What is the noble gas electron configuration for calcium, Ca?
A. [Ar] 4s^2 3d^5
B. [Ar] 4s^2 3d^{10}
C. [Ar] 4s^2
D. [Ar] 4s^2 3d^{10} 4p^3
Answer (2)
Calcium has 20 electrons.
Argon (Ar) has 18 electrons, so we use [Ar] as a starting point.
The remaining 2 electrons occupy the 4s orbital, resulting in [ A r ] 4 s 2 .
The noble gas electron configuration for calcium is [ A r ] 4 s 2 .
Explanation
Understanding the Problem The question asks for the noble gas electron configuration for calcium (Ca). We need to determine the correct electron configuration that represents the distribution of electrons in calcium's electron shells, using the noble gas Argon (Ar) as a shorthand.
Identifying Key Information Calcium (Ca) has an atomic number of 20. This means a neutral calcium atom has 20 electrons. The noble gas that precedes calcium in the periodic table is Argon (Ar), which has an atomic number of 18. Therefore, we can use Argon's electron configuration as a starting point and then add the remaining electrons to reach a total of 20.
Determining the Electron Configuration The electron configuration of Argon (Ar) is 1 s 2 2 s 2 2 p 6 3 s 2 3 p 6 . We can represent this as [Ar]. Since calcium has 20 electrons and Argon has 18, we need to account for the remaining 2 electrons. These 2 electrons will occupy the next available energy level, which is the 4s orbital. Therefore, the electron configuration for calcium is [ A r ] 4 s 2 .
Selecting the Correct Option Comparing our result, [ A r ] 4 s 2 , with the given options, we find that it matches the third option.
Final Answer Therefore, the noble gas electron configuration for calcium (Ca) is [ A r ] 4 s 2 .
Examples
Understanding electron configurations is crucial in chemistry for predicting how elements will interact to form chemical bonds. For example, knowing that calcium has a configuration of [ A r ] 4 s 2 helps us understand that it will readily lose two electrons to form a C a 2 + ion, which can then bond with elements like oxygen to form calcium oxide (CaO), a key component of lime and cement. This principle extends to understanding the properties of various materials and designing new compounds with specific characteristics.
The noble gas electron configuration for calcium (Ca) is [Ar] 4s^2, indicating it has 20 electrons with 2 in the 4s orbital after noble gas Argon. The correct answer is option C: [Ar] 4s^2.
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