Periodic Table & Periodic Properties

Periodic Table & Periodic Properties


1. Dobereiner's law of triads: When elements having similar properties are placed in increasing order of atomic weight in group of three, then atomic weight of middle element is arithmetic mean of other two elements. e.g. Ca, Sr, Ba, I. But all elements can't be classified like this.

2. Newlands law of octaves: When elements are arranged in increasing order of atomic weights, every eighth element has properties similar those of first element just like eighth note of an octave of music.

3. Lother Mayer volume curve: When a graph is plotted between atomic volumes and atomic weights of elements, the element with similar properties occupy similar position on the curve.

4. Telluric Helix is the idea of periodic arrangements of elements (was given by Chancourtois)

5. Mendeleev's periodic table:

(i) Based on atomic weights

(ii) Mendeleev's period law: The physical and chemical properties of elements are periodic function of their atomic weights.

(iii) Only 63 elements were known at that time.

(iv) It has 8 vertical columns called group I - VIII. Except VIII group all groups are divided in to 2 subgroups i.e., A and B.

(v) It has 7 horizontal columns called periods 1 - 7.

(vi) Order of atomic weights was changed at placed to justify properties of element.

(vii) It has vacant places for elements which were discovered later. E.g. eka aluminium (now known as gallium) and eka silicon (now known as germanium).


6. Moseley gave modern periodic law which states that chemical and physical properties of elements are periodic function of their atomic numbers.

7. Modern or Long form of periodic table (Bohr's table):

(i) It has 7 - horizontal rows - called periods.

(ii) It has 18 vertical rows - called groups.




(iii) Representative elements : s and p block

(iv) Transition elements: d - block

(v) Inner transition elements f - block

(vi) Alkaline earth metals - group 2

Chalcogens group 16

Halogens group 17


Noble gases or aerogens group 18

(vii) Typical elements - numbers third period.

(viii) Bridge element - members of second period.

(ix) Lanthanides - Elements at. no.58 - 71

(x) Actanides - Elements at no. 90 - 103

(xi) Transuranics - All elements after Uranium (atomic number 92).



8. Nomenclature of elements with Z > 100:

(i)	Digit	0	1	2	3	4	5	6	7	8	9
	Root Abbreviation	nil. n	un. u	bi. b	tri. t	quad. q	pent. p	hex. h	sept. s	oct. 0	enn. E

e.g. element with atomic no. 102 Unnibium (Unb)

(ii) Common names of some elements

101 - Mendelevium, 104 - Rutherfordium, 107 - Bohrium

(iii) Name of elements on countries :

Ru - Ruthernium (County - Rthenia)

Ge - Germanium (Country - Germany)

Po - Polonium (County - Poland)

Am - Americium (Country - America)


9. Diagonal relationship is similarity in properties of second period elements with third period element of next of next higher group. It is caused due to

(i) similar ionic size.

(ii) similar polarizing power.

(iii) similar I.P. (ionization potential)

Example - Li - Mg, Be - Al, B - Si.

10. Anomalous behaviour of first element of the group:

First member of every group differs from rest of the members due to

(i) very small size

(ii) high electronegativity

(iii) absence of vacant d-orbitals.

11. Atomic size is distance between nucleus of the atom and outer most electron.

(i) Absolute value of atomic size cannot be determined because exact position of electron cannot located.

(ii) Covalent radius (r_cov) r(_cov) = 1/2 (distance between two covalently bonded atoms)

(iii) van der Waal's radius (r_v. Waal) m(r_v. Waal) = 1/2 (distance between nuclei of two non bonded isolated atoms or adjacent atoms belonging to neighbouring molecules of an element)

(iv) Metallic radius is half of distance between centres of nuclei of two adjacent atoms in metallic crystal.

(v) Ionic radius:

(a) Cation is always smaller in size than corresponding neutral atom. M > M⁺ > M²⁺ > M³⁺

(b) Anion is always larger in size than corresponding neutral atom. A^3- > A^2- > A^- > A

(vi) Isoelectronic species have same number of electrons but different number of protons. For isoelectronic species

(a) Cation with highest positive charge is smallest in size.

(b) Anion with highest negative charge is largest size.

12. Ionization energy / ionization enthalpy (IE)

(i) It is amount of energy required to take out most loosely bond electron from isolated gaseous arm to change it into gaseous cation. Its value is positive (because energy is supplied).
A_(g) + I. E. A_(g)+ + e^-

(ii) I. E₃ > I.E₂ > I.E₁ (of increased force of attraction after removal of electron)

(iii) Units ev/atom of Kcal.mol^-1 or KJmol^-1

(iv) Factors effecting ionization enthalpy

(a) Nuclear charge

(b) Atomic size

(c) Penetrating power of electron (s > p > d > f)

(d) Screening effect

(e) Stable configurations (half and fulfilled orbitals)


13. Electron Affinity (EA)

(i) Its is amount of energy released when gaseous atom accepts an electron to form gaseous anion.



(ii) EA1 is always negative while EA2 and successive electron affinities are positive because it becomes difficult to add electron to anion.

e.g. EA₁ = -141 KJ mol^-1

EA₂ = +780 KJ mol^-1

(iii) Factors effecting electron affinity :

(a) Atomic size

(b) Nuclear charge

(c) Stable electronic configuration. (half filled and filled orbitals)

14. Electronegativity (EN)

(i) It is tendency of an atom to attract shared pair of electrons in a molecule.

(ii) The value of electronegativity depends on

(a) Charge on the nucleus

(b) Size of atom

(c) Shielding effect

(iii) Measurement of electronegativity


(a) Mullikan scale

Electronegativity = where I.E. and EA are expressed in eV
.

(b) Pauling Scale

If A and B are two covalently bonded atom and c is electronegativity.

X_A - X_B = 0.18(where is in K cal/mole)

=

where

= Bond dissociation energy of A-A bond

= Bond dissociation energy of A-B bond

= Bond dissociation energy of B-B bond

It is mot commonly used scale. Electronegativity of F is 4.0 on this scale. (which is the highest value)

(c) Allred and Rochow's method :



where = electronegativity element A

Z = effective nuclear charge

R = covalent radius is Å

(iv) It helps to predicting polarity of bond


15. The generalised trends for above four properties are:




16. Atomic volume :

(i) It is volume occupied by one mole atoms of the element at its melting point in solid state.

(ii) Atomic volume =

17. Acid-base behaviour of oxides and hydroxides :

(i) Basicity of oxides and hydroxides increases down group. CsOH > RbOH > KOH > NaOH > LiOH

(ii) Acidic character of oxides and hydroxides decreases down group HClO₄ > HBrO₄ > HIO₄