Intellectual demands of learning outcomes in the intended curriculum have always been a concern across the field of science education. In particular, the representation of those learning outcomes stipulated by the intended curriculum in science textbooks has become a big issue for both science curriculum studies and science teaching practice. To address this issue, the concepts of semantic gravity (SG) and semantic density (SD), as part of the dimension of Semantics from Legitimation Code Theory (LCT), were employed in this study with the purpose of examining the degrees of abstraction and complexity of chemical knowledge under the topic “common substances” in four series of chemistry textbooks, which were compiled in compliance with the national chemistry curriculum of the compulsory education (Grades 1–9) in China. Based on the principles of LCT (Semantics), a new scheme for differentiating the strengths of SG and SD was developed in the current study to analyze the representation of 34 knowledge points in the four series of chemistry textbooks. Results show that these knowledge points are embodied with less complexity and avoid more abstraction in the four series of chemistry textbooks. Specifically, it was found that the overwhelming majority of the knowledge points are represented with strong semantic gravity and weak semantic density. Uniqueness was also identified with individual series of chemistry textbooks. The implications of the results of this study are discussed for the effective representation of science (chemistry) knowledge in textbooks.

预期课程中学习成果的智力要求一直是科学教育领域关注的问题。特别是，科学教科书中预期课程规定的学习成果的表征已成为科学课程研究和科学教学实践的一个大问题。为了解决这个问题，本研究采用了语义引力（SG）和语义密度（SD）的概念，作为合法化代码理论（LCT）语义维度的一部分，旨在检验抽象程度和语义密度。根据我国义务教育（一至九年级）国家化学课程编写的四套化学教材中“常见物质”主题下化学知识的复杂性。本研究基于LCT（语义）原理，提出了区分SG和SD优劣的新方案，分析了化学四套教材中34个知识点的表征。结果表明，四套化学教材中这些知识点的体现较为简单，避免了较多的抽象。具体来说，发现绝大多数知识点都是以强语义引力和弱语义密度来表示的。个别系列的化学教科书也具有独特性。讨论了本研究结果对于教科书中科学（化学）知识的有效表述的影响。