Basic Points about the Periodic Table
● The periodic table is a table where chemical elements are arranged according to their
atomic number.
● Atomic number means the number of protons present in the nucleus of an atom.
● The modern periodic table is based on the Modern Periodic Law.
● Modern Periodic Law states:
“The physical and chemical properties of elements are periodic functions of their atomic
numbers.”
● Elements are arranged in horizontal rows called periods.
● Elements are arranged in vertical columns called groups.
● There are 7 periods and 18 groups in the modern periodic table.
● Elements in the same group have similar chemical properties.
● Elements in the same period have the same number of electron shells.
● Metals are mostly found on the left side.
● Non-metals are mostly found on the right side.
● Metalloids are found between metals and non-metals.
● Group 1 elements are called alkali metals.
● Group 2 elements are called alkaline earth metals.
● Group 17 elements are called halogens.
● Group 18 elements are called noble gases.
● Noble gases are chemically stable because their outermost shell is complete.
Important Periodic Properties
1. Atomic Radius
● Atomic radius means the distance from the nucleus to the outermost electron shell.
● Across a period (left to right), atomic radius decreases.
● Down a group (top to bottom), atomic radius increases.
Reason: Nuclear charge increases across a period, but number of shells increases down a
group.
2. Ionization Energy
● Ionization energy is the energy required to remove an electron from a gaseous atom.
● Across a period, ionization energy increases.
● Down a group, ionization energy decreases.
Reason: Smaller atoms hold electrons more strongly.
3. Electron Affinity
● The periodic table is a table where chemical elements are arranged according to their
atomic number.
● Atomic number means the number of protons present in the nucleus of an atom.
● The modern periodic table is based on the Modern Periodic Law.
● Modern Periodic Law states:
“The physical and chemical properties of elements are periodic functions of their atomic
numbers.”
● Elements are arranged in horizontal rows called periods.
● Elements are arranged in vertical columns called groups.
● There are 7 periods and 18 groups in the modern periodic table.
● Elements in the same group have similar chemical properties.
● Elements in the same period have the same number of electron shells.
● Metals are mostly found on the left side.
● Non-metals are mostly found on the right side.
● Metalloids are found between metals and non-metals.
● Group 1 elements are called alkali metals.
● Group 2 elements are called alkaline earth metals.
● Group 17 elements are called halogens.
● Group 18 elements are called noble gases.
● Noble gases are chemically stable because their outermost shell is complete.
Important Periodic Properties
1. Atomic Radius
● Atomic radius means the distance from the nucleus to the outermost electron shell.
● Across a period (left to right), atomic radius decreases.
● Down a group (top to bottom), atomic radius increases.
Reason: Nuclear charge increases across a period, but number of shells increases down a
group.
2. Ionization Energy
● Ionization energy is the energy required to remove an electron from a gaseous atom.
● Across a period, ionization energy increases.
● Down a group, ionization energy decreases.
Reason: Smaller atoms hold electrons more strongly.
3. Electron Affinity
