Fine: Chapter 5, Problem 47

Problem   On page 218: Classify each of the following species according to charge (neutral, anion, or cation) and state (ground, excited, or impossible):

1. ¹H(1s¹)
2. ¹⁶O(1s²2s²2p⁶)
3. ¹⁴N(1s²2s²2p³)
4. ¹⁹F(1s²2s²2p⁴2d¹)
5. ¹²C(1s²2s²2p³)

Solution   See table 5.7 for the ground states of most elements in the periodic table. If we start with problem (a), lets examine which species is specified. The ¹H means that we have a hydrogen atom with mass 1 (amu). In this problem, the mass is not of importance. The second part, between parentheses, specifies in which state the electron is(are). If we look at table 5.7, we immediately see that this represents the ground state of the hydrogen atom. As the number of electrons is equal to the atomic number of hydrogen (see the first column of table 5.7, or the periodic system in figure 5.13). It is also a neutral atom.

1. As explained above, species ¹H(1s¹) is a neutral hydrogen atom in the ground state.
2. If we compare the species ¹⁶O(1s²2s²2p⁶) with table 5.7, we can conclude that there are 2 electrons more (namely 10) than in a neutral oxygen atom (atomic number 8). Therefore, we have here an anion. As the specified states are the lowest possible, this is the ground state of the O^2- anion. Concluding, this is the ground state of an oxygen anion.
3. The species ¹⁴N(1s²2s²2p³) contains 7 electrons, equal to the atomic number of nitrogen. Therefore, this is a neutral atom. Comparing the species with table 5.7 again, we see that this is the ground state of neutral nitrogen.
4. This fluor species (atomic number 9) ¹⁹F(1s²2s²2p⁴2d¹) has according to the specified states 9 electrons, so it is neutral. However, there is a problem with the electronic configuration. For n = 2, l £ n-1 or l £ 1, see table 5.6 on page 197, so a 2d state can not exist. Concluding, this is a neutral but impossible species.
5. Species ¹²C(1s²2s²2p³) has 7 electrons, which is 1 more than a neutral carbon atom has, so this is an anion. As with the nitrogen before, the electron states occupied are the lowest possible. Therefore, what we have here is a carbon anion in its ground state.