1. Compound 化合物= a chemical substance that consists of two or more elements that together form a molecule.
e.g. Water is a compound of hydrogen and oxygen.
2. Periodic 周期的
E.g. They are usual arranged on a chart called the periodic table.
3. Inert= someone who is inert does nothing when they should be taking action呆滞的， 无效的（化学）
E.g. He is a inert person.
4. Revolve= to turn or spin around a central point
revolve on: The Earth revolves on its axis.
revolve around: The planets revolve around the Sun.
5. axis轴
6. Orbit V.盘旋
N. = the path that is taken by an object moving around a larger object in space
E.g. the planet’s orbit around the sun
in orbit (=moving around a larger object): Space stations are designed to remain in orbit for years.
7. Modify= to change something slightly, especially in order to improve it or to make it less extreme修改
E.g. The repair work involved modifying two of the windows.
