Chem 107 -- Chapter 2 notes
Chem 107 -- Chapter 2 notes Chem 107
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This 6 page Class Notes was uploaded by Charissa Notetaker on Friday September 23, 2016. The Class Notes belongs to Chem 107 at Liberty University taught by Mr. Allan in Fall 2016. Since its upload, it has received 94 views.
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Date Created: 09/23/16
Chapter 2, Atomic Structure and Nuclear Radiation Terms to Know 1. All matter is composed of atoms. 2. An element is a substance that is composed of only one type of atom. 3. A compound is a substance composed of two or more different atoms held together by chemical bonds. Elements and the Structure of the Atom 1. The atom is the smallest intact, stable component of matter. a. An atom is composed of protons, neutrons, and electrons. i. Protons have a positive charge, electrons have a negative charge, and neutrons have no charge. 1. Proton +1 1 amu. a. How many? The number of protons = atomic number = Z. 2. Neutron 0 1 amu. a. How many? Atoms are neutral, they have no net positive or negative charge, so e. 3. Electron -1 0.00055 amu. a. How many? An atom of a given element will always have protons = electrons = atomic number, but the number of neutrons can vary. b. The mass of an atom depends on the number of protons and neutrons it contains. i. Atomic mass = (A) = number of protons + number of neutrons . 0 ii. Atomic mass is also called the mass number. c. Protons and neutrons are located in the dense nucleus at the center of the atom. d. Electrons are located in electron orbitals and have a negligible mass. i. An s orbital has a spherical shape. ii. The three p orbitals are perpendicular and have a dumbbell-like shape. 2. An element is composed of atoms that contain the same number of protons. a. An element cannot be broken down into a simpler form of matter. b. The atomic number for an element corresponds to the number of protons its atoms contain. c. Elements are made of atoms (not ions). d. They differ in how the atoms are arranged: i. He, Ne, Ar – atoms. ii. H2, Cl2, 4 ,8S – molecules. iii. C(diamond)Fe, Ni – interconnected solids. e. Carbon “C”: i. Most unique in its unlimited capacity to bond with other elements to form biomolecules: 1. RNA. 2. DNA. 3. Cellulose, etc. ii. No other element can replace even one or two C atoms in biomolecules without destroying the biological integrity and function of that biomolecule. f. Oxygen “O”: i. Exists in nature as a diatomic molecule (O 2. ii. Two electron pairs on O 2llow it to bind to the iron (Fe) atoms in hemoglobin. iii. Other molecules, such as CO and NO can replace O in 2inding to hemoglobin, but they completely destroy the hemoglobin function. 3. Isotopes of an element are atoms with the same number of protons but a different number of neutrons. a. The mass number for an isotope is the sum of its protons and neutrons. b. The average atomic mass of an element is the weighted average of its isotopes based on the natural abundance of each isotope and the mass of each isotope. 4. Every element has a one- or two-letter atomic symbol. Navigating the Periodic Table of Elements 1. The periodic table of elements shows the 114 element from the lowest to highest atomic number in a unique organization of seven rows, periods, columns, and groups. a. Elements in the same column in the periodic table belong to the same group or family. b. Elements in the same row in the periodic table belong to the same period. c. Elements in the same group contain the same number of valence electrons, accounting for their similar chemical and physical properties. d. The main group elements are in groups 1A through 8A. i. Group 1A – alkali metals. ii. Group 2A – alkaline earth metals. iii. Group 7A – halogens. iv. Group 8A – noble gases. v. Metals and non-metals are separated by the bold diagonal zigzag line on the right side of the table. 1. Metals (Cu, Au, Ag) a. Malleable, lustrous, ductile, good conductors of heat and electricity. 2. Non-metals (S) a. Gases or brittle solids at room temperature, poor conductors of heat and electricity (insulators). vi. Metalloids are the elements along both sides of this line. 1. Metalloids (Si) a. Dull, brittle, semi-conductors (used in computer chips). e. Group’s 1B-8B are transition metals. 2. Many elements have an important role in biochemistry as either building block elements, micronutrients, or macronutrients Electrons 1. Electrons occupy different energy levels, n, where n = 1, 2, 3, 4… a. Our current model of the electron comes from quantum mechanics, which states that the energy of an electron is fixed in one of certain allowed energy levels. b. Atoms in the ground state (the lowest energy state of the atom) have their electrons in the lowest energy levels, up to the maximum allowed in any given energy level. 2. If an atom gains or loses electrons it becomes an ion. a. Gains electrons: “-” charge. b. Loses electrons: “+” charge. i. Like charges repel. ii. Opposite charges attract. 3. Electrons must include: a. Shape: a physical picture of where to find the e (the shape is called an orbital). b. Labels: like an address (tells you where to find the e ). c. Energy diagram: what is the energy in a given location? (At the given address). 4. Valence electrons are the outermost electrons of an atom, in the energy level with the highest value of n. a. The other electrons, in lower energy levels, are inner core electrons. b. Elements in the same group have the same number of valence electrons, which corresponds to the group number. c. Atoms with their valence shell full are the happiest and are called noble gases. d. Atoms who don’t have their valence shell full want their shell full. Key to All Chemical Understanding Electrons move from one atom to another, or they are shared between atoms in order to occupy either completely filled or completely empty electron energy levels. Ions 1. A cation is formed when a metal atom loses electrons. a. The forming of this is known as ionization. b. Main group metals lose their valence electrons. c. For metals to have full valence shells, they give to the noble gas in the period beneath it. 2. An anion is formed when a non-metal gains electrons. a. Main group non-metals can gain valence electrons until they have a full valence shell, like the noble gas nearest them on the periodic table. b. For non-metals, it is the noble gas in the same period. 3. Many transition metals and some main group metals lose a variable number of electrons and therefore exist in more than one ionic form. Radioisotopes 1. Radioactive isotopes—radioisotopes—are unstable isotopes that achieve stability by radioactive decay. a. Radioactive decay: a process in which electromagnetic radiation and/or high energy particles are emitted from the radioisotope. i. Can be described by a nuclear equation. ii. The sum of the subscripts on both sides of the equation must be equal, and similarly with the superscripts. 1. Subscripts represent the atomic number of the nuclides. 2. Superscripts represent the mass number. iii. Four major types of radioactive decay: 1. α-particle emission. a. ( 2) is a helium nucleus: two protons and two neutrons. b. Carries a 2+ charge, and it is a high-energy, relatively slow- moving particle. 2. β-particle emission. 0 a. High-energy electron ( β)-1 b. β-decay yields a daughter nuclide with an atomic number one greater than the parent nuclide and the same mass number. 3. X-ray emission. 4. γ-ray emission. a. Most radioactive decay is accompanied by it. b. High-energy electromagnetic radiation. iv. A half-life is the time it takes a particular radioisotope to decay to one-half its mass—exponential decay. 1. Knowing how long a radioisotope will remain hazardous is an important factor in controlling exposure to radiation 2. Radioactive decay produces ionizing radiation that can damage or destroy cells through ionization. 3. Radioact222 decay o218adon-224: a. 86n 84Po + α2(half-life of 3.8 days). 4. Ionization: the loss of an orbital electron, producing an ion. 2. Electromagnetic radiation is a form of energy that travels through space as a wave at the speed of light. a. It is described by its wavelength, which is related to its frequency. i. Different wavelengths of light contain different amounts of energy. ii. The longer the wavelength, the lower the frequency and the lower its energy. 3. The biological effects of nuclear radiation depend on the energy and penetrating power of the radiation. a. α-particles have the highest energy but least penetrating power. b. β-particles and x-rays have less energy but greater penetrating power. c. Gamma (γ) rays have more energy and greater penetrating power. 4. The units of measurement that indicate the number of radioactive emissions produced by a radioisotope are the Becquerel (Bq) and the curie (Ci). 5. The absorbed dose in a unit of radiation measurement that takes into account the energy of the radiation absorbed. a. Common units are: the gray (Gy) and the rad. 6. The effective dose is a unit of radiation that takes into account the energy of the radiation absorbed together with the penetrating power of the radiation. a. Common units are: Sievert (Sv) and the rem. 7. Radiation sickness occurs with acute exposure to radiation. a. Acute: a single large dose. Radioisotope Use in Medicine 1. Technetium-99m: a. Used as a radioactive tracer. b. Can be detected in the body by medical equipment (gamma cameras). c. Half-life for gamma emission is 6.0 hours (meaning 93.7% of it decays to 99mTC in 24 hours). d. The relatively “short” physical half-life of the isotope and its biological half-life of 1 day—in terms of human activity and metabolism—allows for scanning procedures which collect data rapidly but keep total patient radiation exposure low.