📚 AS Chemistry Unit 1: AQA Mark Scheme Guide (Jan 2022) | AS 化学第一单元：AQA 评分方案指南（2022年1月）
This guide follows the style of the AQA AS Chemistry Unit 1 paper from the January 2022 session. It focuses on the definitions, calculations and explanations that gain credit, based on how the mark scheme awards each point.
本指南围绕 AQA AS 化学第一单元试卷（2022年1月考季）的评分思路编写，重点梳理那些在定义题、计算题和解释题中真正拿分的知识点，并按照评分方案的行文方式给出答题要点。
1. Atomic Structure | 原子结构
Atomic number and mass number. Atomic number Z = number of protons = number of electrons in a neutral atom. Mass number A = number of protons + number of neutrons.
原子序数与质量数。原子序数 Z = 质子数 = 中性原子中的电子数；质量数 A = 质子数 + 中子数。
| Particle | Relative charge | Relative mass |
| Proton | +1 | 1 |
| Neutron | 0 | 1 |
| Electron | -1 | 1/1836 |
Isotopes. Isotopes are atoms of the same element with the same number of protons
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