What causes ions to form ionic bonds?

An ionic bond is formed when a metal combines with a non-metal to produce a compound.
The compound formed is called an ionic compound.
Metal + Non-metal → Ionic compound
The ionic bond is formed through the transfer of electrons from the metal atoms to the non-metal atoms.
The metal atoms lose their valence electrons to achieve a stable noble gas electron arrangement. Thus, positively-charged ions are formed.
The non-metal atoms accept the electrons donated by the metal atoms to achieve a stable noble gas electron arrangement. Thus, negatively-charged ions are formed.
The positively-charged ions and negatively-charged ions are then attracted to each other by strong electrostatic forces which are closely-packed in an orderly manner in a crystal lattice, forming an ionic compound.
The strong electrostatic forces of attraction between the oppositely-charged ions is called ionic bond.
Figure shows a chart that summarises the formation of an ionic bond from a metal atom and non-metal atom.
Examples of ionic compounds:

People also ask

Formation of Ions

In an atom, the number of protons is equal to the number of electrons. Hence, the atom is neutral.
An ion is a charged particle formed when an atom loses or accepts electrons.
An ion is a charged particle because the number of protons is not equal to the number of electrons.
Table compares the formation of cations and anions from their respective elements.

Formation of cations:

An atom that loses electrons from its valence shell forms a positive ion called cation.
The cation is positively-charged because it has more protons than electrons.
Metals form positive ions (cations) by donating electrons.

Formation of anions:

An atom that accepts electrons into its valence shell forms a negative ion called anion.
The anion is negatively-charged because it has more electrons than protons.
Non-metals form negative ions (anions) by accepting electrons.

Figure shows how a neutral atom becomes an ion by donating or accepting electrons.
What causes ions to form ionic bonds 5

How positive and negative ions are formed?

Formation of Cations (Positive Ions)

Metals from Group 1, 2 and 13 of the Periodic Table, form cations (positively-charged ions) by donating their valence electrons.
Metals are generally more electropositive.
(a) This means that metals readily lose their valence electrons to achieve stable duplet or octet electron arrangements similar to noble gases.
(b) By doing so, cations (positively-charged ions) are formed.

Formation of cations by Group 1 elements:

Metal atoms of Group 1 elements have one valence electron.
It is easier for each of these atoms to lose one electron than to gain seven electrons to achieve stable duplet or octet electron arrangements.
As a result, a Group 1 metal atom loses one valence electron to form a cation with a charge of +1.
Example: Lithium
- A lithium atom has an electron arrangement of 2.1.
- It has one valence electron.
- In bond formation, each lithium atom loses one valence electron to achieve a stable duplet electron arrangement similar to helium (noble gas).
- Hence, a lithium ion, Li⁺ is formed.
- The figure below shows the formation of a lithium ion from a lithium atom:

Formation of cations by Group 2 elements:

Metal atoms of Group 2 elements have two valence electrons.
It is easier for each of these atoms to lose two electrons than to gain six electrons to achieve stable noble gas electron arrangement.
As a result, a Group 2 metal atom loses two valence electrons to form a cation with a charge of +2.
Example: Calcium
- A calcium atom has an electron arrangement of 2.8.8.2.
- It has two valence electrons.
- Thus, each calcium atom loses two valence electrons to achieve a stable octet electron arrangement similar to argon.
- Hence, a calcium ion, Ca²⁺ is formed.
- The figure below shows the formation of a calcium ion from a calcium atom:

Formation of cations by Group 13 elements:

Metal atoms of Group 13 elements have three valence electrons.
In order to achieve a stable noble gas electron arrangement, each of the Group 13 metal atoms loses all the three valence electrons to form a cation with a charge of +3.
Example: Aluminium
- An aluminium atom has an electron arrangement of 2.8.3.
- It has three valence electrons.
- Thus, each aluminium atom loses three valence electrons to achieve a stable octet electron arrangement similar to neon.
- Hence, an aluminium ion, Al³⁺ is formed.
- The figure below shows the formation of an aluminium ion from an aluminum atom:

Changes in the number of subatomic particles during the formation of cations:

Below is a list of four important facts regarding the formation of a cation from an atom.
When an atom of a metal changes to a cation,
- the number of protons and neutrons in the nucleus remains unchanged.
- only the number of electrons decreases.
- the electron arrangement changes to achieve a stable noble gas electron arrangement.
- the number of protons (total positive charge) is more than the number of electrons (total negative charge) in the cation formed.
In general, a metal atom X loses n electrons (all its valence electrons) to form a positive ion (cation) with a charge of +n.

Method to determine the charge of a positive ion:

A particle is positively-charged if the number of protons (total positive charge) is more than the number of electrons (total negative charge).
The charge can be calculated as below:

Formation of Anions (Negative Ions)

Non-metals, from Group 15, 16 and 17 of the Periodic Table, form anions (negatively-charged ions) by accepting electrons into their valence shells.
Non-metals are generally more electronegative.
(a) This means that non-metals readily accept electrons into their valence shells to achieve stable octet electron arrangements (similar to those of noble gases).
(b) By doing so, anions (negatively-charged ions) are formed.

Formation of anions by Group 15 elements:

Non-metal atoms of Group 15 elements have five valence electrons.
It is easier for each of these atoms to accept three electrons than to lose five electrons to achieve a stable octet electron arrangement.
As a result, a Group 15 non-metal atom accepts three electrons into its valence shell to form an anion with a charge of -3.
Example: Nitrogen
- A nitrogen atom has an electron arrangement of 2.5.
- It has five valence electrons.
- In bond formation, each nitrogen atom gains three electrons to achieve a stable octet electron arrangement (similar to neon).
- Hence, a nitride ion, N^3- is formed.
- The figure below shows the formation of a nitride ion from a nitrogen atom:

Formation of anions by Group 16 elements:

Non-metal atoms of Group 16 elements have six valence electrons.
It is easier for each of these atoms to accept two electrons than to lose six electrons to achieve a stable noble gas electron arrangement.
Hence, a Group 16 non-metal atom accepts two electrons into its valence shell to form an anion with a charge of -2.
Example: Sulphur
- A sulphur atom has an electron arrangement of 2.8.6.
- It has six valence electrons.
- Hence, each sulphur atom accepts two electrons into its valence shell to achieve a stable octet electron arrangement (similar to argon).
- Thus, a sulphide ion, S^2- is formed.

Formation of anions by Group 17 elements:

Non-metal atoms of Group 17 elements have seven valence electrons.
It is easier for each of these atoms to accept one electron than to lose seven electrons to achieve a stable octet electron arrangement.
Hence, a Group 17 non-metal atom accepts one electron into its valence shell to form an anion with a charge of -1.
Example: Chlorine
- A chlorine atom has an electron arrangement of 2.8.7.
- It has seven valence electrons.
- In bond formation, each chlorine atom accepts one electron into the valence shell to achieve a stable octet electron arrangement (similar to argon).
- Thus, a chloride ion, Cl^– is formed.
- The figure below shows the formation of a chloride ion from a chlorine atom:

Changes in the number of subatomic particles during the formation of anions:

Below is a list of four important facts about the formation of an anion from an atom. When an atom of a non-metal changes to an anion,
- the number of protons and neutrons in the nucleus remains unchanged.
- only the number of electrons increases.
- the electron arrangement changes to achieve a stable noble gas electron arrangement.
- the number of electrons (total negative charge) is more than the number of protons (total positive charge) in the anion formed.
In general, a non-metal atom, Y, accepts m electrons into the valence shell to achieve a stable noble gas electron arrangement. As a result, a negative ion (anion) with a charge of -m is formed.

Method to determine the charge of a negative ion

The charge of a negative ion can be determined based on the number of subatomic particles.
In a negatively-charged ion, the number of electrons (total negative charge) is more than the number of protons (total positive charge)
The charge can be calculated as below:

Ion Formation Examples

1. An ion of an element, Y, has the following number of subatomic particles:
25 protons, 30 neutrons, 23 electrons
(a) Is this ion positively or negatively-charged? Explain your answer.
(b) Calculate the charge of this ion.
(c) Write the formula of this ion.
Solution:

2. Element W has a nucleon number of 27. It has 14 neutrons. It forms an ion with the formula W³⁺.
(a) What is the number of protons and electrons in an ion of W³⁺?
(b) Write the electron arrangement of a W³⁺ ion. Solution
Solution:

3. An element, G, forms an ion with the formula G⁺. An atom of G has 20 neutrons. The electron arrangement of an ion of G⁺ is 2.8.8. What is the nucleon number of element G?
Solution:

4. Element J has a proton number of 16 and a nucleon number of 32. Atom J forms a negative ion, J^n-.
(a) Determine the number of protons, neutrons and electrons in a J^n- ion.
(b) What is the value of n?
Solution:

5. An ion of element M has the following number of subatomic particles:
15 protons, 16 neutrons, 18 electrons
(a) What is the charge of this ion?
(b) Write the formula of this ion.
Solution:
What causes ions to form ionic bonds 24

6. Atom R has a nucleon number of 19. It forms an ion with the formula R^–. A R^– ion has an electron arrangement of 2.8. What is the number of neutrons in an atom of R?
Solution:

7. Element D forms a D²⁺ ion.
The electron arrangement of D²⁺ ion is 2.8.8.
(a) Where is element D located in the Periodic Table?
(b) What is the proton number of element D?
Solution:

8. Element G is placed in Group 16 and Period 2 of the Periodic Table. When atom G forms an ion, its electron arrangement will be changed.
(a) Is the ion formed by element G positively or negatively charged?
(b) What is the formula of the ion formed by element G?
(c) Write the electron arrangement of the ion formed by element G.
Solution: