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2g. The ionic bonding of the compounds sodium oxide & potassium 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 2g. A Group 1 Alkali 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 SODIUM OXIDE and POTASSIUM OXIDE

Where the elements sodium, potassium and and oxygen are in the Periodic Table

 

e.g. sodium/potassium + oxygen ==> sodium/potassium oxide Na2O/K2O or ionic formula (Na+)2O2–/(K+)2O2–

In terms of electron arrangement in the formation of the ionic compound sodium oxide, the two sodium/potassium atoms donate their outer electron to one oxygen atom.

This results in two single positive potassium ions 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).

Valencies, sodium/potassium 1, oxygen/sulfur 2. giving the following formulae:

Lithium oxide, Li2O, sodium oxide Na2O, sodium sulfide Na2S and potassium K2S etc.

sodium oxide

2Na (2.8.1) + O (2.6) ==> 2Na+ (2.8.8) O2– (2.8)

can be summarised electronically as 2[2,8,1] + [2,6] ==> [2,8]+2 [2,8]2–

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

TWO (c) doc batoms combine withONE (c) doc batom to form (c) doc b

or

(c) doc b + (c) doc b + (c) doc b ==> (c) doc b(c) doc b(c) doc b

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

The outer electrons of the sodium atoms (2.8.1) 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 sodium ion also attains a stable noble gas electron structure (2.8).

full electronic structure diagram of sodium oxide, the blue circle represents the nucleus.

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

is the Lewis diagram for the formation of sodium oxide

Melting point of sodium oxide is 1132oC

 

 

potassium oxide

2K (2.8.8.1) + O (2.6) ==> 2K+ (2.8.8) O2– (2.8)

can be summarised electronically as 2[2,8,8,1] + [2,6] ==> [2,8,8]+2 [2,8]2–

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

TWO (c) doc batoms combine 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 outer electrons of the potassium atoms (2.8.8.1) 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 potassium ion also attains a stable noble gas electron structure (2.8.8).

full electronic structure diagram of potassium oxide,  the blue circle represents the nucleus.

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

is the Lewis diagram for the formation of potassium oxide

 

Melting point of potassium oxide is 740oC

 

The electronic similarities between the two examples are very obvious.

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 1 Alkali Metal combining with a Group 6 non–metallic element

 

Predicted formulae

Gp1\6 O S
Li Li2O Li2S
Na Na2O Na2S
K K2O K2S
Rb Rb2O Rb2S
Cs Cs2O Cs2S

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

The Group 1 Alkali Metal atom loses one electron to form a singly charged positive ion

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

 


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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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