Electrons do not stay in excited states for very long - they soon return to their ground states, emitting a photon with the same energy as the one that was absorbed. Transitions among the various orbitals are unique for each element because the energy levels are uniquely determined by the protons and neutrons in the nucleus.
When the electrons of a certain atom return to lower orbitals from excited states, the photons they emit have energies that are characteristic of that kind of atom. This gives each element a unique fingerprint, making it possible to identify the elements present in a container of gas, or even a star. Astronomer's Toolbox. Understanding the Atom The nucleus of an atom is surround by electrons that occupy shells, or orbitals of varying energy levels.
The overall shell shape will also be more complex because of the suborbitals as you have more electrons. Creating Bonds Electrons play a major role in all chemical bonds. There is one type of bonding called electrovalent bonding ionic , where an electron from one atom is transferred to another atom. You wind up creating two ions as one atom loses an electron and one gains one. The second type of bonding is called covalent bonding, where electrons are actually shared between two or more atoms in a cloud.
Both types of bonds have specific advantages and weaknesses. Power Up! Electrons are very important in the world of electronics. The very small particles can stream through wires and circuits, creating currents of electricity.
Students will also be able to explain that the attraction between positive protons and negative electrons holds an atom together. Download the student activity sheet , and distribute one per student when specified in the activity. Students should be familiar with the parts of the atom from Chapter 3 but reviewing the main points is probably a good idea. Note : The picture shows a simple model of the carbon atom.
It illustrates some basic information like the number of protons and neutrons in the nucleus. It also shows that the number of electrons is the same as the number of protons. This model also shows that some electrons can be close to the nucleus and others are further away. One problem with this model is that it suggests that electrons orbit around the nucleus in perfect circles on the same plane, but this is not true.
Students will be introduced to these ideas in a bit more detail in Lesson 3. But for most of our study of chemistry at the middle school level, the model shown in the illustration will be very useful. Also, for most of our uses of this atom model, the nucleus will be shown as a dot in the center of the atom.
Project the animation Protons and Electrons. Explain to students that two protons repel each other and that two electrons repel each other. But a proton and an electron attract each other. Since opposite charges attract each other, the negatively charged electrons are attracted to the positively charged protons. Tell students that this attraction is what holds the atom together.
Explain to students that in a hydrogen atom, the negatively charged electron is attracted to the positively charged proton. This attraction is what holds the atom together. Tell students that hydrogen is the simplest atom. It has only 1 proton, 1 electron, and 0 neutrons. It is the only atom that does not have any neutrons. Explain that this is a simple model that shows an electron going around the nucleus. It shows the electron in the space surrounding the nucleus that is called an electron cloud or energy level.
It is not possible to know the location of an electron but only the region where it is most likely to be. The electron cloud or energy level shows the region surrounding the nucleus where the electron is most likely to be.
This is a great question. This force is much stronger than the force of repulsion of one proton from another. Again, a detailed answer to this question is beyond the scope of middle school chemistry. But a simplified answer has to do with the energy or speed of the electron.
As the electron gets closer to the nucleus, its energy and speed increases. It ends up moving in a region surrounding the nucleus at a speed that is great enough to balance the attraction that is pulling it in, so the electron does not crash into the nucleus. Have students answer questions about the illustration on the activity sheet. Students will record their observations and answer questions about the activity on the activity sheet.
Students can see evidence of the charges of protons and electrons by doing an activity with static electricity. Note : When two materials are rubbed together in a static electricity activity, one material tends to lose electrons while the other material tends to gain electron. In this activity, human skin tends to lose electrons while the plastic bag, made of polyethylene, tends to gain electrons.
Hold the plastic strip firmly at one end. Then grasp the plastic strip between the thumb and fingers of your other hand as shown. The plastic will be attracted to your hand and move toward it. Students may notice that the plastic is also attracted to their arms and sleeves. Let students know that later in this lesson they will investigate why the plastic strip is also attracted to surfaces that have not been charged neutral.
Note : If students find that their plastic strip does not move toward their hand, it must not have been charged well enough. Have them try charging their plastic strip by holding it down on their pants or shirt and then quickly pulling it with the other hand. Then they should test to see if the plastic is attracted to their clothes. If not, students should try charging the plastic again. Tell students that the plastic strip and their skin are made of molecules that are made of atoms.
Tell students to assume that the plastic and their skin are neutral—that they have the same number of protons as electrons. Project the image Charged plastic and hand. Point out that before the students pulled the plastic between their fingers, the number of protons and electrons in each is the same. Then, when students pulled the plastic through their fingers, electrons from their skin got onto the plastic.
Since the plastic has more electrons than protons, it has a negative charge.
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