Question 15 of 48beginner🧠 RememberVery Short1 mark

Write the atomic number of the element present in the third period and seventeenth group of the periodic table.

Correct Answer

17

Exercise: EXERCISES | Q: 3.6 | (Page 23)
For More Understanding

Explanation

The third period begins at sodium (Z=11) and contains 8 elements up to argon (Z=18). The seventeenth group corresponds to the halogen family, which has 7 valence electrons. In the third period, the element with 7 valence electrons (configuration 3s23p53s^2 3p^5) is chlorine, which has an atomic number of 17.

Solution Steps

  1. Step 1: Identify the range of the third period. The third period begins at sodium (Z=11Z=11) and ends at argon (Z=18Z=18).

  2. Step 2: Identify the group. Group 17 is the halogen family, which requires 7 valence electrons.

  3. Step 3: Determine the element in the third period with 7 valence electrons. Sodium (11) has 1, so the 7th element in the period is 11+7−1=1711 + 7 - 1 = 17. Thus, the atomic number is 17.

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