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Chapter 2 — chapter 2
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📘Easy summary
In 1913 Moseley bombarded different elements with cathode rays and found that the square root of the frequency of the X-rays produced is directly proportional to the nuclear charge (√ν ∝ Z). The atomic number (proton number, Z) is the number of protons in the nucleus and is the identity of an element. The nucleon (mass) number A is the total number of protons and neutrons. Neutrons N = A − Z. In a neutral atom electrons = protons; an ion of charge −1 has one extra electron. Isotopes have the same Z but different A.
⭐Key points
- Z = protons = identity.
- A = protons + neutrons.
- √ν ∝ Z (Moseley).
🔬Diagram
🌿Real-life example
³⁵₁₇Cl: 17 p, 18 n, 17 e; Cl⁻: 17 p, 18 n, 18 e.
💡Exam tip
- Practise p, n, e for ions.
✅Quick check
1. Atomic number is also called:
2. Neutrons in ³⁵₁₇Cl:
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