They already know that every object in nature as well as man-made is made of one substance or another. So where do substances come from? That question was asked thousands of years ago, today, science has a clear answer: It is the Atom.

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So what is an atom? The nucleus of an atom is made up of what particles? What is Electron class? We will find out through the article below.

I. What is an atom?

• Atoms are extremely small and electrically neutral particles.

• Atoms include:

– The nucleus has a positive charge

The shell is made up of one or more negatively charged electrons.

Electron symbol is e, negative charge (-), very small size 10-8cm.

II. Nuclear

• The nucleus of an atom is made up of protons and neutrons.

– Proton: The symbol is p with a positive charge (+).

– Neutron Particle: Symbol is n without charge.

• Atoms of the same type that have the same number of protons in the nucleus

• In an atom: number of p = number of e

– Protons and neutrons have the same mass, while electrons have a very small mass (only 0.0005 times the mass of a proton), insignificant. So the mass of the nucleus is considered as the atomic mass.

III. Electron class

– In an atom, electrons move very quickly around the nucleus and are arranged in layers, each layer has a certain number of electrons.

Number of electron shells of an atom:

H2: 1 (1e) → the outermost 1e

O2: 8 (1e) → outermost 6e

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Na: 3 (1e) → the outermost 1e

– The maximum number of electrons in shell 1 is 2e; in 2nd grade is 8e.

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IV. Atomic Exercises

* Lesson 1 (page 15 of class 8): Copy the following sentences into your workbook with all the appropriate words or phrases.

“…..is an extremely small, electrically neutral particle: from ….. creates all substances. The atom is composed of . . . has a positive charge and a shell made of . . . ”

° Solution to lesson 1, page 15, textbook of course 8:

“The atom is an extremely small, electrically neutral particle: from the atom all substances are made. An atom consists of a positively charged nucleus and a shell made up of one or more negatively charged electrons.

* Lesson 2 (page 15 sgk vol 8): a) Atoms are made up of three smaller particles, which are they?

b) Name, symbol and charge of charged particles?

c) Which atoms of the same type have the same number of particles in the nucleus?

° Solution for lesson 2, page 15, textbook of course 8:

a) Atoms are made up of three smaller types: protons, electrons, and neutrons.

b) Names, symbols, and charges of charged particles

Name Proton Electron Symbol p e Charge +1 -1

c) Atoms of the same type have the same number of protons in the nucleus.

* Lesson 3 (page 15 sgk course 8): Why is it said that the mass of the nucleus is considered the mass of an atom?

° Solution of lesson 3, page 15, textbook of course 8:

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– Atomic mass includes the mass of the nucleus and the mass of electrons, but the mass of electrons is too small (insignificant) compared to the mass of the nucleus, so it can be ignored. Therefore, the nuclear mass can be considered as the atomic mass.

* Lesson 4 (page 15 sgk 8): In an atom, how do electrons move and arrange? Take an example with an oxygen atom.

° Solution of lesson 4, page 15, textbook of course 8:

– Electrons are always moving quickly around the nucleus and arranged in layers.

– Example: An oxygen atom has 8 electrons divided into two shells, the inner shell has 2 and the outer shell has 6 electrons.

* Lesson 5 (page 15 of the 8th textbook): Give the diagrams of some of the following atoms:

Show: The number of p in the nucleus, the number of electrons in the atom, the number of electron shells, and the number of electrons in the outermost shell of each atom.

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° Solution of lesson 5, page 15, textbook of course 8:

Atom Number of p in the nucleus Number of electrons in the atom Number of electrons in the outermost shell He 2 2 2 1 C 6 6 4 2 Al 13 13 3 3 Ca 20 20 2 4

Hopefully, the article about atoms, the structure of the atomic nucleus and the electron shell above will help you better understand, good luck with your studies.