Order of Elements in the Modern Periodic Table

The modern periodic table is organised based on atomic number, beginning with hydrogen which has an atomic number of 1.
Atomic number represents the number of protons in the nucleus of an atom. For instance, helium has an atomic number of 2 because it has two protons.
As you move left to right across a period (horizontal row), the atomic number gradually increases.
The number of electron shells also increases as you move down a group (vertical column), owing to the increase of electron energy levels.
Each period corresponds to a new principal energy level (shell) being filled with electrons. The first period has only one energy level (shell), the second period has two, and so on.
Elements in the same group will have the same number of electron shells that are not fully filled, indicating they have similar chemical properties.
The transition metals, positioned in the central block of the table, are characterised by filling of an inner d-subshell.
There are 18 groups in the periodic table. Group 1 elements are known as alkali metals, while Group 17 elements are known as halogens.
Group 0 elements, also known as noble gases, are noted for their full outer electron shells making them very unreactive.
The lanthanides and actinides are part of a series called the inner transition metals, located at the bottom of the periodic table.
There is a division line that separates metals from nonmetals; metals are found on the left of the line and nonmetals on the right, with metalloids bordering the division line.