules together

Answer 35

intermolecular forces (NOT covalent bonds)

Question 36

london / induced dipole-dipole forces

Answer 36

experienced by all molecules weakest IMF

Question 37

how do London forces work

Answer 37

- electrons move randomly within the e⁻ cloud - this creates temporary dipoles - these induce dipoles in neighbouring molecules (like charge repulsion). - the opposite dipoles attract

Question 38

what factors affect the strength of induced dipole-dipole forces

Answer 38

Mᵣ of the molecule (bigger → more electrons) surface area contact between molecules

Question 39

how does molecule size affect the melting point and why

Answer 39

the larger the molecule, the stronger the IMFs so the more energy is needed to overcome them; hence the higher the melting/boiling points

Question 40

what imfs do nonpolar molecules have

Answer 40

ONLY idd/London forces

Question 41

why are permanent dipole-dipole forces stronger than London?

Answer 41

the dipoles are always there

Question 42

when do you get permanent dipole-dipole forces

Answer 42

between polar molecules (attraction between ẟ⁺ and ẟ⁻) on adjacent molecules

Question 43

which atoms can form hydrogen bonds

Answer 43

F-H O-H N-H

Question 44

how do hydrogen bonds work

Answer 44

F,N,O are the most electronegative atoms there is a big difference in electronegativities so they attract the electron pair very strongly the hydrogen nucleus is left very ẟ⁺ a lone pair on F, N or O on a neighbouring molecule is attracted to the hydrogen

Question 45

features of a hydrogen bond (MUST show + label)

Answer 45

partial charges on all atoms lone pairs clearly displayed hydrogen bond between lone pair and ẟ⁺ H

Question 46

why is ice less dense than liquid water

Answer 46

h-bonds molecules are held further apart in the solid state than in the liquid fewer molecules per unit volume more space between molecules ('open lattice')

Question 47

why does water have a relatively high melting and boiling point

Answer 47

anomalously high (when looking at group 6 hydrides) due to the presence of hydrogen bonds