Question

Choose the element having two valence electrons, from the following elements- Chlorine, Helium, Phosphorus, Magnesium, Cesium.

Answer 1

• Helium belongs to Group 18 and period 2, its atomic number is 2, so it has 2 valence electrons.
• Chlorine belongs to group 17. That means it has 7 (17-10) valence electrons. The electronic configuration of Chlorine is (2,8,7).
• Phosphorus belongs to group 15. That means it has 5 valence electrons. The electronic configuration of Phosphorus is (2,8,5).
• Magnesium belongs to group 2. That means it has 2 valence electrons. The electronic configuration of Magnesium is (2,8,2).
• Cesium belongs to group 1. That means it has 1 valence electron.
• Hence, both Helium and Magnesium have 2 valence electrons.