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Chapter 2 (Part 1) General

by: Cassandra Danhof

Chapter 2 (Part 1) General CHEM 1411

Marketplace > Lone Star College-CyFair > Chemistry > CHEM 1411 > Chapter 2 Part 1 General
Cassandra Danhof
Lone Star College-CyFair
GPA 3.21
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Chap. 2 Notes go over the atomic theory of matter, the structure of an atom, isotopes, atomic mass, and the periodic table of elements
General Chemistry I
Prof. Chakranarayan
Class Notes
General Chemistry




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This 7 page Class Notes was uploaded by Cassandra Danhof on Saturday September 24, 2016. The Class Notes belongs to CHEM 1411 at Lone Star College-CyFair taught by Prof. Chakranarayan in Fall 2016. Since its upload, it has received 36 views. For similar materials see General Chemistry I in Chemistry at Lone Star College-CyFair.

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Date Created: 09/24/16
General Chemistry Chapter 2: Atoms, Molecules, and Ions Learning Objectives  Important Terms 2.1 Atomic Theory of Matter List the postulates of atomic theory Atomic Theory: An explanation of the  1. All matter is composed of  structure of matter in terms of different  indivisible atoms.  combinations of very small particles  2. Each atoms (or element) of a  Atom: An extremely small particle of matter  given kind has the same properties.  that retains its identity during chemical  (Law of Conservation of Mass) Ex.  reactions  Mass. All hydrogen atoms have the  Element: A type of matter composed of only  same mass one kind of atom 3. The relative numbers of any  Compound: A type of matter composed of  two kinds of atoms in a compound  atoms of two or more elements chemically  occur in simple ratios. Ex. Water is in combined (bonding) in fixed proportions a 2:1 Hydrogen:Oxygen ratio Chemical Reaction: The rearrangement of the 4. Atoms cannot be created,  atoms present in the reacting substances to  destroyed, or broken into smaller  give new chemical combinations present in  particles by any chemical reaction the substances formed by the reaction  Define element, compound, and chemical  Atomic Symbol: One­ or two­letter notation  reaction in the context of these postulates  used to represent an atom corresponding to a ● An element is an example of  particular event postulate 2. For example, you can  Law of Multiple Proportions: When two  distinguish Hydrogen and Oxygen  elements form more than one compound, the  from one another because those  masses of one element in these compounds  elements have distinct properties, like form a fixed mass of the other element are in  different masses that correlate to that ratios of small whole numbers  element. ● A compound is an example of  postulate 3. Each compound has the  same proportions, otherwise it would  be considered a different compound.  For example, Water will always have 2 Hydrogen and 1 Oxygen atom, or else it would not be water  ● Chemical reactions would be  an example of postulate 4. When you  have a chemical reaction, nothing  about the atoms within that reaction  can be created nor destroyed. For  example, if you boil water, the gas  particles of water will not change and  become H3O Recognize the atomic symbols of the  elements  ● Ex. Aluminum, Al ● Oxygen, O ● Hydrogen, H Explain the significance of the law of multiple  proportions ● The significance of the law of  multiple proportions is to understand  that the mass of the elements in a  compound will always be ratios of  whole numbers. Ex. 1 g N is  ○ NO Mass  (16.0gO) Ratio =   =  (14.0gN) 1.143 O ○ N 2 Mass  (32.0gO) Ratio =  (14.0gN) =  2.286 ■ 2.286 1.143 =2.0 g O 2.2 The Structure of the Atom Describe Thomson’s experiment in which he  Nucleus: The atom’s central core, which is  discovered the electron positively charged and contains most the  ● Thomson’s experiment was  atom’s mass based on an instrument that could,  Electron: A very light, negatively charged  through high voltage, detect negativparticle that exists in the region around the  and positive electrodes. Negative was  atom’s positively charged nucleus  a cathode and positive was a anode.  From discovering that the cathode  rays are independent of the material  making up the cathode.  ● From this, he found that a  cathode ray consists of negatively  charged particles (or electrons) and  that electrons are constituents of all  matter.  ● Robert Millikan calculated the  charge on the electron. He determined the charge on carious drops of oil and  found the smallest increment charge ­  that is, the charge on the electron.  Describe Rutherford’s experiment that led to  the nuclear model of the atom ● Rutherford's experiment  consisted of scientists bombarding  thin foils with alpha radiation. The  noticed the alpha rays consisted of  positively charged particles ● Because electrons are very  small and spread apart, they were not  detected though the metal sheets.  2.3 Nuclear Structure: Isotopes Name and describe the nuclear particles  Proton (nucleon particle): A nuclear particle  making up the nucleus of the atom having a positive charge equal in magnitude  ● The parts of an atom that  to that of the electron and a mass more than  make up the nucleus are the proton  1800 times that of the electron and the neutron. The proton is the  Atomic Number (Z): The number of protons in positive atoms, and the neutron is the  the nucleus of an atom neutral atoms.  Neutron (nucleon particle): A nuclear particle  Define atomic number, mass number, and  having a mass almost identical to that of the  nuclide proton but no electric charge  ● The atomic number is the  Mass Number (A): The total number of  number of protons in an atom. This  protons and neutrons in a nucleus makes the element distinguishable  Nuclide: An atom characterized by an atomic  and is found on the top of the  number and mass number  element’s symbol Isotope: Atoms whose nuclei have the same  ● The mass number is the total  atomic number but different mass numbers;  mass of the nucleus. This mass is  that is, the nuclei have the same number of  composed of both the protons and  protons but different number of neutrons  neutrons and it found on the bottom of Isobars: Atoms of different elements, having  the element’s symbol different atomic number (Z) but same mass  ● A nuclide symbol is the atomic  number (A) (ex. Fe and Zn) number and the mass number  together on the subscript  Write the nuclide symbol for a given nuclide Define and provide examples of isotopes of  an element ● Isotopes are elements that  have the same atomic numbers but a  different mass. For example, you can  have  O , O , or  O 16 17 18 Write the nuclide symbol of an element  (example 2.1) What is the nuclide symbol that contains 38  protons and 50 neutrons?  ● The number of protons  matches the element's atomic  number. The elements with 38 protons is element Strontium (Sr). ● To get the mass of the atom,  you add the protons with the neutrons: ○ 38+50=88 88 ● The nuclide symbol is  ❑ 38 Sr 2.4 Atomic Mass Define atomic mass unit and atomic mass Atomic Mass Unit (amu): A mass unit equal to ● Atomic mass is used to explain exactly one­twelfth the mass of a carbon­ 12  the relative masses within various  atom (the standard mass unit) isotopic elements. They are scaled by  Atomic Mass: The average atomic mass for  the standard of carbon, which has 6  the naturally occurring element, expressed in  protons and 6 neutrons in its nucleus atomic mass units  ● The atomic mass is the  Fractional (Percent) Abundance: The fraction  average mass of an element. This is  (percent) of the total number of atoms that is  considering their isotopic variants as  composed of a particular isotope  well. For example,  O16 , O 17 , or O are calculated in the atomic  18 mass of Oxygen to an average Describe how a mass spectrometer can be  used to determine the fractional abundance of the isotopes of an element ● A mass spectrometer helps  calculate the atomic masses of all the  isotopes of an element ● With this, it can help determine the abundances of an isotope to a  precise fraction Determine the atomic mass of an element  from the isotopic masses and fractional  abundances (example 2.2) Chromium, Cr, has the following isotopic  masses and fractional abundances  Mass  Isotopic  Fractional  Number  Mass (amu) (Percent)  Abundance 50 49.9461 0.0435 52 51.9405 0.8379 53 52.9407 0.0950 54 53.9389 0.0236 What is the atomic mass of chromium?  ● Multiply each isotopic mass by  its fractional abundance, then sum: ○ 49.9461 x  0.0435 = 2.17 amu ○ 51.9405 x  0.8379 = 43.52 amu ○ 52.9407 x  0.0950 = 5.03 amu ○ 53.9407 x  0.0236 = 1.27 amu ● 5 1.99 amu 2.5 Periodic Table of Elements  Identify periods and groups on the periodic  Periodic Table: A tabular arrangement of  table elements in rows and columns, highlighting  ● Periods are the elements  the regular repetition of properties of the  position placed horizontally on the  elements  table  Period (of periodic table): The elements in  ● Groups are elements that are  any one horizontal row of the periodic table  placed vertically on the table  Group (of periodic table): The elements in any Find the main­group and transition elements  one column of the periodic table  on the periodic table  Metal: A substance that has a characteristic  ● The main group elements are  luster, or shine, and is generally a good  groups 1, 2 and 13­18 conductor of heat and electricity Nonmetal: An element that does not exhibit  the characteristics of a metal Metalloid (semimetal):An element having both metallic and nonmetallic properties  ● The transition group elements  are groups 3­17 Locate the alkali metal and halogen groups  on the periodic table  ● The alkali metals are the very  left group on the table and the  halogens are the very right group on  the table Recognize the portions of the periodic table  that contains metals, nonmetals, and  metalloids (semimetals)  ● The periodic table has  nonmetals on its outer sides, meals in  the middle, and metalloids on a  staircase on the right side in between  the metals and the non­metals


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