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.