Answered

Given the following electronic configurations, identify how many valence electrons each atom has.




Element		Electron ConfigurationNumber of Valence Electrons

Sodium (Na)		$1 s^2 2 s^2 2 p ^6 3 s^1$A

Oxygen (O)		$1 s^2 2 s^2 2 p ^4$B

Iron (Fe)		$1 s^2 2 s^2 2 p ^6 3 s^2 3 p ^6 4 s^2 3 d^6$C






A =

B =

C =

Verified Answer :

  • Sodium (Na) has a valence shell of \(n=3\) with 1 electron: \(A=1\).
  • Oxygen (O) has a valence shell of \(n=2\) with 6 electrons (\(2+4\)): \(B=6\).
  • Iron (Fe) has valence electrons in the \(4s\) and \(3d\) orbitals summing to 8 (\(2+6\)): \(C=8\).
  • Final answers: \(A=1, B=6, C=8\).

Explanation

  1. Determining Valence Electrons for Na, O, and Fe

To determine the number of valence electrons, we need to identify the electrons present in the outermost shell (the shell with the highest principal quantum number \(n\)) for each atom. Valence electrons are crucial as they determine the chemical reactivity and bonding behavior of an atom.

For Sodium (Na): The electron configuration is \(1s^2 2s^2 2p^6 3s^1\). The highest principal quantum number is \(n=3\). The electrons in this shell are found in the \(3s\) orbital. There is 1 electron in the \(3s\) orbital, so \(A=1\).

For Oxygen (O): The electron configuration is \(1s^2 2s^2 2p^4\). The highest principal quantum number is \(n=2\). The electrons in this shell are found in the \(2s\) and \(2p\) orbitals. There are 2 electrons in the \(2s\) orbital and 4 electrons in the \(2p\) orbital. Summing these, \(B = 2 + 4 = 6\).

For Iron (Fe): The electron configuration is \(1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^6\). The highest principal quantum number is \(n=4\). For transition metals like Iron, valence electrons are typically defined as those in the outermost \(s\) orbital plus any electrons in the incomplete \(d\) subshell. Thus, we consider the \(4s^2\) electrons and the \(3d^6\) electrons. Summing these, \(C = 2 + 6 = 8\).

Examples

Valence electrons are essential for understanding how atoms interact to form compounds. For example, sodium atoms easily lose their 1 valence electron to oxygen atoms, which have 6 valence electrons, to form stable compounds like sodium oxide (\(Na_2O\)). Knowing the number of valence electrons allows chemists to predict stoichiometry and the structure of chemical bonds in everything from table salt to complex structural materials like iron alloys.

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