Question 45: [Physical > Atomic Strcuture]
which of the following solids has a simple molecular lattice?
A magnesium oxide
B sodium
C silicon(IV) oxide
D sulphur
Reference: Past Exam Paper -June 2003 Paper Q5
Solution 45:
Answer: D
magnesium oxide is an ionic compound therefore the ions Mg 2+ and O 2- are held in a giant ionic lattice
sodium is a metal therefore the cation is held in a sea of delocalised electrons in a metallic lattice
in silicon(IV) oxide structure each silicon is bonded to 4 oxygen atoms and each oxygen atom is bonded to 2 silicon atoms in a giant molecular structure
sulphur is held in a simple molecular structure with weak van der Waals’ forces or also known as instantaneous dipole induced dipole forces. between sulphur molecules therefore answer is D.
Question 44: [Physical > Atomic Structure]
Reference: Past Exam Paper -June 2003 Paper 1 Q4
Solution 44:
Answer: C
Ionisation energy is the energy required to remove an electron from each atom in 1 mole of gaseous atoms to form 1 mole of gaseous ions. We can see a general increase in ionisation energies of element X because as each electron is removed from the outer shell the shielding effect decreases and the distance between the nucleus and electron decrease because as electrons are removed the protons become more in number than electrons therefore the nuclear charge increase and the protons force of attraction of electrons increase therefore resulting in an even smaller atom than the usual atom . therefore the ion now is more stable than the usual atom. its easy to identify the element by looking at the sharp increase , sharp increase in ionisation energies indicate that all electrons that were in the outermost shell were removed , number of shells now decreased therefore resulting in even more than a smaller atom , therefore a huge amount of energy is now required to remove the next electron that is close to the nucleus. if we look at the question the sharp increase is after the 6th ionisation energy this indicates that the 7th electron is in a shell closer to the nucleus and that there is 6 electrons in the outermost shell. number of electrons in the outer shell indicates the group number of the element, Te is the only element from group 6 in the options given therefore the answer is C.
Question 3: [Physical > Atomic Structure]
Use of the Data Booklet is relevant to this question.
In the gas phase, aluminium and a transition element require
the same amount of energy to form one mole of an ion with a 2+ charge.
What is the transition element?
A Co
B Cr
C Cu
D Ni
Reference: Past Exam Paper – November 2002 Paper 1 Q3
Solution 3:
Answer: A.
For aluminium to form an ion with a 2+ charge we must add
its 1st ionisation energy, to remove one electron and gain 1
positive charge, with its 2nd ionisation energy, to remove another
electron from the 1+ aluminium ion to make it a 2+ ion. This total energy,
according to the data booklet, is 577 + 1820 = 2397. Thus we have to find a
transition element that has the same total energy required for removing 2
electrons.
A Co: 757 + 1640 = 2397
B Cr: 653 + 1590 = 2243
C Cu: 745 + 1960 = 2705
D Ni: 736 + 1750 = 2486
As you can see Co is the only exact match thus
is the A is the correct answer.
Question 2: [Physical > Atomic Structure]
One of the most important chemical species responsible for
the removal of ozone from the stratosphere is a free radical of chlorine, 35Cl
• .
What does 35Cl • contain?
|
|
protons
|
neutrons
|
electrons
|
|
A
|
17
|
18
|
16
|
|
B
|
17
|
18
|
17
|
|
C
|
18
|
17
|
17
|
|
D
|
18
|
17
|
18
|
Reference: Past Exam Paper – November 2002 Paper 1 Q2
Solution 2:
Answer: B.
Using the data booklet we find that for a particle to be
described as chlorine it needs to have 17 protons. 35 is the given mass number
of the free radical thus 35 – 17 = 18. There are 18 neutrons because protons
and neutrons are the only particles in an atom that carry mass. The free
radical does not carry a charge thus meaning that opposing charge carrying
particles (protons and electrons) must be equal in number so they cancel out to
give no overall charge.
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