Copy and complete the following table Element Number of Neutrons Electronic Configuration Group in the periodic Table \(^{23}_{11}Na\) --- \(1s^{2}2s^{2}2p^...

Assessment: WAEC SSCE - Chemistry - 1998 (Essay) Subject: Chemistry

Question 1 Report

Copy and complete the following table

Element Number of Neutrons Electronic Configuration Group in the periodic Table
\(^{23}_{11}Na\) --- \(1s^{2}2s^{2}2p^{6}3s^{1}\) 1
\(^4_2He\) 2 ---- ---
---- 7 \(1s^{2}2s^{2}2p^{2}\) ----
Answer Details

Completed table

Reasoning for each entry:

  • \( ^{23}_{11}Na \): number of neutrons \( = 23 - 11 = 12 \). The configuration \( 1s^2\,2s^2\,2p^6\,3s^1 \) ends in \( 3s^1 \) (one outer electron), so it is in Group 1.
  • \( ^{4}_{2}He \): neutrons \( = 4 - 2 = 2 \); with 2 electrons the configuration is \( 1s^2 \). Its outer shell is full, so it is a noble gas in Group 0.
  • Third element: the configuration \( 1s^2\,2s^2\,2p^2 \) has 6 electrons, so the atomic number is 6 (carbon). With 7 neutrons the mass number is \( 6 + 7 = 13 \). The two \( p \) electrons make it a Group IV (Group 4) element.
ElementNumber of neutronsElectronic configurationGroup in the periodic table
\( ^{23}_{11}Na \)12\( 1s^2\,2s^2\,2p^6\,3s^1 \)1
\( ^{4}_{2}He \)2\( 1s^2 \)0
\( ^{13}_{6}C \) (carbon)7\( 1s^2\,2s^2\,2p^2 \)IV (4)

The group number for a main-group element equals the number of electrons in its outermost shell (helium being the exception, placed in Group 0 with the noble gases).

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