magnesium chloride MgCl2 calcium chloride CaCl2 ionic bondng Lewis 2D dot & cross electronic diagrams 3D ball & stick close packed space filling models crystal lattice melting point ionic bond compound Doc Brown's chemistry revision notes

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2d. The ionic bonding of the compounds magnesium chloride MgCl₂ and calcium chloride CaCl₂ e.g. combining a group 2 alkaline earth metal with a group 7 halogen element

[Author © Dr Phil Brown GRIC, PhD: Doc Brown's chemistry exam revision notes on the ionic bonds of magnesium chloride & calcium chloride, suitable for students of UK GCSE Science level AQA, Edexcel, OCR, WJEC Eduqas and CCEA GCSE chemistry courses, ~US grades 9-10 chemistry, also useful for more advanced pre-university A level chemistry courses [ionic bonding page RE-EDIT]

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Part 2 Ionic Bonding: compounds and properties

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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 e.g. 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 and calcium combine with oxygen in the Periodic Table - a classic combination of a metal and non-metal to give an ionic bond

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 b atom combines withTWO atoms to form

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 simplified Lewis dot and cross diagram for the formation of magnesium chloride

Melting point of magnesium chloride is 714^oC

(see extra comments after calcium chloride diagrams)

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

Extra comments on magnesium chloride and calcium chloride

Melting point of calcium chloride is 772^oC and magnesium chloride is 714^oC - very high and expected for a giant ionic lattice of a typical ionic compound with a strongly bonded 3D crystal lattice of alternating positive (calcium/magnesium) and negative ions (chloride) that strongly attract each other.

This means the solid magnesium/calcium chloride particles need much higher kinetic energies of vibration to break apart from the giant ionic lattice to form a liquid.

This means the solid magnesium/calcium chloride particles need much higher kinetic energies of vibration to break apart from the giant ionic lattice to form a liquid.

Molten magnesium/calcium chloride will conduct electricity because the ions are free to move to carry the current and will undergo electrolysis to extract magnesium/calcium (or any group 2 metal and release chlorine (or any free Group 7 halogen element) from a similar salt.

See also Using the ionic bonding model to describe and explain the properties of ionic compounds

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 e.g. 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 and names for combing a group 2 metal with a group 7 non-metal halogen

Gp2\7	F	Cl	Br	I
Mg	magnesium fluoride MgF₂	magnesium chloride MgCl₂	magnesium bromide MgBr₂	magnesium iodide MgI₂
Ca	calcium fluoride CaF₂	calcium chloride CaCl₂	calcium bromide CaBr₂	calcium iodide CaI₂
Sr	strontium fluoride SrF₂	strontium chloride SrCl₂	strontium bromide SrBr₂	strontium iodide SrI₂
Ba	barium fluoride BaF₂	barium chloride BaCl₂	barium bromide BaBr₂	barium iodide 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
Note that these formulae are empirical formula - the simplest whole number ratio of atoms in the formulae

All of these solid fluorides, chlorides, bromides and iodides consist of a giant ionic lattice.

All the comments about magnesium chloride and calcium chloride apply to ALL of the ionic compounds tabulated above.

Learning objectives for the ionic compound formed by combining a group 2 alkali earth metal with a group 7 halogen non-metal element

Know where the elements of compounds like magnesium chloride and calcium chloride are in the periodic table.

Know that when a metal element chemically combines with a non-metal element, an ionic compound like magnesium/calcium chloride is formed.

Be able to work out the electron arrangement of the metallic element and non-metallic element in magnesium/calcium chloride or similar compound.

Be able to work out the electron configuration of the ions in group 2 halide from reasoning the electron transfers involved.

Be able to draw the dot and cross electronic diagram for the ionic structure of group 2 halide salts.

Be able to deduce the charges on the ions and work out the formula of the ionic compound of group 2 halide salts.

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Ionic Bonding: compounds and properties

Index for ALL chemical bonding and structure notes

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