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The Periodic Table - Groups, Periods &

Atomic Number Explained!

The Periodic Table is probably one of the most iconic scientific documents, a single table

that holds within itself almost all chemical knowledge amassed by man. The periodic

table is a tabular arrangement of 118 elements, organized by atomic number, number of

free electrons, and grouped together by similarity in chemical properties. Read this

article on Periodic Table, to know all about chemical elements, atomic no., grouping

method, and useful tips to learn the periodic table to ace the Railways, SSC, UPSC

exams.

Periodic Table Atomic Number

The Periodic Table has 118 elements which organized on the basis of atomic number and

grouped based on similarity in chemical properties. The first element is Hydrogen (H)

with atomic number 1 and the last element is Oganesson (Og) with atomic number 118.

• All chemical elements have unique atomic numbers or Z.

• Atomic numbers signify the number of protons in its nucleus. Atoms of the same

element having a different number of neutrons in the nucleus are called isotopes.

• Isotopes differ in mass number (n) but have the same atomic number. Isotopes

are never separated in the periodic table; they are always grouped together under

a single element.

This image covers details about the Neutrons, Protons and Electrons.

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The elements are indexed in order of increasing atomic number in the periodic table.

When a new electron shell receives its first electron, we enter a new row in the table.

Electron configurations of the atoms determine their columns: elements with the same

number of electrons in a particular subshell fall into the same columns, eg. Sodium and

Potassium. Elements in the same group tend to have similar chemical properties and

reactivities. Hence, if we know one element of a group, it is relatively easy to ascertain

the properties of the rest.

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Periodic Table History

The periodic table wasn’t always like today’s. The periodic table has been through

several iterations of attempted systemization before we reached the one we use now.

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The first attempt was by Antoine Lavoisier in 1789 when he published a list of 33

chemical elements. He grouped them into gases, metals, nonmetals and earth. In 1829,

Johann Wolfgang improved this table by observing the similarities in the chemical

properties of triads of elements and grouping them, thus giving rise to the Law of

Triads. Several chemists made revisions to the table, but no scheme could satisfy the

correct groupings.

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Alexandre-Emile Béguyer de Chancourtois published a periodic table in the form of a

helix in 1862. The elements were arranged in a spiral on a cylinder and were the first

arrangement to hint at periodicity in the properties. De Chancourtois indexed the

elements by increasing atomic weight and showed that similar chemical properties were

reflected after regular intervals. However, his work did not receive too much attention.

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The first edition of the modern periodic table was published by Mendeleev in 1871.

Mendeleev’s periodic table had eight columns, each column containing elements with

similar properties. The columns were numbered I to VIII and also had empty cells for

elements that hadn't been discovered yet, but Mendeleev predicted they should exist. As

chemists discovered more and more elements, these gaps were filled.

The common or standard form of the modern periodic table is attributed to Horace

Groves Deming. He published the short and medium forms of the table in 1923 that

soon came into circulation and universal acceptance.

Periodic Table Grouping Method

Groups

The 18 vertical columns of the table are called Groups. The number of electrons in the

outermost shell of the atom, i.e. valence shell, is equal for all elements in the same

group.

The leftmost group contains alkali metals and the rightmost contains noble gases.

Elements in the same column exhibit similar chemical properties and display periodicity

with an increase in atomic number. Elements in the same group tend to show patterns

in atomic radius, ionisation energy, and electronegativity

The groups are numbered 1 to 18 from left to right. Earlier, naming conventions differed

in Europe and America. However, after the IUPAC naming was put in place in 1988, old

names went out of use.

As we move down a group:

• Atomic radius increases

• Electronegativity decreases (except for group 11)

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• Ionization energy decreases

Periods

Vertical rows are called periods of the periodic table. Lanthanides and actinides in the f-

block display more similarity in the same period than in the same group.

On moving left to right in a period:

• Atomic size decreases due to stronger nuclear force

• Ionisation Energy increases

• Electronegativity increases

• Electron affinity increases (except for noble gases)

Blocks

Sections of the table are called blocks. Each block gets its name from the letter of the

outermost subshell that receives an electron.

The four blocks are:

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1. s-block

Comprises of alkali metals ( group 1 ) and alkaline earth metals ( group 2).

2. p-block

Contains groups 13 to 18, including the metalloids.

3. d-block

Consists of groups 3 to 12 and has all the transition metals.

4. f-block

Home of the lanthanides and actinides, these groups don’t have group numbers.

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Metals, nonmetals and metalloids

On the basis of their physical and chemical properties, elements are divided into:

• Metals

Highly conducting solids that make ionic compounds with other elements. They are also

further divided into alkali metals (Group 1), alkaline earth metals (Group 2),

lanthanides and actinides (f - block), and post-transition metals. Metals form alloys with

each other.

• Nonmetals

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Colored or colorless solids, liquids or gases that undergo covalent bonding with other

elements. They are usually further classified into polyatomic, diatomic and monatomic

(inert) nonmetals.

• Metalloids

Their properties are a mixture of the properties of metals and nonmetals.

Types of Periodic Table

• Long Table

This form is obtained by inserting the f-block between the s and d blocks, instead of

placing the rows at the bottom, disconnected from the table. It makes the trends and

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increases in atomic numbers easier to see, however is avoided on account of difficulty in

printing.

• Benfey’s Spiral Table

Made by Otto Theodor Benfey, the elements are arranged in a continuous spiral, with

hydrogen at the centre and the transition metals, lanthanides, and actinides occupying

peninsulas.

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• Janet’s Left Step Table

Made by Charles Janet, it organizes elements according to orbital filling, as compared to

valence, and is widely used by physicists.It is congruent with the order in which electron

shells are ideally filled.

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Memory Tips to Learn the Periodic Table

Learning the periodic table can be a hard task. Hence, mentioned below are a few

mnemonics to help you learn some of the important groups:

1. HeLiNa Ke Rubber Csste Free

Group 1

Hydrogen (H) -> Lithium (Li) -> Sodium (Na) -> Potassium (K) -> Rubidium (Rb) ->

Caesium (Cs) -> Francium (Fr)

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2. Beta Maange Scooter Baap Raazi

Group 2

Beryllium (Be) -> Magnesium (Mg) -> Calcium (Ca) -> Strontium (Sr) -> Barium (Br) -

> Radium (Ra)

3. Baingan Aloo Gajar Indian Thaali

Group 13

Boron (B) -> Aluminium (Al) -> Gallium (Ga) -> Indium (In) -> Thallium (Tl)

4. CaSi Geye Shankar Prabhu

Group 14

Carbon (C) -> Silicon (Si) -> Germanium (Ge) -> Tin (Sn) -> Lead (Pb)

5. He Never Arrived; Kara Xero Run pe out

Group 18

Helium (He) -> Neon (Ne) -> Argon (Ar) -> Krypton (Kr) -> Xenon (Xe) -> Radon (Rn)

The Periodic Table is easy to learn and capture maximum marks, therefore, we aurge

you to learn the Periodic Table thoroughly. To help learn quickly we are sharing with

you videos that will help you learn the entire Periodic Table easily.

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