Chapter 02 periodic table and atomic periodicity or properties

Chapter 02
periodic table and atomic periodicity or properties:

Modern periodic table: the table in which elements are arrange in order of increasing atomic number.

Modern periodic law: physical and chemical properties of elements are periodic function of their atomic number.

periodic function: repelition of properties after certain interval of time.

periodicity of elements: the repelition of properties after certain interval of time.

the elements repeats their properties because their valence shell electron configuration repeats.

eg. li 2 1
Na 2 8 1
k 2 8 8 1

114 elements are known today. for their systematic study they have been classified into group and period.

Group :vertical column are called group there are 18 vertical column. so their are 18 groups.

Periods: horizontal rows are called periods there are 7 horizontal rows. so their are 7 periods .

A/c to periods no. of elements

1 period 2 elements
2 period 8 elements
3 period 8 elements
4 period 18 elements
5 period 18 elements
6 period 32 elements
7 period 32 elements

the elements constituent groups 1,2,13,14,15,16,17,18 are called normal elements or representation elements.

the elements of 3,4,5,6,7,8,9,10,11,12 are called transistion elements. because they show transistion (change) in property.

# from highly +ve s block to least + ve P block

Two rows of elements which are placed at the bottom of periodic table are called lanthanoids and actinoids.

Comments

Radial probability distribution curves

Radial probhjjhajajbability distribution curves: The probability of finding the electron is given by the quantity sie^2.By radial probability us probability of finding the electron within small Radial space around the nucleus. volume of spherical shell between radius r and r+dr =4πr^2 and probability of finding the electron will be 4πr^2dr sie^2. radial probability distribution curves are obtained by plotting radial probability at various distance from the nucleus . 1.Radial probability distribution curves for S orbital n=1, l= 0. distance from nucleus here A° is called angstrom. the probability of finding of electron in a shell is maximum at distance r=r° (r not) which is 0.529 A° for H atom. diagram shows that probability plot for 2s has(two region of high probability) or (two peaks) separated by node. we conclude that no. of high probability region in S orbital = n no. of node = ( n-1)

Radial probability distribution for p and d orbital, radial wave functions

Radial probability distribution for p and d orbital Radial and Angular wave function: the radial part of wave function depends upon quantum no. n and l and gives the distribution of electron w. r. t distance .it is governed mainly exponential term e^-Zr/na°(a not) here e based on natural log. Z Atomic number r distance from nucleus n principal quantum no. or radial quantum no. a° 0.529A° for hydrogen ( Bohr radii) the exact mathematical expression for radial part of wave function for 1s or 2s and 2p orbitals. n= 1 ,l=0 s orbital R(r) =2× (z/a°) ^3/2 ×(2-zr/a°) ×e^-zr/2a° n= 2 ,l=0 2s orbital R(r) = (z/a°) ^3/2 ×(2-zr/a°) ×e^-zr/2a° n= 2 ,l=1 2p orbital R(r) = 1√3×(z/2a°) ^3/2 ×(zr/a°) ×e^-zr/2a ° the rad...

Electronegativity scales and disadvantage of scales and its nunericals

Electronegativity scales: 1.Pauling scale of electronegativity: in diatomic molecule (A-B) ,the bond formed between two atoms A and B will be intermediate between pure Covalent (A-B) and pure ionic character, the bond between A and B will be strong than bond energy increased. if bond (A-B) has been purily covalent than bond energy can be calculated as average bond energy of bond (A-A) and bond (B-B). that means it is equal to bond energy of bond (A-B) E(A-B) = 1/2[ E(A-A) +E(B-B) ] however experiemental value of bond (A-B) more than this value because of difference in electronegativity of A and B the difference ∆ is given by simple expression ∆ = E(A-B) - 1/2 [E(A-A) +E(B-B) ] where E(A-B) is experimental value of bond energy. if Ҳ(A) and Ҳ(B) are the electronegative of elements A and B than Ҳ(A) - Ҳ(B) = 0.18√∆ for numerical ∆ = E(A-B) -[√(E(A-A) ×E(B-B) )] Disadvan...

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