1.2.2Additional lessons
Subatomic Particles — IB Chemistry HL Revision Notes & Topical Questions
5 min read 4 parts Lesson 5 of 172
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Part 1 of 4Three Subatomic Particles
Atoms consist of protons and neutrons in the nucleus, with electrons outside it.
Proton
- Proton Relative mass 1 and relative charge +1; the number of protons defines the element.
Neutron
- Neutron Relative mass 1 and no charge; neutrons add mass and help stabilise the nucleus.
Electron
- Electron Relative mass about 1/1836 of a proton and relative charge −1;
- electrons are found in energy levels around the nucleus.
Neutral atom
- Neutral atom The number of electrons equals the number of protons, so the charges cancel.
| Particle | Relative mass | Relative charge | Location |
|---|---|---|---|
| Proton | 1 | +1 | Nucleus |
| Neutron | 1 | 0 | Nucleus |
| Electron | 5.4 × 10⁻⁴ | −1 | Outside nucleus |
Part 2 of 4Nuclide Notation
Nuclide Notation
Atomic number Z
- Atomic number Z The number of protons in the nucleus, written at the lower left of the symbol.
Mass number A
- Mass number A The total number of protons and neutrons, written at the upper left.
Neutrons
- Neutrons Number of neutrons = A − Z.
Example
- Example ²³₁₁Na has 11 protons, 12 neutrons and, as a neutral atom, 11 electrons.
Part 3 of 4Ions
Ions form when atoms gain or lose electrons, while the nucleus stays the same.
1
Metal atoms tend to lose electrons, forming positive ions called cations with fewer electrons than protons.
2
Non-metal atoms tend to gain electrons, forming negative ions called anions with more electrons than protons.
3
The charge on an ion equals the number of protons minus the number of electrons.
4
For ²⁷₁₃Al³⁺ there are 13 protons, 14 neutrons and 10 electrons.
5
Ions of different elements can have the same number of electrons, for example Na⁺, Mg²⁺ and O²⁻ each have 10.
Part 4 of 4Exam Checklist & Tips
1.2.2 – Key Points for the Exam
- Atomic number The number of protons in the nucleus of an atom.
- Mass number The total number of protons and neutrons in a nucleus.
- Cation A positively charged ion formed by loss of electrons.
- Anion A negatively charged ion formed by gain of electrons.
Common Mistakes
- Using the mass number as the number of neutrons instead of subtracting the atomic number.
- Changing the number of protons when an ion forms.
- Giving an electron the same mass as a proton.
- Forgetting to subtract electrons from the number of protons when finding ionic charge.
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