An atom of element X has one more shell of electrons than an atom of beryllium, but it has one less valence electron than beryllium. Which element is element X?
sodium (Na)
boron (B)
magnesium (Mg)
lithium (Li)
The element X in this case would be boron (B).
Beryllium (Be) has 4 electrons and 2 valence electrons, while boron (B) has 5 electrons and 3 valence electrons. Therefore, element X, which has one more shell of electrons than beryllium but one less valence electron, is boron (B).
To determine which element X is, let's compare the given information with the electron configuration of each element:
- Beryllium (Be) has an electron configuration of 1s² 2s². It has 2 shells and 2 valence electrons.
- Sodium (Na) has an electron configuration of 1s² 2s² 2p⁶ 3s¹. It has 3 shells and 1 valence electron.
- Boron (B) has an electron configuration of 1s² 2s² 2p¹. It has 2 shells and 3 valence electrons.
- Magnesium (Mg) has an electron configuration of 1s² 2s² 2p⁶ 3s². It has 3 shells and 2 valence electrons.
- Lithium (Li) has an electron configuration of 1s² 2s¹. It has 2 shells and 1 valence electron.
From the given information, element X has one more shell of electrons than beryllium but one less valence electron.
Based on this, the only element that satisfies both conditions is Boron (B). Therefore, element X is Boron (B).