Chapter 4Chapter 4

The Structure of the AtomThe Structure of the Atom

Chapter 4 Chapter 4

Democritus:Democritus: Greek philosopher coined the word Greek philosopher coined the word “atom”. Greek word comes from “atom”. Greek word comes from “atomos” “atomos” meaning meaning indivisible.indivisible.

Antoine Lavoisier: Antoine Lavoisier: Law of Conservation of MatterLaw of Conservation of Matter

Joseph ProustJoseph Proust: Law of Constant Composition : Law of Constant Composition (aka Law of Definite Proportion)(aka Law of Definite Proportion)

John Dalton’s Atomic TheoryJohn Dalton’s Atomic Theory

All matter is made up of atoms, which are All matter is made up of atoms, which are indivisible.indivisible.All atoms of the same element are All atoms of the same element are identical, but differ from those of other identical, but differ from those of other elements.elements.Atoms are neither created nor destroyed in Atoms are neither created nor destroyed in any chemical reaction.any chemical reaction.A given compound always has the same A given compound always has the same relative numbers and kinds of atoms.relative numbers and kinds of atoms.

Dalton Model of the AtomDalton Model of the Atom

Atoms are indivisibleAtoms are indivisible

No subatomic No subatomic particles have been particles have been discovered!discovered!

Atoms of each Atoms of each element are identicalelement are identical

Isotopes unknown at Isotopes unknown at this time!this time!

1803!1803!

ElectricityElectricity

Ben Franklin: Ben Franklin: studied studied static electricity; static electricity; objects could have objects could have negative or positive negative or positive chargecharge..The word electricity The word electricity comes from comes from elektron elektron (Greek for (Greek for amber)amber)Static electricity is Static electricity is charge in motion.charge in motion.

Discovering Atomic StructureDiscovering Atomic Structure

Opposite charges Opposite charges attractattract

Like charges Like charges repelrepel

Crookes:Crookes: studied studied behavior of gases in a behavior of gases in a vacuum tube.vacuum tube.

Cathode Ray TubeCathode Ray Tube

Thomson: Discovered Electrons Thomson: Discovered Electrons

He used a magnet in the CRT to deflect the rays He used a magnet in the CRT to deflect the rays away from the away from the negativenegative pole of the magnet (rays pole of the magnet (rays were pulled toward the were pulled toward the positive polepositive pole).).No deflection without the magnet, so the rays No deflection without the magnet, so the rays must be must be negativenegative..Using other gases in the tube gave the same Using other gases in the tube gave the same effect, so it is characteristic to all elements.effect, so it is characteristic to all elements.Thomson discovered electrons.Thomson discovered electrons.He thought the positive charges were like He thought the positive charges were like pudding and that electrons were like raisins!pudding and that electrons were like raisins!

Plum Pudding ModelPlum Pudding Model

Millikan’sMillikan’s Oil Drop Experiment Oil Drop Experiment

He is known for measuring the He is known for measuring the charge on charge on an electronan electron (from which he calculated the (from which he calculated the massmass of an electronof an electron).).

He concluded the charge on an electron He concluded the charge on an electron was was 1.60 x 101.60 x 10-19-19 coulombs coulombs

He used a charge/mass ratio to calculate He used a charge/mass ratio to calculate the mass of an electron as the mass of an electron as 9.109 x 109.109 x 10-28-28 g. g.

Millikan’s ExperimentMillikan’s Experiment

Rutherford’s Rutherford’s Gold-FoilGold-Foil Experiment Experiment

He discovered the He discovered the positively charged positively charged nucleusnucleus by shooting positive alpha by shooting positive alpha particles through gold foil. Most went particles through gold foil. Most went through, but some were deflected.through, but some were deflected.

Since some of the particles deflected Since some of the particles deflected backwards, it had to get close to backwards, it had to get close to something positive; the nucleus is something positive; the nucleus is positive;positive; protons were discoveredprotons were discovered..

RutherfordRutherford

He concluded the He concluded the most most dense part of dense part of the atom was in the the atom was in the center, which he center, which he called the called the nucleusnucleus..

Most of the atom was Most of the atom was empty space (shells).empty space (shells).

Rutherford’s Lighter SideRutherford’s Lighter Side

Rutherford ModelRutherford Model

The NeutronThe Neutron

Discovered in 1932 Discovered in 1932 by James Chadwick by James Chadwick (Coworker of (Coworker of Rutherford)Rutherford)

Same mass as protonSame mass as proton

No electrical chargeNo electrical charge

Also found in the Also found in the nucleusnucleus

Subatomic ParticlesSubatomic Particles

ParticleParticle LocationLocation MassMass ChargeCharge

ProtonProton NucleusNucleus 1 amu1 amu +1+1

NeutronNeutron NucleusNucleus 1 amu1 amu 00

ElectronElectron OutsideOutside

NucleusNucleus

1/18361/1836

amuamu

-1-1

RadioactivityRadioactivity

Henri Becqerel Henri Becqerel accidently discovered accidently discovered uranium exhibits uranium exhibits radioactivity.radioactivity.

Marie and Pierre Marie and Pierre Curie Curie isolated radium isolated radium (Ra) and polonium (Ra) and polonium (Po) which are both (Po) which are both radioactive.radioactive.

Types of RadiationTypes of Radiation

Modern Atomic TheoryModern Atomic Theory

Atoms consist of subatomic particles: Atoms consist of subatomic particles: protons, neutrons, and electrons.protons, neutrons, and electrons.

Atoms are not permanently changed Atoms are not permanently changed during chemical reactions, merely during chemical reactions, merely rearranged.rearranged.

Atoms can be changed to other elements, Atoms can be changed to other elements, but not by but not by ordinary chemical reactions ordinary chemical reactions (nuclear).(nuclear).

Cont.Cont.

Atoms of the same element are not all Atoms of the same element are not all alike (masses may differ-alike (masses may differ-ISOTOPESISOTOPES).).

Atomic Number (Z)Atomic Number (Z)

An atom’s An atom’s identityidentity comes from the number comes from the number of of protonsprotons in its nucleus. in its nucleus.

Atomic number is defined as the number Atomic number is defined as the number of of protonsprotons (which is also the number of (which is also the number of electronselectrons) in an atom’s nucleus.) in an atom’s nucleus.

Atoms are electrically Atoms are electrically neutralneutral..

Atomic # = Atomic # = # protons = # electrons# protons = # electrons

(abbrev. Z)(abbrev. Z)

Mass Number (Mass Number (AA))

The total number of protons and The total number of protons and neutronsneutrons

of an isotope.of an isotope.

# neutrons = mass # - atomic ## neutrons = mass # - atomic #

or A - Zor A - Z

IsotopesIsotopes

Atoms of the same element with the same Atoms of the same element with the same number of number of protonsprotons, but different , but different number of number of neutrons.neutrons.

Ex. 3 isotopes of hydrogenEx. 3 isotopes of hydrogen

Hydrogen 1 (protium) 1 pHydrogen 1 (protium) 1 p++, 0 n, 0 noo, 1 e, 1 e--

Hydrogen 2 (deuterium) 1 pHydrogen 2 (deuterium) 1 p++, 1 n, 1 noo, 1 e, 1 e--

Hydrogen 3 (tritium) 1 pHydrogen 3 (tritium) 1 p++, 2 n, 2 n00, 1 e, 1 e--

radioactive!radioactive!

It gets heavier!It gets heavier!

Designating IsotopesDesignating Isotopes

Hyphen notation- the mass # is added with Hyphen notation- the mass # is added with a hyphen to the a hyphen to the name name of the element. Ex. of the element. Ex. Carbon – 12Carbon – 12

**LOOK UP THE ATOMIC # on the periodic **LOOK UP THE ATOMIC # on the periodic chart to find chart to find protonsprotons, (which is = to the , (which is = to the electrons). Carbon -12 has 6 protons, 6 electrons). Carbon -12 has 6 protons, 6 electrons, and 6 neutrons (12-6 = 6).electrons, and 6 neutrons (12-6 = 6).

Isotopes, cont.Isotopes, cont.

Nuclear symbol- the atomic # is added to Nuclear symbol- the atomic # is added to the symbol for the element as a subscript the symbol for the element as a subscript to the LEFT and the mass # is added as a to the LEFT and the mass # is added as a superscript on the left.superscript on the left.

Ex. Ex. 17173737Cl How many protons, neutrons Cl How many protons, neutrons

and electrons does this isotope of chlorine and electrons does this isotope of chlorine have? have?

Ex.Ex.

How many protons, neutrons, and How many protons, neutrons, and electrons does uranium -238 have?electrons does uranium -238 have?

IonsIons

An atom that has gained or lost one or An atom that has gained or lost one or more electrons.more electrons.

An ion may have a positive or negative An ion may have a positive or negative charge.charge.

Cations Cations are positively charged because are positively charged because they they loselose electrons. electrons.

Anions Anions are negatively charged because are negatively charged because they they gaingain electrons. electrons.

ExampleExample

Calculate the charges Calculate the charges on the following ions on the following ions and indicate whether and indicate whether the ions are cations or the ions are cations or anions.anions.

IONION ProtonsProtons ElectronsElectrons

XX 3535 3636

YY 33 22

ZZ 2020 1818