01.
2.Periodic Classification of Elements
basic concepts:-
matter-> substance has mass & take up space
atom: neuclious -> +ve charge proton, no charge neutron, -ve charge
electron, e- revolving in orbit
Atomic mass -> mass concentrated in neucleaous -> no. of protons +
neutrons
Atomic mass-> Atomic radius -> distance between neucleaous and e-
present in last orbit
e- configuration -> orbit strength = 2n^2
isotopes of element-> same no. of protons but differ in neutrons no. in
each atom
element-> no. of atoms-> all atoms have same no. of protons eg O2
molecule-> have different no. of atom eg H2O
molecular mass -> addiiton of atomic masses of each element
compounds: two or more atoms chemically bounded together
metaloids-> semi metals
outermost orbit
valence e-
atomic redius
nucleus
, 02.
Classification of elements:
-It is necessary to study properties of element easily. So scientists started
studying ' How to classify elements' which gives information about
elements.
-The initial classification elements were classified into the groups of
metals and nonmetals.
-Later on another class of elements called metalloids was noticed. As the
knowledge about elements and their properties went on increasing.
-So different scientists started trying out different methods of
classification of elements.
I) Dobereiner’s Triads (groups of three elements):
-In the year 1817 a German scientist Dobereiner suggested that
properties of elements are related to their atomic masses.
-Made groups of three elements each, having similar chemical
properties and called them triads.
-Arranged the three elements in a triad in an increasing order of atomic
mass and showed that the atomic mass of the middle element
was approximately equal to the mean of the atomic masses of the other
two elements .
-But, all the known elements could not be classified into the
Dobereiner’s triads.
eg- statement Triad Element Atomic No. Average
sodium = avg of lithium I Li 6.9 (7) 6.9+39.1 = 23
& potassium Na 23 2
K 39.1 (39)
strontium = avg of calcium II Ca 40.1(40) 40+137 =88.5
& barium Sr 87.6(87) 2
Ba 137.3(137)
bromine = avg of chlorone III Cl 35.5 35.5+127
& iodine Br 79.9(80) 2
I 126.9(127) =81.25
, 03.
Is Dobereiner’s triads satisfy following groups of elements having
similar chemical properties. (check it by taking avg.)
1. Mg (24.3), Ca (40.1), Sr (87.6)
2. S (32.1), Se (79.0), Te (127.6)
3. Be (9.0), Mg (24.3), Ca (40.1)
II) Newlands’ Law of Octaves:
-The English scientist John Newlands classify element on the basis of
atomic mass in different way.
-Law of Octaves: When the element arranged in increasing order of
atomic mass, then property of every eighth element has properties
similar to those of first one.
Musical (Sa) (Re) (Ga) (Ma) (Pa) (Dha) (Ni)
Elements H Li Be B C N O
F Na Mg Al Si P S
Cl K Ca Cr Ti Mn Fe
Co &Ni Cu Zn Y In As Se
Br Rb Sr Ce & La Zr -- --
- For example, sodium is the eighth element from lithium and both have
similar properties.
-Also, magnesium shows similarity to beryllium and chlorine shows
similarity with fluorine.
- This relationship is just like an octave of music. Every 8th note is
similar to 1st note.
- Limitations: 1)This law worked upto element Ca and not for element
which has large atomic mass.
2) Inert gases & several other new elements did not obeys this law of
octave.
3) He adjusted 2 elements in same slot. eg. Ni & Co
4) lly, Ni & Co were placed in same column as fluorine, chlorine, &
bromine, which have very different properties.
2.Periodic Classification of Elements
basic concepts:-
matter-> substance has mass & take up space
atom: neuclious -> +ve charge proton, no charge neutron, -ve charge
electron, e- revolving in orbit
Atomic mass -> mass concentrated in neucleaous -> no. of protons +
neutrons
Atomic mass-> Atomic radius -> distance between neucleaous and e-
present in last orbit
e- configuration -> orbit strength = 2n^2
isotopes of element-> same no. of protons but differ in neutrons no. in
each atom
element-> no. of atoms-> all atoms have same no. of protons eg O2
molecule-> have different no. of atom eg H2O
molecular mass -> addiiton of atomic masses of each element
compounds: two or more atoms chemically bounded together
metaloids-> semi metals
outermost orbit
valence e-
atomic redius
nucleus
, 02.
Classification of elements:
-It is necessary to study properties of element easily. So scientists started
studying ' How to classify elements' which gives information about
elements.
-The initial classification elements were classified into the groups of
metals and nonmetals.
-Later on another class of elements called metalloids was noticed. As the
knowledge about elements and their properties went on increasing.
-So different scientists started trying out different methods of
classification of elements.
I) Dobereiner’s Triads (groups of three elements):
-In the year 1817 a German scientist Dobereiner suggested that
properties of elements are related to their atomic masses.
-Made groups of three elements each, having similar chemical
properties and called them triads.
-Arranged the three elements in a triad in an increasing order of atomic
mass and showed that the atomic mass of the middle element
was approximately equal to the mean of the atomic masses of the other
two elements .
-But, all the known elements could not be classified into the
Dobereiner’s triads.
eg- statement Triad Element Atomic No. Average
sodium = avg of lithium I Li 6.9 (7) 6.9+39.1 = 23
& potassium Na 23 2
K 39.1 (39)
strontium = avg of calcium II Ca 40.1(40) 40+137 =88.5
& barium Sr 87.6(87) 2
Ba 137.3(137)
bromine = avg of chlorone III Cl 35.5 35.5+127
& iodine Br 79.9(80) 2
I 126.9(127) =81.25
, 03.
Is Dobereiner’s triads satisfy following groups of elements having
similar chemical properties. (check it by taking avg.)
1. Mg (24.3), Ca (40.1), Sr (87.6)
2. S (32.1), Se (79.0), Te (127.6)
3. Be (9.0), Mg (24.3), Ca (40.1)
II) Newlands’ Law of Octaves:
-The English scientist John Newlands classify element on the basis of
atomic mass in different way.
-Law of Octaves: When the element arranged in increasing order of
atomic mass, then property of every eighth element has properties
similar to those of first one.
Musical (Sa) (Re) (Ga) (Ma) (Pa) (Dha) (Ni)
Elements H Li Be B C N O
F Na Mg Al Si P S
Cl K Ca Cr Ti Mn Fe
Co &Ni Cu Zn Y In As Se
Br Rb Sr Ce & La Zr -- --
- For example, sodium is the eighth element from lithium and both have
similar properties.
-Also, magnesium shows similarity to beryllium and chlorine shows
similarity with fluorine.
- This relationship is just like an octave of music. Every 8th note is
similar to 1st note.
- Limitations: 1)This law worked upto element Ca and not for element
which has large atomic mass.
2) Inert gases & several other new elements did not obeys this law of
octave.
3) He adjusted 2 elements in same slot. eg. Ni & Co
4) lly, Ni & Co were placed in same column as fluorine, chlorine, &
bromine, which have very different properties.
