化学元素 (huàxué yuánsù) - chemical elements: These are the fundamental substances that cannot be broken down into simpler forms by ordinary chemical reactions.
周期表 (zhōuqī biǎo) - periodic table: It is a tabular arrangement of chemical elements that organizes them based on their atomic number, electron configuration, and recurring chemical properties.
元素周期律 (yuánsù zhōuqī lǜ) - periodic law of elements: This law states that when the chemical elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties.