Chemistry Flashcards
Predict the shape of a molecule of SbCl3.
Explain your answer.
Shape: Trigonal pyramidal
Sb has three bonding pairs and one lone pair of
electrons
Electron pairs repel as far apart as possible and
lone pairs repel more than bonding pairs
SbCl3 molecules are polar.
Explain why.
Sb and Cl have different electronegativities OR
Sb–Cl bonds are polar.
An SbCl3 molecule is not symmetrical AND the dipoles don’t cancel each other out.
State and explain 2 properties of ice that are a direct result of hydrogen bonding.
Ice is less dense than water
Because H2O molecules in ice are held apart by
hydrogen bonds in open lattice structure
Ice has a higher melting point than expected
Because hydrogen bonds are stronger than
other intermolecular forces so more energy is
needed to break the hydrogen bonds
Explain the term Electronegativity.
The ability of an atom to attract electrons in a covalent bond
Explain what is meant by the term Covalent Bonding.
The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms.
Show, using Delta + and Delta - symbols, the permanent dipoles on each of the following bonds.
N—F and N—Br.
δ+ N–F δ– and δ– N–B δ+
Chemists are able to predict the shape of a simple covalent molecule from the number of electron pairs surrounding the central atom.
Explain how this enables chemists to predict the shape.
Pairs of electrons surrounding a central atom
repel
The shape is determined by the number of bond
pairs AND the number of lone pairs of electrons
Hydrogen chloride is a colourless gas which forms white fumes in moist air.
Molecules of hydrogen chloride, HCl, and molecules of fluorine, F2 contain the same number of electrons. Hydrogen chloride boils at -85 °C and fluorine boils at -188 °C.
Explain why there is a difference in the boiling points of HCl and F2. In your answer you should refer to the types of force acting between molecules and the relative strength of the forces between the molecules.
F2 has London (or van der Waals’) forces between molecules
HCl also has permanent dipole–dipole interactions between molecules
In HCl, the intermolecular forces are stronger and require more energy to break
What are CDCl3 and D2O used for?
CDCl3 is used as a solvent
D2O is used as to identify an OH group (from COOH or Alcohol) and NH protons
What are the special cases in which the oxidation numbers of Hydrogen and Oxygen changes?
Special cases:
Hydrogen in metal hydrides - Have a 1- charge. E.g. NaH,CaH2
Oxygen in peroxides - Have a 1- charge. E.g. H2O2
Oxygen bonded to Fluorine - Have a 2+ charge. E.g. F2O
In an industrial process involving a reversible gas phase reaction, the following tiles of products are obtained under different operating conditions.
Use this information to answer the following questions
a) i) Explain whether the reaction is exothermic or endothermic
ii) Explain whether there are more or fewer moles of gaseous products than reactants
b) i) What would be the effect (if any) on the value of Kc y changing the conditions from 300K and 100 atm to 500K and 100 atm ?
ii) What would be the effect (if any) on the value of Kc by changing the conditions from 300K and 100 atm to 300K to 300 atm ?
iii) What would be the effect (if any) on the value of Kc by introducing a catalyst at 300K and 100 atm.
a) i) Exothermic because yield decreases with increasing
temperature
ii) Fewer moles because yield increases with increasing pressure.
b) i) Kc decreases because temperature has been
increased and forward reaction is exothermic.
ii) No change as temperature has not changed.
iii) No change as temperature has not changed.
This question looks ta trends across a period in the periodic table. Four sequences of elements across Period 3 are shown below.
1) Na,Mg, Al 2) Al,Si,P 3) Si,P,S 4) P,S,Cl
a) Which sequence shows the melting point increasing across Period 3?
b) Which sequence shows the 1st Ionisation energy increasing across Period 3?
c) Which sequence shows the 2nd Ionisation energy increasing across Period 3?
d) Which 2 sequences contains elements that have the same structure in the solid state?
Identify these 2 and state the structure of each.
a) 1
b) 2
c) 3
d) 1 & 4
State the region of the electromagnetic spectrum used in 1H NMR spectroscopy.
Radio Waves
Explain why CDCl3 is used as a solvent in 1H NMR spectroscopy.
Because it doesn’t contain any H / Protons
D
C
C
C
B
B
C
C
A
D
Part b
C
