Summary CIE AS Level Chemistry Note Unit 10 - Group 2
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Course
Unit 10 - Group 2 (9701)
Institution
CIE
These notes cover the whole syllabus of 9701 Cambridge International Examination, AS Level Chemistry Notes what divided into to different Units. You may find each notes have corresponded specifically in each term from syllabus.
Alevel Chemistry Revision IC 10
Revision Material
Duration: 2nd – 8th March
Topic 10 Group 2
The physical and chemical properties of the elements of Group 2 (the alkaline Earth metals) are introduced in this topic.
Learning outcomes
Candidates should be able to:
10.1 Similarities and trends (a) describe the reactions of the elements with oxygen, water and dilute acids
in the properties of the (b) describe the behaviour of the oxides, hydroxides and carbonates with water and dilute acids
Group 2 metals, (c) describe the thermal decomposition of the nitrates and carbonates
magnesium to barium, (d) interpret, and make predictions from, the trends in physical and chemical properties of the
and their compounds elements and their compounds
(e) state the variation in the solubilities of the hydroxides and sulfates
10.2 Some uses of Group 2 (a) describe and explain the use of calcium hydroxide and calcium carbonate (powdered
compounds limestone) in agriculture
, 10.1 Similarities and trends in the properties of the Group 2 metals, magnesium to barium, and their compounds
The elements in Group 2 of the Periodic Table are sometimes referred to as the alkaline earth metals.
Beryllium (Be) 1s22s2
Magnesium (Mg) 1s22s22p63s2
Calcium (Ca) 1s22s22p63s23p104s2
Strontium (Sr) 1s22s22p63s23p63d104s24p65s2
Barium (Ba) 1s22s22p63s23p63d104s24p64d105s25p66s2
Group 2 element Metallic atomic Melting Density First Ionisation Second Ionisation reactivity
-1 -1 -1
radius / nm number point / °C / gcm energy / kJmol energy / kJmol
Beryllium (Be) 0.122 4 1280 1.85 900 1760 increasing
Magnesium (Mg) 0.160 12 650 1.74 736 1450
Calcium (Ca) 0.197 20 838 1.55 590 1150
Strontium (Sr) 0.215 38 768 2.6 548 1060
Barium (Ba) 0.217 56 714 3.5 502 966
(a) Explanations to those trend
1. ∆𝐻𝑖𝑙 decreasing
- The proton number increases and the shielding (repulsion from the inner electrons) is also increasing
- The atomic size increase due to the increasing in shell number
- The overall nuclear attraction decreases down the group
2. The element become more reactive
- The number attraction gets weaker as the atoms become large in size
- Therefore, the outer electrons are easier to be removed
M → M2+ + 2e-
Ø (from Mg to Ba) larger (atomic) radius / more shells / more shielding
electron(s) are less tightly held (by nucleus) / less attracted (to nucleus)
ionisation energy / ies decrease(s) / electron(s) lost (more) easily (down the group)
lower activation energy (for the reactions down the group)
3. Melting point / boiling point decrease
- All the group II element have the same number of free electrons and the metal cations have the same relative
charge +2
- The size of metal cation gets large down the group so that the metallic become weaker
Ø increasing (cation) size / (cat)ionic radius increases / increasing size of atoms
overall charge on (cation) is constant / (+)2 / decreasing charge density of (+2 charged cation)
number of delocalised / outer / valence electrons (per atom) remains the same / 2
increased shielding
decreasing (strength of) attraction between (cat)ion / nucleus / nuclear charge AND delocalised electron(s)
(b) describe the reactions of the elements with oxygen, water and dilute acids
with oxygen
2Mg(s) + O2(g) → 2MgO(s) bright white flame, white solid
2Ca(s) + O2(g) → 2CaO(s) glows red, white smokes
CaO(s) + H2O(l) → Ca(OH)2(s) vigorous reaction
Excess water, dissolves to form a weakly alkaline solution
Ca(OH)2(s) → 𝑤𝑎𝑡𝑒𝑟 Ca2+(aq) + 2OH-(aq)
ionic equation O2-(s) + H2O(l) → 2OH-(aq)
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