He arranged similar elements in the groups of three elements called as triads , in which the atomic mass of the
central element was merely the arithmetic mean of atomic masses of other two elements or all the three
elements possessed nearly the same atomic masses.
He was the first to correlate the chemical properties of the elements with their atomic masses.
According to him if the elements are arranged in the order of their increasing atomic masses
the eighth element starting from given one is similar in properties to the first one.
This arrangement of elements is called as Newland’s law of Octave
He determined the atomic volumes by dividing atomic masses with their densities in solid states.
He plotted a graph between atomic masses against their respective atomic volumes for a number
of elements. He found the following observations
According to him the physical and chemical properties of the elements are the periodic functions of their
atomic masses.
He studied (1909) the frequency of the X-ray produced by the bombardment of a strong beam of
electrons on metal target. He found that the square root of the frequency of X-rays ( ï® ) is directly
proportional to number of effective nuclear charge (Z) of metal i.e. to atomic number and not to atomic
mass of the atom of that metal (as nuclear charge of metal atom is equal to atomic number), i.e. ï®
= a (Z - b).
There are seven periods numbered as 1, 2, 3, 4, 5, 6 and 7.
There are eighteen groups numbered as 1, 2, 3, 4, 5, ........... 13, 14, 15, 16, 17, 18.
Group consists of a series of elements having similar valence shell electronic configuration
When shells upto (n – 1) are completely filled and the last electron enters the s-orbital of the outermost (nth)
shell, the elements of this class are called s-block elements.
When shells upto (n – 1) are completely filled and differentiating electron enters the p-orbital of the
nth orbit, elements of this class are called p-block elements.
When outermost (nth) and penultimate shells (n – 1)th shells are incompletely filled and differentiating electron
enters the (n – 1) d orbitals (i.e., d-orbital of penultimate shell) then elements of this class are called d-block
elements.
When n, (n – 1) and (n – 2) shells are incompletely filled and last electron enters into f-orbital of antepenultimate
i.e., (n – 2)th shell, elements of this class are called f-block elements. General electronic configuration is
(n – 2) f1-14 (n – 1) d0-1 ns2
1 Period of an element corresponds to the principal quantum number of the valence shell.
2 The block of an element corresponds to the type of subshell which receives the last electron
The metals are characterised by their nature of readily giving up the electron(s) and
from shinning lustre. Metals comprises more than 78% of all known elements and
appear on the left hand side of the periodic table. Metals are usually solids at room
temperature (except mercury, gallium). They have high melting and boiling points
and are good conductors of heat and electricity. Oxides of metals are generally
basic in nature (some metals in their higher oxidation state form acid oxides e.g.
CrO3).
It can be under stood from the periodic table that nonmetallic character increases as
we move from left to right across a row. It has been found that some elements which
lie at the border of metallic and nonmetallic behavior, possess the properties that are
characteristic of both metals and nonmetals. These elements are called semi metals
or metalloids.
Third period elements are called as typical elements. These include Na, Mg,
Al, Si, P, S, Cl
Some elements of certain groups of 2nd period resemble much in properties with the elements of third period
of next group i.e. elements of second and third period are diagonally related in properties. This phenomenon
is known as diagonal relationship. For example, the similarity between lithium (the first member of group 1)
and magnesium (the second element in group 2) is called a diagonal relationship. Diagonal relationship also
exist between other pairs of elements Be and Al, B and Si as shown in figure
Between the outer most valence electrons and the nucleus of an atom, there exists number
of shells containing electrons. Due to the presence of these intervening electrons, the
valence electrons are unable to experience the attractive pull of the actual number of
protons in the nucleus.
Probability of finding the electron is never zero even at large distance from the nucleus. Based on
probability concept, an atom does not have well defined boundary. Hence exact value of the atomic
radius can’t be evaluated. Atomic radius is taken as the effective size which is the distance of the
closest approach of one atom to another atom in a given bonding state
It is one-half of the internuclear distance between two adjacent
atoms in two nearest neighbouring molecules of the substance
in solid state as shown in figure.
It is one-half of the distance between the nuclei of
two adjacent metal atoms in the metallic crystal
lattice as shown in figure
The effective distance from the centre of nucleus of the ion up to which it has an influence in the ionic bond
is called ionic radius
Ionisation energy (IE) is defined as the amount of energy required to remove the most loosely
bound electron from an isolated gaseous atom to form a cation
The ionisation energy increases with increase in the nuclear charge.
This is due to the fact that with increase in the nuclear charge, the electrons of
the outer most shell are more firmly held by the nucleus and thus greater amount
of energy is required to pull out an electron from the atom.
The electrons in the inner shells act as a screen or shield between the nucleus and the electrons
in the outer most shell. This is called shielding effect. The larger the number of electrons in the
inner shells, greater is the screening effect and smaller the force of attraction and thus ionization
energy (IE) decreases.
The ionization energy also depends on the type of electron which is removed. s, p, d
and f electrons have orbitals with different shapes.
The electron gain enthalpy ï„egHï‘, is the change in standard molar enthalpy when a neutral gaseous
atom gains an electron to form an anion
Electronegativity is a measure of the tendency of an element to attract shared electrons
towards itself in a covalently bonded molecules.
The magnitude of electronegativity of an element depends upon its ionisation potential &
electron affinity. Higher ionisation potential & electron affinity values indicate higher
electronegativity value.
Linus Pauling developed a method for calculating relative electronegativities of most elements. According to
Pauling
Electronegativity ï£ (chi) can be regarded as the average of the ionisation energy (IE) and the electron
affinity (EA) of an atom (both expressed in electron volts
Nomenclature :
Compounds formed from two nonmetals are called binary compounds. Name of more
electronegative element is written at the end and ‘ide’ is suffixed to it. The name of less
electronegative element is written before the name of more electronegative element of the
formula. For example
The outer shell ‘s’ electrons (ns2) penetrate to (n–1)d electrons and thus become closer to nucleus
and are more effectively pulled towards the nucleus. This results in less availability of ns2 electron
pair for bonding or ns2 electron pair becomes inert
