Chapter 5: Periodic Classifications of Elements

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Periodic Classifications of Elements


An atom has electronic configuration 2, 8, 7:

(a) What is the atomic number of this element?

(b) To which of the following elements would it be chemically similar? (Atomic numbers are given in parentheses.)

N (7), F (9), P (15), Ar (18)


(a)- The atomic number is the number of protons present in the nucleus of an atom. The number of protons is equal to the number of electrons in a neutral atom. The electronic configuration of an atom is (2, 8, 7). This means that the atom contains 17 electrons. So, it contains 17 protons and its atomic number should be 17.

(b)- The electronic configuration of an atom is (2, 8, 7). It means that the given atom has 7 valence electrons and it needs one electron to complete its octet. This element will show a similar chemical property with the element that has 7 valence electrons.

The electronic configuration of given elements:

1. N (7): (2, 5)             {5 valance electrons}

2. F (9): (2, 7)              {7 valance electrons}

3. P (15): (2, 8, 5)        {5 valance electrons}

4. Ar (18): (2, 8, 8)        {8 valance electrons}

Thus, F(9) will show similar chemical properties with the given element.

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