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Atoms, Ions and Molecules. Chapter 2. Dalton’s Atomic Theory (1808). All matter is composed of extremely small particles called atoms Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties.

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Atoms, Ions and Molecules

Chapter 2


Dalton’s Atomic Theory (1808)

  • All matter is composed of extremely small particles called atoms

  • Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties

John Dalton

  • Atoms cannot be subdivided, created, or destroyed

  • Atoms of different elements combine in simple whole-number ratios to form chemical compounds

  • In chemical reactions, atoms are combined, separated, or rearranged


Atomic Theory of Matter

  • All matter is made of tiny indivisible particles called atoms.

    • This proposal has been verified experimentally. Single atoms of a variety of elements have been photographed with a scanning transmission electron microscope.


Atomic Theory of Matter

2. Atoms of the same element are identical and atoms of a different element have different masses and chemical properties.

  • However you will learn that atoms of the same element can have different masses.


Atomic Theory of Matter

  • Atoms of different elements combine in whole number ratios to form compounds

    • One molecule of water always consists of two atoms of hydrogen and one atom of oxygen.


Atomic Theory of Matter

4. Chemical reactions involve the rearrangement of atoms. No new atoms are created or destroyed.

  • Modern research has altered this proposal. Atoms are not indestructible and may lose their identity when split during nuclear reactions. However Dalton’s proposal remains true, for chemical reactions.


Law of Multiple Proportions

  • Atoms of two or more elements may combine in different ratios to produce more than one compound.


Law of Constant Composition

  • A compound always contains two or more elements combined in a definite proportion by mass.


Law of Conservation of Mass

  • The total mass of materials present after a chemical reaction is the same as the total mass before the reaction

  • This is the basis for which postulate?


Parts of an Atom

  • J. J. Thomson - English physicist. 1897

  • Made a piece of equipment called a cathode ray tube.

    • Determined the charge to mass ratio

  • It is a vacuum tube - all the air has been pumped out.


Voltage source

Thomson’s Experiment

+

-

Vacuum tube

Metal Disks


Voltage source

Thomson Experiment

+

-

  • Passing an electric current makes a beam appear to move from the negative to the positive end


Voltage source

Thomson’s Experiment

+

-

  • By adding an electric field


Voltage source

Thomson’s Experiment

+

-

  • By adding an electric field he found that the moving pieces were negative


What Did Thomson Demonstrate?

  • Cathode rays:

    • Travel in straight lines

    • Are negatively charged

    • Are deflected by electric and magnetic fields


Thomson’s Model

  • Found the electron

  • Said the atom was like plum pudding

  • A bunch of positive stuff, with the electrons able to be removed


Robert Millikan

  • American Scientist

  • Goal: Determine the charge on the electron to determine its mass


The Discovery of Atomic Structure

  • Cathode Rays and Electrons

  • Consider the following experiment:

  • Oil drops are sprayed above a positively charged plate containing a small hole.

  • As the oil drops fall through the hole, they are given a negative charge.

  • Gravity forces the drops downward. The applied electric field forces the drops upward.

  • When a drop is perfectly balanced, the weight of the drop is equal to the electrostatic force of attraction between the drop and the positive plate.

Chapter 2


Atomizer

Oil droplets

+

-

Oil

Telescope

Millikan’s Experiment


Millikan’s Experiment

X-rays

X-rays give some drops a charge.


Millikan’s Experiment

Some drops would hover

From the mass of the drop and the charge on

the plates, he calculated the mass of an electron


Radioactivity

  • Discovered by accident

  • French scientist Henri Bequerel

    • Studying pitchblende (oxides of uranium)

    • Discovered that it spontaneously emits high energy radiation

  • Three types

    • alpha- helium nucleus (+2 charge, large mass)

    • beta- high speed electron

    • gamma- high energy light


  • (Uranium compound)

    2.2


    Rutherford’s Experiment

    • Ernest Rutherford English physicist. (1910)

    • Believed in the plum pudding model of the atom.

    • Used uranium to produce alpha particles.


    Rutherford’s Experiment

    • Aimed alpha particles at gold foil by drilling hole in lead block.

    • Since the mass is evenly distributed in gold atoms alpha particles should go straight through.

    • Used gold foil because it could be made atoms thin.


    Rutherford’s Experiment

    • When the alpha particles hit a florescent screen, it glows.


    Rutherford’s Experiment

    Florescent

    Screen

    Uranium

    Lead block

    Gold Foil


    What he expected


    Why ??

    • The alpha particles would pass through without changing direction very much

    • The negative charges were spread out evenly. Alone they were not enough to stop the alpha particles


    What he got


    How He Explained It

    • Atom is mostly empty

    • Small dense, positive piece at center

    • Alpha particles are deflected by it if they get close enough


    +

    How He Explained It


    Density and the Atom

    • Since most of the particles went through, it was mostly empty.

    • Because the pieces turned so much, the positive pieces were heavy.

    • Small volume, big mass, big density

    • This small dense positive area is the nucleus


    +

    Discovery of the Neutron

    +

    James Chadwick bombarded beryllium-9 with alpha particles,

    carbon-12 atoms were formed, and neutrons were emitted.

    *Walter Boethe

    Dorin, Demmin, Gabel, Chemistry The Study of Matter 3rd Edition, page 764


    Modern View

    • The atom is mostly empty space

    • Two regions

    • Nucleus- protons and neutrons

    • Electron cloud- region where you might find an electron


    Structure of Atom

    • There are two regions:

      • The nucleus: with protons and neutrons

        • Almost all the mass

      • Electron cloud- Most of the volume of an atom

        • The region where the electron can be found


    Size of Atom

    • Atoms are small.

    • Measured in picometers, 10-12 meters

    • Hydrogen atom, 32 pm radius


    Size of Atom

    • Nucleus tiny compared to atom

    • IF the atom was the size of a stadium, the nucleus would be the size of a marble.

    • Radius of the nucleus near 10-15m.

    • Density near 1014 g/cm3


    QUARKS

    equal in a neutral atom

    Most of the atom’s mass.

    Subatomic Particles

    ATOM

    NUCLEUS

    ELECTRONS

    NEUTRONS

    PROTONS

    Negative Charge

    Positive

    Charge

    Neutral

    Charge


    Subatomic particles

    Actual

    mass (g)

    Relative

    mass

    Name

    Symbol

    Charge

    Electron

    e-

    -1

    1/1840

    9.11 x 10-28

    Proton

    p+

    +1

    1

    1.67 x 10-24

    Neutron

    no

    0

    1

    1.67 x 10-24


    A

    X

    Mass Number

    Element Symbol

    Z

    Atomic Number

    1

    3

    2

    H (D)

    H (T)

    H

    1

    1

    1

    235

    238

    U

    U

    92

    92

    Atomic number (Z) = number of protons in nucleus

    Mass number (A) = number of protons + number of neutrons

    = atomic number (Z) + number of neutrons

    Isotopes are atoms of the same element (X) with different numbers of neutrons in their nuclei


    Symbols

    • Find the

      • number of protons

      • number of neutrons

      • number of electrons

      • Atomic number

      • Mass Number

    19

    F

    9


    Symbols

    • Find the

      • number of protons

      • number of neutrons

      • number of electrons

      • Atomic number

      • Mass Number

    80

    Br

    35


    Symbols

    • if an element has an atomic number of 34 and a mass number of 78 what is the

      • number of protons

      • number of neutrons

      • number of electrons

      • Complete symbol


    Atomic Mass

    • How heavy is an atom of oxygen?

    • There are different kinds of oxygen atoms.

    • More concerned with average atomic mass.

    • Based on abundance of each element in nature.

    • Don’t use grams because the numbers would be too small


    Measuring Atomic Mass

    • Unit is the Atomic Mass Unit (amu)

    • One twelfth the mass of a carbon-12 atom.

    • Each isotope has its own atomic mass we need the average from percent abundance.


    Calculating averages

    • You have five rocks, four with a mass of 50 g, and one with a mass of 60 g. What is the average mass of the rocks?

    • Total mass = 4 x 50 + 1 x 60 = 260 g

    • Average mass = 4 x 50 + 1 x 60 = 260 g 5 5


    Calculating averages

    • Average mass = 4 x 50 + 1 x 60 = 260 g 5 5 5

    • Average mass = .8 x 50 + .2 x 60

    • 80% of the rocks were 50 grams

    • 20% of the rocks were 60 grams

    • Average = % as decimal x mass + % as decimal x mass + % as decimal x mass +


    Atomic Mass

    • Calculate the atomic mass of copper if copper has two isotopes. 69.1% has a mass of 62.93 amu and the rest has a mass of 64.93 amu.


    17

    Cl

    35.4594

    100

    Mass spectrum of chlorine. Elemental chlorine (Cl2) contains

    only two isotopes: 34.97 amu (75.53%) and 36.97 (24.47%)

    90

    Cl-35

    80

    70

    AAM = (34.97 amu)(0.7553) + (36.97 amu)(0.2447)

    60

    AAM = (26.412841 amu) + (9.046559 amu)

    AAM = 35.4594 amu

    50

    Abundance

    40

    30

    Cl-37

    20

    10

    0

    36

    37

    35

    34

    Mass


    Atomic Mass

    • Magnesium has three isotopes. 78.99% magnesium 24 with a mass of 23.9850 amu, 10.00% magnesium 25 with a mass of 24.9858 amu, and the rest magnesium 26 with a mass of 25.9826 amu. What is the atomic mass of magnesium?

    • If not told otherwise, the mass of the isotope is the mass number in amu


    The Periodic Table


    Noble Gas

    Halogen

    Alkali Earth Metal

    Period

    Alkali Metal

    Group

    2.4


    Atoms and ions

    Atoms are electrically neutral.

    Same number of protons and electrons.

    Ions are atoms, or groups of atoms, with a charge.


    Atoms and Ions

    • Different numbers of protons and electrons.

    • Only electrons can move.

    • Gain or lose electrons.


    Anion

    • A negative ion.

    • Has gained electrons.

    • Non metals can gain electrons.

    • Charge is written as a super script on the right.

    F-1

    Has gained one electron

    O-2

    Has gained two electrons


    Cations

    • Positive ions.

    • Formed by losing electrons.

    • More protons than electrons.

    • Metals form cations.

    K+1

    Has lost one electron

    Ca+2

    Has lost two electrons


    Two Types of Compounds

    • Molecular compounds

      • Made of molecules.

      • Made by joining nonmetal atoms together into molecules.


    Two Types of Compounds

    • Ionic Compounds

      • Made of cations and anions.

      • Metals and nonmetals.

      • The electrons lost by the cation are gained by the anion.

      • The cation and anions surround each other.

      • Smallest piece is a FORMULA UNIT.


    Two Types of Compounds

    Ionic

    Molecular

    Smallest piece

    Formula Unit

    Molecule

    Types of elements

    Metal and Nonmetal

    Nonmetals

    Solid, liquid or gas

    State

    solid

    Melting Point

    High >300ºC

    Low <300ºC


    Chemical Formulas

    Shows the kind and number of atoms in the smallest piece of a substance.

    Molecular formula- number and kinds of atoms in a molecule.

    CO2


    Charges on ions

    For most of the Group A elements, the Periodic Table can tell what kind of ion they will form from their location.

    Elements in the same group have similar properties.

    Including the charge when they are ions.


    +1

    +2

    +3

    -3

    -2

    -1


    Naming ions

    • We will use the systematic way.

    • Cation- if the charge is always the same (Group A) just write the name of the metal.

    • Transition metals can have more than one type of charge.

      • Indicate the charge with roman numerals in parenthesis.


    Name these

    Na+1

    Ca+2

    Al+3

    Fe+3

    Fe+2

    Pb+2

    Li+1


    Write Formulas for these

    Potassium ion

    Magnesium ion

    Copper (II) ion

    Chromium (VI) ion

    Barium ion

    Mercury (II) ion


    Naming Anions

    Anions are always the same.

    Change the element ending to – ide

    F-1 Fluoride


    Name these

    Cl-1

    N-3

    Br-1

    O-2


    Write these

    Sulfide ion

    iodide ion

    phosphide ion

    Strontium ion


    Polyatomic ions

    • Groups of atoms that stay together and have a charge.

    • You must memorize these (table 2.5).

      • Acetate C2H3O2-1

      • Nitrate NO3-1

      • Nitrite NO2-1

      • Hydroxide OH-1

      • Permanganate MnO4-1

      • Cyanide CN-1


    Polyatomic ions

    Sulfate SO4-2

    Sulfite SO3-2

    Carbonate CO3-2

    Chromate CrO4-2

    Dichromate Cr2O7-2

    ChlorateClO3-

    Phosphate PO4-3

    Phosphite PO3-3

    Hydronium H3O +

    PerchlorateClO4-

    Ammonium NH4+1

    Chlorite ClO2 -


    Polyatomic Ions

    • Hypochlorite ClO-

    • Hydrogen carbonate ion HCO3-

    • Dihydrogen phosphate ion H2PO4-


    Ions and Ionic Compounds


    Fe2+

    Fe2+

    Fe2+

    Fe2+

    Fe2+

    Fe2+

    Fe2+

    Fe2+

    Nomenclature - Humor

    BaNa2

    “BaNaNa”

    “Ferrous Wheel”

    What weapon can you make

    from the elements nickel,

    potassium and iron?

    Fe = iron (Latin = ferrum)

    A KNiFe

    Fe2+ = lower oxidation state = ferrous

    Fe3+ = higher oxidation state = ferric


    Naming Binary Ionic Compounds

    Binary Compounds - 2 elements.

    Ionic - a cation and an anion.

    To write the names just name the two ions.

    Easy with Representative elements.

    Group A

    NaCl = Na+ Cl- = sodium chloride

    MgBr2 = Mg+2 Br- = magnesium bromide


    Naming Binary Ionic Compounds

    The problem comes with the transition metals.

    Need to figure out their charges.

    The compound must be neutral.

    same number of + and – charges.

    Use the anion to determine the charge on the positive ion.


    Naming Binary Ionic Compounds

    Write the name of CuO

    Need the charge of Cu

    O is -2

    copper must be +2

    Copper (II) oxide

    Name CoCl3

    Cl is -1 and there are three of them = -3

    Co must be +3 Cobalt (III) chloride


    Naming Binary Ionic Compounds

    Write the name of Cu2S.

    Since S is -2, the Cu2 must be +2, so each one is +1.

    copper (I) sulfide

    Fe2O3

    Each O is -2

    Fe must be = + 3

    iron (III) oxide


    Naming Binary Ionic Compounds

    Write the names of the following:

    KCl

    Na3N

    CrN

    Na2Se


    Ternary Ionic Compounds

    Will have polyatomic ions

    At least three elements

    name the ions

    NaNO3

    CaSO4

    CuSO3

    (NH4)2O


    Ternary Ionic Compounds

    LiCN

    Fe(OH)3

    (NH4)2CO3

    NiPO4


    Writing Formulas

    The charges have to add up to zero.

    Get charges on pieces.

    Cations from name of table.

    Anions from table or polyatomic.

    Balance the charges by adding subscripts.

    Put polyatomics in parenthesis.


    Writing Formulas

    Write the formula for calcium chloride.

    Calcium is Ca+2

    Chloride is Cl-1

    Ca+2 Cl-1

    CaCl2


    Write the formulas for these

    Lithium sulfide

    tin (II) oxide

    tin (IV) oxide

    Magnesium fluoride

    Copper (II) sulfate

    Iron (III) phosphide

    gallium nitrate

    Iron (III) sulfide


    Write the formulas for these

    Ammonium chloride

    ammonium sulfide

    barium nitrate


    Things to look for

    • If cations have (), the number is their charge.

      • Transition metal

    • If anions end in -ide they are probably off the periodic table (Monoatomic)

    • If anion ends in -ate or -ite it is polyatomic


    Molecular Compounds


    Molecular compounds

    made of just nonmetals

    smallest piece is a molecule

    can’t be held together because of opposite charges

    can’t use charges to figure out how many of each atom


    Easier

    • Ionic compounds use charges to determine how many of each

      • Have to figure out charges

      • Have to figure out numbers

    • Molecular compounds name tells you the number of atoms

      • Uses prefixes to tell you the number


    Prefixes

    1 mono-

    2 di-

    3 tri-

    4 tetra-

    5 penta-

    6 hexa-

    7 hepta-

    8 octa-


    Prefixes

    9 nona-

    10 deca-

    One exception is we don’t write mono- if there is only one of the first element.


    Name These

    N2O

    NO2

    Cl2O7

    CBr4

    CO2

    BaCl2


    Write formulas for these

    diphosphorus pentoxide

    tetraiodide nonoxide

    sulfur hexaflouride

    nitrogen trioxide

    Carbon tetrahydride

    phosphorus trifluoride

    aluminum chloride


    Naming Acidsa little tricky so pay attention


    Acids

    Compounds that give off hydrogen ions when dissolved in water

    Must have H in them (somewhere)

    will always be some H next to an anion

    The anion determines the name.


    Naming acids

    If the anion attached to hydrogen ends in -ide, put the prefix hydro- and change -ide to -ic acid

    HCl - hydrogen ion and chloride ion

    hydrochloric acid

    H2S hydrogen ion and sulfide ion

    hydrosulfuric acid


    Naming Acids

    If the anion has oxygen in it

    it ends in -ate or -ite

    change the suffix -ate to -ic acid

    HNO3 Hydrogen and nitrate ions

    Nitric acid

    change the suffix -ite to -ous acid

    HNO2 Hydrogen and nitrite ions

    Nitrous acid


    Name these

    HF

    H3P

    H2SO4

    H2SO3

    HCN

    H2CrO4


    Writing Formulas

    Hydrogen will always be first

    name will tell you the anion

    make the charges cancel out.

    Starts with hydro- no oxygen, -ide

    no hydro, -ate comes from -ic, -ite comes from -ous


    Write formulas for these

    hydroiodic acid

    acetic acid

    carbonic acid

    phosphorous acid

    hydrobromic acid


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