Daily Junction.mobi portalScience · January 22, 2026 · Dr. Nadia Okoro · 4 min
The periodic table organises every known chemical element by its structure and properties. This plain-English guide explains what the elements are, how groups and periods work, and how to actually read the table.
The periodic table is a single chart that organises every known chemical element in a way that reveals the patterns in their behaviour. Read correctly, it is less a list to memorise than a map: where an element sits tells you a great deal about how it will act.
The periodic table is an arrangement of all the known chemical elements, ordered by increasing atomic number and grouped so that elements with similar properties line up together.
An element is a pure substance made of just one kind of atom — hydrogen, oxygen, iron, gold and so on. There are over 110 known elements, around 90 of which occur naturally, with the rest made in laboratories. Everything around you, and you yourself, is built from combinations of these elements.
To read the table, it helps to recall what an atom is made of:
The number of protons is called the atomic number, and it defines the element. Every carbon atom has 6 protons; every oxygen atom has 8. Change the number of protons and you change the element entirely. The arrangement of an atom's electrons, especially those in its outermost shell, determines how it bonds and reacts — and the whole structure of the table reflects this.
The genius of the table is that its shape encodes chemistry.
The horizontal rows are called periods. As you move across a period from left to right, the atomic number increases one at a time, and the elements shift gradually in character — from reactive metals on the left, through to non-metals on the right, ending in the very unreactive noble gases.
The vertical columns are called groups. Elements in the same group have the same number of electrons in their outer shell, which gives them similar chemical properties. This is the single most useful idea in the whole table.
Some groups are well known by name:
Because elements in a group behave alike, knowing how one member reacts lets you make a good prediction about the others. That predictive power is what makes the table so valuable.
Each element sits in its own box. While layouts vary slightly, a typical box shows:
| Feature | What it means |
|---|---|
| Chemical symbol | A one or two-letter abbreviation, such as O for oxygen or Na for sodium |
| Atomic number | The number of protons; usually shown above the symbol |
| Name | The full name of the element |
| Relative atomic mass | The average mass of the atom, usually below the symbol |
So a box reading 6, C, Carbon, 12.011 tells you carbon has 6 protons and an average atomic mass of about 12.
A broad pattern runs across the table:
Below the main body sit two rows, the lanthanides and actinides, pulled out to keep the table a manageable width.
The periodic table is one of the great achievements of science because it is predictive, not merely descriptive. When Dmitri Mendeleev arranged the elements by their properties in 1869, he deliberately left gaps where no known element fit the pattern, and predicted the properties of elements that had not yet been discovered. When those elements were later found, they matched his predictions closely — a striking confirmation that the table reflects something real about nature.
That underlying order comes from the way electrons fill their shells, which is also the basis of how chemical reactions happen. The same chemistry explains everyday processes from how batteries work to photosynthesis in plants.
Far from being an abstract chart, the periodic table underpins medicine, materials science, energy and electronics. Choosing the right element or combination of elements is fundamental to designing everything from drugs to semiconductors to battery technology. It is the shared language chemists use to navigate the building blocks of matter.
The periodic table organises all known elements by atomic number and arranges them so that those with similar properties fall into the same columns, or groups, while rows are called periods. Its layout reflects how electrons are arranged in atoms, which is why an element's position predicts how it will behave. From Mendeleev's gap-filled draft to today's refined chart, it remains one of science's most powerful tools — a map of the very stuff the universe is made from, and a foundation for understanding what DNA is and the molecules of life.
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