Which element has the electron configuration 1s2 2s2
The Correct Answer and Explanation is:
The correct answer is B) Ruthenium.
The given electron configuration is: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d⁶
To determine which element this represents, we count the total number of electrons:
- 1s² → 2 electrons
- 2s² 2p⁶ → 8 electrons
- 3s² 3p⁶ → 8 electrons
- 4s² 3d¹⁰ 4p⁶ → 18 electrons
- 5s² 4d⁶ → 8 electrons
Total = 2 + 8 + 8 + 18 + 8 = 44 electrons
A neutral atom has equal numbers of protons and electrons. Therefore, the atomic number is 44. The element with atomic number 44 is Ruthenium, a transition metal located in group 8 and period 5 of the periodic table.
Now for the explanation:
This electron configuration reflects the order in which atomic orbitals are filled, as described by the Aufbau principle. Electrons fill from lower to higher energy levels. The first three shells (1s through 3p) fill completely. The fourth shell then fills with the 4s orbital, followed by the 3d orbital because of their close energy levels. The 4p orbital comes next, completing the fourth shell. Then the fifth shell begins filling with the 5s orbital, followed by the 4d orbital.
In transition metals such as Ruthenium, the 4d subshell is partially filled. This specific arrangement affects the chemical and physical properties of the element, including common oxidation states and coordination behavior in complexes. Ruthenium often exhibits oxidation states ranging from +2 to +8, and it is known for catalytic applications in chemical reactions.
Understanding these configurations helps explain periodic trends, elemental classification, and reactivity. This also supports accurate predictions of electron arrangements during chemical bonding and reactions. The configuration confirms Ruthenium’s status as a typical second-row transition metal with unique electronic characteristics.
