To determine the atomic number of the element with the electronic configuration 2, 8, 7, we can start by adding up the number of electrons in each shell. The configuration indicates that there are 2 electrons in the first shell, 8 in the second, and 7 in the third. This gives us a total of:
- 2 (first shell) + 8 (second shell) + 7 (third shell) = 17 electrons
Since the atomic number of an element is equal to the number of protons, and in a neutral atom, the number of protons equals the number of electrons, the atomic number of this element is 17.
Identifying Chemical Similarity
Next, let’s look at which element this configuration would be chemically similar to among the options provided: N (7), F (9), P (15), and Ar (18). To do this, we should consider the position of the element in the periodic table and its valence electrons.
The element with an atomic number of 17 is chlorine (Cl). Chlorine is located in Group 17 (the halogens) of the periodic table, which means it has 7 valence electrons. Elements in the same group typically exhibit similar chemical properties because they have the same number of electrons in their outer shell.
Comparing the Options
- N (7): Has 5 valence electrons (Group 15)
- F (9): Has 7 valence electrons (Group 17)
- P (15): Has 5 valence electrons (Group 15)
- Ar (18): Has 8 valence electrons (Group 18)
Among these options, fluorine (F) is the only element that shares the same number of valence electrons as chlorine, which is 7. Therefore, chlorine would be chemically similar to fluorine.
Summary
In summary, the atomic number of the element with the electronic configuration 2, 8, 7 is 17, corresponding to chlorine. This element is chemically similar to fluorine, as both belong to the same group in the periodic table and have similar valence electron configurations.
