oltre什么牌子 3.3: Parts of the Atom and Ions

Learning Objectives Know the charges and locations within an atom of protons, neutrons, and electrons.

Although atoms are very tiny, they consist of even smaller particles. Mendeleev never actually believed in these tiny particles that younger scientists were beginning to observe towards the end of his life. But as it turns out, these very particles were the very reason why the Periodic Law was even true!

Three main types of particles that make up all atoms are:

protons, which he a positive electric charge and a large mass. electrons, which he a negative electric charge and a small mass. neutrons, which are neutral in electric charge and a large mass.

The model in the figure is a representation of how these particles are arranged in an atom. (Note: there are some inaccuracies in this model, particularly related to the position of the electrons. We will learn more about what the electrons are doing later in this chapter.) The particular atom represented by the model is helium, but the particles of all atoms are arranged in a similar way. At the center of the atom is a dense area called the nucleus, where all the protons and neutrons are clustered closely together. The electrons constantly move around the nucleus. Helium has two protons and two neutrons in its nucleus and two electrons moving around the nucleus. Atoms of other elements he different numbers of subatomic particles, but the number of protons always equals the number of electrons. This makes atoms neutral in charge because the positive and negative charges "cancel out." We will explore the atomic nucleus in greater detail later in this text. But it turns out it is the electrons that are of the greatest interest in terms of explaining the periodic law, as we shall see in the next section.

There are many ways to discuss the parts of the atom and the relationship of the parts of the atom to properties we can observe in elements. For now we will introduce one of those that was discussed earlier in this chapter: the atomic number. The atomic number is simply the number of protons that are present in an atom. As we look at the periodic table, which is arranged by atomic numbers, we can see that it is organized based on the increasing number of protons.

Figure \(\PageIndex{1}\): Model of a helium atom. (Credit: CK-12 Foundation; Source: CK-12 Foundation; License: CK-12 Curriculum Materials license) Section Summary Three main types of particles that make up all atoms are protons, neutrons, and electrons. Protons he a positive charge, electrons he a negative charge, and neutrons he no charge. Protons and neutrons are located in the nucleus of an atom, and electrons are located outside of the nucleus. The atomic number is the number of protons in an atom of an element. Glossary atomic number the number of protons in an atom. electron negatively charged, subatomic particle of relatively low mass located outside the atomic nucleus neutron uncharged, subatomic particle located in the atomic nucleus nucleus massive, positively charged center of an atom made up of protons and neutrons proton positively charged, subatomic particle located in the atomic nucleus