A reaction intermediate or an intermediate is a molecular entity that is formed from the reactants (or preceding intermediates) and reacts further to give the directly observed products of a chemical reaction.

1. Dr. Tanuja Nautiyal
Department of Chemistry
Sharda Public School
Almora
Radicals and Chemical Formulae

2. Radicals
Ions
How to write a chemical formula
Radicals and Chemical Formulae

3. Radicals are atomic or molecular
species with unpaired electrons which
are capable of independent existence.
Radicals

4. Electrophiles
Nucleophiles
Free- radicals
Type of Radicals

5. •The attacking reagents are classified into three types:
Electrophiles
•Positively charged or neutral species, which are deficient of
electrons and can accept a pair of electrons are called
electrophiles. These are also called electron loving (philic)
species.
•For example: H+, H3O+, Cl+, CH3
+, NO2
+ (Positively
charged)AlCl3, BF3, SO3 (Neutral)
•Both Al and B act as electrophiles as they have total of six
electrons i.e. two less than the octet, and so they try to
complete their octets. These are also called as Lewis acids.
Electrophile

6. •A nucleophile is a reagent containing an atom having unshared
or lone pair of electrons.
•As a nucleophile is electron rich it seeks electron deficient sites
i.e., nucleus (nucleus loving).
•According to Lewis concept of acids and bases, nucleophiles
behave as Lewis bases.
•For example: NH3, H2O, ROH, ROR (neutral)
Nucleophiles

7. A free radical may be defined as an atom or group of atoms
having an unpaired electron.
Free radicals are produced during the homolytic fission of a
covalent bond.
Free Radical

8. Free radicals are very reactive as they have strong tendency to
pair up their unpaired electron with another electron from
wherever available.
These pairs are very short lived and occur only as reaction
intermediates during reactions.
For example, dissociation of chlorine gas in the presence of
ultra-violet light produces chlorine free radicals:
Free Radical

9. The alkyl free radical may be obtained when free radical
chlorine attacks methane.
Free Radical

10. Free radicals may be classified as primary, secondary or tertiary
depending upon whether one, two or three carbon atoms are
attached to the carbon atom carrying the odd electron:
Free Radical

11. The order of stability of alkyl free radicals is: CH3 <>o <>o <>o
This order of stability can easily be explained on the basis of
hyperconjugation.
Larger the number of alkyl groups, attached to the carbon atom
carrying the odd electron, greater is the delocalisation of the
odd electron and hence more stable is the free radical.
Accordingly, the tertiary free radical with three alkyl groups
attached to the carbon atom carrying the odd electron is more
stable than the secondary free radical containing two alkyl
groups and so on.
Stability of free radicals

12. The carbon atom in alkyl free radicals involves
sp2 hybridization. Therefore, it has a planar structure. Three
hybrid orbitals are used in the formation of three s-bonds with
three H atoms or alkyl group. The unpaired electron is present
in unhybridized p orbital.
Structure of alkyl free radical
Orbital structure of free radicals

13. Types of Radicals
 Acid radicals:-The acid radical is an anion left
after removal of hydrogen atoms from an acid.
 Basic radicals:-The basic radical is the cation left
after removal of OH or other alkaline group from
the bases.

14. •An ion is a charged species in which an atom or a
group of atoms possess a net electric charge.
•The net electric charge of an ion can either be
positive or negative.
•Positively charged ions are called cations and
negatively charged ions are called anions.

15.  Cations are atoms that have lost an electron to
become positively charged.
 The ions of all the metal elements are cations.
 If an atom loses one electron, then the cation
formed has 1 unit positive charge.
 Examples:- Na+ , Zn2+, Mg2+, Al3+ etc.

16.  A neutral lithium (Li) has 3 protons and 3
electrons, and it is missing an electron. Then we
have 3 protons and 2 electrons. So lithium loses
one electron to become a 1+cation.

18.  Anions are atoms or groups of atoms that have
gained electrons. Having more negatively
charged electrons than positively charged
protons, they are negatively charged.
 Most anions are composed from multiple atoms,
and are called polyatomic ions.
 Examples:- Cl− , O2- , co3
2-, PO4
3- etc.
ANIONS

19.  A neutral chlorine Cl has 17 protons and 17 electrons,
and it is gaining one electron. Then we have 17
protons and 18 electrons. So, chlorine gained one
electron to become a 1- anion.
ANIONS

20. ANIONS

21.  Chemical formula of a compound is the symbolic
representation of its atomic constituents. In other
words, a chemical formula represents the
composition of a molecule in terms of the
symbols of the elements present in that
molecule. To write the chemical formula of a
compound, one should have prior knowledge of
two things.
 1.The symbols of the constituent elements.
 2.The combining capacity of each atom
constituting the compound

22.  The combining power or the combining capacity of an atom or
an element is called its valency. The number of atoms of other
elements with which one atom of an element combines is
decided by the valency of that element.
For example, both hydrogen and chlorine have a valency of 1.
Therefore, one atom of hydrogen reacts with one atom of
chlorine to formone molecule of hydrogen chloride.
The valency of an ion is equal to the charge on it.

23. 

24. The valencies of some common ions are given in the following
table.
Name of
ion
Symbol Valency Name of
ion
Symbol Valency
Aluminium Al3+ 3 Sulphite SO3
2- 2
Ammoniu
m
NH4
+ 1 Bromide Br− 1
Calcium Ca2+ 2 Carbonate CO3
2- 2
Copper(II) Cu2+ 2 Chloride Cl− 1
Hydrogen H+ 1 Hydride H− 1
Iron(III) Fe3+ 3 Hydroxide OH− 1
Potassium K+ 1 Oxide O2− 2
Zinc Zn2+ 2 Sulphide S2− 2

25. STEPS TO WRITE A CHEMICAL
FORMULA
1.Write the symbols of the elements which
form a compound.
If we have to write the formula of hydrogen
sulphide. First write down the symbols of hydrogen
and sulphur.
Symbols: H S

26. 2. Below the symbol of each element, write
down its valency.
Symbols: H S
Valencies: 1 2
STEPS TO WRITE A CHEMICAL
FORMULA

27. 3.Finally cross-over the valencies of the combining
atoms. This will give the required formula.
Symbols: H S
Valencies: 1 2
STEPS TO WRITE A CHEMICAL
FORMULA

28. Formula of some compounds
Chemical compounds Chemical Formula
Silver chloride AgCl
Aluminium nitrate Al(NO3)3
Barium chloride BaCl2
Calcium carbonate CaCO3
Potassium nitrate KNO3
Magnesium aluminate Mg(AlO2)2
Sodium carbonate Na2CO3

29. Dr. Tanuja Nautiyal
Department of Chemistry
Sharda Public School
Almora
Thank you