To determine the number of valence electrons in chloride ions (Cl⁻), we need to consider the electron configuration of a chlorine atom (Cl) and account for the extra electron gained when it becomes an ion.
The electron configuration of a chlorine atom is [Ne] 3s² 3p⁵, indicating that chlorine has 7 valence electrons in its outermost energy level.
When chlorine gains an electron to become a chloride ion (Cl⁻), it achieves a stable noble gas configuration, which is the electron configuration of argon (Ar) [Ne] 3s² 3p⁶. In this configuration, the outermost energy level is filled with 8 electrons.
To find the number of valence electrons in 8.5 grams of chloride ions, we need to convert the given mass to moles using the molar mass of chloride ions.
The molar mass of chloride ions (Cl⁻) is the molar mass of chlorine (Cl) plus the molar mass of one additional electron. The molar mass of chlorine is approximately 35.45 g/mol, and the molar mass of an electron is negligible (0.00054858 g/mol).
Thus, the molar mass of chloride ions is approximately 35.45 + 0.00054858 = 35.45054858 g/mol.
Using the molar mass, we can calculate the number of moles:
Number of moles = Mass / Molar mass = 8.5 g / 35.45054858 g/mol ≈ 0.2397 mol
Since each chloride ion (Cl⁻) has 8 valence electrons, we can calculate the number of valence electrons in 0.2397 moles of chloride ions:
Number of valence electrons = Number of moles × Number of valence electrons per ion = 0.2397 mol × 8 electrons/mol ≈ 1.9176 electrons
Since we cannot have fractional valence electrons, the number of valence electrons in 8.5 grams of chloride ions would be 2 (rounded to the nearest whole number).