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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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slide2

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
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 matter1
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 matter2
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 matter3
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
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
Law of Constant Composition
  • A compound always contains two or more elements combined in a definite proportion by mass.
law of conservation of 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
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.
thomson s experiment

Voltage source

Thomson’s Experiment

+

-

Vacuum tube

Metal Disks

thomson experiment

Voltage source

Thomson Experiment

+

-

  • Passing an electric current makes a beam appear to move from the negative to the positive end
thomson s experiment1

Voltage source

Thomson’s Experiment

+

-

  • By adding an electric field
thomson s experiment2

Voltage source

Thomson’s Experiment

+

-

  • By adding an electric field he found that the moving pieces were negative
what did thomson demonstrate
What Did Thomson Demonstrate?
  • Cathode rays:
      • Travel in straight lines
      • Are negatively charged
      • Are deflected by electric and magnetic fields
thomson s model
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
Robert Millikan
  • American Scientist
  • Goal: Determine the charge on the electron to determine its mass
slide18

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

slide19

Atomizer

Oil droplets

+

-

Oil

Telescope

Millikan’s Experiment

millikan s experiment
Millikan’s Experiment

X-rays

X-rays give some drops a charge.

millikan s experiment1
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
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
rutherford s experiment
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 experiment1
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 experiment2
Rutherford’s Experiment
  • When the alpha particles hit a florescent screen, it glows.
rutherford s experiment3
Rutherford’s Experiment

Florescent

Screen

Uranium

Lead block

Gold Foil

slide29
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
how he explained it
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
density and the atom
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

+

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
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
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
Size of Atom
  • Atoms are small.
  • Measured in picometers, 10-12 meters
  • Hydrogen atom, 32 pm radius
size of atom1
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
subatomic particles

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 particles1
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

slide41

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
Symbols
  • Find the
      • number of protons
      • number of neutrons
      • number of electrons
      • Atomic number
      • Mass Number

19

F

9

slide43

Symbols

  • Find the
    • number of protons
    • number of neutrons
    • number of electrons
    • Atomic number
    • Mass Number

80

Br

35

symbols1
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
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
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
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 averages1
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 mass1
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.
slide50

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 mass2
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
slide53

Noble Gas

Halogen

Alkali Earth Metal

Period

Alkali Metal

Group

2.4

slide54

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
Atoms and Ions
  • Different numbers of protons and electrons.
  • Only electrons can move.
  • Gain or lose electrons.
anion
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

slide57

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
Two Types of Compounds
  • Molecular compounds
    • Made of molecules.
    • Made by joining nonmetal atoms together into molecules.
two types of compounds1
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 compounds2
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

slide61

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

slide62

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.

slide63

+1

+2

+3

-3

-2

-1

slide64

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.
slide65

Name these

Na+1

Ca+2

Al+3

Fe+3

Fe+2

Pb+2

Li+1

slide66

Write Formulas for these

Potassium ion

Magnesium ion

Copper (II) ion

Chromium (VI) ion

Barium ion

Mercury (II) ion

slide67

Naming Anions

Anions are always the same.

Change the element ending to – ide

F-1 Fluoride

slide68

Name these

Cl-1

N-3

Br-1

O-2

slide69

Write these

Sulfide ion

iodide ion

phosphide ion

Strontium ion

slide70

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
slide71

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
Polyatomic Ions
  • Hypochlorite ClO-
  • Hydrogen carbonate ion HCO3-
  • Dihydrogen phosphate ion H2PO4-
nomenclature humor

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

slide75

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

slide76

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.

slide77

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

slide78

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

slide79

Naming Binary Ionic Compounds

Write the names of the following:

KCl

Na3N

CrN

Na2Se

slide80

Ternary Ionic Compounds

Will have polyatomic ions

At least three elements

name the ions

NaNO3

CaSO4

CuSO3

(NH4)2O

slide81

Ternary Ionic Compounds

LiCN

Fe(OH)3

(NH4)2CO3

NiPO4

slide82

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.

slide83

Writing Formulas

Write the formula for calcium chloride.

Calcium is Ca+2

Chloride is Cl-1

Ca+2 Cl-1

CaCl2

slide84

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

slide85

Write the formulas for these

Ammonium chloride

ammonium sulfide

barium nitrate

slide86

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
slide88

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

slide89

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
slide90

Prefixes

1 mono-

2 di-

3 tri-

4 tetra-

5 penta-

6 hexa-

7 hepta-

8 octa-

slide91

Prefixes

9 nona-

10 deca-

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

slide92

Name These

N2O

NO2

Cl2O7

CBr4

CO2

BaCl2

slide93

Write formulas for these

diphosphorus pentoxide

tetraiodide nonoxide

sulfur hexaflouride

nitrogen trioxide

Carbon tetrahydride

phosphorus trifluoride

aluminum chloride

slide95

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.

slide96

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

slide97

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

slide98

Name these

HF

H3P

H2SO4

H2SO3

HCN

H2CrO4

slide99

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

slide100

Write formulas for these

hydroiodic acid

acetic acid

carbonic acid

phosphorous acid

hydrobromic acid

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