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CHEM 101 Chapter 2

by: Lyna Nguyen

CHEM 101 Chapter 2 Chem 101

Marketplace > Texas A&M University > Chemistry > Chem 101 > CHEM 101 Chapter 2
Lyna Nguyen
Texas A&M

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textbook + lecture notes
General Chemistry 1
Dr. Daniel Collins
Class Notes
Chemistry, Chem, CHEM 101, tamu
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This 6 page Class Notes was uploaded by Lyna Nguyen on Friday January 29, 2016. The Class Notes belongs to Chem 101 at Texas A&M University taught by Dr. Daniel Collins in Fall 2015. Since its upload, it has received 16 views. For similar materials see General Chemistry 1 in Chemistry at Texas A&M University.


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Date Created: 01/29/16
09/10/15­09/15/15 Chemistry 101 Chapter 2  Proof Electron  JJ Thompson  1906 Nobel Prize in physics  Electric charge (-)  Magnetic field  Beam of particles w/ the 2 plates differently by the negative and attracted to positive  Dalton’s Theory  Elements are made of atoms  Atoms are identical  Compound=simple fraction  Does not create/destroy  Millikan’s experiment (Dropping oil) -  Measured mass of e  e charge = -1.60 x 10 -19  e mass = 9.10 x 10 -28  Rutherford Experiment  Rutherford  1908 in chemistry  Atoms positive charge is concentrated in the nucleus  Proton (p) has opposite (+) charge of electron (-) - -24  Mass of p is 1840x mass of e (1.67 x 10 g)  Atom is mostly empty space -10  Atomic radius is ~100 pm = 10 x 10 m  Nucleus radius is ~5 x 10 pm = 5 x 10 m -7  Atomic Structure – Protons, Electrons, and Neutrons  Atoms are made of subatomic particles  3 important ones  Protons: electrically positive  Unique identity of each element  Electrons: electrically negative  Neutrons: electrically neutral  Small nucleus: contains all positive charge and almost all mass  Electrons surround the nucleus  Occupy most volume  Chemical properties depend on electrons 1 09/10/15­09/15/15  Atomic number and Atomic Mass (AMU – mass of an atom)  Atomic Number: number of protons in nucleus  Identifier  All atoms of a given element have the same number of protons  Average Atomic Mass: weighted average of all of the naturally occurring isotopes of the elements  On periodic table Coppe Atomic number r 29 Symbol Cu  Relative Atomic Mass and the Atomic Mass  Standard: Carbon 12  Masses of fundamental atomic particles are expressed in atomic mass units (u)  1 u = 1/12 mass of carbon  u = 1.661 x 10 -24g  Mass Number (A): sum of the number of protons and neutrons  A = mass number = number of protons + number of neutrons  Gives the isotope  Isotopes: atoms w/ the same atomic number but different mass numbers  Same number of proton, mass difference is due to neutrons  Ex: hydrogen  1) Protium  2) Deutenum  3) Tritium  Isotope Abundance  Percent abundance = # of atoms of isotope/total # of isotopes x 100%  Determining Atomic Mass and Isotope Abundance  By mass spectrometry  Introduced into spectrometer, converted into ions (positively charged particles), deflected by magnetic field (lighter moves more than heavier), separated by mass  Samples are bombarded w/ electrons  The greater the charge/mass ration, the more the particle moves  Same charge, same element  Atomic Weight: average mass  Atomic weight=(% abundance/100)(mass of isotope)+…  The Periodic Table  Features of the periodic table  Vertical columns: similar chemical and physical properties 2 09/10/15­09/15/15  Called groups or families  1-8  1, 2, 3-8 main group, others are transition metals  Good reaction predictor  Horizontal rows: periods; 7 rows  Divided into regions  Metals  @ Room temp and normal pressure (atmospheric), are solids, can conduct electricity, usually ductile and malleable and can form alloys  Nonmetals  Some are solids (C, S, P, I)  10 are gases (H, O, N, F, Cl, H, Ne, Ar, Kr, Xe)  1 liquid (Br)  Do not conduct electricity  Metalloids (Semimetals)  Has some physical properties of a metal, but chemical characteristics of a nonmetal  Gradually become less metallic as you move left to right  Brief overview  Group 1A: Alkali metals  Good for salts  Reactive w/ water and halogens  Group 2A: Alkaline Earth Metals  Less reactive than 1A  Group 3A: metals  Form compounds w/ analogous formulas  Group 4A: change from nonmetallic -> metallic behavior  Allotropes: exist in several different and distinct forms, each having its own properties  Group 5A: N occurs naturally in form of diatomic molecules  Group 6A: Oxygen  Group 7A: Halogens  Nonmetals  Most reactive elements  Salts w/ Alkali metals  Group 8A: Noble gases  Least reactive; most stable  Transition elements: 2A and 3A  Metals 3 09/10/15­09/15/15  Have commercial use  Lanthanides: bottom 2 rows  Rare earth elements  Worldwide shortage  Molecules, Compounds, and Formulas  Molecule: smallest identifiable unit which pure substances can be divided  Diatomic molecule: only 2 atoms  Polyatomic: 2+  Aggregate of 2+ in a definite arrangement held together by chemical forces  Formulas  Molecular formula: describes the composition of molecules  What element, how many  Structural information: how atoms are connected and how molecules fill spaces  Condensed Formula: indicates how certain atoms are grouped together  Structural formulas: gives a higher level of structural detail, showing how all of the atoms are attached within a molecule  What, how many, connectivity  Empirical formulas: shows the simplest whole # ratio of the atoms  Molecular models  Physical and chemical properties of a molecular compound are related to its structure  Ball and stick model: spheres of different colors represent the atoms and sticks represent the bonds holding them together  Represents 3-D structure  Space-filling model: better representation of relative sizes of atoms and their proximity to each other  Disadvantage: atoms can often be hidden from view  Ionic Compounds: Formulas, Names and Properties  Molecular compounds: compounds that consist of discrete molecules at the particular level  Ionic compounds: formed by combination of positive and negative ions  Ions: atoms that bear a positive or negative electric charge  Metals generally lose one or more electrons  Nonmetals frequently gain one or more electrons  Monatomic cat ions: positively charged ion  Cat ions are smaller and loses electrons  Group 1A -> loses 1; +1  Group 2A -> loses 2; +2  Group 3A -> loses 3; +3 4 09/10/15­09/15/15  How to predict?  Charge equal to the group number of the metal  Electrons remaining on the cat ion is the same as noble gas that precedes it  Transition metals form cat ions; less predictable  Monatomic anions: negatively charged ion by gaining electrons  Ex: oxygen=grains 2 electrons  Observations  Nonmetals in group 5A-7A form negative ions having charge equal to group # -8  # Electrons is the same as noble gas that follows  Polyatomic Ion: made up of 2 or more atoms w/ electric charge  Stable together  Formulas of Ionic Compounds  Salts, cat ions/ anions  Electrically neutral, no net charge  1:1 ratio of protons and electrons  When writing (same as empirical): the symbol of the cat ion is given first, followed by the anion symbol  Names of Ions  Naming positive ions (cat ions)  Name = metal + “cat ion”  Charge indicated by roman numeral  Naming negative ions (anions - nonmetals)  Monatomic is named by adding “-ide” to the stem  Anions of halogens are called halide ions  Polyatomic are common  Oxyanions: containing oxygen  Greater number of oxygen atoms: “-ate”  Smaller number of oxygen atoms: “-ite”  Oxyanions w/ hydrogen: add hydrogen before  Properties of Ionic Compounds  When particles of opposite charge are near each other, there is an attractive force  Repulsive force when particles have same charge  Forces are called electrostatic forces  Attraction/repulsion force is given by coulomb’s law  Force = -k((n e)(n e))/d )2  K: constant  n: charge on ions  d: distance b/w 5 09/10/15­09/15/15  e: charge on electron  Force increases:  As ion charge increases  As distance b/w ions gets smaller  Crystal lattice: ionic solid consists of millions upon millions of ions arranged in an extended 3-D network  B/s each ion is surrounded by oppositely charged neighbor, it is held in position  Most are “hard solids”  6


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