definition :

A table in which the chemical elements are arranged in order of increasing atomic number

The Periodic Table is like a map of all the chemical elements in the universe. Each element has a unique number called the atomic number, which tells how many protons are in its atom.

The elements are arranged in rows, called periods, and columns, called groups or families.

• Elements in the same group act similarly in chemical reactions because they have the same number of outer electrons.

• As you move from left to right across a period, elements go from being metals to nonmetals.

• Metals are on the left and center. They are shiny, conduct heat, and are bendable.

• Nonmetals are on the right. They don’t conduct electricity well and are often gases or brittle solids.

• In between metals and nonmetals are metalloids, which have mixed properties.

Some special columns have names:

• Group 1: Alkali metals – very reactive (like sodium).

• Group 17: Halogens – also very reactive (like chlorine).

• Group 18: Noble gases – not reactive at all (like helium and neon).

The bottom part of the table (the two rows below) includes rare earth elements called lanthanides and actinides.

notes

• periodic table is made up of columns and rows

• there are the groups in it Alkali metals ,Halogens ,Noble gases

• There are 118 elements in the periodic table.