unit 1 KA2 - structure and bonding

Question 1

what is a covalent bond

Answer 1

the result of two positive nuclei being held together by their common attraction for the shared pair of electrons. in covalent bond, atoms share pairs of electrons

Question 2

when are polar covalent bonds formed

Answer 2

when the attraction of the atoms for the pair of bonding electrons is different

Question 3

what does delta positive δ+ and delta negative δ- notation indicate

Answer 3

they can be used to indicate the partial charges on atoms, which give rise to a dipole

Question 4

how can ionic formulae be written

Answer 4

giving the simplest ratio of each type of ion in the substance

Question 5

what are ionic bonds

Answer 5

ionic bonds are the electrostatic attraction between positive and negative ions. ionic compounds form lattice structures of oppositely charged ions

Question 6

what is the order of the bonding continuum

Answer 6

pure - polar - ionic

Question 7

what does the difference in electronegativities indicate

Answer 7

ionic character

Question 8

if there is a large difference between electronegativities is the polarity larger or smaller

Answer 8

larger

Question 9

how do ions form

Answer 9

when the difference between electronegativities is large, the movement of bonding electrons from the element of lower electronegativity to the element of higher electronegativity is complete, resulting in the formation of ions

Question 10

are the compounds formed between metals and non-metals always ionic

Answer 10

no, just often

Question 11

how can you deduce the type of bonding and structure in the compound

Answer 11

through the physical properties of a compound, such as its state at room temperature, melting point and boiling point, solubility and electrical conductivity

Question 12

do all molecular elements and compounds and monatomic elements condense and freeze at sufficiently low temperatures

Answer 12

yes

Question 13

what are van der Waals forces

Answer 13

inter molecular forces acting between molecules

Question 14

what are the types of van der waal’s forces

Answer 14

London dispersion forces and permanent dipole-permanent dipole interactions that include hydrogen bonding

Question 15

what are London dispersion forces

Answer 15

these are force of attraction that can operate between all atoms and molecules. these forces are much weaker than all other types of bonding.

Question 16

how are LDFs formed

Answer 16

they are formed as a result of electrostatic attraction between temporary dipoles and induced dipoles caused by movement of electrons in atoms and molecules.

Question 17

what is the strength of LDFs related to

Answer 17

the number of electrons within an atom or molecule

Question 18

what is a molecule described as if it has a permanent dipole

Answer 18

polar

Question 19

what can the spatial arrangement of polar covalent bonds result in

Answer 19

it can result in the molecule being polar

Question 20

what are permanent dipole-permanent dipole interactions

Answer 20

they are additional electrostatic forces of attraction between polar molecules

Question 21

are pd-pd interactions stronger than LDFs

Answer 21

yes they are for molecules with similar numbers of electrons

Question 22

are the bonds consisting of a hydrogen atom bonded to an atom of a strongly electronegative element such as fluorine, oxygen or nitrogen highly polar?

Answer 22

yes the bonds consisting of a hydrogen atom bonded to an atom of a strongly electronegative element such as fluorine, oxygen or nitrogen are highly polar

Question 23

what are hydrogen bonds

Answer 23

hydrogen bonds are electrostatic forces of attraction between molecules that contain these highly polar bonds. they are stronger than other forms of permanent dipole-permanent dipole interaction but weaker than a covalent bond

Question 24

how can melting points, boiling points and viscosity be rationalised

Answer 24

in terms of the nature and strength of the intermolecular forces that exist between molecules. by considering the polarity and number of electrons present in molecules, it is possible to make qualitative predictions of the strength of the intermolecular forces

Question 25

are the melting/boiling points of polar substances higher or lower than the m/b points of non-polar substances with similar numbers of electrons

Answer 25

higher

Question 26

what are properties of substances that are affected by hydrogen bonding

Answer 26

• boiling points
• melting points
• viscosity
• solubility/miscibility in water

Question 27

why are the boiling points of ammonia, water and hydrogen fluoride so anomalous

Answer 27

because they have hydrogen bonding

Question 28

why is ice less dense than water

Answer 28

the hydrogen bonding between the molecules in ice results in an expanded structure that causes the density of ice to be less than that of water at low temperatures

Question 29

which tend to be soluble in polar solvents such as water and insoluble in non-polar solvents:

A ionic compounds and polar molecular compounds
B non-polar (pure) molecular substances

Answer 29

A

Question 30

which tend to be soluble in non-polar solvents and insoluble in polar solvents?

A ionic compounds and polar molecular compounds
B non-polar molecular substances

Answer 30

B

Question 31

what are the key features to be considered when predicting the solubility of a compound?

Answer 31

• presence in molecules of O-H or N-H bonds, which implies hydrogen bonding
• spatial arrangement of polar covalent bonds, which could result in a molecule possessing a permanent dipole