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ATOMS, ELECTRON STRUCTURE AND PERIODICITY HW MS

1.	(a)	(i)	atoms of same element/same atomic number….. with
different numbers of neutrons/different masses 	1
(ii)	isotope	protons	neutrons	electrons	2
	^46Ti		22	24	22 
	^47Ti		22	25	22 
 (b)	 
     = 47.7 	2
[5]

 2.	isotope	protons	neutrons	electrons
nickel-58	28	30	28
nickel-60	28	32	28
nickel-62	28	34	28
	           	
For ecf, 3rd column same as first column.
[3]
 
3.	(i)	

| protons | neutrons | electrons
^24Mg | 12 | 12 | 12
^25Mg | 12 | 13 | 12
	^24Mg line correct 
^25Mg line correct 
mark by row
2
(ii)	
	OR 18.8640 + 2.5275 + 2.9354
	OR	24.3269 
	A_r = 24.33 (to 4 sig figs) 
ALLOW two marks for A_r = 24.33 with no working out
ALLOW one mark for ecf from incorrect sum provided final answer is between 24 and 26 and is to 4 significant figures, e.g. 24.3235  gives ecf of 24.32 
2

(iii)	The (weighted) mean mass of an atom
OR (weighted) average mass of an atom 
	relative to 1/12^th (the mass) 
	of (one atom of) ^12C 
ALLOW The (weighted) mean mass
OR (weighted) average mass of an atom
OR average atomic mass 
compared with (the mass of) carbon-12 
which is 12 
For 1st marking point, ALLOW mean mass of the isotopes
OR average mass of the isotopes
Do NOT ALLOW the singular: isotope
ALLOW mass of one mole of atoms 
compared to 1/12^th 
(the mass) of one mole / 12 g of carbon-12 
	mass of one mole of atoms
1/12^ththe mass of one mole / 12 g of carbon-12 
3
[7]

4.	(a)	(atoms of) same element/same atomic number….. with
	different numbers of neutrons/different masses 	1
(b)		3

isotope

percentage
composition

number of

| | protons | neutrons | electrons
^85Rb | 71 to 73 | 37 | 48 | 37
^87Rb | 27 to 29 | 37 | 50 | 37

mark

must add
up to 100

ie 1 mark for each atomic structure; 1 for % compositions.

= 85.6  2nd mark for significant figures	2
71/29: 85.58 = 85.6
73/27: 85.54 = 85.5
 
(c)	carbon-12/^12C 	1
[7]

5.	(i)	^79Br has two  less neutrons than ^81Br 	2
(ii)	^79Br have same numbers of protons 
and same number of electrons 	2
[4]

6.	(i)	Potassium AND argon 
ALLOW K and Ar
1
(ii)	They are arranged in increasing atomic number
OR
Neither would show properties OR trends of rest of group
OR
Neither would show properties OR trends of rest of period
OR
They are arranged by electron configuration 
ALLOW any correct property difference
e.g. This would place a reactive metal in the same group as noble gases
ALLOW they do not fit in with the rest of the group
1
[2]

7.	1s^22s^22p^2 
[1]

8.	3d^10 4s^2 4p^5 
ALLOW 4s^2 3d^10 4p^5
ALLOW subscripts or 3D^10
ALLOW answers with 1s^2 2s^2 2p^6 3s^2 3p^6 appearing twice
[1]

 9.	1s^22s^22p^63s^23p^63d^24s^2 
[1]
 
10.		1s^22s^22p^63s^23p^6 
ALLOW subscripts
 [1]

11.	the energy required to remove one electron  from each
atom in one mole  of gaseous atoms 
ALLOW 3 marks for:
the energy required to remove one mole of electrons 
from one mole of atoms 
atoms in the gaseous state 
If no definition, ALLOW one mark for the equation below, including state symbols.
X(g) → X^+(g) + e^– / X(g) – e^– → X^+(g)
ALLOW e for electron
IGNORE state symbol for electron
[3]
 
12.	(From 2 ®10 ®18 / down group)
1st ionisation energies decrease/easier to remove electrons 
electron is further from nucleus/ atomic radius increases/
electron in a different shell/ atoms increase in size 
(not sub-shell or orbital)
electron experiences more shielding 
(more is essential here)
distance and shielding outweigh the increased nuclear charge 
NOT: attraction/pull; effective nuclear charge
[4]

13.	(i)	First  ionisation (energy) 	2
Ra(g) ® Ra^+(g) + e^− 
1 mark for equation
1 mark for state symbols
‘-‘ not required on ‘e’	2
(ii)	atomic radii of Ra > atomic radii of Ca/
Ra has electrons in shell further from nucleus than Ca/
Ra has more shells 
Ra has more shielding than Ca 
: ‘more’ is essential
Ra electron held less tightly/less attraction on electron 	3
[7]

14.	(a)	Energy change when each atom in 1 mole 
of gaseous atoms 	3
loses an electron  (to form 1 mole of gaseous 1+ ions).
 
(b)	increasing nuclear charge/number of protons 
electrons experience greater attraction or pull/atomic
radius decreases/electrons added to same shell/same or
similar shielding 	2
[5]

15.	(i)	Energy change when each atom in 1 mole 
of gaseous atoms 
loses an electron  (to form 1 mole of gaseous 1+ ions).	3
(ii)	O^2+(g) ® O^3+(g) + e^− 	2
1 mark for correct species; 1 mark for state symbols
No charge required on electron.
Ignore (g) on e
(iii)	Large difference between 6th and 7th IEs 	2
marking a different shell (closer to nucleus) 
allow ‘inner shells’/new shell/full shell/first shell
marking points independent.
not sub-shell or orbital
[7]
 
16.	(a)	Energy change when each atom in 1 mole
of gaseous atoms
loses an electron  (to form 1 mole of gaseous 1+ ions).	3
(b)	From Li ® N, ionisation energy increases
number of protons/nuclear charge increases
nuclear attraction increases / shell drawn in by increased
nuclear charge/ atomic radius decreases
across period, electrons added to same shell
Not same subshell
From Be ® B, ionisation energy decreases
for B, electron is removed from a p sub-shell/p
orbital/different sub-shell
which has a higher energy	7
watch for distinction between nuclear attraction and
nuclear charge in candidates’ scripts.
Also watch for confusion between shell and subshell.
Al
Sharp rise in successive ionisation energy between 3rd and
4th IE
marking a change to a new or different shell / there are 3
electrons in the outer shell	3
mention of ‘orbital’ or ‘sub-shell cancels ‘shell mark’ Each marking point for Al is independent
	QoWC:	links together two pieces of information
	correctly within two of the sections below:
	1. General trend across period
	2. Be to B
	Successive ionisation energies
[13]

17.	(i)	O^+(g) → O^2+(g) + e^– 
answer must have state symbols
ALLOW e for electron
ALLOW O^+(g) – e^- → O^2+(g)
DO NOT ALLOW O^+(g) + e^– → O^2+(g) + 2e^–
IGNORE state symbol for electron
1
(ii)	the O^+ ion, is smaller than the O atom
OR
the electron repulsion/shielding is smaller
OR
the proton : electron ratio in the 2+ ion is greater than in
the 1+ ion 
ALLOW the outer electrons in an O^+ ion are closer to the nucleus than an O atom
DO NOT ALLOW ‘removed from next shell down’
1
[2]

18.	N has less protons than O (ora) 
electrons are in same shell
/have same or similar shielding 
weaker nuclear attraction in N (ora) 
shell drawn in less by nuclear charge in N (ora) 
watch for distinction between nuclear attraction and nuclear
charge in candidates’ scripts.
QoWC:	links together two statements in at least two of
the sections (a)(ii), (b) and (c) 
[4]

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