The electronic configurations of two elements A and B are 2, 8, 1 and 2, 8, 7respectively. Which one of them is a metal and which is a non-metal?

To determine which element, A or B, is a metal and which is a non-metal based on their electronic configurations, we can analyze their valence electron configurations.

Analysis of Electronic Configurations

1. Element A: The electronic configuration is $2, 8, 1$:

   • This indicates that element A has 1 electron in its outermost shell (valence shell).
   • Elements with 1 valence electron are typically found in Group 1 of the periodic table, known as alkali metals, which are metals.

2. Element B: The electronic configuration is $2, 8, 7$:

   • This indicates that element B has 7 electrons in its outermost shell.
   • Elements with 7 valence electrons are found in Group 17, known as halogens, which are non-metals.

Summary

• Element A is a metal (specifically an alkali metal).
• Element B is a non-metal (specifically a halogen).

Final Answer

• Element A: Metal
• Element B: Non-metal