l3 - covalent & non covalent bonding

Question 1

2 ways hydrogen can achieve a full outer shell

Answer 1

1. ionisation via losing an electron to form H+
2. sharing an electron with another atom

Question 2

ionic bonding

Answer 2

• metal + non metal ion
• metals lose electrons to form salts
• stable due to energy of electrostatic interactions

Question 3

covalent bonding

Answer 3

the electrostatic force of attraction between the positively charged nuclei of the 2 bonded atoms and their shared pair of electrons

Question 4

what type of spins do electrons have in covalent bonding?

Answer 4

opposite spins

Question 5

do the electrons in a covalent bond necessarily belong to any of the atoms?

Answer 5

no as each electron is able to exist in any part of the bond orbital so belongs so both of the nuclei of the bonded atoms

Question 6

bond dissociation energy

Answer 6

measure of how strong a bond is.
when you bring 2 atoms together there is a release of energy, so to break the bond you need to put energy back in

Question 7

the stronger the overlap of orbitals, the….

Answer 7

the stronger the bond

Question 8

sigma bonds

Answer 8

• strongest covalent bond
• 2e-
• overlap of orbitals
• when 1s and 2p orbitals overlap you end up with a small lobe of electron density on far side of nuclei

Question 9

pi bonds

Answer 9

• weaker as c=c bond has lower energy
• formed from sideways overlap of 2 orbitals lobes on one atoms and 2 orbital lobes on another
• nodes between the lobes have no electron density
• lobe above and below sigma bond
• pi bonds form with an existing sigma bond
• carbons are sp2 hybridised

Question 10

lone pairs

Answer 10

• unshared electron pairs
• decrease bond angle by 2.5 as lone pairs repel more strongly
• not involved in bonding

Question 11

hydrogen bonding

Answer 11

• electrostatic attraction between H and an electronegative atom
• lone pairs are H bond acceptors
• so h bonds are donors
• strength depends on the donor and acceptor atoms, their environments + geometries

Question 12

h bonding in small molecules

Answer 12

causes inc in MP, BP, solubility & viscosity

Question 13

why is ice less dense than water?

Answer 13

due to H bonding, as H bonds hold the molecules in a more open space

Question 14

van Der walls (induced/ permanent dipole dipole forces)

Answer 14

• molecules with permanent dipoles can temporarily distort the electric charge in a nearby polar or nonpolar molecule acting as an induced dipole
• Molecules with temporary dipoles can be caused by electron moving randomly within atoms, these can then induce a dipole on neighbouring atoms causing an attraction (short lived): london forces

Question 15

pi stacking (pi pi interactions)

Answer 15

non covalent interactions between aromatic rings

Question 16

3 arrangements of pi stacking

Answer 16

1. sandwich
2. t shaped
3. parallel displaced

Question 17

evidence of pi staking

Answer 17

1. in gas phase and at a low temp benzene forms a dimer and has a bonding energy o 2-3 kcal mol-1
2. x ray crystallography gives perpendicular + offset parallel configurations in simple aromatic compounds

Question 18

micelles & protein folding

Answer 18

• amphiphilic molecules form micelles in water
• head found on outside, tail on inside
• proteins have hydrophobic a.a which fold + form hydrophobic cores
• miming hydrophobic side chains exposed to water is main reason why proteins fold

Question 19

primary protein structure

Answer 19

sequence of a.a in a polypeptide chain, a.a held together by peptide bonds (ca + amide)

Question 20

secondary structure

Answer 20

alpha helix and beta pleated sheets held together by hydrogen bonds

Question 21

tertiary structure

Answer 21

3d shape of proteins. folded in compact globular structures, salt bridges, ionic bonding, h bonding, hydrophobic & hydrophilic interactions, disulphide bridges

Question 22

quaternary structures

Answer 22

multiple polypeptide structures folded into 1 functional unit