Which element has seven energy levels?
a. rubidium (RD)
b. potassium (K)
c. cesium (Cs)
d. francium (Fr)
The Correct Answer and Explanation is:
The correct answer is d. francium (Fr).
Explanation:
The number of energy levels (also known as electron shells) in an element is determined by its position on the periodic table, specifically by its period (row). The elements in the periodic table are arranged into periods (horizontal rows) and groups (vertical columns). The period number indicates how many electron shells an element has. For example, elements in Period 1 have 1 energy level, elements in Period 2 have 2 energy levels, and so on.
Let’s look at the elements listed:
- Rubidium (Rb): Rubidium is in Period 5 of the periodic table. This means it has 5 energy levels (or electron shells).
- Potassium (K): Potassium is in Period 4, so it has 4 energy levels.
- Cesium (Cs): Cesium is in Period 6, meaning it has 6 energy levels.
- Francium (Fr): Francium is in Period 7, so it has 7 energy levels.
Thus, francium (Fr) is the element that has seven energy levels.
Understanding Electron Configuration:
The electron configuration of an element shows how electrons are arranged in energy levels or shells around the nucleus. For example, the electron configuration of francium (atomic number 87) is:
[ \text{Fr}: [Rn] 5f^{14} 6s^2 7s^1 ]
This configuration shows that francium has electrons in 7 energy levels. The outermost shell, which is the 7th shell, contains one electron (in the 7s orbital).
Elements with more energy levels typically have larger atomic radii and lower ionization energies, which are related to the greater distance between the nucleus and the outermost electrons, making it easier to remove those electrons.