Chemistry Review Unit 1 Study Guide

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Elinor Hodges
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1 1. Draw and label a Bohr model of a C 14 atom. 2. Describe the following about a proton a. mass: the mass of a proton is 1 atomic mass unit (AMU) b. charge: protons have a positive charge c. location: a proton can be found in the nucleus in the center of an atom d. relative size (compared to neutrons and electrons): a proton is about the same size as a neutron and about 2000 times larger than an electron 3. Describe the following about a neutron a. mass: the mass of a neutron is 1 atomic mass unit (AMU) b. charge: neutrons are neutral (have no charge) c. location: a neutron can be found in the nucleus in the center of an atom d. relative size (compared to protons and electrons): a neutron is about the same size as a proton and about 2000 times larger than an electron 4. Describe the following about an electron a. mass: the mass of an electron is about 1/2000 AMU ( AMU) we round to zero because it is so small compared to other subatomic particles b. charge: an electron has a negative charge c. location: electrons can be found in the electron cloud far from the nucleus and the electron cloud defines the outer surface of the atom d. relative size (compared to protons and neutrons): electrons are about 2000 times smaller than protons and neutrons 5. Describe what can be found in the nucleus of an atom and its relative size compared to the atom. The nucleus is very small compared to the atom as a whole. All of the protons and neutrons are inside the nucleus and the nucleus would be similar to the size of a grain of sand on the

50 yard line of a football stadium. The entire atom would then be the size of a football stadium including bleachers all the way out to the exterior of the building.

Describe what can be found in the electron cloud and its relative size compared to the atom.

2 50 yard line of a football stadium. The entire atom would then be the size of a football stadium including bleachers all the way out to the exterior of the building. The electron clouds exist at the edges of the stadium, but in between the nucleus (grain of sand) there is nothing but empty space. 6. Describe what can be found in the electron cloud and its relative size compared to the atom. Electrons can be found in the electron cloud and make up the outer surface of an atom and gives an atom its shape. This is the surface of the atom but only is a small percentage of the size of the atom. 7. An atom is made mostly of empty space. 8. Is most of the volume of an atom is taken up by the electron cloud (which defines the volume). 9. Describe the experiment that led to the discovery of the electron. Thomson s cathode ray experiment led to the discovery of the electron. Thompson used charged plates to show that cathode rays were composed of a previously unknown negatively charged particle. Thus, he concluded that the beam was made of something that contained electric charge. This is essentially the discovery of the first subatomic particle. 10. Describe the experiment that led to the discovery of the nucleus. Rutherford s gold foil experiment led to the discovery of the nucleus. Rutherford fired alpha particles (helium atoms with no electrons) through a very thin sheet of gold foil that was only a few atoms thick. He noted that the particles usually went through the gold foil and landed on a surface directly behind the sheet of foil. He knew this because the surface would luminesce (light up) when exposed to an alpha particle. However, occasionally, a particle would bounce off the nucleus and the surface would luminesce in a different location.

3 11. What is a chemical symbol? A chemical symbol is a one or two letter code that appears the periodic table. It is used to signify specific atoms. The first letter of a chemical symbol is always capitalized. 12. Name the chemical symbol for a. carbon: C b. nitrogen: N c. oxygen: O d. helium: He e. lead: Pb f. bismuth: Bi 13. Describe what an isotope is and give an example. An isotope is a variation on an atom of a specific element. For example, the element carbon (C) has several isotopes. ALL carbon atoms have the same number of protons (6 in the case of carbon, it is a different number for each unique element). However, different carbon atoms may contain different numbers of neutrons. Some carbon atoms contain 6 neutrons, others may contain 7. The carbon atom that has 6 protons and 6 neutrons is called carbon 12 (C 12). The 12 signifies the atomic mass and can be calculated by adding the number of neutrons and protons. Carbon that contains 7 neutrons is carbon 13 (C 13). 14. How are He 3 and He 4 different? What does the He stand for? What does the 3 stand for? He 3 and He 4 are isotopes of helium and contain different numbers of neutrons (He 3 has one neutron and He 4 has 2 neutrons). He is the chemical symbol for helium and the 3 in He 3 stands for the atom s mass, which is 3 AMU (helium always has 2 protons, which each weigh 1 AMU and 1 neutron which also weighs 1 AMU). 15. What is the mass number of He 3? How many protons does it have? How many neutrons? How many electrons? Mass number is the mass of a specific atom. So, the atomic mass of He 3 is 3 AMU. It has 2 protons, 1 neutron, and 2 electrons (since we are talking about a neutral atom, it must have the same number of protons and electrons to balance charge). 16. Describe the difference between average atomic mass and mass number. Average atomic mass is the average mass of all of the atoms of that element found on earth. For example boron (B) has two isotopes: B 11 and B 10. Most boron atoms are B 11 and less than 20% are B 10. If we take a weighted average, we find the average weight of all boron atoms is AMU. This number (10.81) is the average atomic mass, which is the number that appears on the periodic table. We often use this number because it is rare we do not have a mix of atoms when dealing with atoms in chemistry. Additionally, when we are making calculations, we are dealing with hundreds of billions (or more) atoms, even in a very small sample.

4 17. For an alpha (α) particle, describe: a. charge: positive (2 protons give it a charge of 2+) b. what it is made of: two protons and two neutrons (a helium atom with no electrons) c. how it is created: the atom ejects two protons and neutrons d. how dangerous it is: least dangerous nuclear radiation e. how far it travels: only travels a few inches or feet, it is very heavy f. symbol: see notes g. what will stop its travel: a sheet of paper this particle is only dangerous to us if ingested 18. For a beta (β) particle, describe: a. charge: negative b. what it is made of: an electron c. how it is created: a neutron in the nucleus of an atom splits and creates a proton and an electron. The proton stays in the nucleus and the electron is emitted. The emitted electron is the actual particle. d. how dangerous it is: medium danger e. how far it travels: several feet f. symbol: see notes g. what will stop its travel: skin, metal foil this particle is dangerous to us in large does or to those who are immunocompromised 19. For a gamma (γ) particle, describe: a. charge: none b. what it is made of: a photon c. how it is created: this is usually produced when a nucleus emits a gamma or alpha particle and the nucleus is emitting extra energy we did not discuss, nor do you need to understand the mechanism for its creation d. how dangerous it is: very dangerous/the most dangerous radiation e. how far it travels: very far several meters, through walls, etc f. symbol: γ g. what will stop its travel: several feet of lead 20. A neutral atom of He 4 contains how many protons, neutrons, and electrons? How do you know it is neutral? An atom of He 4 contains 4 protons, 4 neutrons, 4 electrons. You know it is neutral because it has the same number of protons and electrons. 21. Describe what is different between an alpha particle and a beta particle?

5 See above. Alpha particle is heavier, less dangerous, contains a proton and neutron (instead of electron), cannot travel as far, can be stopped by paper (instead of skin or metal foil). 22. Describe what is different between a beta particle and a gamma particle? See above. Beta particle is heavier, less dangerous, contains an electron (instead of a photon), cannot travel as far, can be stopped by skin or foil (instead of needing several feet of lead). 23. What is different between a gamma particle and an alpha particle? See above. Alpha particle is heavier, much less dangerous, contains a proton and neutron (instead of a photon), cannot travel as far, can be stopped by paper (instead of needing several feet of lead). 24. Describe the energy in a nuclear reaction compared to the energy of a chemical reaction. A nuclear reaction releases A LOT more energy (about 200,000,000 TIMES more energy in a nuclear reaction than a chemical reaction). 25. Describe the difference between a fission and fusion reaction. Are they both nuclear reactions? Why or why not? Fission is the splitting of a nucleus where an atom splits off protons. Alpha particles come from a fission reaction. Fusion is the joining of a two nuclei, such as what occurs in the sun when two hydrogen atoms join to form a helium atom. They are both nuclear reactions because they involve the nucleus. 26. The half life of Mm is 64 days. How much of this radioactive isotope is left in a 500 gram sample after 128 days? 125 g 27. The half life of Tt is 22 years? If you have a sample with 10 grams of Tt, how much did you have 44 years ago? 40 g 28. What is the band of stability? Stable nuclides, if plotted on a graph of number of protons vs. number of neutrons, would all fall in an area enclosed by two curved lines known as the band of stability. All stable isotopes fall between these two lines. 29. Why will an atom with 120 protons and 5 neutrons be radioactive? YES (although it would not exist in real life). Tehre is not enough neutrons in the atom to shield positive charges and thus the atom would be unstable and the nucleus would break apart. This is nuclear fission, which is radioactive decay. 30. What is the difference between a radioactive isotope and a stable isotope? A radioactive isotope has an unstable nucleus that will undergo radioactive decay and eventually turn into another type of atom. A stable isotope has a stable nucleus will not undergo radioactive decay.

Unit 1 Atomic Structure

Unit 1 Atomic Structure Defining the Atom I. Atomic Theory A. Modern Atomic Theory 1. All matter is made up of very tiny particles called atoms 2. Atoms of the same element are chemically alike 3. Individual