What is the significance of a period and a group in the periodic table?

Here's the significance of PERIOD and GROUP in the periodic table:

• Period (Horizontal Rows):

  • The period number indicates the number of electron shells or energy levels an atom has. For example, elements in Period 3 have electrons occupying three main energy shells.
  • As you move across a period from left to right, the atomic number increases, and the number of valence electrons generally increases, leading to a gradual change in chemical properties.

• Group (Vertical Columns):

  • The group number (for main group elements) indicates the number of valence electrons an atom has. For example, all elements in Group 1 have one valence electron.
  • Elements within the same group share similar chemical properties because they have the same number of valence electrons, which largely determines how an atom reacts.