Junior high school chemistry must memorize knowledge points

The essential knowledge points of junior middle school chemistry are as follows:

1. Molecules are the smallest particles that keep chemical properties. Atoms are the smallest particles in chemical changes.

2. Elements are the general names of the same kind of atoms with the same nuclear charge number (i.e. proton number).

3. The main difference between molecules and atoms is that in chemical reactions, molecules can be separated and atoms cannot be separated.

4. The chemical properties of elements are mainly determined by the outermost electron number of atoms.

5. In an atom, the number of protons = the number of nuclear charges = the number of extranuclear electrons.

6. Relative atomic mass = proton number+neutron number.

7. Magnesium ions and magnesium atoms have the same number of protons or nuclear charges.

8. The most abundant element in the earth's crust is oxygen. The most common metal element is aluminum.

9. The type of determining element is proton number or nuclear charge number.

1. Air is a mixture of several simple substances and several compounds.