- An element is the simplest pure form of a substance that cannot be broken down further by chemical means. It is made of only one type of atom. - Atoms are the smallest particles that make up elements and can participate in chemical reactions. They have protons and neutrons in the nucleus surrounded by electrons. - Compounds are formed by the combination of two or more elements in a fixed ratio. They have different properties than their constituent elements.

1. Classification of Elements
ATOMIC STRUCTURE ELECTRONIC CONFIGURATION VALENCY MOLECULAR
FORMULA RADICALS

2. What is chemistry? Discuss and Share!

4. Element
 An element is the simplest pure form of a substance
which cannot be split up into simpler substances by
any chemical method.
 An Element is made up of similar kinds of atoms
 Example : Hydrogen, Potassium, Gold ,Silver etc .

5. Atom
 The smallest particle of an element that can take
part in chemical reactions without division is called
atom.
 All the atoms of an element are the same whereas
atoms of different elements are different.
 For example , all the atoms of gold in a gold ring are
the same but an atom of gold is different from an
atom of silver.

6. Compound
 Compound is a chemical substance formed by the
combination of two or more elements in a fixed proportion by
weight.
 Examples: water(H2O) , Sodium Chloride (NaCl)
 Formation of compound is a chemical change ,so the
properties of compound differ from it’s constituent elements.
For example ,Sodium is toxic metal and chlorine is a toxic gas
but when they combine together they give edible salt. (NaCl)

7. Molecule
 The smallest particle of an element or compound which
is capable of independent existence is called molecule.
 Molecule represents the smallest stable condition of
matter but it is so small that it can not be seen with our
naked eyes. In molecule there may be one or more than
one atom. These atoms may be similar or dissimilar.
 For example ,helium (He) molecule has one atom,
Oxygen(o2) has two similar atoms where as carbon
dioxide (CO2) molecule has one carbon and two oxygen
atoms.

8. Symbol
 A symbol is the abbreviation of full name of an element which is represented by
one or two English letters.
 It is used to make the study easy and fast.
 If the symbol of an element has one letter ,it is written in capital letter. If it has two
letters , the first letter is written in capital and second letter small.
 Example : Helium- He, Hydrogen –H , Chlorine -Cl

11. There are certain elements whose names are written in
English but symbols are used from latin names
English names Latin/German names Symbol
Iron Ferrum(Latin name) Fe
Copper Cuprum(Latin) Cu
Gold Aurum(Latin) Au
Silver Argentum(Latin) Ag
Mercury Hydrargyrum (Latin) Hg
Sodium Natrium (Latin) Na
Potassium Kalium(Latin) K
Tungesten Wolfram (German) W

12. Structure of an Atom

13. Structure of an Atom
 An atom is composed of two regions: the nucleus, which
is in the center of the atom and contains protons and
neutrons, and the outer region of the atom, which holds
its electrons in orbit around the nucleus.
 Protons and neutrons have approximately the same
mass, about 1.67 × 10-24 grams, which scientists define
as one atomic mass unit (amu) or one Dalton.
 Each electron has a negative charge (-1) equal to the
positive charge of a proton (+1).
 Neutrons are uncharged particles found within the
nucleus.

14. Structure of an Atom

15. Summary of subatomic particles of an
atom
Sub-at9mic
Particles
symbol Position Mass( in a.m.u)
Electron e- Shell 1/1837
proton p+ Nucleus 1 amu
neutron n0 Nucleus 1 amu
1 amu = 6x 10-23 g ,amu= atomic mass unit

16. Atom is electrically neutral ,why?

17. Atom is electrically neutral ,why?

18. Atomic Number
 The total number of protons present in the nucleus of an atom is called atomic
number. It is denoted by Z.
 Chemical properties of an atom depend upon the atomic number of that atom.
Atomic number of an atom is also equal to the number of electrons present in a
neutral atom.
 Atomic Number = No.of protons = No. of electrons in a neutral atom

19. Atomic Mass
 The sum of the number of protons and the number of neutrons present in the
nucleus of an atom is called atomic mass. It is denoted by A. Atomic mass of an
atom is calculated by given formula.
 Atomic Mass= No.of protons + No. of neutrons
 Question:
 The atomic number and atomic mass of potassium atom are 19 and 39
respectively. Find the number of electrons, protons and neutrons in that
atom.

20. Electronic configuration
 The systematic distribution of
electrons in different shells of
an atom is called electronic
configuration. The number of
shells in an atom ranges from
1 to 7 i.e. K,L,M,N,O,P and Q.
The K shell is the nearest and
Q is the farthest.

21. Bohr and Bury Law(2n2 law)
 The maximum
number of
electrons in
each shell is
determined
by 2n2
formula where
’n’ denotes
the number of
shell in an
atom.

24. Valence shell and Valence Electrons
 The outermost shell of a atom from where loss or
gain of electrons takes place is called valence shell
and the total number of electrons which are present
in valence shell (outer shell) are called valence
electrons.
 For example valence electrons in sodium ,magnesium
and chlorine are 1,2 and 7 respectively. Valence
electrons determine the valency of an atom.

25. Valency
 The combining capacity of an element or a radical with
another element or radical to form compound or molecule is
called valency.
 According to new concept , “ The total number of electrons
lost, gained or shared by an atom during chemical
combination is called valency”
 Valency of Sodium is one as it loses one electron and valency
of oxygen is 2 as it gains two electrons. The valency of
Chlorine is 1 as it gains one electron from other elements .
Similarly, the valency of carbon is 4 as it shares 4 electrons
during chemical reactions.

26. Examples
 Find out the valency of aluminum in AlCl3.
In AlCl3. three atoms of chlorine combine with one atom of aluminium,so valency of
aluminum is 3.
What is the valency of Iron in FeSO4 , FeCl3 ?
What is the valency of Hydrogen in H3PO4 and HNO3 ?

27. General idea to find out valency of some
elements
 On the basis of modern periodic table ,the valency of an element is equal to the
number of group from first to fourth group. For first,second,third and fourth , the
valency is 1,2 ,3 and 4 respectively.
 Valency of elements in group fifth,sixth ,seventh and eight is 3,2 ,1 and 0
respectively.’
 Valency of zero group elements like He, Ne, Ar,Kr ,Xe and Rn is zero.
 Valency of radical is equal to the number of charges present in it. For example
Valency of Na+ =1
CO3
-- =2
PO4
- - - =3

28. General idea to find out valency of some
elements
 In case of transition elements, they have two incomplete outer shells ,so the
elements of these two shells participate in bonding by showing variable valencies.
For example
Cuprous Cu + = 1 Cupric Cu++ = 2
Stannous Sn ++ = 2 Stannic Sn++++ =4
Mercurous Hg += 1 Mercuric Hg++ =2
Aurous Au ++ =2 Auric Au+++ =3
Note: The lower valency is ended by suffix –’ous” and higher valency is ended by
suffix –’ic”

29. Sub-shell
 Each and every main shell contain one or more than one subshell which is
denoted by s,p,d and f.
 The main shells along with their sub-shells are listed in the given box.
Main shells Sub-shells ( orbitals)
K (n=1) s
L (n=2) s and p
M (n=3) S ,p and d
N(n=4) S ,p ,d and f

30. The maximum number of electrons that can be
accommodated by each subshell
sub-shells Maximum number of electrons
S (sharp) 2
P ( principal) 6
d (diffuse) 10
f ( fundamental) 14
The last electron present in sub-shell determines the block of an element.

31. Aufbau Principle
 The Aufbau principle dictates the
manner in which electrons are
filled in the atomic orbitals of an
atom in its ground state. It states
that electrons are filled into
atomic orbitals in the increasing
order of orbital energy level.
According to the Aufbau
principle, the available atomic
orbitals with the lowest energy
levels are occupied before those
with higher energy levels.

32. Aufbau Principle
 Aufbau principle states that,” the electrons in an atom are so distributed that they
occupy shells in the order of their increasing energy.”
 1 s ⟨2S ⟨2P ⟨3 S ⟨ 3P ⟨ 4 S ⟨ 3 d ⟨ 4 p ⟨5 s ⟨4 d ⟨5 p ⟨6s ⟨4 f⟨5 d⟨6 p⟨7s⟨5f⟨6d⟨
7p
 1 s ⟨2S ⟨2P ⟨3 S ⟨ 3P ⟨ 4 S

33. First 20 elements
Name Atomic Number
Electron
Configuration
Period 1
Hydrogen 1 1s1
Helium 2 1s2
Period 2
Lithium 3 1s2 2s1
Beryllium 4 1s2 2s2
Boron 5 1s2 2s22p1
Carbon 6 1s2 2s22p2

34. Elements 7-13
Nitrogen 7 1s2 2s22p3
Oxygen 8 1s2 2s22p4
Fluorine 9 1s2 2s22p5
Neon 10 1s2 2s22p6
Period 3
Sodium 11 1s2 2s22p63s1
Magnesium 12 1s2 2s22p63s2
Aluminum 13 1s2 2s22p63s23p1

35. Elements 14-20
Silicon 14 1s2 2s22p63s23p2
Phosphorus 15 1s2 2s22p63s23p3
Sulfur 16 1s2 2s22p63s23p4
Chlorine 17 1s2 2s22p63s23p5
Argon 18 1s2 2s22p63s23p6
Period 4
Potassium 19 1s2 2s22p63s23p64s1
Calcium 20 1s2 2s22p63s23p64s2

36. Radicals
 Radicals are charged atoms or group of atoms having a common charge which act
as a single unit during a chemical reaction.
 They have either positive or negative charge. Radicals are charged particles so
they are highly reactive and least stable. Hence they donot occur in free form and
make different types of compounds. On the basis of electric charge radicals are
two types.
 The atoms or group of atoms which have positive charge in them are called
electropositive radicals or basic radicals and with negative charge are called
electronegative radicals or acidic radicals.

37. Electropositive radicals

38. Electronegative Radicals

39. Radicals contain charge ,why?

40. Radicals contain charge,why?
 Radicals are atoms or group of atoms having a common charge which are formed
by losing (donating) or gaining electron/s to attain duplet or octet state. Hence
they contain positive charge due to loss of electron/s and negative charge due to
gain of electron/s. Therefore ,radicals contain charge.

41. Molecular Formula
 The Molecular formula of a molecule is the symbolic representation of the
molecule of an element or a compound in a molecular form. It represents the
number of atoms of different elements in a molecule.
 For example the molecular formula of Sodium Chloride is NaCl and that of water is
H2O. It shows that one molecule of Sodium Chloride consists of one atom of
sodium and one atom of chlorine.

42. Methods of writing Molecular Formula
 Write the symbol of basic (positive) and acidic ( negative) radicals side by side.
 Write the valency of each radical on upper right corner of each.
 Exchange the valency of these radicals. Take HCF if it is necessary.
 Combine radicals with exchanged valency.
 If radicals have different atoms, it is enclosed within brackets.

43. examples

44. Information obtained from molecular
formula
 Molecular formula represents one molecule of a substance.
 It indicates the total number of atoms of the same or different elements in each
molecule.
 It indicates percentage composition of each element in the compound.
 The valency or combining capacity of each element can be found from molecular
formula. Example, In ammonia molecule (NH3) ,the valency of nitrogen is three
and that of hydrogen is one.
 We can calculate the molecular weight from molecular formula.For example the
molecular weight of ammonia (NH3) = Nx1 + Hx3
14x1 + 1x3= 17.

45. Molecular Weight
 The molecular weight of a molecule is the sum of atomic weight of all atoms of
the molecule. It is calculated by adding the atomic weight of the atoms present in
a molecule.

47. Calculate Molecular weight
 Potassium Dichromate
 Calcium phosphate

48. Inert Gases
 The elements which have eight electrons in their valence shell ( except helium) and
do not take part in chemical reactions are called inert gases. They are kept in the
zero group or group VIII A of modern periodic table.
 Inert gases have complete Octet or duplet and show zero valency.
 The arrangement of two electrons in the k-shell of an atom is called duplet state.
 The state of having eight electrons in valence shell (last shell) of an atom is called
octet state.
 The tendency of elements by which they try to maintain eight electrons in
their valence shell either by transferring or sharing of electrons is called
octet rule.

49. Chemical Bond
 The force of attraction by which atoms are held
together in a molecule is called chemical bond.

50. Electrovalent/Ionic Bond
 Electrovalent bonds are produced when
electrons are transferred from atoms of
one element to atoms of another element,
producing positive and negative ions. The
bond which is formed by the transfer of
electrons between the atoms is called
electrovalent bond or ionic bond.
Electrovalent bonds are only formed
between metals and non-metals.
Electrovalent bonds are not formed
between two non-metals.

51. Electrovalent bond continue
 An Ionic bond is the bond formed by the complete transfer of valence electron to
attain stability.
 This type of bonding leads to the formation of two oppositely charged ions –
positive ion known as cations and negative ions are known as anions.
 The presence of two oppositely charged ions results in a strong attractive force
between them. This force is an ionic or electrovalent bond.
 Ionic bonds form between atoms with large differences in electronegativity,
whereas covalent bonds formed between atoms with smaller differences in
electronegativity.
 The compound formed by the electrostatic attraction of positive and negative ions
is called an ionic compound.

52. Continue
 Ionic Bond Properties
Due to the presence of a strong force of attraction between cations and anions in ionic
bonded molecules, the following properties are observed:
 The ionic bonds are the strongest of all the bonds.
 The ionic bond has charge separation, and so they are the most reactive of all the
bonds in the proper medium.
 The ionic bonded molecules have high melting and boiling point.
 The ionic bonded molecules in their aqueous solutions or in the molten state are good
conductors of electricity. This is due to the presence of ions which acts as charge
carriers.


53. Example

54. Formation of NaCl

55. Covalent Bond
 A covalent bond is a type of chemical bond
that is formed due the electron sharing
between two atoms. This type of bond is
formed between atoms that have a less (than
1.7) or no difference between their
electronegativity values. Therefore, most
nonmetals form covalent bonds between
them. Moreover, the atoms of the same
element only form covalent bonds.

56. Properties
 If the normal valence of an atom is not satisfied by sharing a single electron pair
between atoms, the atoms may share more than one electron pair between
them. Some of the properties of covalent bonds are:
 Covalent bonding does not result in the formation of new electrons. The bond
only pairs them.
 They are very powerful chemical bonds that exist between atoms.
 Covalent bonds rarely break spontaneously after it is formed.

57. continue
 Most compounds having covalent bonds
exhibit relatively low melting points and
boiling points.
 Compounds formed by covalent bonding
don’t conduct electricity due to the lack of
free electrons.
 Covalent compounds are not soluble in water.

58. Formation of CH4

59. Difference between Electrovalent and
Covalent Compounds