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Atoms in the second period (row) of the periodic table, such as beryllium (Be) and boron (B), sometimes have fewer than 8 electrons around them. For example, beryllium typically forms compounds where it has only 4 electrons around it, like in BeCl2.
Atoms in the third period and beyond of the periodic table, such as sulfur (S), phosphorus (P), and chlorine (Cl), can have more than 8 electrons around them. This is because these atoms have d orbitals available for bonding. For example, sulfur can have 10 electrons around it in SF6, phosphorus can have 10 electrons in PF5, and chlorine can have 12 electrons in ClF3.
Odd-electron species are generally very reactive and uncommon because having an unpaired electron makes the molecule or ion highly reactive, seeking to pair up the unpaired electron through chemical reactions. This instability makes odd-electron species less common in nature. An example of an odd-electron molecule is the nitric oxide molecule (NO).
Correct answer: Atoms in the second period (row) of the periodic table sometimes have fewer than 8 electrons around them, and atoms in the third period and beyond can have more than 8 electrons around them. Odd-electron species are generally very reactive and uncommon due to their high reactivity.
