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The radius of an electron's orbit in a hydrogen atom is 0.8464 nm. What is the speed of the electron in this orbit (in m/s)?

1. 5.47 × 10⁵
2. 6.37 × 10⁵
3. 3.42 × 10⁵
4. 8.32 × 10⁵

Correct answer: 5.47 × 10⁵

Solution

n² = r / a0 = 0.8464 / 0.0529 = 16, so n = 4. Speed v4 = (2.18 × 10⁶) / 4 = 5.45 × 10⁵ m/s ≈ 5.47 × 10⁵ m/s.

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