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. Ask students: What did you observe when the charged balloon was held near the pieces of paper?
The paper pieces moved up and stuck on the balloon. Use what you know about electrons, protons, and charges to explain why this happens.
When you rub the balloon on your hair or clothes it picks up extra electrons, giving the balloon a negative charge. When you bring the balloon near the paper, the electrons from the balloon repel the electrons in the paper. Since more protons are at the surface of the paper, it has a positive change. The electrons are still on the paper, just not at the surface, so overall the paper is neutral. Opposites attract, so the paper moves up toward the balloon. Extra Extend Demonstrate how electrons can attract a stream of water.
Materials for the demonstration Sink Balloon Procedure Rub a balloon on your shirt or pants to give it a static charge. Turn on the faucet so that there is a very thin stream of water. Slowly bring the charged part of the balloon close to the stream of water. Expected results The stream of water should bend as it is attracted to the balloon. Ask students: What did you observe when the charged balloon was held near the stream of water?
The stream of water bent toward the balloon. The darker the shade, the more likely that an electron will be there. A femtometre fm is 10 m. Subsequent shells can hold more electrons, but the outermost shell of any atom holds no more than eight electrons. The electrons in the outermost shell play an important role in bonding between atoms. Elements that have a full outer shell are inert in that they do not react with other elements to form compounds.
They all appear in the far-right column of the periodic table: helium, neon, argon, etc. For elements that do not have a full outer shell, the outermost electrons can interact with the outermost electrons of nearby atoms to create chemical bonds. The electron shell configurations for 29 of the first 36 elements are listed in Table 2. Figure 2. Skip to content Chapter 2 Minerals. It took , years for the universe to cool enough to slow down the electrons so that the nuclei could capture them to form the first atoms.
The earliest atoms were primarily hydrogen and helium , which are still the most abundant elements in the universe, according to Jefferson Lab. Gravity eventually caused clouds of gas to coalesce and form stars, and heavier atoms were and still are created within the stars and sent throughout the universe when the star exploded supernova.
Protons and neutrons are heavier than electrons and reside in the nucleus at the center of the atom. Electrons are extremely lightweight and exist in a cloud orbiting the nucleus. The electron cloud has a radius 10, times greater than the nucleus, according to the Los Alamos National Laboratory. Protons and neutrons have approximately the same mass. However, one proton is about 1, times more massive than an electron.
Atoms always have an equal number of protons and electrons, and the number of protons and neutrons is usually the same as well. Adding a proton to an atom makes a new element, while adding a neutron makes an isotope, or heavier version, of that atom. The nucleus was discovered in by Ernest Rutherford, a physicist from New Zealand. In , Rutherford proposed the name proton for the positively charged particles of the atom. He also theorized that there was a neutral particle within the nucleus, which James Chadwick, a British physicist and student of Rutherford's, was able to confirm in Virtually all the mass of an atom resides in its nucleus, according to Chemistry LibreTexts.
The protons and neutrons that make up the nucleus are approximately the same mass the proton is slightly less and have the same angular momentum, or spin. The nucleus is held together by the strong force , one of the four basic forces in nature.
This force between the protons and neutrons overcomes the repulsive electrical force that would otherwise push the protons apart, according to the rules of electricity. Some atomic nuclei are unstable because the binding force varies for different atoms based on the size of the nucleus. These atoms will then decay into other elements, such as carbon decaying into nitrogen Protons are positively charged particles found within atomic nuclei.
Rutherford discovered them in experiments with cathode-ray tubes that were conducted between and Protons are about The number of protons in an atom is unique to each element.
For example, carbon atoms have six protons, hydrogen atoms have one and oxygen atoms have eight. The number of protons in an atom is referred to as the atomic number of that element.
0コメント