molecular atom molecular

1. Invisible to the naked eye 2. There are interactive forces, repulsion and attraction between particles 3. The particles of matter make endless and irregular movements, and the intensity of the movement is related to the temperature. (The higher the temperature, the more intense the exercise)

1. The inside of an atom is very empty, and the nucleus only occupies a very small part. 2. The atomic nucleus concentrates almost all the mass of the atom and the mass of the external electrons is very small and can be ignored. 3. The nucleus is positively charged and the electrons outside the nucleus are negatively charged.

1. Atoms can form molecules or directly form substances (metals) 2. Atoms are the smallest particles in chemical changes

A general term for atoms of the same type with the same nuclear charge (that is, the number of protons)

The sun contains the most hydrogen, followed by helium

Oxygen is the most abundant in the earth's crust, followed by silicon and aluminum

The core of the Earth is mainly composed of iron and nickel

Nitrogen is the most abundant in the air, followed by oxygen

1. Number of protons Number of neutrons = relative atomic mass 2. The mass number of an atom = the number of protons in the atom and the number of neutrons in the atom 3. Number of protons = number of neutrons

(a mixture of two or more substances)

Pure substance (a substance)

Pure substances have precise compositions and thus precise properties; mixtures have no fixed combinations and no definite properties.

The various components in the mixture still retain their properties; they simply mix with each other and do not react.

Purify

Formulas representing the composition of substances using element symbols and numbers

Note: Chemical formulas that can be expressed directly with element symbols include (noble gases, non-metallic solid elements, non-metallic solid elements.)

Macro: 1. Which substance; 2. Express what elements the substance is composed of

Microscopic: 1. The chemical formula of a substance composed of molecules expresses one molecule of the substance; 2. The number of atoms contained in a molecule 3. For a substance composed of atoms, the chemical formula represents one atom of the substance.

Others: 1. Quality of the substance 2. Mass The sum of the relative atomic masses of each atom in the chemical formula 3. If it is the ratio of the number of atoms in the composition of a compound

Definition: The number of atoms gained and lost when atoms of different elements form compounds.

Expression method: The compound price can be divided into positive price and negative price. Negatively charged electrons show a negative valence; missing electrons and a positive charge show a positive valence.

atomic group