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Monday, 30 March 2020

Facts about Periodic Table

Periodic Table

Periodic table is an arrangement of elements with similar properties placed together.

 Lavoisier classified the elements into metals and non-metals.

Dobereiner classified the elements as triads, in which the atomic weight of the middle element was the arithmetic mean of the other two.

The law of octaves was proposed by Newland.

Mendeleev's periodic table is based on atomic weights.

Mendeleev's periodic table consists of 7 periods and 9 groups.

Modern periodic table is based on atomic number of elements.

Modern periodic table contains 7 horizontal rows called periods and 18 vertical columns called groups and 118 elements.

Elements of group 1 are called Alkali metals.

The periodic table is divided into four main blocks

1. s-block - Elements of group 1 and 2
2. p-block - Elements of group 13 to group 18
3. d-block - Elements of group 3 to group 12
4. f-block - Lanthanides and Actinides

Elements of group 2 are called Alkaline earth metals.

Elements of group 17 are called Halogens.

There are 118 elements known today, out of which 90 are naturally existing.

First period contains only 2 elements, this is the shortest period.

The sixth period consists of 32 elements, this is the longest period.

Elements of group 18 show little reactivity and are termed noble gases.

Elements from atomic number 58 to 71 are lanthanides or rare earths.

Elements from atomic number 90 to 103 are termed as actinides.

The atomic number was first calculated by Moseley.

Man made elements are known as transuranics.

Elements from atomic number 93 onwards do not occur in nature. So they are called synthetic or transuranic elements. 

s and p-block elements are called representative elements.

d-block elements are called transition elements.

f-block elements are called inner transition elements.

In a group, from top to bottom atomic size increases.

What is electro negativity ?

Ans: The power of atom to attract electron pairs. The order of electro negativity is F (4.00) > O (3.50) > Cl (3.10) > N (3.00). The electro negativity scale was introduced by Linus Pauling.

Atomic size decreases from left to right in a period.

Ionization Energy is the energy required to remove an electron completely from an isolated gaseous atom or ion of an element.

Ionization energy generally increases from left to right in a period with increase in atomic number or decrease in atomic size.

In a group, from top to bottom ionization energy decreases.

Electron Affinity is the energy change when an electron is gained by a neutral gaseous atom converting it into a negatively charged ion.

In a group electron affinity, decreases from top to bottom and in a period it increases as we move from left to right.

Classification of Elements 

1. Metals and non metals - Lavoisier  
2. Triads – Dobereiner
3. Law of octaves – Newland
4. Based on atomic weight – Mendeleev
5. Based on atomic number – Moseley

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