1.3.4 Bonding & Physical Properties Flashcards
What type of crystal structure do compounds made of metals & non-metals form?
ionic lattice
Explain why ionic lattices have high melting points.
→ strong electrostatic forces of attraction
→ between oppositely charged ions
→ require lots of energy to overcome
Explain why boiling points of group 6 (covalent) compounds increase down the group. e.g. from H₂S to H₂Te
→ going down, the no. of electrons increase
→ generates bigger temporary dipoles
→ stronger VDW forces
Why can metals conduct electricity?
- metallic bonding contains delocalised electrons
- these can move around & carry a charge throughout the structure
Explain, in terms of the intermolecular forces present in each compound, why HF has a higher boiling point than HCl.
HF = hydrogen bonding
HCl = (permanent) dipole-dipole bonding
hydrogen bonding is stronger
State the meaning of the term electronegativity.
the power of an atom to attract the electron
density in a covalent bond towards itself
Explain how the hydrogen bonding arises between two molecules of ammonia.
- large electronegativity difference between N & H
- this creates dipole with 𝛿− N & a 𝛿+ H
- there is an attraction between the lone pair on N & the 𝛿+ H
Why is ice less dense than water?
molecules in ice are held further apart than in liquid water due to an extra hydrogen bond
Describe the bonding in a metal.
in metallic bonding:
- strong electrostatic forces of attraction between
- positive ions (cations)
- & delocalised electrons
Explain why magnesium has a higher melting point than sodium.
- Mg is smaller ion
- with more protons (higher nuclear charge)
- so stronger attraction to delocalised electrons
- metallic bonding is stronger than in Mg
Why do diamond and graphite both have high melting points?
- both are giant covalent structures (macromolecular)
- with strong covalent bonds
- that require lots of energy to overcome/break
Why is graphite a good conductor of electricity?
- contains delocalised electrons
- that can move & carry a charge through the structure
Why is graphite soft?
- layers with weak VDW forces between them
- this allows the layers to slide over each other
Explain why the O–H bond in a methanol molecule is polar.
- oxygen is more electronegative than hydrogen
- electrons drawn towards oxygen
- causes higher e– density round oxygen
- forms a polar bond as H is δ+ & O is δ–
Deduce why the bonding in nitrogen oxide is covalent rather than ionic.
Small electronegativity difference
In terms of atomic structure, explain why the VDW forces in liquid argon are very weak.
- argon particles are single atoms with electrons closer to nucleus
- cannot easily be polarised
In terms of structure and bonding, explain why sulfur has a higher melting point than phosphorus.
- sulfur molecules (S₈) are larger than phosphorus (P₄)
- stronger VDW forces between S₈ molecules
- more energy required to overcome these
In terms of intermolecular forces, suggest the main reason why phosphine is almost insoluble in water.
- phosphine does not form hydrogen bonds with water
- difference in electronegativity between P & H is too small
Van der Waals’ forces exist between all molecules.
Explain how these forces arise.
- random movements of electrons generates a temporary dipole
- induces temporary dipoles in neighbouring molecules
- δ+ end of one dipole attracts δ- in different molecules
Describe the structure and bonding of iodine.
→ solid lattice of I2 molecules held together by weak intermolecular forces
Describe the diagram used to represent the structure of ice.
→ tetrahedral with central water molecule
→ two H bonds from the lone pairs on oxygen
→ one H bond from each H atom
