questions Flashcards
Deduce two possible reasons why the density of iron (7.86 g cm−3) is much greater than the density of graphite (2.2 to 2.8 g cm−3)
iron atoms have a greater mass than carbon atoms
iron atoms are packed closer unlike carbon atoms
Explain, in terms of the structure and bonding of silicon and chlorine, the difference between these values
silicon - 1683
chlorine - 172
silicon - giant covalent structure
chlorine - simple molecular structure and contains london forces
- covalent bonds in silicon are stronger than london forces
Describe the bonding in the element chromium and use your answer to justify why it has
such a high melting temperature.
lattice of positive ions
in a sea of delocalised electrons
strong electrostatic forces of attractions between the positive ions and the sea of delocalised electrons
metallic bonds
Explain how changes in the cation affect the bond strength in an
ionic compound
LiF - 1031
KF - 817
CaF2 - 2957
- the higher the charge on the cation the stronger the attraction between ions and mention of a 2+ cation in CaF2 compared to a 1+ cation in LiF
- the smaller the radius of the cation the stronger the attraction between ions and mention of Li+ being smaller than K+
State all the conditions under which magnesium bromide conducts electricity
in an aqueous solution
Explain the difference in the melting temperatures of magnesium oxide(3125) and potassium bromide (1007)
- MgO has doubly charged ions and KBr has singly charged ions
- Mg2+ smaller than K+
- more energy needed to overcome the electrostatic attractions
Explain why phosphorus forms PCl5 but nitrogen does not form NCl5
phosphorus can expand its outer shell
nitrogen does not have 2 d orbitals
Explain why hydrogen bonding causes ice to be less dense than liquid water
more space between molecules due to lattice
hydrogen bonds longer than covalent bonds
Water might be expected to have a lower boiling temperature than hydrogen sulfide but it actually has a higher boiling temperature.
Comment on this statement by referring to the intermolecular forces in both these substances
a lower boiling temperature is expected bc
- water has fewer electrons than hydrogen sulfide
- water has london forces
a higher boiling temperature is expected bc
- water has hydrogen bonding
- hydrogen bonding is stronger than london forces and requires more energy to break
Nitrogen trichloride, NCl3, has a boiling temperature of 344 K, and
nitrogen trifluoride, NF3, has a boiling temperature of 144 K.
Explain this difference in boiling temperatures, by referring to all the
intermolecular forces present
- london forces are greater in NCI3
- NCI3 has more electrons
- dipole forces stronger in NF3
- F is more electronegative than CI
- more energy needed to overcome intermolecular forces between NCI3 molecules than NF3 molecules
Explain why ethene has a boiling temperature of −104 °C, whereas ethanol has a boiling
temperature of 78 °C
ethanol has hydrogen bonding
ethene has weaker london forces
more energy required to break the intermolecular forces
Explain why 2,2-dimethylpropane has a much lower boiling temperature than its isomer
pentane
branching results in weaker london forces due to less surface area
Describe how London forces form between halogen molecules
uneven distribution of electrons results in a temporary dipole which causes second dipole on another molecule
- Water has two significant anomalous properties:
- it has a higher melting temperature than hydrogen sulfide, H2S, even though it has
fewer electrons in its molecules - the density of ice at 0 °C is less than that of water at 0 °C.
Explain these properties
- lone pair on oxygen in hydrogen bond and dipole shown with delta positive H and delta negative O
- drawn shape
- hydrogen sulfide has stronger london forces
- hydrogen bonds are longer than covalent bonds
- water molecules are closer
