CHEM 101 Chapter 2
CHEM 101 Chapter 2 Chem 101
Popular in General Chemistry 1
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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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