Example of an essay question

by **farah_nad** Mon Sep 06, 2010 12:22 pm

(a)An atom of element T has 12 neutrons and a nucleon number of 23. An atom of element G has 16
protons.
(i) Explain how element T can combine with element G to form a white solid R.
(ii) Describe an experiment to investigate the electrical conductivity of substance R. In your answer, include the observation and conclusion that can be made.

(b) Element M combines with element J to form a covalent compound with the molecular formula JM2. Element M has a proton number of 9. Suggest one possible electron arrangement for the atom of element J. Give reasons for your answer.

[Answer]
(a)(i) - atom of element T has an electron arrangement of 2.8.1
- atom of element G has an electron arrangement of 2.8.6
- two atoms of element T lose one electron each to achieve a stable octet electron arrangement to form T+ ions
- ~~both these electrons are transfered to the outermost shell of an~~ atom of element G reveive two electrons so as to achieve stable octet electron arrangement
- G2- ion is formed

- *ionic bond diagram

- the oppositely charged ions, T+ and G2- formed are strongly attracted ~~attached~~ to each other by strong electrostatic forces
- thus, white solid R with the formula T2G is formed

(ii)
[Procedure]
- a crucible is filled with white solid R until it is almost full
- two carbon electrodes is dipped into solid R
- the electrodes are connected to a battery and an ammeter using connecting wires
- the switch is turned on
- reading of the ammeter is observed
- the switch is turned off again.
- solid R is heated until it is completely melted
- the switch is turned on again and the ammeter reading is observed.

- observation :
solid R - ammeter shows reading more than zero
molten R - ammeter shows zero reading

- Substance R cannot conduct electricity in solid state but can conduct electricity in molten state

(b) - one possible electron arrangement of atom J is 2.6 or 2.8.6

- electron arrangement of atom M is 2.7
- atom M has 7 valence electron, M is a non-metal
- a covalent compound is formed when non-metal combines with non-metal
- element M combines with element J to form J2M
- thus, element J must be a non-metal with 6 valence electrons