HIGH SCHOOL SCIENCE Physical Science 9: Atomic Structure WILLMAR PUBLIC SCHOOL 2013-2014 EDITION CHAPTER 9 Atomic Structure In this chapter you will: 1. Compare and contrast quarks, leptons, and bos- ons. 2.Describe the standard model. Identify three subatomic particles and compare their proper- ties. 3.Distinguish the atomic number of an element from the mass number of an isotope, and use these numbers to describe the structure of at- oms. 4.Describe ancient Greek models of matter. 5.Describe Dalton’s atomic theory and his evi- dence for the existence of atoms. 6.Explain Thomson’s, Rutherford’s, and Bohr’s atomic models as well as the electron cloud model. 7.Distinguish the ground state from excited states of an atom based on electron configurations. SECTION 9.1 For decades scientists have known that atoms consist of electrons and other particles called protons and neutrons. Standard Model They created the explosion in the picture in their search for even smaller particles of atoms. Today, scientists think that electrons truly are fundamental particles that cannot be broken down into smaller, simpler particles. They are a type of fundamental particles called leptons. Protons and neutrons, on the other hand, are no longer thought to be fundamental particles. Instead, they are now thought to consist of smaller, simpler particles of matter called quarks. Quarks and leptons are classified as fermions. A fermion is the true building blocks of matter. Scientists theorize that fermions are held OBJECTIVES: together by yet another type of fundamental particles called bosons. 1. Compare and contrast quarks, leptons, and bosons. 2. Describe the standard model. Vocabulary: fermion quark lepton boson standard model 2 A quark is a tiny fundamental particle or fermion that make of matter. According to the model, all known matter consists up protons and neutrons. There are six types of quarks. In of quarks and leptons that interact by exchanging bosons, ordinary matter, virtually all quarks are of the types called up which transmit fundamental forces. The standard model is a and down quarks. All quarks have mass, and they have an good theory because all of its predictions have been verified electric charge of either +2/3 or -1/3. For example, up quarks by experimental data. However, the model doesn’t explain have a charge of +2/3, and down quarks have a charge of -1/3. everything, including the force of gravity and why matter has Quarks also have a different type of charge, called color mass. Scientists continue to search for evidence that will allow charge, although it has nothing to do with the colors that we them to explain these aspects of force and matter as well. see. Quarks are never found alone but instead always occur in groups of two or three quarks. A lepton is a weak fundamental particle or fermion. There are also six types of leptons, including electrons. Leptons have an electric charge of either -1 or 0. Electrons, for exam ple, have a charge of -1. Leptons have mass, although the mass of electrons is extremely small. There are four known types of bosons, which are force- carrying particles. Each of these bosons carries a different fundamental force between interacting particles. In addition, there is a particle called the "Higgs Boson", which gives objects the masses they have. Some types of bosons have mass; others are massless. Bosons have an electric charge of +1, -1, or 0. Based on their knowledge of subatomic particles, scientists have developed a theory called the standard model to explain all the matter in the universe and how it is held together. The model includes only the fundamental particles in the table. No other particles are needed to explain all kinds 3 Section Review: 1. Make a table comparing and contrasting the three types of fundamental particles. Include an example of each type in your table. 2. In what ways is the standard model incomplete? 4 SECTION 9.2 Atoms are the smallest particles of an element that still have the element’s properties. Individual atoms are extremely Atomic Structure small. In fact, they are so small that trillions of them would fit inside the period at the end of this sentence. Although atoms are very tiny, they consist of even smaller particles. Three main types of particles that make up all atoms are: protons, neutrons, and electrons. Protons, elections, and neutrons are subatomic particles which can be distinguished by mass, charge, and location in OBJECTIVE: an atom. 1. Identify three subatomic particles and compare their properties. Relative Relative Symbol Location Charge Mass 2. Distinguish the atomic number of an element Outside the Electron e- 1- 1/1836 from the mass number of an isotope, and use Nucleus Proton p+ 1+ 1 Nucleus these numbers to describe the structure of Neutron n 0 1 Nucleus atoms. A proton is a positive charged subatomic particle that is found in the nucleus of an atom. Protons have two up quarks Vocabulary: and one down quark. Each nucleus must contain at least one particle with a positive charge. atoms proton A neutron is a neutral subatomic particle that is found in the neutron electron nucleus of an atom. It has a mass almost exactly equal to that atomic number mass number of a proton. Neutrons have one up quark and two down quarks. isotope An electron is a negatively subatomic particles that is found in the space outside the nucleus. It would take 1836 electrons 5 to equal to the mass of a proton. Thus people say it does not The mass number of an atom is the sum of the protons and have enough mass to be considered or almost 0. Electrons are neutrons in the nucleus on that atom. If you know the atomic one type of lepton thus have very difference properties than number and the mass number of an atom, you can find the protons and neutrons. number of neutrons by subtracting. The atoms of any given elements always have the same Number of Neutrons = Mass number – Atomic number number of protons. For example, there is one proton in the Every atom of a given element has the same number of nucleus of each and every hydrogen atom. Atoms of different protons and electrons. Some atoms of the same element may elements have different number of protons, therefore, the have different numbers of neutrons. For example, some number of protons determines the element. carbon atoms have seven or eight neutrons instead of the Atomic number of an element equals the number of usual six. Isotopes are atoms of the same element that have protons in an atom of that element. Atoms of different different numbers of neutrons and different mass numbers. elements have different atomic numbers. The number of Isotopes of an element have the same atomic number but protons is the atomic number. different mass numbers because they have different numbers of neutrons. Each positive charge in an atom is balanced by a negative charge because atoms are neutral. So the atomic number of Some atoms of hydrogen have no neutrons and a mass an element also equals the number of electrons in an atom. number of one. Some atoms of hydrogen have one neutrons and a mass number of two. Some atoms of hydrogen have two Electrons have almost no mass. Instead, almost all the mass of neutrons and a mass number of three. When it is important an atom is in its protons and neutrons in the nucleus. The to distinguish one hydrogen isotope from another, the nucleus is very small, but it is densely packed with matter. isotopes are referenced to as hydrogen-1, hydrogen-2, and The SI unit for the mass of an atom is the atomic mass unit hydrogen-3. The number after the element is the mass (amu). One atomic mass unit equals the mass of a proton, number. which is about 1.7 × 10−24 g. Each neutron also has a mass of 1 amu. Therefore, the sum of the protons and neutrons in an atom is about equal to the atom’s total mass in atomic mass units. 6 Section Review: 1. How are protons, neutrons and electrons distinguished? 2. Which subatomic particles are in the nucleus? 3. Which subatomic particles have charge? 4. Since the up quark has a charge of +2/3 and a down quark has a charge of -1/3, explain how the proton has a 1+ charge? 5. Since the up quark has a charge of +2/3 and a down quark has a charge of -1/3, explain how the neutron has a 0 charge? 6. Why do some say that the electron does not have mass? 7. Why do electrons have very different properties than protons and neutrons? 8. How are atoms of one element different from atoms of other elements? 9. How do you determine the number of protons? 10.How do you determine the number of electrons? 11.How do you determine the number of neutrons? 12.What is the difference between two isotopes of the same element? 13.How do you distinguish between different isotopes of the same element? 7 SECTION 9.3 The history of the atom begins around 450 B.C. with a Greek philosopher named Democritus. Democritus wondered what Atomic Models would happen if you cut a piece of matter, such as an apple, into smaller and smaller pieces. He thought that a point would be reached where matter could not be cut into still smaller pieces, and believed that all matter consists of extremely small particles that could not be divided.