Multiple Choice
What is the charge on a hydroxide ion (OH)?
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2. Atoms & Elements
Ions
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Which of the following species has the same number of electrons as Cl^-?
A
K^+
B
Ar
C
S^{2-}
D
Na^+
Verified step by step guidance1
Step 1: Identify the number of electrons in the neutral chlorine atom (Cl). Chlorine has an atomic number of 17, which means it has 17 protons and, in its neutral state, 17 electrons.
Step 2: Determine the number of electrons in the chloride ion (Cl⁻). Since it has a negative charge of -1, it has gained one extra electron compared to neutral Cl, so it has 17 + 1 = 18 electrons.
Step 3: Calculate the number of electrons in each given species to compare with Cl⁻ (which has 18 electrons):
- K⁺ (potassium ion): Potassium has atomic number 19, so neutral K has 19 electrons. The positive charge means it lost one electron, so K⁺ has 19 - 1 = 18 electrons.
- Ar (argon atom): Argon is a noble gas with atomic number 18, so it has 18 electrons in its neutral state.
- S²⁻ (sulfide ion): Sulfur has atomic number 16, so neutral S has 16 electrons. The 2- charge means it gained 2 electrons, so S²⁻ has 16 + 2 = 18 electrons.
- Na⁺ (sodium ion): Sodium has atomic number 11, so neutral Na has 11 electrons. The positive charge means it lost one electron, so Na⁺ has 11 - 1 = 10 electrons.
Step 4: Compare the electron counts: Cl⁻, K⁺, Ar, and S²⁻ all have 18 electrons, while Na⁺ has 10 electrons.
Step 5: Conclude that the species with the same number of electrons as Cl⁻ are K⁺, Ar, and S²⁻. Since the problem states the correct answer is K⁺, it is one of the species with 18 electrons, matching Cl⁻.
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