Date Assigned: Monday, Feb 22, 2016 CK12 assignments--> unit 2 scientists and organization of atoms--> electrons -->practice --> answer review questions only assignments--> unit 2 scientists and organization of atoms--> protons -->practice --> answer review questions only assignments--> unit 2 scientists and organization of atoms--> neutrons -->practice --> answer review questions only Electrons (review questions only) Defining characteristics of negatively charged subatomic particles and their role in atomic structure · Describe electrons. · Explain where electrons are found in atoms. · Describe energy levels in atoms.
 Watch out! Lightning is extremely dangerous. A single bolt of lightning can carry a billion volts of electricity. That’s enough energy to light a 100-watt light bulb—for three months! As impressive as it is, lightning is nothing more than a sudden flow of extremely tiny particles. What are the particles that flow in a lightning bolt? The answer is electrons. What Are Electrons? Electrons are one of three main types of particles that make up atoms. The other two types are protons and neutrons. Unlike protons and neutrons, which consist of smaller, simpler particles, electrons are fundamental particles that do not consist of smaller particles. They are a type of fundamental particles called leptons. All leptons have an electric charge of -1 or 0. For an excellent video about electrons and other fundamental particles in atoms, go to this URL: http://www.youtube.com/watch?v=Vi91qyjuknM (7:44) Properties of Electrons Electrons are extremely small. The mass of an electron is only about 1/2000 the mass of a proton or neutron, so electrons contribute virtually nothing to the total mass of an atom. Electrons have an electric charge of -1, which is equal but opposite to the charge of proton, which is +1. All atoms have the same number of electrons as protons, so the positive and negative charges “cancel out,” making atoms electrically neutral. Where Are Electrons? Unlike protons and neutrons, which are located inside the nucleus at the center of the atom, electrons are found outside the nucleus. Because opposite electric charges attract each other, negative electrons are attracted to the positive nucleus. This force of attraction keeps electrons constantly moving through the otherwise empty space around the nucleus. The Figure below is a common way to represent the structure of an atom. It shows the electron as a particle orbiting the nucleus, similar to the way that planets orbit the sun.
Orbitals The atomic model in the Figure above is useful for some purposes, but it’s too simple when it comes to the location of electrons. In reality, it’s impossible to say what path an electron will follow. Instead, it’s only possible to describe the chances of finding an electron in a certain region around the nucleus. The region where an electron is most likely to be is called an orbital. Each orbital can have at most two electrons. Some orbitals, called S orbitals, are shaped like spheres, with the nucleus in the center. An S orbital is pictured in Figure below. Where the dots are denser, the chance of finding an electron is greater. Also pictured in Figurebelow is a P orbital. P orbitals are shaped like dumbbells, with the nucleus in the pinched part of the dumbbell. You can see animated, three-dimensional models of orbitals at the following URL. http://www.youtube.com/watch?v=K-jNgq16jEY (1:37)
Q: How many electrons can there be in each type of orbital shown in the Figureabove? A: There can be a maximum of two electrons in any orbital, regardless of its shape. Q: Where is the nucleus in each orbital? A: The nucleus is at the center of each orbital. It is in the middle of the sphere in the S orbital and in the pinched part of the P orbital. What’s Your Energy Level? Electrons are located at fixed distances from the nucleus, called energy levels. You can see the first three energy levels in the Figure below. The diagram also shows the maximum possible number of electrons at each energy level. · Electrons at lower energy levels, which are closer to the nucleus, have less energy. At the lowest energy level, which has the least energy, there is just one orbital, so this energy level has a maximum of two electrons. · Only when a lower energy level is full are electrons added to the next higher energy level. Electrons at higher energy levels, which are farther from the nucleus, have more energy. They also have more orbitals and greater possible numbers of electrons. · Electrons at the outermost energy level of an atom are called valence electrons. They determine many of the properties of an element. That’s because these electrons are involved in chemical reactions with other atoms. Atoms may share or transfer valence electrons. Shared electrons bind atoms together to form chemical compounds. You can see all of these ideas in action at the following URL (scroll down to the animation at the bottom of the Web page). http://www.brooklyn.cuny.edu/bc/ahp/SDPS/SD.PS.electrons.html
Q: If an atom has 12 electrons, how will they be distributed in energy levels? A: The atom will have two electrons at the first energy level, eight at the second energy level, and the remaining two at the third energy level. Q: Sometimes, an electron jumps from one energy level to another. How do you think this happens? A: To change energy levels, an electron must either gain or lose energy. That’s because electrons at higher energy levels have more energy than electrons at lower energy levels. Summary · Electrons are one of three main types of particles that make up the atom. They are extremely small and have an electric charge of -1. All atoms have the same number of electrons as protons. · Negative electrons are attracted to the positive nucleus. This force of attraction keeps electrons constantly moving around the nucleus. The region where an electron is most likely to be found is called an orbital. · Electrons are located at fixed distances from the nucleus, called energy levels. Electrons at lower energy levels have less energy than electrons at higher energy levels Explore More Research the discovery of electrons at the following URLs, and then answer the questions below. · http://www.youtube.com/watch?v=IdTxGJjA4Jw (2:54) · http://www.aip.org/history/electron/jjhome.htm 1. Who discovered electrons? When were they discovered? 2. Outline how electrons were discovered. 3. What was the significance of the discovery of electrons? 4. Where did Thomson think electrons were located in the atom? How does this differ from the modern view of electrons presented above? Review 1. What are electrons? 2. Compare and contrast electrons and protons. 3. Sketch a model of a beryllium atom, which has four protons, five neutrons, and four electrons. Your model should include the placement of electrons at the appropriate energy levels. 4. What are valence electrons? Why are they so important? How many valence electrons does a beryllium atom have (see question 3)? Protons (review questions only) Defining characteristics of positively charged sub atomic particles and their role in atomic structure · Describe protons. · State the relationship between protons and elements. · Identify particles that make up protons.
This glowing sphere represents the sun, which has a diameter of 1.4 × 109 meters. The sun has a special relationship to another object that is only about 1.7 × 10-17meters in diameter—the subatomic particle called the proton. How is the giganticsun related to the extremely tiny proton? Read on to find out. What Is a Proton? A proton is one of three main particles that make up the atom. The other two particles are the neutron and electron. Protons are found in the nucleus of the atom. This is a tiny, dense region at the center of the atom. Protons have a positive electrical charge of one (+1) and a mass of 1 atomic mass unit (amu), which is about 1.67 × 10-27 kilograms. Together with neutrons, they make up virtually all of the mass of an atom. For an excellent video on protons and otherfundamental particles in atoms, go to this URL: http://www.youtube.com/watch?v=Vi91qyjuknM (7:44) Q: How do you think the sun is related to protons? A: The sun’s tremendous energy is the result of proton interactions. In the sun, as well as in other stars, protons from hydrogen atoms combine, or fuse, to form nuclei of helium atoms. This fusion reaction releases a huge amount of energy and takes place in nature only at the extremely high temperatures of stars such as the sun. Identical Protons, Different Elements All protons are identical. For example, hydrogen protons are exactly the same as protons of helium and all other elements, or pure substances. However, atoms of different elements have different numbers of protons. In fact, atoms of any given element have a unique number of protons that is different from the numbers of protons of all other elements. For example, a hydrogen atom has just one proton, whereas a helium atom has two protons. The number of protons in an atom determines the electrical charge of the nucleus. The nucleus also containsneutrons, but they are neutral in charge. The one proton in a hydrogen nucleus, for example, gives it a charge of +1, and the two protons in a helium nucleus give it a charge of +2. To learn more about the relationship between protons and elements, go to this URL: http://www.youtube.com/watch?v=lP57gEWcisY (1:57) Q: There are six protons in each atom of carbon. What is the electrical charge of a carbon nucleus? A: The electrical charge of a carbon nucleus is +6. What Are Protons Made of? Protons are made of fundamental particles called quarks and gluons. As you can see in the Figure below, a proton contains three quarks (colored circles) and three streams of gluons (wavy white lines). Two of the quarks are called up quarks (u), and the third quark is called a down quark (d). The gluons carry the strong nuclear force between quarks, binding them together. This force is needed to overcome the electric force of repulsion between positive protons. Although protons were discovered almost 100 years ago, the quarks and gluons inside them were discovered much more recently. Scientists are still learning more about these fundamental particles. You can take an animated tour of the atom, including protons and their fundamental particles, at this URL:http://education.jlab.org/atomtour/index.html.
Summary · A proton one of three main particles that make up the atom. It is found in the nucleus. It has an electrical charge of one +1 and a mass of 1 atomic mass unit(amu). · Atoms of any given element have a unique number of protons that is different from the numbers of protons of all other elements. · Protons consist of fundamental particles called quarks and gluons. Gluons carry the strong nuclear force between quarks, binding them together. Explore More Do the activity at the URL below for a better appreciation of the size of a proton. http://www.pbs.org/wgbh/nova/teachers/activities/pdf/3012_elegant_13.pdf Review 1. Describe protons. 2. What is the relationship between protons and elements? 3. Atoms, which are always neutral in electric charge, contain electrons as well as protons and neutrons. An electron has an electrical charge of -1. If an atom has three electrons, infer how many protons it has. 4. Identify the fundamental particles that make up a proton. Neutrons (review questions only) Defining characteristics of neutrally charged sub atomic particles and their role in atomic structure · Describe neutrons. · Explain how isotopes of an element differ from one another. · Identify fundamental particles in neutrons.
The arrow in this photo is pointing to a star that doesn’t look like much compared with some of the other stars in the picture. It’s certainly much smaller than most other stars. In fact, it’s only about 20 kilometers in diameter. Compare that with the 1.4-million-kilometer diameter of our own sun. Despite its small size, however, this star has greater mass than the sun, making it incredibly dense. It also has tremendous gravity. In fact, gravity on its surface is about 2 × 1011 times the gravity we feel on Earth! What type of star is it? It’s called a neutron star. That’s because it consists solely of neutrons. You can learn more about these fascinating stars at the URL below. You will read about neutrons in this article. http://imagine.gsfc.nasa.gov/docs/science/know_l1/pulsars.html What Is a Neutron? A neutron is one of three main particles that make up the atom. The other two particles are the proton and electron. Atoms of all elements—except for most atoms of hydrogen—have neutrons in their nucleus. The nucleus is the small, dense region at the center of an atom where protons are also found. Atoms generally have about the same number of neutrons as protons. For example, all carbon atoms have six protons and most also have six neutrons. A model of a carbon atom is shown in the Figure below. For an excellent video explaining the structure of atoms, including neutrons, go to this URL: http://www.youtube.com/watch?v=Vi91qyjuknM (7:44)
Properties of Neutrons Unlike protons and electrons, which are electrically charged, neutrons have no charge. In other words, they are electrically neutral. That’s why the neutrons in the diagram above are labeled n0. The zero stands for “zero charge.” The mass of a neutron is slightly greater than the mass of a proton, which is 1 atomic mass unit (amu). (An atomic mass unit equals about 1.67 × 10-27 kilograms.) A neutron also has about the same diameter as a proton, or 1.7 × 10-17 meters. Same Element, Different Numbers of Neutrons All the atoms of a given element have the same number of protons andelectrons. The number of neutrons, however, may vary for atoms of the same element. For example, almost 99 percent of carbon atoms have six neutrons, but the rest have either seven or eight neutrons. Atoms of an element that differ in their numbers of neutrons are called isotopes. The nuclei of these isotopes of carbon are shown in the Figure below. The isotope called carbon-14 is used to find the ages of fossils. You can learn how at this URL:http://science.howstuffworks.com/environmental/earth/geology/carbon-14.htm.
Q: Notice the names of the carbon isotopes in the diagram. Based on this example, infer how isotopes of an element are named. A: Isotopes of an element are named for their total number of protons and neutrons. Q: The element oxygen has 8 protons. How many protons and neutrons are there in oxygen-17? A: Oxygen-17—like all atoms of oxygen—has 8 protons. Its name provides the clue that it has a total of 17 protons and neutrons. Therefore, it must have 9 neutrons (8 + 9 = 17). Particles in Neutrons Neutrons consist of fundamental particles known as quarks and gluons. Each neutron contains three quarks, as shown in the diagram below. Two of the quarks are called down quarks (d) and the third quark is called an up quark (u). Gluons (represented by wavy black lines in the diagram) are fundamental particles that are given off or absorbed by quarks. They carry the strong nuclear force that holds together quarks in a neutron. Summary · A neutron is one of three main particles that make up the atom. It is found in the nucleus and is neutral in electric charge. It has about the same mass and diameter as a proton. Neutrons are found in all atoms except for most atoms of hydrogen. · All the atoms of a given element have the same number of protons andelectrons, but they may vary in their numbers of neutrons. Atoms of the same element that differ in their numbers of neutrons are called isotopes. · Neutrons consist of fundamental particles known as quarks and gluons. Gluons carry the strong nuclear force that binds together the quarks in a neutron. Explore More Read the article on neutrons at the following URL, and then complete the fill-in statements below. http://www.chem4kids.com/files/atom_neutron.html 1. _________ are created when you change the normal number of neutrons in an atom. 2. If many neutrons are added to an atom, it becomes _________. 3. Extra neutrons may be knocked out of the nucleus during the process of _________. 4. The only element that normally lacks neutrons is _________. Review 1. What is a neutron? 2. Compare and contrast neutrons and protons. 3. Explain how isotopes of an element differ from one another. Give an example. 4. Identify the fundamental particles that make up a neutron. |
What is the number of orbiting electrons in each when the isotopes are electrically neutral?
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