Structure and Bonding AS

Question 1

ionic bonding

Answer 1

electrostatic attraction between oppositely charged ions

Question 2

covalent bonding

Answer 2

electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms

Question 3

metallic bonding

Answer 3

electrostatic attraction between the sea of delocalised electrons and lattice of positive ions

Question 4

ions are formed when

Answer 4

electrons are transferred from a metal atom to a non metal

Question 5

bond strength depends on

Answer 5

charge density of the ions. the higher the charge density the stronger the attraction between the ions and the stronger the bonds. small and highly charged ions have a high charge density

Question 6

structure of ionic bonding

Answer 6

regular lattice structure - oppositely charged ions attracted in all directions

Question 7

high melting points and boiling points of ionic bonds

Answer 7

• strong electrostatic attraction between oppositely charged ions
• a lot of energy needed to break these strong bonds

Question 8

conduction of electricity when molten or dissolved ionic bonds

Answer 8

solids - ions are in the fixed positions so no mobile charge carriers present
liquids and solutions - ionic lattice is broken and ions can move

Question 9

solubility of ionic bonds

Answer 9

depends on the relative strengths of the attraction between the ions in the lattice and the attraction between ions and polar water molecules

Question 10

covalent bonding bond length

Answer 10

distance between the nuclei and 2 covalently bonded atoms

Question 11

average bond energy / enthalpy

Answer 11

energy required to break a bond in every molecule in one mole of gaseous molecules

Question 12

covalent bond strength depends on:

Answer 12

• number of electrons being shared
• bond length ( shorter bonds mean shared e’s are closer to 2 nuclei so stronger)
• additional ionic character

Question 13

bond strength is reflected by…

Answer 13

the bond energy. the lower the bond energy the easier it is to break a bond

Question 14

what is dative covalent bonding

Answer 14

• a covalent bond where both shared electrons are donated by the same atom
• need one electron rich atom (lone pair of electrons)
• also need one electron poor atom ( capable of accepting lone pair of electrons )

Question 15

how can dative bonds be represented

Answer 15

by an arrow

Question 16

100% covalent

Answer 16

• equal share of electrons
• identical electronegativity
  eg cl2

Question 17

100% ionic

Answer 17

• complete transfer of electrons
• very big difference in electronegativities
  eg nacl

Question 18

intermediate bonding

Answer 18

either covalent w some ionic character or other way around

Question 19

covalent bonds with some ionic character

Answer 19

• ionic character arises as a result of uneven sharing of bonding pair of electrons
• occurs when the 2 atoms involved have different electron activities

Question 20

cl2

Answer 20

• same electronegativity
• electrons shared evenly
• non polar bond
• 100% covalent

Question 21

hcl

Answer 21

• cl is more electronegative than h
• electrons are more strongly attracted to the cl
• uneven distribution of electrons
• cl delta negative
• h delta positive
• additional character adds strength
• polar bond

Question 22

electronegativity

Answer 22

the ability of an atom to attract the bonding pair of electrons towards itself in a covalent bond

Question 23

how is a bond polar

Answer 23

a bond is polar if the atoms involved have different electronegativities
- the difference in charge between the delta + and the delta - ends is called a dipole

Question 24

induced dipole dipole interaction

Answer 24

• between ALL molecules
• electron in a molecule are moving. at any instant in time there might be more e- on one side of a molecule than the other - causes a small instantaneous dipole
• dipole will induce a dipole in the neighbouring molecule and so on
• attractions between the dipoles is a weak and temporary force of attraction
• the more electrons there are in the molecules the larger the instantaneous and induced dipoles and the greater the attraction

Question 25

why do melting and boiling points increase down the noble gases

Answer 25

• more electrons
• stronger induced d-d attractions
• more energy needed to overcome the forces
• higher melting/boiling points

Question 26

permanent dipole dipole interactions

Answer 26

• attraction between molecules with a permanent dipole
• stronger than id-id
• exist in addition to id-id
• only occur in polar molecules
• polar molecules dissolve in polar solvents and non polar in non polar solvents

Question 27

hydrogen bonding

Answer 27

• particularly strong intermolecular force
• the electrostatic attraction between a very delta + H atom and a lone pair of electrons of an O N or F atom in a neighbouring molecule
• only occur in molecules that contain hydrogen bonded to N O or F (very electronegative elements so very polar bonds)
• mp and bp higher than expected

Question 28

what does strength of hydrogen bond depend on

Answer 28

the electronegativity of the atom bonded to the H so F > O > N the overall effect also depends on the number of hydrogen bonds formed

Question 29

anomalous properties of water

Answer 29

• ice less dense due to molecules being pushed a part when water freezes, hydrogen bonds are long bonds
• unexpectedly high mp and bp due to sh bonds being the strongest intermolecular force between molecules - more energy required to break them
• unusually high surface tension due to h bonds across surface