The periodicity of properties of elements

 The periodicity of properties of elements

1. The modern periodic law – “ The properties of elements are periodic function of their atomic number

2. Property of elements vary periodically due to periodic variation of electronic configuration and reoccurrence of similar  number of valence electrons.

3.The modern periodic table has 18 groups (vertical columns) and 7 periods (horizontal rows)

As we go down the group the number of shells (atomic orbits) increases so atomic size increases down the group along with variation of other chemical properties as shown below in the mind map.

4. From left to right on comparing the electronic configuration we can see that number of shells remain same but effective nuclear charge increases resulting to the variation of other periodic properities as shown in the mind map below
(THE ARROW HEADS ARE DIRECTED TOWARDS INCREASE IN ANY OF THE PROPERTIES)

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

1

H

THIS IS A MIND MAD OF THE PERIODIC TABLE TO KEEP THE TRENDS IN MEMORY WITHOUT MUGGING UP SENTENCES

He

2

Li

Be

B

C

N

O

F

Ne

3

Na

Mg

Al

Si

P

S

Cl

Ar

4

K

Ca

Ga

Ge

As

Se

Br

Kr

5

Rb

Sr

In

Sn

Sb

Te

I

Xe

6

Cs

Ba

Tl

Pb

Bi

Po

At

Rn

7

Fr

Ra

                                                                       

A.    Cesium is the most electropositive stable element. Francium is more electropositive (at least in theory) but only about 30 grams exists on the entire planet as it is highly radioactive so no one has been able to check.

B.    Fluorine is most electronegative. It is the smallest atom on the table (except for H and He). Its nuclear charge is much greater than H or He, to its large nuclear charge can get very close to the electrons of neighboring atoms. Since electrostatic attraction decreases with the square of the distance, it forms the strongest electron/nucleus bond of any atom on the periodic table.

C.    Although fluorine is more electronegative than chlorine, it has a lower electron affinity than chlorine.This is due to the small size of flourine atom. Due to the small size, the seven valence electrons experience greater repulsive force among them. For chlorine, the extra electron shell will be able to reduce this repulsive force among the electrons.

D.    Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons.

E.     The electron affinity of an atom or molecule is defined as the amount of energy released when an electron is added to a neutral atom or molecule to form a negative ion.

F.     The ionization energy of an atom or molecule is defined as the amount of energy required to remove an electron from that atom or molecule in the gas phase. 

G.    Metallic character describes the set of chemical properties that are associated with the elements classified as metals in the periodic table like low I.E, highly electropositive, high m.pt.

H.    The atomic radius of a chemical element is a measure of the size of its atoms, usually the mean or typical distance from the nucleus to the boundary of the surrounding cloud of electrons. Since the boundary is not a well-defined physical entity, there are various non-equivalent definitions of atomic radius

I.     Larger the atomic radius more will be metallic character (tendency to lose electron and form cation) and lesser will be the I.P, i.e it would be easy to eject valence electron.

J.     Metallic property decreases across a period with increase in number of valence electrons as well as a decrease in atomic radius, and it increases down the group with increase in number of shells and atomic radius.

K.    Non-metallic property increases across a period and decreases down the group due to the same reason.

L.     More readily an atom can lose electron more easily it can reduce other molecule/atom so with increase in metallic character reducing nature also increases.

M.    More readily an atom can gain electron from other molecule/atom more readily it can oxidize the other element. So oxidizing power/ nature of the element increases with increase in NON METALLIC CHARACTER and decreases with increase in metallic character.

N.     .A diagonal relationship is said to exist between certain pairs of diagonally adjacent elements in the second and third periods of the periodic table. These pairs (lithium (Li) and magnesium(Mg), beryllium (Be) and aluminium (Al), boron (B) and silicon (Si) etc.) exhibit similar properties; for example, boron and silicon are both semiconductors, forming halides that are hydrolysed in water and have acidic oxides

                                                                                                                                         

 

 

CHEMICAL BONDING

1. Atoms which don’t have its octet or duet in valence shell tries to lose electron, gain electron , share electron or accept a lone pair of electron to get nearest noble gas like valence shell electron configuration and as a result ionic bond, covalent bond or coordinate bond is formed.
2. A chemical bond is the force of attraction due to which atoms, molecules or ions are held to each other tightly.
3. Covalent bond is formed by sharing of electron by two or more electronegative elements. If the difference in the electronegativity of combining chemical species is high then the distribution of electrons across the covalent bond will be ununiform and hence polar covalent bond is formed, where as in case of homo atomic molecules or atoms which don’t have appreciable difference in the electro negativity the distribution of electron is uniform and the covalent bond as well as covalent molecule is called non polar covalent compound.

Hetero atomic Non polar covalent molecule , Methane	Homo atomic Non polar covalent molecule, Halogen	Polar covalent molecule, Water, always heteroatomic.
Formation of Ammonium Ion Formation of Ionic bond		Definition A Coordinate  bond between two atoms that is produced when one atom shares a pair of electrons with another atom lacking such a pair.   An electron pair is donated from electron rich species to electron deficient species An ionic bond is a type of chemical bond formed throughan electrostatic attraction between two oppositely charged ions.   These ions are formed due to gain and lose of electron in order to complete the octet in their valence shell.