2c. Describing and explaining the ionic bonding of the compound sodium chloride NaCl (Na⁺Cl^-) and other similar M⁺X^- compounds formed by combining a group 1 alkali metal with a group 7 halogen and associated ideas

Example 2c. A Group 1 Alkali Metal combining with a Group 7 Halogen non–metal

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

e.g. sodium + chlorine ==> sodium chloride NaCl or its ionic formula Na⁺Cl^– 

In terms of electron arrangement in the formation of the ionic compound sodium chloride, the sodium donates its outer electron to a chlorine atom forming a single positive sodium ion and a single negative chloride ion.

The atoms have become stable ions, because electronically via electron transfer ...

... sodium becomes like neon (sodium ion, Na⁺) and chlorine like argon (chloride ion, Cl^–).

Original full electronic structure of sodium and chlorine

  which become stable electronic structures like neon and argon  

on ion formation and can be summarised electronically to give the stable 'noble gas' structures as [2,8,1] + [2,8,7] ==> [2,8]⁺ [2,8,8]^–  so both the sodium and chloride ions have a full outer shell like a noble gas

ONE atom combines withONE atom

to form

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

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

The valency of Na and Cl are both 1, that is, the numerical charge on the ions. sodium fluoride NaF, potassium bromide KBr and lithium iodide LiI etc. will all be electronically similar.

Only the outer valency electrons of the chloride ion are shown, the 'blob' electron represents the electron from the sodium atom which is accepted by the chlorine atom to form the chloride ion.

The charge on the sodium ion Na⁺ is +1 units (by convention shown as just +) because there is one more positive proton than there are negative electrons in the sodium ion (11p, 10e).

The charge on the chloride ion Cl^– is –1 units (by convention shown as just –) because there is one more negative electron than there are positive protons in the chloride ion (17p, 18e).

Note:

The above diagram would represent the full electronic structure diagram of the sodium ion [2.8] and the chloride ion [2.8.8], hence the full electronic structure of sodium chloride.

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

Above is the electronic dot & cross diagram for the ionic bonding in the ionic compound sodium chloride,

is the simplified Lewis dot & cross diagram for the formation of sodium chloride from its elements.

Limitations of these dot and cross diagrams:

Although these electron arrangement diagrams show how the ionic bond is formed and the electronic structure and electrical charge on the ions, they do not give any idea on the relative size of the ions or the 3D spatial arrangement of the ions in the crystal lattice.

The electronic diagrams give little specific information about the properties of sodium chloride, BUT you would expect it to have the typical properties of an ionic compound.

The crystal structure of sodium chloride NaCl, alternating Na⁺ and Cl^- ions.

 The compound names tabulated below for when a group 1 alkali metal combines with a group 7 halogen non-metal

All the formula highlighted in yellow can be described in the same way as sodium chloride

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

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

The 1:1 ration gives the electrical charge balance and the simple correct formula!

Note that these formulae are empirical formula - the simplest whole number ratio of atoms in the formulae AND they can all be predicted based on the arguments for sodium chloride.

Gp 1\Gp 7	fluorine	chlorine	bromine	iodine	astatine *
lithium	lithium fluoride	lithium chloride	lithium bromide	lithium iodide	lithium astatide
sodium	sodium fluoride	sodium chloride	sodium bromide	sodium iodide	sodium astatide
potassium	potassium fluoride	potassium chloride	potassium bromide	potassium iodide	potassium astatide
rubidium	rubidium fluoride	rubidium chloride	rubidium bromide	rubidium iodide	rubidium astatide
caesium	caesium fluoride	caesium chloride	caesium bromide	caesium iodide	caesium astatide
francium *	francium fluoride	francium chloride	francium bromide	francium iodide	francium astatide

* Francium and caesium (cesium) are highly radioactive elements.

All the comments about sodium chloride apply to ALL of the ionic compounds tabulated above.

Know where the elements of compound sodium chloride are in the periodic table.

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

Be able to work out the electron arrangement of the metallic element and non-metallic element in sodium chloride.

Be able to work out the electron configuration of the ions in sodium chloride from reasoning the electron transfers involved.

Be able to draw the dot and cross electronic diagram for the ionic structure of sodium chloride.

Be able to deduce the charges on the ions and work out the formula of the ionic compound sodium chloride.

Be able to describe the bonding of other ionic compounds when a group 1 alkali metal combines with a group 7 halogen non-metal and predict the name and formula of the compound.