Many metals form ionic bonds when they react with non-metals. Compounds formed due to inoic bond are known as ionic compounds.
|Positive Ion||An ion in which number of electrons is less than that of protons. Positive charge comes because of extra proton.|
|Negative Ion||An ion in which number of electrons is more than that of protons. Negative charge comes because of extra electron.|
Positive or negative charged atoms are known as ions. Ions are formed because of loss or gain of electrons. You have read that noble gases are stable because they have fully filled outermost shell. Atoms of other elements try to attain fully filled outermost shell in order to become stable. This can be done by gain or loss of electrons or sharing of electrons.
A positive ion is formed because of loss of electrons by an atom. When an atom lose an electron, it is left with an extra proton compared to the number of electrons left in it. Due to the extra proton, it gets a psitive charge. Following are some examples of positive ions.
Sodium forms sodium ion because of loss of one electron. Because of loss of one electron, one positive charge comes over sodium.
Na ⇨ Na+ + e−
Similarly, potassium gets one positive charge by loss of one electron.
K ⇨ K+ + e−
Magnesium forms positive ion because of loss of two electrons. Two positive charges come over magnesium because of loss of two electrons.
Mg ⇨ Mg+ + + 2e−
Similarly, calcium gets two positive charges over it by loss of two electrons.
Ca ⇨ Ca+ + + 2e−
A negative ion is formed because of gain of electron. When an atom gains an electron, it gets an extra electron compared to the number of protons in it. Due to this, there is an extra negative charge. Some examples are given below.
Chlorine gains one electron in order to achieve stable configuration. After loss of one electron chlorine gets one negative charge over it forming chlorine ion.
Cl + e− ⇨ Cl−
Similarly, fluorine gets one negative charge over it by gain of one electron forming chloride ion, in order to achieve stable configuration./p>
F + e− ⇨ F−
Oxygen gets two negative charge over it by gain of two electrons forming oxide ion, in order to obtain stable configuration.
O + 2e− ⇨ O− −
You have read that ionic bonds are formed because of transfer of electrons from metal to non-metal. In this course, metals get positive charge because of loss of electrons and non-metal gets negative charge because of gain of electrons. In other words, bond formed between positive and negative ion is called ionic bond.
Since, a compound is electrically neutral, so to form an ionic compound both negative and positive both ions be combined. Some examples are given below.
Formation of sodium chloride (NaCl):
In sodium chloride, sodium is a metal (alkali metal) and chlorine is non-metal.
Atomic number of sodium = 11
Electronic configuration of sodium: 2, 8, 1
Number of electrons in outermost orbit = 1
Valence electrons = Electrons in outermost orbit = 1
Atomic number of chlorine = 17
Electronic configuration of chlorine: 2, 8, 7
Electrons in outermost orbit = 7
Therefore, valence electrons = 7
Sodium has one valence electron and chlorine has seven valence electrons. Sodium needs to lose one electron to obtain stable configuration and chlorine needs to gain one electron in order to obtain stable electronic configuration. Thus, in order to obtain stable configuration sodium transfers one electron to chlorine.
After loss of one electron sodium gets one positive charge (+) and chlorine gets one negative charge after gain of one electron. Sodium chloride is formed because of transfer of electrons. Thus, ionic bond is formed between sodium and chlorine. Since, sodium chloride is formed because of ionic bond, thus it is called ionic compound.