2e. The ionic bonding of the compounds magnesium oxide and calcium oxide

Doc Brown's Chemistry: Chemical Bonding and structure GCSE level, IGCSE, O, IB, AS, A level US grade 9-12 level Revision Notes


Example 2e. A Group 2 Alkaline Earth Metal combining with a Group 6 non–metallic element

* metals \ non-metals (zig-zag line)

Pd metals Part of the modern Periodic Table

Pd = period, Gp = group

metals => non–metals
Gp1 Gp2 Gp3 Gp4 Gp5 Gp6 Gp7 Gp0
1

1H  Note that H does not readily fit into any group

2He
2 3Li 4Be atomic number Chemical Symbol eg 4Be 5B 6C 7N 8O 9F 10Ne
3 11Na 12Mg 13Al 14Si 15P 16S 17Cl 18Ar
4 19K 20Ca 21Sc 22Ti 23V 24Cr 25Mn 26Fe 27Co 28Ni 29Cu 30Zn 31Ga 32Ge 33As 34Se 35Br 36Kr
5 37Rb 38Sr 39Y 40Zr 41Nb 42Mo 43Tc 44Ru 45Rh 46Pd 47Ag 48Cd 49In 50Sn 51Sb 52Te 53I 54Xe
6 55Cs 56Ba Transition Metals 81Tl 82Pb 83Bi 84Po 85At 86Rn
The ionic compounds MAGNESIUM OXIDE and CALCIUM OXIDE

Where the elements magnesium, calcium and oxygen are in the Periodic Table

 

e.g. magnesium/calcium + oxygen ==> magnesium/calcium oxide MgO/CaO or ionic formula Mg2+O2–/Ca2+O2–

In terms of electron arrangement in the formation of the ionic compound magnesium oxide, one magnesium/calcium atom donates its two outer electrons to one oxygen atom.

This results in a double positive calcium ion to one double negative oxide ion via electron transfer.

All the ions have the stable electronic structures 2.8.8 (argon like) or 2.8 (neon like). the valency of both calcium and oxygen is 2.

magnesium oxide

ONE (c) doc batom combines withONE (c) doc batom to form (c) doc b(c) doc b

Note in this electron diagram, only the original outer electrons are shown above.

The two outer electrons of the magnesium atoms (2.8.2) are transferred to the outer shell of the oxygen atom (2.6) until it has a complete octet shell of outer electrons, just like a noble gas (2.8). At the same time, the magnesium ion also attains a stable noble gas electron structure (2.8).

full electronic structure of magnesium oxide

For magnesium oxide: Mg (2.8.2) + O (2.6) ==> Mg2+ (2.8) O2– (2.8)

the stable 'noble gas' structures can be summarised electronically as [2,8] + [2,6] ==> [2,8]2+ [2,8]2–

so both the magnesium and oxide ions have a full outer shell like a noble gas

The electronic dot & cross diagram for the ionic bonding in the ionic compound magnesium oxide

is the Lewis diagram for the formation of magnesium oxide

Melting point of magnesium oxide is 2852oC

 

calcium oxide

Ca (2.8.8.2) + O (2.6) ==> Ca2+ (2.8.8) O2– (2.8)

can be summarised electronically as [2,8,8,2] + [2,6] ==> [2,8,8]2+ [2,8]2–

ONE (c) doc batom combines withONE (c) doc batom to form (c) doc b(c) doc b

Note in this electron diagram, only the original outer electrons are shown above.

The two outer electrons of the calcium atoms (2.8.8.2) are transferred to the outer shell of the oxygen atom (2.6) until it has a complete octet shell of outer electrons, just like a noble gas (2.8). At the same time, the calcium ion also attains a stable noble gas electron structure (2.8.8).

full electronic structure of calcium oxide

The electronic dot & cross for the ionic bonding in the ionic compound calcium oxide

is the Lewis diagram for the formation of calcium oxide

Melting point of calcium oxide is 2572oC

 

Pd metals Part of the modern Periodic Table

Pd = period, Gp = group

metals => non–metals
Gp1 Gp2 Gp3 Gp4 Gp5 Gp6 Gp7 Gp0
1

1H  Note that H does not readily fit into any group

2He
2 3Li 4Be atomic number Chemical Symbol eg 4Be 5B 6C 7N 8O 9F 10Ne
3 11Na 12Mg 13Al 14Si 15P 16S 17Cl 18Ar
4 19K 20Ca 21Sc 22Ti 23V 24Cr 25Mn 26Fe 27Co 28Ni 29Cu 30Zn 31Ga 32Ge 33As 34Se 35Br 36Kr
5 37Rb 38Sr 39Y 40Zr 41Nb 42Mo 43Tc 44Ru 45Rh 46Pd 47Ag 48Cd 49In 50Sn 51Sb 52Te 53I 54Xe
6 55Cs 56Ba Transition Metals 81Tl 82Pb 83Bi 84Po 85At 86Rn
A Group 2 Alkaline Earth Metal combining with a Group 6 non–metallic element

Predicting formulae

Gp2\6 O S
Mg MgO MgS
Ca CaO CaS
Sr SrO SrS
Ba BaO BaS

All the formula highlighted in yellow can be described in the same way as magnesium oxide, magnesium sulfide, calcium oxide or calcium sulfide

The Group 2 Alkaline Earth Metal atom loses two electrons to form a doubly charged positive ion

The Group 6 non–metal atom gains two electrons to form a doubly charged negative ion

 

KCl, MgO, CaO, have NaCl structure

 

 


What next?

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Sub-index for: Part 2 Ionic Bonding: compounds and properties

 

Index for ALL chemical bonding and structure notes

 

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