2d. The ionic bonding of the compounds magnesium chloride and calcium chloride

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


Example 2d. A Group 2 Alkaline Earth Metal combining with a Group 7 Halogen non–metal

* 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 CHLORIDE and CALCIUM CHLORIDE

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

 

e.g. magnesium + chlorine ==> magnesium chloride MgCl2 or ionic formula Mg2+(Cl)2 

In terms of electron arrangement in the formation of the ionic compound magnesium chloride, the magnesium donates its two outer electrons to two chlorine atoms forming a double positive magnesium ion and two single negative chloride ions via electron transfer.

The atoms have become stable ions, because electronically, magnesium becomes like neon and chlorine like argon.

Mg (2.8.2) + 2Cl (2.8.7) ==> Mg2+ (2.8) 2Cl (2.8.8)

can be summarised electronically as [2,8,2] + 2[2,8,7] ==> [2,8]2+ [2,8,8]2  via electron transfer

so both the magnesium and chloride ions have a full outer shell of electrons like a noble gas

ONE (c) doc batom combines withTWO (c) doc b atoms to form (c) doc b(c) doc b

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

The outer electrons of the magnesium atoms (2.8.2) are transferred to the outer shell of the chlorine atom (2.8.7) giving it a complete octet shell of outer electrons, just like a noble gas (2.8.8). At the same time, the magnesium ion also attains a stable noble gas electron structure (2.8).

NOTE

You can draw two separate chloride ions, but in these examples square brackets and a number subscript have been used, as in ordinary chemical formula.

The valency of Mg is 2 and chlorine 1, i.e. the numerical charges of the ions.

Beryllium fluoride BeF2, magnesium bromide MgBr2, calcium chloride CaCl2 or barium iodide BaI2 etc. will all be electronically similar.

represents the full electronic structure diagram of the magnesium ion [2.8] and the chloride ion [2.8.8], hence the full electronic structure of magnesium chloride.

Note that the 'blob' and 'x' electrons are identical, but their use is just a useful visual device to show how the ion is formed. The blue circle represents the nucleus.

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

is the Lewis diagram for the formation of magnesium chloride

Melting point of magnesium chloride is 714oC

 

Ca is 2.8.8.2, Cl is 2.8.7, F is 2.7 rest of dot and cross diagrams are up to you, but calcium chloride is shown below.

The calcium atoms transfer their two outer electrons to the outer shell of two chlorine atoms

calcium chloride

The two outer electrons of the calcium atoms (2.8.8.2) are transferred to the outer shell of two chlorine atoms (2.8.7) until it has a complete octet shell of outer electrons, just like a noble gas (2.8.8). At the same time, the calcium ion also attains a stable noble gas electron structure (2.8.8). The blue circle represents the nucleus.

is the Lewis diagram for the formation of calcium chloride

Melting point of calcium chloride is 772oC

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 7 Halogen non–metal

Predicting formulae

Gp2\7 F Cl Br I
Mg MgF2 MgCl2 MgBr2 MgI2
Ca CaF2 CaCl2 CaBr2 CaI2
Sr SrF2 SrCl2 SrBr2 SrI2
Ba BaF2 BaCl2 BaBr2 BaI2

All the formula highlighted in yellow can be described in the same way as magnesium chloride or calcium chloride

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

The Group 7 Halogen atom gains one electron to form a singly charged negative ion

 


What next?

Recommend next: ?

 

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

 

Index for ALL chemical bonding and structure notes

 

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