Periodic table
It is a chart in which various elements are arranged and grouped together according to its similarity and dissimilarity.
Period – Horizontal row of elements.
Group – Vertical column of elements.
Advantages of Periodic table
- Helps to memorize general characteristics.
- To predict the formula of compounds and type of bonding.
- New elements having similar properties can be predicted.
- Easier to remember and guides for scientific investigations.
Mendeleev's periodic law
Mendeleev’s periodic law states that “The physical and chemical properties of the elements are the periodic function of their atomic weight”. The tabular arrangement of elements (known at that time) in order of increasing atomic weight is called the Mendeleev’s periodic table.
The old form of Mendeleev’s periodic table contained only eight groups and six periods and only 63 elements were discovered.
Modern periodic law
Modern periodic law states that “The physical and chemical properties of the elements are the periodic function of their atomic numbers”. The tabular arrangement of elements in order of increasing atomic number is called the Modern periodic table.
Advantages of Modern periodic table :-
- Removal of anomalous pairs.
- Position of isotopes is clear.
- Position of Hydrogen (placed in I-A and VII-A).
- Clear classification of different kind of elements such as metal, non-metal, metalloids, transition elements, inert gas, etc.
- Position of Lanthanides and actinides are clear.
- Groups are classified further in subgroups A and B to study easily.
Defects of Modern periodic table :-
- Position of Hydrogen still controversial.
- Fails to fix lanthanides and actinides in main body of periodic table.
- Position of Helium: – It has duplet rule but placed in position according to octet rule.
- Barium and lead, Copper and Mercury have similar properties but placed differently.
Alkali metals
Those metals which forms alkali when react with water is known as alkali metals.
2K + 2H2O → 2KOH+ H2
Properties of Alkali metals
- Belongs in group I-A elements.
- Low electronegativity.
- Low ionization energy.
- Low melting points.
- Low densities.
- Easily reacts with halogens.
- Highly reactive and not found freely in nature.
Alkali earth metals
The metals that reacts with water to form alkali and their oxides exists in earth even at high temperature.
Mg + 2H2O → Mg(OH)2 + H2
Properties of Alkali earth metals
- Belongs to group II-A .
- Have two valence electrons.
- Low ionization energy and and low electronegativity.
- Highly reactive and often forms divalent cations.
- Good conductor of electricity.
Metalloids
Elements having properties of both metals and non-metals are known as metalloids.
Properties of metalloids :-
- Belongs to group IV-A.
- Insulator of electricity at low temperature.
- Good conductor of electricity at high temperature.
- Have metallic lusture but brittle in nature.
- Physical appearance similar to metals and chemical properties more similar to non-metals.
Inert gases
The elements which does not undergo any chemical reaction are called inert gases.
Properties of Inert gases :-
- Stable electronic configuration.
- Does not form any compound.
- Odorless, colorless and non flammable.
- Low chemical reactivity.
- High ionization.
- Belongs to Group VIII-A or 0 Group.
Halogens
Chemical elements that forms salt when react with metals of group IA are known as halogens. e.g:- Fluorine, Chlorine, Bromine, Iodine, etc.
Properties of Halogens:-
- They are salt producers.
- Low melting and boiling points.
- High electronegativity in nature.
- Soluble in nature.
Transition elements
Elements belonging to the d-block with incompletely filled d sub-orbitals are known as Transition elements.
Properties of Transition elements:-
- Good conductor of heat and electricity.
- Usually form colored compounds.
- Act as good catalyst due to incompletely filled d-orbitals which allows them to donate as well as accept electrons easily.
Lanthanides
The series of elements from atomic number 57 (Lanthanum) to 71 (Lutetium) following lanthanum are known as Lanthanides.
Properties of Lanthanides :-
- One valence electron in 5d shell.
- Relatively soft metals.
- High melting and boiling points.
- Silvery white metals that tarnish when exposed to air forming oxides.
- Chemical behaviors is almost identical.
- Resembles with each others very closely.
- Very difficult to isolate.
Actinides
The series of elements from atomic number 89 (Actinium) to 103 (Lowrencium) following actinium are know as actinides.
Properties of Actinides :-
- Highly radioactive elements.
- Highly electropositive.
- React with boiling water or dilute acid to release hydrogen gas.
- Tarnish readily in air.
Similarities between Hydrogen and Alkali metals.
- Same valence electron in valence shell.
- Alkali metals and Hydrogen are collected in cathode during electrolysis.
- Alkali metals and Hydrogen both lose one electron to form univalent cation.
Similarities between Hydrogen and Halogens.
- Require one electron to be in stable (duplet/octet) state.
- Halogens and Hydrogen both gain one electron to form univalent anion.
- Both are diatomic elements, i.e., they have two atoms in one molecule (H2, F2, Cl2, Br2 and I2 ).
