Answer:
Step-by-step explanation:
Within a family or group on the periodic table, as you move from top to bottom (increasing atomic number), the atomic radius of the elements generally increases. This trend can be explained by the following factors:
Increase in Energy Levels (Principal Quantum Number, n): Each period or row in the periodic table represents a new energy level (shell). As you move down a group, new energy levels are added, leading to an increase in the average distance of the outermost electrons from the nucleus. This results in a larger atomic radius.
Shielding Effect: With the addition of energy levels, there are more inner electrons (core electrons) that shield the outermost electrons from the positive charge of the nucleus. This increased electron shielding further contributes to the expansion of the atomic radius.
For Group 1 (the alkali metals), as you move down the group (from lithium at the top to francium at the bottom), the atomic radius increases. This increase in atomic size is responsible for the observed trends in physical and chemical properties within the group. As the atomic radius increases:
The elements become more metallic in character.
The outermost electron is located farther from the nucleus, making it easier to lose, leading to higher reactivity.
The melting and boiling points decrease.
The elements are more likely to form ionic compounds with nonmetals, such as halogens from Group 17.
For Group 17 (the halogens), as you move down the group (from fluorine at the top to iodine at the bottom), the atomic radius also increases. The increase in atomic size affects the chemical reactivity of the elements within the group:
Reactivity decreases as you move down the group because the outermost electrons are located farther from the nucleus, making it more difficult for them to attract an extra electron.
The ability of the elements to form halide ions (e.g., F-, Cl-, Br-) increases with atomic size.
The melting and boiling points of the elements increase.
In summary, within a family on the periodic table, the atomic radius increases as you move down the group, which has significant effects on the chemical and physical properties of the elements within that family.