Topic 2

Question 1

What is a dative covalent bond

Answer 1

A covalent bond that’s electrons only come from one of the bonding atoms

Question 2

What’s electronegativity

Answer 2

The relative tendency of an atom in a covalent bond in a molecule to attract electrons in a covalent bond to itself

Question 3

What increases electronegativity and how

Answer 3

Going across a period increases electronegativity because protons increase and atomic radius decrease because electrons in the same shell are pulled in more

Question 4

What decreases electronegativity

Answer 4

Going down a group decreases it because the Distance between the nucleus and Valence electrons increases and shielding increases

Question 5

What are London forces

Answer 5

A temporary attractive force that cause non polar substances to condense, they’re induced dipoles

Question 6

What are induced dipoles and how are they formed

Answer 6

And attraction that results when a polar molecule induces a dipole in an atom

Question 7

How do shapes of molecules affect London forces

Answer 7

Long straight chain alaknes have a larger surface area of contact between molecules for London forces to form, so have stronger London forces

Question 8

Give features of dipole dipole forces

Answer 8

-Occurs between polar molecules
-Stronger than London forces (higher boiling point)
-Have a permanent dipole
-Asymmetrical
-Have a bond where there’s a significant difference in electronegativity between atoms

Question 9

Explain hydrogen bonding

Answer 9

-Occurs when compounds have a hydrogen atom attached to one of the three most electronegative atoms (nitrogen ,flourine and Oxygen)
-Must have an available lone pair of electrons

Question 10

Give features of hydrogen bonding

Answer 10

Occurs in addition to London forces
Hydrogen bond should have a bond Angle of 180 degrees
Water can form 2 hydrogen bonds

Question 11

how does electronegativity work with covalent bonds

Answer 11

one atom in the molecule will have more electronegativity, and thus attract the electron pair more than the other

this means the electron pair will not be in the centre of the bond

this causes the build up of a partial charge on one atom (delta positive/ negative)

Question 12

explain polarity

Answer 12

the more electronegative atom in a bond will have a partial delta negative charge and vice versa- this is called a permanent dipole

example of permanent dipole is HCl

a non polar bond is when the atoms have similar electronegativity so the bond is not polar

Question 13

explain how polarity in bonds affects polarity

Answer 13

molecules can be polar if it has polar bonds

if the molecule has a charge separation/ asymmetry there will be a permanent dipole- for example CHCl3

a molecule with polar bonds is not always polar
if the bonds are symmetrical the charges will be symmetrical

therefore a non polar molecule- for example CCl4

Question 14

what is the strength relation between intermolecular forces(weakest to strongest)

Answer 14

induced dipole-dipole interactions
permanent dipole-dipole interactions
hydrogen bonds

covalent bonds are the strongest

Question 15

explain temporary dipoles

Answer 15

the electron clouds around molecules are always moving, and at one point all of the electron density can be on one side

this is called a temporary dipole-there a constantly changing partial charges

Question 16

explain induced dipoles

Answer 16

if one molecule has a temporary dipole, its partial charges will exert a force on nearby molecules

the partial charge on one molecule can push away the electrons in nearby molecules
-this means that temporary dipoles will induce dipoles in nearby molecules
-once a dipole has been induced, it will be attracted to the initial dipole

Question 17

explain how strength of induced dipole interactions varies

Answer 17

the strength depends on the number of electrons in a molecule

molecules with more electrons will have stronger induced dipole interactions

this is because they will have larger fluctuations in electron density

this leads to larger temporary dipoles and stronger dipole-dipole interactions

induced dipole interactions are also called London forces

Question 18

explain how an induced dipole is formed

Answer 18

molecule has temporary dipole

its partial charges exert a force on nearby molecules

the partial charge on one molecule can push electrons away in another molecule

this induces a dipole on the other molecule

the 2 temporary dipoles then attract each other

Question 19

explain permanent dipole-dipole interactions

Answer 19

permanent dipoles have a delta positive and negative side

the delta positive side of one molecule will interact with the delta negative side of another molecule

this means that that the molecules will line up throughout a liquid or solid in this fashion

permanent dipole-dipole interactions are only possible in molecules that have a permanent dipole- so they’re only found between polar molecules

Question 20

explain hydrogen bonds

Answer 20

with very electronegative elements, hydrogen can form extremely strong dipole-dipole interactions-when they’re strong enough to be considered a bond, they are called a hydrogen bond

they’re made when hydrogen bonds to either fluorine, oxygen or nitrogen

the hydrogen atom will form a strong permanent dipole-dipole interaction with another oxygen, nitrogen or fluorine atom E.g H2O, NH3, HF

Question 21

why do hydrogen bonds form

Answer 21

when hydrogen is bonded to an extremely electronegative element it develops a strong delta positive charge

hydrogen is a very small atom, so it has a high charge density in this situation, which allows it to form a strong bond with any highly delta negative atom

Question 22

explain the trends of boiling points in alkanes in terms of intermolecular forces

Answer 22

for straight chain alkanes the boiling points increases with chain length
longer chained molecules have the opportunity for greater interactions via induced dipole-dipole interactions when they’re aligned to each other.

branching reduces the boiling point of alkanes because branching reduces the extent to which 2 molecules can align and form induced dipole-dipole interactions

Question 23

why’re alkanes unreactive

Answer 23

high bond enthalpy (energy needed to break bond)
s

sigma bonding present which means there is a lack of bond polarity

Question 24

explain the difference in alcohols and alkanes

Answer 24

the boiling point of alcohols is always much higher than alkanes with the same number of carbons- butanol has higher boiling point than butane

this is because alcohols have hydrogen bonds which need a lot more bonds to break that the van der Waals forces in the alkane

as more carbons are added, the hydrogen bonding and dipole-dipole interactions will remain the same for all alcohols, but the van der Waals forces increases with more carbons

Question 25

explain the trend in hydrogen halides boiling points

Answer 25

fluorine is able to form hydrogen due to its high electronegativity chlorine and bromine can not form hydrogen bonds hydrogen bromide will be stronger than hydrogen chloride because bromide is bigger than chloride , so bromide has stronger van der Waals forces

Question 26

what is the trend in hydrogen halides boiling points

Answer 26

1.hydrogen fluoride 2.hydrogen iodide 3.hydrogen bromide 4.hydrogen chloride

Question 27

explain the structure in metallic bonding

Answer 27

valence electrons delocalise and can move about the entire material like a sea of free electrons metallic bonding is a sea of free electrons surrounding positive ion cores, where the positive ion cores attracted to the free elctrons

Question 28

what are the features of metallic bonding

Answer 28

metals are good conductors because the free electrons can move and carry a current the melting point of a metal is related to its group a group 2 metal will donate 2 electrons to the sea of electrons and therefore the positive ion cores will have a 2+ charge more electrons in the sea the higher boiling point

Question 29

what are the 4 types of solid structure

Answer 29

ionic- formed by compounds of metals with non-metals, any salt is ionic E.g sodium chloride and lithium bromide metallic-pure metals E.g magnesium and sodium molecular-1 of the 2 structures formed by covalent bonding E.g iodine giant covalent-1 of the 2 structures formed by covalent bonding E.g diamond and graphite

Question 30

what are the crystalline properties of molecular solids

Answer 30

weak intermolecular forces low melting points -often gasses or liquids at room temperature do not conduct electricity some molecular solids may dissolve in water but many will not

Question 31

what are the crystalline properties of giant covalent crystals

Answer 31

giant covalent crystals have strong covalent bonds throughout the structure high melting and boiling points many giant covalent crystals will sublime (go from solid to gas ) do not dissolve in anything

Question 32

what are the crystalline properties of ionic crystals

Answer 32

strong electrostatic attractions between ions high melting points ions fixed in place, so ionic crystals cannot conduct electricity when solid ions are charged, and so are soluble in polar solvents like water in solution can conduct electricity

Question 33

what are the crystalline properties in metals

Answer 33

sea of free electrons strong electrostatic attraction means high boiling point conducts electricity when solid because free electrons usually dont dissolve in water because many will react to form metal hydroxides

Question 34

give features of intermolecular forces in molecular solids

Answer 34

molecular solids are held together by intermolecular forces intermolecular forces are forces between molecules that are not bonds these forces are weak and easy to break in melting a molecular solid, the intermolecular forces are broken but the covalent bond are not broken

Question 35

give features of giant covalent solids

Answer 35

in giant covalent solids the entire solid is the one molecule the only forces present are INTRAmolecular forces these forces are known as covalent bonds INTRAmolecular forces are much stronger than intermolecular forces this means that giant covalent structures have much higher melting points because covalent bonds must be broken