Element

Definition

An chemical element is a substance made up of identical atoms (atoms that have the same number of protons in their nucleus). For example, a hydrogen atom has 1 proton, while a carbon atom has 6 protons.

The number of electron and neutron in an element can be different.
It cannot be broken down into another substance.
Each element is represented by a unique chemical symbol, such as “H” for hydrogen and “O” for oxygen.
Change in the number of electrons in an atom of an element produces ions.
Change in the number of neutrons produces isotopes.
The term “element” was first introduced by the English scientist Robert Boyle.

Atomic Structure: Atoms of an element have a specific structure consisting of a nucleus composed of protons (positively charged particles) and neutrons (particles with no charge), surrounded by a cloud of electrons (negatively charged particles) in various energy levels or orbitals.

Chemical Symbols: Each element is represented by a chemical symbol, typically one or two letters derived from its name. For example, “H” represents hydrogen.

Periodic Table: Elements are organized systematically in the periodic table based on their atomic number, electron configuration, and chemical properties.

Geochemical Classification of Elements

Elements can be classified based on their properties and affinity for other elements. Goldschmidt’s classify the chemical elements into four groups-

Siderophile elements (iron loving): Elements that concentrate in metallic iron such as Ni, Co, Os, Ir
Chalcophile elements: Elements that concentrate in sulfides, are chalcophile elements such as Se, As, Zn, Cd
Lithophile elements (Rock Loving): Elements that concentrate in silicate phases are grouped in this category, such as Rb, Sr, Ba, Nb, Ta, Th, U, REE
Atmophile elements: These are naturally occurring gaseous elements such as N and rare gases

Types of Elements

Elements can be categorised into several groups based on their properties:

Metals: Elements that are typically shiny, malleable, ductile, and good conductors of heat and electricity (e.g., iron, copper, gold).
Non-metals: Elements that are generally brittle, poor conductors of heat and electricity, and often exist in gaseous form (e.g., oxygen, carbon, sulphur).
Metalloids: Elements that possess properties intermediate between metals and nonmetals (e.g., silicon, germanium, arsenic).
Noble Gases: Elements that are inert, colourless, odourless gases with very low reactivity (e.g., helium, neon, argon).
Transition Metals: Elements found in the d-block of the periodic table, characterised by their variable oxidation states and ability to form coloured compounds (e.g., iron, copper, zinc).
Rare Earth Elements: A group of elements found in the lanthanide and actinide series of the periodic table, known for their unique magnetic, electrical, and optical properties.

Periodic Classification of Element

The periodic classification of elements refers to the systematic organisation of chemical elements according to their atomic number, electron configuration, and chemical properties.

In 1864, J.A.R. Newlands proposed classifying elements based on increasing atomic weights. The modern periodic table is based on the Periodic Law proposed by Dmitri Mendeleev. Mendeleev organized elements in ascending order of their atomic masses and classified them according to their atomic masses.

The periodic table arranges elements in periods (rows) and groups (columns).
Elements within the same group share similar chemical properties.

Structure of Modern Periodic Table

The modern periodic table is structured in a way that organises elements based on their atomic number, electron configuration, and chemical properties. It consists of:

Periods (horizontal rows)
Groups (vertical columns)

Each square in periodic table represents an element, displaying its chemical symbol and atomic number.

Period (Rows)

There are 7 periods in the periodic table. Elements within the same period have the same number of electron shells. For example, the first period contains only hydrogen and helium.

Groups (Columns)

There are 18 groups in the periodic table. Elements within the same group share similar chemical properties due to the similarities in their outer electron configuration. Some notable groups include:

Group 1 (Alkali Metals): Reactive metals that form strong alkalis with water.
Group 2 (Alkaline Earth Metals): Metals that also form alkalis but are weaker than Group 1 elements.
Group 17 (Halogens): Elements that form salts.
Group 18 (Noble Gases): Inert gases under normal conditions.

s,p,d and f block elements

Depending on which subshell the final electron enters, the elements in the periodic table are divided into four major groups. These blocks are the:

s-block
p-block
d-block
f-block.

s-block Elements

These elements have their outermost electron(s) in the s orbital. They are found in groups 1 and 2 of the periodic table.

Characteristics

Typically, they are (except hydrogen) highly reactive metals .
They lose electrons to form positively charged ions (cations).
They have low electronegativity and low ionisation energies. When burned, they produces a characteristic colour flame.
Most s-block elements are solids at room temperature (except caesium, which is liquid around 35°C).
Examples: Lithium (Li), Sodium (Na), Potassium (K), etc.

p-block Elements

These elements have their outermost electron(s) in the p orbital. They are found in groups 13 to 18 of the periodic table.

Characteristics

They exhibit a wide range of properties, from metals to metalloids and nonmetals.
Various States: They exist as solids, liquids, or gases at room temperature (e.g bromine is a liquid).
Their electronegativity varies widely, with some being highly electronegative (e.g., oxygen) and others being less so (e.g., boron).
They often form covalent bonds by sharing electrons.
They do not impart any characteristic colour to flames.

d-block Elements (also known as transition metals)

These elements have their outermost electron(s) in the d orbital. They are found in groups 3 to 12 of the periodic table.

Characteristics

Most d-block elements are metals.
Many of their compounds are coloured.
Many transition metals are good conductors of heat and electricity.
They often act as catalysts in chemical reactions.
Examples: Iron (Fe), Copper (Cu), Zinc (Zn), etc.

f-block Elements (also known as inner transition metals)

These elements have their outermost electron(s) in the f orbital. They are placed at the bottom of the periodic table, separated to keep it compact. There are two series of f-block elements:

The lanthanides (elements 57-71): Lanthanide (58Ce-71Lu) closely resemble lanthanum, have similar chemical properties, and are widely used in lasers.
The actinides (elements 89-103): Actinides (90Th-103Lr) are radioactive, highly electropositive, and exhibit various oxidation states.

Characteristics

Many are radioactive.
They are typically soft metals. Some have important uses in nuclear reactors, medicine (e.g., radioisotopes for imaging), and other specialized applications.
Examples: Cerium (Ce), Uranium (U), Neptunium (Np), etc.

Fact Sheet

In periodic table, elements are arranged according to their increasing atomic number.
Horizontal rows on the periodic table is termed as periods.
The number of horizontal rows in periodic table are seven and have been numbered from 1 to 7.
The 1st period is the shortest period of all and contains only 2 elements, H and He.
The 2nd and 3rd periods are termed as short periods and contain 8 elements each.
4th and 5th periods are long periods and contain 18 elements each.
6th and 7th period is very long period containing 32 elements.
Vertical columns are called groups. There are 18 groups in the periodic table.
Group 1 on extreme left position contains alkali metals (Li, Na, K, Rb, Cs and Fr).
Group 18 on extreme right side position contains noble gases (He, Ne, Ar, Kr, Xe and Rn).
In the middle of periodic table, we have semi-metals or metalloid because they exhibit some properties of metals and non-metals.