⚗️ Periodic Table of Elements

About the Periodic Table

The periodic table is a tabular arrangement of chemical elements organized by their atomic number, electron configuration, and recurring chemical properties. Elements are presented in order of increasing atomic number.

The table has rows called periods and columns called groups. Elements in the same group have similar chemical behaviors. The standard form consists of 18 groups, with the lanthanides and actinides shown separately below the main body.

History of the Periodic Table

The periodic table has a rich history dating back to the 19th century. In 1869, Russian chemist Dmitri Mendeleev and German chemist Lothar Meyer independently published their own periodic tables. Mendeleev's table was particularly notable because he left gaps for elements not yet discovered and accurately predicted their properties.

Before Mendeleev, several scientists attempted to organize the elements. John Newlands proposed the "Law of Octaves" in 1865, and Antoine-Laurent de Lavoisier created the first extensive list of elements in 1789. However, it was Mendeleev's version that gained widespread acceptance due to its predictive power.

The modern periodic table is organized by atomic number rather than atomic weight, a refinement introduced by Henry Moseley in 1913. Today, the table contains 118 confirmed elements, with the most recent additions — nihonium (Nh), moscovium (Mc), tennessine (Ts), and oganesson (Og) — officially named in 2016.

How to Read the Periodic Table

Each element cell in the periodic table contains key information: the atomic number (number of protons), the element symbol (one or two letters), the element name, and the atomic mass. The atomic number uniquely identifies each element and determines its position in the table.

Periods (rows): There are 7 periods in the periodic table. As you move across a period from left to right, elements gain one proton and one electron. The period number indicates the highest energy level an electron occupies in that element's ground state.

Groups (columns): There are 18 groups. Elements in the same group share similar chemical properties because they have the same number of electrons in their outermost shell (valence electrons). For example, Group 1 elements (alkali metals) all have one valence electron and are highly reactive.

Element Categories Explained

Alkali Metals (Group 1): Lithium, sodium, potassium, and others. These soft, silvery metals are extremely reactive, especially with water. They have one valence electron and are never found free in nature.

Alkaline Earth Metals (Group 2): Beryllium, magnesium, calcium, and others. These are reactive metals with two valence electrons. They are harder and denser than alkali metals and have higher melting points.

Transition Metals (Groups 3–12): Iron, copper, gold, silver, and many more. These elements are known for forming colorful compounds, having multiple oxidation states, and being good conductors of heat and electricity. Many are used widely in industry and daily life.

Nonmetals: Carbon, nitrogen, oxygen, and others. These elements are essential for life. They generally have high ionization energies and electronegativity values. Nonmetals can be gases, liquids, or brittle solids at room temperature.

Halogens (Group 17): Fluorine, chlorine, bromine, iodine, and astatine. These are highly reactive nonmetals with seven valence electrons. They readily form salts with metals and exist in all three states of matter at room temperature.

Noble Gases (Group 18): Helium, neon, argon, krypton, xenon, and radon. These are colorless, odorless, and nearly inert gases with a full outer electron shell. They have very low reactivity and are used in lighting, welding, and as protective atmospheres.

Periodic Trends

Several important properties follow predictable trends across the periodic table:

Atomic Radius: Decreases from left to right across a period (more protons pull electrons closer) and increases from top to bottom within a group (more electron shells are added).

Ionization Energy: The energy required to remove an electron. It increases across a period and decreases down a group. Noble gases have the highest ionization energies in each period.

Electronegativity: A measure of how strongly an atom attracts electrons in a bond. It increases across a period and decreases down a group. Fluorine is the most electronegative element.

Metallic Character: Increases from right to left across a period and from top to bottom in a group. Elements in the lower-left corner of the periodic table are the most metallic.

Frequently Asked Questions

How many elements are there in the periodic table?

As of 2024, there are 118 confirmed elements in the periodic table. Elements 1 (hydrogen) through 94 (plutonium) occur naturally, while elements 95 through 118 have been synthesized in laboratories.

Who invented the periodic table?

Dmitri Mendeleev is widely credited as the creator of the periodic table. He published his first version in 1869, organizing 63 known elements by atomic weight and predicting the existence and properties of elements yet to be discovered.

Why is it called the "periodic" table?

The name comes from the periodic (recurring) trends in element properties. When elements are arranged by atomic number, their chemical and physical properties repeat at regular intervals, or "periods." This periodicity is the fundamental organizing principle of the table.

What is the heaviest element?

Oganesson (Og, element 118) is the heaviest known element. It was first synthesized in 2002 and officially named in 2016 after physicist Yuri Oganessian. Being a synthetic element, it is extremely unstable and only a few atoms have ever been produced.

What are the most abundant elements in the universe?

Hydrogen is by far the most abundant element in the universe, making up about 75% of all normal matter by mass. Helium is the second most abundant at about 24%. Together, these two lightest elements account for roughly 99% of all atoms in the observable universe. On Earth, oxygen and silicon are the most abundant elements in the crust.