认识物质的物理性质和化学性质是学习元素及其化合物的基本方法。物理性质,从物质的颜色、气味、味道、状态、密度、熔点、沸点、水溶性等加以了解;化学性质,是根据物质在一定条件下发生化学反应,了解反应规律。元素及其化合物知识的复习应围绕这两方面并加以归纳和分类,能收到较好的复习效果。一、氧气和氢气的复习 Understanding the physical and chemical properties of matter is a fundamental way to learn about elements and their compounds. Physical properties, from the material color, smell, taste, state, density, melting point, boiling point, water solubility and so on to understand; chemical properties, is based on material under certain conditions chemical reaction, understand the reaction law. Review of knowledge of elements and their compounds should focus on these two aspects and be summarized and classified, can receive a better review results. First, the oxygen and hydrogen review