Bonding Flashcards
Explain why metals are malleable
planes of metal ions can slide over each other
Electronegativity
power of an atom to attract the pair of electrons in a COVALENT bond
Explain hydrogen bonding
- F/N/O are more electronegative than hydrogen
- dipole formed with partially negative atom and partially positive hydrogen
- bond formed between H and lone pair on F/N/O on adjacent molecule
Explain why diamond and graphite both have high melting points
- macromolecular
- MANY STRONG covalent bonds need to BROKEN
Explain why graphite is soft
weaker van der Waals forces between layers of carbon atoms so can slide over each other
Describe change in motion of ions in NaCl below melting point
vibrate faster about a fixed point
Explain why bond angle is equal in a molecule without lone pairs
all bonding pairs of electrons repel equally
Suggest why lone pairs of electrons are opposite each other in a molecule
lone pairs repel each other more than with bonding pairs so are as far apart as possible
Suggest why lone pairs repel more than bonding pairs
- bonding pairs of electrons are held in a bond further from nucleus of central atom
- lone pairs are held close to positively charged nucleus
Define permanent dipole
unequal sharing of electrons which creates a partially positive and partially negative end
Explain why a molecule can be polar
- lone pairs
- one atom is more electronegative so electron density is attracted towards it
Define polar bond
- bonding pair of electrons is shared unequally
- partial charges at each end of bond
Explain why a molecule has covalent bonding over ionic
small difference in electronegativity between atoms so more equal sharing of electrons
Explain why iodine exists as simple molecules where carbon does not
- carbon makes four bonds so it macromolecular
- iodine forms one bond
Explain formation of hydrogen bonding between protein molecules
between lone pair on partially negative O in C=O group and partially positive H in N-H group
Explain how metals conduct heat
- delocalised electrons are free to move and carry heat - metal ions are closely packed so kinetic energy is passed between them
Electronegativity values of the following:
H, C, N, O, F, Cl, Br
H 2.1 C 2.5 N 3.0 O 3.5 F 4.0 Cl 3.0 Br 2.8
Factors increase van der Waals
- higher molecular mass
- straight chains pack closer than branched chains
Compare structure of graphite and diamond
Graphite
- three covalent bonds forming hexagonal planes of carbon atoms (bond angle 120)
- weak van der Waals between hexagonal planes
- delocalised electrons
Diamond
- four covalent bonds (bond angle 109.5)
State anomalous properties of water and the reason for them
- high boiling point
- water is denser than ice (forms tetrahedral structure)
- results from hydrogen bonding
Explain which out of HBr and Br2 has the highest melting point
- Br2 since it has a higher Mr
- van der Waals forces are stronger that permanent dipole-dipole forces and van der Waals forces in HBr
State bond angle in ethene and explain why
- 120 degrees
- x3 bonding sites around carbon
- double bonds almost as strongly as single bonds
Propanone contains oxygen and hydrogen atoms. Explain why is does not contain hydrogen bonding.
- hydrogens are all bonded to carbon atoms
- not a large enough difference in electronegativity values of C and H to create a dipole
- no H bonding between hydrogen and lone pairs on oxygen
Explain why there are induced dipole-dipole forces in alcohol molecules
- random movement of electrons creates instantaneous dipole in C-H bond
- dipole induces dipole in C-H bond of neighbouring molecule
- dipoles attract
Suggest which factor is most important in determining solubility of a molecule in water and why
- strength of dipole-dipole forces between molecules
- compared to energy released by hydrogen bond between molecule and water
- if H bond releases sufficient energy then molecule is soluble in water
(Do not just mention H bonds are STRONGER)
Define ionic, covalent and metallic bond
- ionic = electrostatic attraction between oppositely charged ions in a lattice
- covalent = shared pair of electrons between atoms
- metallic = electrostatic attraction between delocalised electrons and positive ions arranged in a lattice
Explain why a branched alcohol is more soluble in water compared to a straight chain alcohol
- molecules of alcohol cannot pack close together
- weaker instantaneous dipole-dipole forces
- energy from H bonds between alcohol and water is sufficient to overcome attraction between alcohol molecules
(do not mention more contact points for H bonds or reference surface area)
Give other names that refer to van der Waals forces
- induced/ temporary dipole forces
- dispersion forces
- London forces
Key point to remember when describing bonding/forces
must mention between ATOMS or MOLECULES
Electron pair repulsion theory
- electron pairs repel as far apart as possible
- lone pairs repel more than bonding pairs
Suggest why electron pair repulsion theory cannot be used to predict shape of transition metal complex
Too many electrons in d subshell
