* More Protons and Neutrons: Elements in the same group have the same number of valence electrons, but as you move down, they also gain more protons and neutrons in their nucleus. This increase in the number of subatomic particles directly contributes to a higher atomic mass.
* Number of Electron Shells: As you move down a group, elements have additional electron shells. These shells contain electrons that orbit the nucleus, and the increased number of shells contributes to the overall size of the atom and, consequently, its atomic mass.
Example:
Consider Group 1 (alkali metals):
* Lithium (Li): Atomic mass = 6.941 amu
* Sodium (Na): Atomic mass = 22.990 amu
* Potassium (K): Atomic mass = 39.098 amu
* Rubidium (Rb): Atomic mass = 85.468 amu
* Cesium (Cs): Atomic mass = 132.905 amu
As you move down the group, the atomic mass increases significantly due to the addition of more protons and neutrons.
Important Note: There can be slight deviations from this general trend, especially in the case of isotopes. Isotopes are atoms of the same element with different numbers of neutrons, leading to variations in atomic mass.
