2a. Introduction to ionic bonding, ions
and the periodic table
and which elements are most likely to combine to
give an ionic compound
Brown's Chemistry: Chemical Bonding and structure GCSE level, IGCSE, O, IB, AS, A
level US grade
9-12 level Revision Notes
Ionic bonds are formed by one atom transferring electrons to another atom to form ions.
An ionic bond is most likely to be formed
when a metal combines with a non–metal to form an ionic compound.
Elements consist of
neutral atoms or molecules, the electrical neutrality is because the
number of positive protons equals the number of surrounding negative electrons
in their respective energy levels.
Charged particles called IONS
are atoms, or groups of atoms, which have lost or gained one or more electrons
to have a overall net electrical positive charge or negative charge.
In losing or gaining electrons to form
an ion, part of an ionic bond, producing an ionic compound ...
the atoms try to attain a stable electron arrangement of a noble gas e.g. a
full outer shell of electrons,
the number of electrons lost or
gained gives the numerical charge of the ion,
an atom (usually non–metal) with a nearly full
outer shell will try to gain electrons to form a negative ion,
the ion charge of –, 2–, 3– etc.
results from the neutral atom gaining of 1, 2 or 3 electrons etc,
an atom (usually a metal) with a nearly empty
outer shell will tend to lose
electrons to form a positive ion,
the ion charge of +, 2+ or 3+
etc. results from the neutral atom losing 1, 2 or 3 electrons etc,
and it is the mutual attraction
of these positive and negative ions that will constitute the ionic
There are lots of dot and cross
diagrams i.e. Lewis diagrams of ionic (electrovalent) bonding in ionic compounds
The atom losing electrons forms a
positive ion (a cation) and is usually a
The overall charge on the ion is positive due to excess positive nuclear charge (proton
numbers do NOT change in chemical reactions)
Group 1 alkali metals lose their
single outer electron to form single positive ions e.g. Na ==> Na+
Group 2 metals lose their two
outer electrons to form doubly charged positive ions e.g. Mg ==> Mg2+
The atom gaining electrons forms a
negative ion (an anion) and is usually a
The overall charge on the ion is negative because of the gain, and therefore excess, of negative electrons
Group 7 halogen atoms gain one
electron to form a singly charged negative ion e.g. Cl + e–
Group 6 non–metals gain two
electrons to form a doubly charged negative ion e.g. O + 2e–
Therefore an IONIC BOND IS THE
FORCE OF ATTRACTION BETWEEN ADJACENT IONS OF OPPOSITE CHARGE.
Which electronic structures are
the most stable? because this what atoms
will try to get to electronically!
(atomic number) electron arrangement
When atoms LOSE OR GAIN
ELECTRONS, they try to attain the electron structure (electron configuration) of
the electronically very stable atoms of the Group 0 Noble Gases eg helium
(2), neon (2.8) or argon (2.8.8) etc. quite simply because these are the most
stable electron arrangements with a full outer shell of electrons (full
highest energy level).
In advanced level chemistry you
will encounter examples of electronic structures of ions that are NOT those
of a Noble Gas.
Its a good idea to have some idea
of where the elements are in the periodic table, and their electronic structure,
before looking at the theoretical electronic model for ionic bonding in ionic
You should be able to:
work out the electron structure of simple
draw the electronic diagram of an ionic
draw dot and cross diagrams for ionic
compounds formed by metals in Groups 1 and 2 with non–metals in Groups 6 and
work out the charge on the ions produced
by metals in Groups 1 and 2 and by non–metals in Groups 6 and 7 and relate
the charge to the group number of the element in the periodic table
deduce that a compound is ionic from a
diagram of its structure in several different forms
describe the limitations of using dot and
cross, ball and stick, two and three–dimensional diagrams to represent a
giant ionic structure
work out the empirical formula of an
ionic compound from a given model or diagram that shows the ions in the
Which elements form ionic
bonds, therefore ionic compounds?
The black zig–zag line 'roughly' divides the
metals on the left from the non–metals on the right of the elements of the
The electronic structures of the first 20
elements of the Periodic Table
You need to know about these to understand the
details of ionic chemical bonding
Part of the modern Periodic Table
Pd = period,
Gp = group
that H does not readily fit into any group
Chemical Symbol eg 4Be
Alkaline Earth Metals,
Gp 0 Noble Gases
Chemical bonding comments about the
selected elements highlighted in white
e.g. When the metals on the left, highlighted
combine with the non–metals, highlighted in white, on the right
of the periodic table, an ionic bond is
e.g. the formation of an ionic compound like sodium
chloride NaCl or magnesium oxide MgO
ion charge and group number
On this page to form stable ions with a noble gas
electron arrangement occur by electron transfer ...
For (a) to d) below
1/2 metal and
X represents a
Group 1 metals lose their 1 outer
electron to form a singly charged positive ion:
M ==> M+
Group 2 metals
lose their 2 outer electrons to form a doubly charged positive
ion: M ==> M2+ + 2e–
Group 6 non–metals gain 2 electrons to
form a doubly charged negative ion:
X + 2e– ==> X2–
Group 7 halogen non–metals gain 1
electron to form a singly charged negative ion:
X + e–
In a correct ionic formula: total positive
ion charge = total negative ion charge
therefore we can predict the following
formula where M = a
group 1/2 metal and
X = a group 6/7 non–metal:
(a) Group 1 + (c) Group 6
===> M2X or (M+)2X2–
(a) Group 1 + (d) Group 7 ===>
(b) Group 2 + (c) Group 6
===> MX or
(b) Group 2 + (d) Group 7
===> MX2 or
All the atoms of the metallic
elements on the left–hand side of the Periodic Table eg (Groups 1/2) have 1/2
electrons in their outer shell (highest energy level) which are readily lost to
form a positive ion of charge +1/+2 (cations) eg sodium, potassium, magnesium
and calcium etc. The electronic structure of these stable positive ions are
those of a Noble Gas with a full outer shell.
eg Na [2.8.1] ==> Na+
[2.8] like neon + e–, or Ca [22.214.171.124] ==> Ca2+
[2.8.8] like argon + 2e–
The atoms of the non–metallic
elements on the right–hand side of the Periodic Table eg (Groups 6/7) have 6/7
electrons in their outer shell and try to gain 2/1 electrons to become
electronically stable like a Noble Gas with a full outer shell of electrons eg oxygen and sulfur in Group 6 and the
Group 7 Halogens – fluorine, chlorine, bromine and iodine. The electronic
structure of these stable negative ions are those of a Noble Gas with a full
eg O [2.6] + 2e–
==> O2– [2.8] like neon, or Cl [2.8.7] + e–
==> Cl– [2.8.8] like argon
Brief summary of the Periodic Table including
electronic structure and formula patterns
The examples below involve combining a metal from Groups 1 (Alkali Metals), 2 or 3, with a non–metal from Group 6 or Group 7 (The Halogens).
The electron structures are shown in () or . Only the outer electrons of the
original atoms, and where they end up in the ions, are shown in the dot and
cross (ox) diagrams
Ionic bonding is not
directional like covalent bonding, in the sense that the force of attraction
between the positive ions and the negative ions act in every direction around
the ions which will alternate between being positive and negative to maximise
Note: In the examples of ionic bonding it is assumed
YOU can work out the electron configuration (arrangement in shells or energy
levels) given the atomic/proton number of the element from the Periodic Table.
There are lots of dot and cross diagrams
including simplified Lewis diagrams of ionic (electrovalent) bonding in ionic compounds
Lewis diagrams are quite minimalist.
positive metal ions which give a noble gas structure when the electrons are
'lost' from the original metal atom, no outer shell electrons are shown!
most simple non–metal negative ions, only the complete octet of outer shell electrons
is shown for each atom.
Note: Limitations of dot and cross
electronic diagrams of ionic compounds
It is important to appreciate that dot and cross Lewis diagrams
for ionic compounds do not show the structure of the compound in terms of ...
(i) arrangement of the ions in a crystal
lattice of an ionic compound
– an ionic bond is formed by one atom transferring electrons to another atom to form oppositely charged
particles called ions which attract each other – this electrostatic attraction
is called an ionic bond and is most likely formed when a metal combines with a
An ion is an atom
or group of atoms carrying an overall positive or negative
The electric charge is shown as
a superscript +, –, 2+, 2– or 3+ etc.
e.g. Na+, Cl–, [Cu(H2O)6]2+,
If a particle, as in a neutral atom,
has equal numbers of protons (+) and electrons (–) the overall particle charge is zero
i.e. no overall electric charge.
The proton/atomic number in an atom does not change BUT
the number of associated electrons can!
If negative electrons are
excess charge from the protons
produces an overall positive ion.
electrons are gained there is an excess of negative charge, so
a negative ion
The charge on the ion is numerically related to the number of
electrons transferred i.e. electrons lost or gained.
For any atom or group of atoms, for every electron gained
you get a one unit increase in negative charge on the ion, for every electron lost you get
a one unit increase in the positive charge on the ion.
The atom losing electrons forms a
positive ion (cation) and is usually a metallic element.
The atom gaining electrons forms a negative ion
(anion) and is usually a non–metallic element.
The ionic bond then consists of the attractive force between the positive and
negative ions in the structure.
The ionic bonding
forces act in all directions around a particular ion, it is not
directional, as in the case of covalent bonding.
sodium (metal) atom transfers an electron to the chlorine (non–metal) atom
the ionic compound sodium
The bonds between the ions is
very strong and they club together to form a giant ionic lattice with
a very high melting point because it takes a lot of energy to overcome the
attractive forces between the ions - the ionic bonds.
When molten, or dissolved in
water, ionic compounds will conduct electricity because the charged
particles (ions) are free to move and carry the electric current.
Ionic Bonding: compounds and properties
bonding and structure notes
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