Learning Objectives Describe the locations, charges, and masses of the three main subatomic particles. Determine the number of protons and electrons in an atom. Define atomic mass unit amu. Electrons Electrons are one of three main types of particles that make up atoms.
If an electron was the mass of a penny, a proton or a neutron would have the mass of a large bowling ball! Protons A proton is one of three main particles that make up the atom. Neutrons Atoms of all elements—except for most atoms of hydrogen—have neutrons in their nucleus. Summary Electrons are a type of subatomic particle with a negative charge. Protons are a type of subatomic particle with a positive charge. Protons are bound together in an atom's nucleus as a result of the strong nuclear force.
Neutrons are a type of subatomic particle with no charge they are neutral. Like protons, neutrons are bound into the atom's nucleus as a result of the strong nuclear force. Protons and neutrons have approximately the same mass, but they are both much more massive than electrons approximately 2, times as massive as an electron.
The positive charge on a proton is equal in magnitude to the negative charge on an electron. As a result, a neutral atom must have an equal number of protons and electrons. For most of the 16 lightest elements up to oxygen the number of neutrons is equal to the number of protons. For most of the remaining elements, there are more neutrons than protons, because extra neutrons are needed to keep the nucleus together by overcoming the mutual repulsion of the increasing numbers of protons concentrated in a very small space.
For example, silicon has 14 protons and 14 neutrons. Its atomic number is 14 and its atomic mass is The most common isotope of uranium has 92 protons and neutrons.
The dot in the middle is the nucleus, and the surrounding cloud represents where the two electrons might be at any time. The darker the shade, the more likely that an electron will be there.
Both are gasses, but hydrogen gas is violently explosive, whereas helium gas is completely inert and cannot be made to undergo any kind of chemical reactions under normal circumstances. Atoms of hydrogen have a single proton in their center and a single electron in the lowest energy level. Helium atoms, on the other hand, have two protons and two electrons in the lowest energy level. The lowest energy level is filled with its maximum number of electrons.
This is a very stable arrangement, and helium in consequence is an inert gas with few chemical properties. Hydrogen only has one electron in its lowest energy level. This is a very unstable arrangement, and hydrogen gas undergoes a variety of reactions so as to reach a stable electron configuration where its energy level is either empty of electrons, or filled with electrons.
Atoms are at their most stable when their outermost energy level is either empty of electrons or filled with electrons. Sodium atoms have 11 electrons. Two of these are in the lowest energy level, eight are in the second energy level and then one electron is in the third energy level. This is a very unstable arrangement, and the element sodium is a highly reactive, deadly white semi-solid that will burst into flames on exposure to the air or will burn through human flesh on contact.
The nucleus of most hydrogen atoms is composed of just 1 proton. A small percentage of hydrogen atoms have 1 or even 2 neutrons. Atoms of the same element with different numbers of neutrons are called isotopes.
These will be discussed in Lesson 2. What zooms around the nucleus of an atom? Electrons Which one has a positive charge, a negative charge, and no charge? Proton—positive; electron—negative; neutron—no charge. The charge on the proton and electron are exactly the same size but opposite. The same number of protons and electrons exactly cancel one another in a neutral atom. Show animations and explain that protons and electrons have opposite charges and attract each other. Project the animation Hydrogen Atom.
Give each student an activity sheet. Explore Do an activity to show that electrons and protons attract each other. Question to investigate What makes objects attract or repel each other? Materials for each group Plastic grocery bag Scissors Procedure, part 1 Charged plastic and charged skin Cut 2 strips from a plastic grocery bag so that each is about 2—4 cm wide and about 20 cm long. Quickly pull your top hand up so that the plastic strip runs through your fingers.
Do this three or four times. Allow the strip to hang down. Then bring your other hand near it. Expected results The plastic will be attracted to your hand and move toward it. Explain Show students models comparing the number of protons and electrons in the plastic and skin before and after rubbing them together. Explore Have students investigate what happens when a rubbed plastic strip is held near a desk or chair.
Procedure, part 2 Charged plastic and neutral desk Charge one strip of plastic the same way you did previously. This time, bring the plastic strip toward your desk or chair.
Expected results The plastic moves toward the desk. Have students charge two pieces of plastic and hold them near each other to see if electrons repel one other. Ask students to make a prediction: What do you think will happen if you charge two strips of plastic and bring them near each other? Procedure, part 3 2 pieces of charged plastic Charge two strips of plastic Slowly bring the two strips of plastic near each other.
Expected results The strips will move away or repel each other. Ask students: What happened when you brought the two pieces of plastic near each other? The ends of the strips moved away from each other.
Use what you know about electrons and charges to explain why this happens. Each strip has extra electrons so they are both negatively charged. Because like charges repel, the pieces of plastic repelled each other.
Explore Have students apply their understanding of protons and electrons to explain what happens when a charged balloon is brought near pieces of paper. Materials for each group Inflated balloon Small pieces of paper, confetti-size Procedure Rub a balloon on your hair or clothes. Bring the balloon slowly toward small pieces of paper. Expected results The pieces of paper will jump up and stick on the balloon.
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