本专题涉及元素符号的书写及意义;化学式的概念、意义、书写原则及步骤;元素的化合价;根据化学式的计算等内容。这些内容是九年级化学上册的重要内容。搞好本专题的学习,不仅能对已学过的物质结构方面的知识理解得更加深刻,而且还能为后续内容的学习打下厚实的基础。学习本专题时,需要做到以下几点: This topic relates to the writing and meaning of the element symbols; the concept, meaning, writing principles and steps of the chemical formula; the valence of the element; the calculation according to the chemical formula and so on. These content is an important part of the ninth grade chemistry. Doing well the study of this topic can not only deepen the understanding of the knowledge of the material structure that has been learned, but also lay a solid foundation for the study of the follow-up content. When you study this topic, you need to do the following: