3.5- FORCES ACTING BETWEEN MOLECULES

Question 1

How are atoms in molecules and in giant structures held together?

Answer 1

by strong covalent, ionic, or metallic bonds

Question 2

How are molecules and separate atoms attracted to one another?

Answer 2

by weaker forces called intermolecular forces

Question 3

What does inter mean?

Answer 3

between

Question 4

What happens if the intermolecular forces are strong enough?

Answer 4

then molecules are held closely enough together to be liquids or even solids

Question 5

What are the three types of intermolecular forces and order from weakest to strongest?

Answer 5

van der Waals forces

dipole-dipole forces

hydrogen bonding

Question 6

What is polarity the property of?

Answer 6

property of a particular bond

Question 7

What may molecules with polar bonds have?

Answer 7

dipole moment

Question 8

What may happen in molecules with more than one polar bond? (2)

Answer 8

effects of each bond may cancel, leaving molecule with no dipole moment

effects may add up so reinforce each other

Question 9

What is the dipole moment?

Answer 9

sums up the polarity of all the bonds in the molecule

Question 10

What determines what happens in a molecule with more than one polar bond?

Answer 10

shape of the molecule

Question 11

What shape does carbon dioxide have?

Answer 11

linear molecule

Question 12

What happens to the dipoles in carbon dioxide as it’s a linear molecule?

Answer 12

dipoles cancel

Question 13

What shape does tetrachloromethane have?

Answer 13

tetrahedral

Question 14

What happens to the dipoles in tetrachloromethane as it has a tetrahedral shape?

Answer 14

dipoles cancel

Question 15

Where does dipole-dipole forces act between?

Answer 15

molecules that have permanent dipoles q

Question 16

What will two molecules which both have dipoles do?

Answer 16

attract one another

Question 17

Whatever the starting positions of the two molecules which have dipoles, what will they do?

Answer 17

molecules with dipoles will ‘flip’ to give an arrangement where the two molecules attract

Question 18

What are all atoms and molecules made up of although they’re neutral overall?

Answer 18

positive and negative charges

Question 19

What do the charges in all atoms and molecules produce?

Answer 19

very weak electrostatic attractions between all atoms and molecules

Question 20

What is the very weak electrostatic attractions between all atoms and molecules called?

Answer 20

van der Waals forces

Question 21

How long does any particular dipole last for?

Answer 21

just an instant- temporary dipole

Question 22

What does the dipole do to nearby atoms?

Answer 22

affects electron distribution in nearby atoms

Question 23

What happens as the dipole affects the distribution of electrons in nearby atoms?

Answer 23

nearby atoms attracted to atom with dipole

Question 24

What happens when the electron distribution of the original atom changes?

Answer 24

induce new dipoles in the atoms around it, which will be attracted to original one

Question 25

What can van der Waals forces also be called?

Answer 25

instantaneous dipole-induced dipole forces

Question 26

Where and when do van der Waals forces act?

Answer 26

between all atoms or molecules at all times

Question 27

Are VDW forces an addition to any other intermolecular forces?

Answer 27

yes

Question 28

What is the dipole caused by?

Answer 28

changing position of the electron cloud

Question 29

What causes a larger instantaneous dipole?

Answer 29

the more electrons there are

Question 30

What increases the size of VDW forces?

Answer 30

size of VDW forces increases with number of electrons present

Question 31

What types of atoms/molecules will produce stronger VDW forces?

Answer 31

atoms/molecules with larger atomic or molecular masses

Question 32

What does atoms/molecules with larger atomic or molecular masses having stronger VDW forces explain? (2)

Answer 32

boiling points of noble gases increase as atomic numbers of noble gases increase boiling points of hydrocarbons increase with increased chain length

Question 33

What characteristics does hydrogen bonding have?

Answer 33

some characteristics of dipole-dipole attraction and some of a covalent bond

Question 34

What does a hydrogen bond consist of?

Answer 34

hydrogen atom 'sandwiched' between two very electronegative atoms

Question 35

What condition is needed for hydrogen bonding?

Answer 35

need a very electronegative atom with lone pair of electrons covalently bonded to hydrogen atom

Question 36

Example of molecule than can exhibit hydrogen bonding?

Answer 36

water molecules

Question 37

Is water polar?

Answer 37

yes

Question 38

Why is water polar?

Answer 38

oxygen is much more electronegative than hydrogen

Question 39

Why is the intermolecular bonding in water much stronger than expected? (2)

Answer 39

oxygen atoms in water molecules have lone pairs of electrons in water hydrogen atoms highly electron deficient because oxygen very electronegative and attracts shared electrons in bond towards it hydrogen atoms in water positively charged and very small these exposed protons have very strong electric field because of their small size

Question 40

Between where is the hydrogen bonding formed in water molecules?

Answer 40

lone pair of electrons on oxygen atom of another water molecule strongly attracted to electron deficient hydrogen atoms

Question 41

How are hydrogen bonds usually represented?

Answer 41

by dashes

Question 42

What must there be for a hydrogen bond to form?

Answer 42

hydrogen atom that's bonded to very electronegative atom. this will produce strong partial positive charge on hydrogen atom very electronegative atom with lone pair of electrons these will be attracted to partially charged hydrogen atom in another molecule and form the bond

Question 43

What are the only atoms that are electronegative enough to form hydrogen bonds?

Answer 43

oxygen, nitrogen and fluorine

Question 44

How can the effects of hydrogen bonding between molecules be seen?

Answer 44

looking at boiling points of hybrids of elements of groups 4, 5, 6, and 7 against period number

Question 45

What do the noble gases show against period number?

Answer 45

gradual increase in boiling point as only forces acting between atoms are VDW + these increase with number of electrons present

Question 46

Why is boiling point of water and ammonia higher than those of hybrids of other elements in their group?

Answer 46

hydrogen bonding present between molecules in each of these intermolecular forces of attraction make molecules more difficult to separate

Question 47

What happens to hydrogen bonding in water in its liquid state/?

Answer 47

hydrogen bonds break and reform easily as molecules moving about

Question 48

What happens to hydrogen bonding when water freezes?

Answer 48

water molecules no longer free to move about and hydrogen bonds hold molecules in fixed positions

Question 49

What happens to the structure when water is frozen?

Answer 49

results in three-dimensional structure

Question 50

What happens in order for water molecules to ft the three-dimensional structure when water is frozen?

Answer 50

molecules are slightly less closely packed than in liquid water

Question 51

What does it mean as the water molecules are slightly less closely packed when water is frozen?

Answer 51

ice is less dense than water

Question 52

As ice is less dense than water how do they form on ponds?

Answer 52

forms on top of ponds rather than at the bottom

Question 53

Why is ice forming on top of ponds good?

Answer 53

insulates ponds and enables fish to survive through the winter