ORDER OF INCREASING ATOMIC SIZE:
Cs, Li, and Rb
To determine the order of increasing atomic size among Cs (cesium), Li (lithium), and Rb (rubidium), we need to consider the trends in the periodic table.
Atomic size refers to the size of the atom, which is typically represented by the atomic radius. As we move from left to right across a period (horizontal row) in the periodic table, the atomic size generally decreases. This is because as we move across a period, electrons and protons are added to the atom, resulting in increased nuclear charge. The increased attraction provided by the increased nuclear charge pulls the electrons closer to the nucleus, causing a decrease in atomic size.
On the other hand, as we move down a group (vertical column) in the periodic table, atomic size generally increases. This is because each period has a new energy level (shell) added, resulting in increased distance between the nucleus and the outermost electrons. The increased number of energy levels and increased shielding effect from inner electrons counteract the increased nuclear charge, causing a net increase in atomic size.
Now, let's determine the order of increasing atomic size among Cs, Li, and Rb:
1. Cs (Cesium):
- Cesium is located in Group 1 (the alkali metals) and period 6 of the periodic table.
- As we move down Group 1, atomic size generally increases.
- Therefore, Cs has the largest atomic size among the three elements.
2. Rb (Rubidium):
- Rubidium is also located in Group 1 (the alkali metals) and period 5 of the periodic table.
- Since it is located one period above Cs, the atomic size of Rb is smaller than that of Cs but larger than that of Li.
3. Li (Lithium):
- Lithium is located in the same group as Cs and Rb (Group 1) but in period 2 of the periodic table.
- Since it is located one period above Cs and Rb, the atomic size of Li is the smallest among the three elements.
Therefore, the order of increasing atomic size is:
Li < Rb < Cs