Question 2
. (a) Consider the following atoms;
.
T T
(i) State the phenomenon exhibited by the two atoms.
(ii) What is the difference between the atoms?
(iii) Give two examples of elements that exhibit the phenomenon stated
in 2 (a)(i).
(iv) If T is 17, write the electron configuration of the element. [6marks]
(b) (i) State two differences between metals and non-metals with respect
to their:
I. physical properties;
II. chemical properties.
(ii) Give one example of each for the following compounds;
I. an amphoteric oxide;
II. a hydride which evolves hydrogen when reacted with water;
III. a trioxocarbonate (IV) salt which is readily decomposed on
heating;
IV. a chloride salt which is readily hydrolyzed. [8 marks]
(c) (i) State three characteristic properties of transition metals
(ii) Write the electron configuration of 30Zn.
(iii) Explain briefly why zinc is not considered as a typical
transition element. [6 marks]
(d) Consider the reaction represented by the following equation.
Na2CO3(aq) + MgCl2(aq) ---> 2NaCl(aq) + MgCO3(aq)
Calculate the mass of sodium trioxocarbonate (IV) needed to produce
3.36g of magnesium trioxocarbonate (IV).
[C = 12.0, O = 16.0, Na = 23.0, Mg = 24.0]
[3 marks]
Observation
The question was a popular choice among the candidates, and most of them showed
good understanding of the question.
In part (a), majority of the candidates responded correctly, except a few ones that stated the phenomenon as isotope instead of isotopy.
In part (b), majority of the candidates stated correctly, the differences between metals and non-metals with respect to their physical and chemical properties. However,
few candidates did not know that the differences should correspond.
In part (c), majority of the candidates stated correctly why zinc is not considered a typical transition element. However some stated that it was because zinc has +2 oxidation, while few candidates stated that it did not form a coloured ion.
In part (d), majority of the candidates were able to calculate the mass of Na2 CO3
needed to produce 3.36g of MgCO3 from the given equation. Some could not
calculate it, because they could not establish the mass/mass relationship from the
stoichiometry of the reaction equation.
The expected answers include:
(a) (i) Isotopy Do not accept isotopes
(ii) They have different mass numbers/ number of neutrons
(iii) - Hydrogen
- Chlorine
- Carbon
- Oxygen etc
( Accept any two elements)
(iv) 
(b) (i) I. DIFFERENCES IN PHYSICAL PROPERTIES
METALS |
NON – METALS |
- good conductors of heat and electricity |
- poor conductors of heat and electricity |
- malleable – can be beaten into thin sheets |
- not malleable / brittle |
- ductile – can be stretched into wire |
- non ductile / brittle |
- possess metallic luster |
- do not possess metallic luster |
- are sonorous |
- not sonorous |
- solid at room temperature except Mercury/high melting point |
- solids, liquids or gases at room |
II. DIFFERENCES IN CHEMICAL PROPERTIES
METALS |
NON – METALS |
- lose their valence electrons |
- gain or share valence electrons easily / ionize by electron gain |
- form oxides that are basic |
- form oxides that are acidic /neutral |
- are good reducing agents |
- are good oxiding agents |
- have lower electronegativities |
- have higher electronegativities |
- have low ionization energy |
- have high ionization energy |
-(some reactive metals) react with dilute acids to give off hydrogen |
- do not react with dilute acids to give off hydrogen |
Differences must correspond to score
ii.
(c) (i) - form coloured compounds / ions
- exhibit variable oxidation states
- form complex compounds / ion
- have magnetic properties (Paramagnetism)
- have catalytic properties
(ii) 
(iii) Because zinc has completely filled 3d – orbitals/
the 3d orbitals of zinc are fully filled
OR
