11

Internal Structure of Internal Structure of AtomsAtoms

Chapter 3-Section 2Chapter 3-Section 2

22

Subatomic ParticlesSubatomic Particles

Electrons, protons, and Electrons, protons, and neutronsneutrons

Electricity – J.J.Thomson – Electricity – J.J.Thomson – ElectronsElectrons

Metal plates – electrodesMetal plates – electrodes–Cathode -Cathode -–Anode +Anode +

33

Cathode Ray Tube

44

ElectronsElectrons

The wheel in the cathode The wheel in the cathode ray tube-massray tube-mass

Originate at negatively Originate at negatively charged side – negatively charged side – negatively charged electronscharged electrons

MagnetMagnet

55

MassMassFurther experiments found the Further experiments found the

mass of an electron to be mass of an electron to be 5.485799 x 105.485799 x 10-4-4 amu amu

2000 times lighter than an atom2000 times lighter than an atomThe charge was found to be The charge was found to be

-1.602189 x 10-1.602189 x 10-19-19 C C C = Coulombs – SI unitC = Coulombs – SI unit

66

ChargesCharges

An atom is not the An atom is not the simplest form of mattersimplest form of matter

Since electrons (e-) are Since electrons (e-) are negative, how is an atom negative, how is an atom neutral?neutral?

77

The NucleusThe Nucleus

Thompson’s Thompson’s plum plum pudding pudding modelmodel

This is no This is no longer a longer a valid modelvalid model

88

Rutherford’s NucleusRutherford’s Nucleus

Gold foil experimentGold foil experiment–Alpha particlesAlpha particles–Some passed through Some passed through and some were repelled and some were repelled away from the foilaway from the foil

Rutherford’s NucleusRutherford’s Nucleus

2 years later…2 years later… Must be a concentrated Must be a concentrated

tiny space with a mass tiny space with a mass larger than the larger than the αα particle particle

The rest of the gold foil The rest of the gold foil would be empty space.would be empty space.

99

1010

The modern nucleusThe modern nucleusThe nucleus is a dense The nucleus is a dense

central portion of the atom central portion of the atom that is positively charged.that is positively charged.

The nucleus has most of The nucleus has most of the mass of the atom, but the mass of the atom, but is very small compared to is very small compared to the entire atom. the entire atom.

Marble and football Marble and football

1111

Protons and NeutronsProtons and Neutrons

Protons = +Protons = +Charge = 1.602189 x 10Charge = 1.602189 x 10-19-19

CCMass = 1.0073 amu (2000 Mass = 1.0073 amu (2000

times the mass of an times the mass of an electron)electron)

1212

Protons and NeutronsProtons and Neutrons

A neutral atom has equal A neutral atom has equal numbers of protons and numbers of protons and electronselectrons

Masses of all atoms (except H) Masses of all atoms (except H) were greater than the mass of were greater than the mass of e- and p+ combined so where e- and p+ combined so where does this mass come from?does this mass come from?

1313

NeutronsNeutrons Joliot-Curie and Chadwick Joliot-Curie and Chadwick

experiment with berylliumexperiment with beryllium–Alpha particlesAlpha particles–Beam of power not deflected Beam of power not deflected by electric or magnetic fieldsby electric or magnetic fields

These particles must be neutral These particles must be neutral

Mass of 1.0087 amuMass of 1.0087 amu

1414

Coulomb’s LawCoulomb’s Law

States that the force States that the force between two charged between two charged particles is inversely particles is inversely proportional to the square proportional to the square of the distance between of the distance between them.them.

1515

Coulomb’s LawCoulomb’s Law

Force = 2.32 N

Distance = 0.010 pm

Force = 0.58 N Distance = 0.020 pm

1616

Strong ForceStrong Force

The force that holds the protons The force that holds the protons and neutrons in a nucleus.and neutrons in a nucleus.

It is greater than the repulsive It is greater than the repulsive forces at close distances.forces at close distances.

Must be neutrons in nucleus if Must be neutrons in nucleus if there is more than one proton.there is more than one proton.

1717

Atomic NumberAtomic NumberAtomic numberAtomic number – the number – the number

of protons in the nucleus of of protons in the nucleus of an atoman atom

# of protons =#of electrons# of protons =#of electronsAlways whole numbersAlways whole numbersSame for all atoms of the Same for all atoms of the

same element.same element.

1818

Mass NumberMass NumberThe total number of protons The total number of protons

and neutrons in the nucleus and neutrons in the nucleus of an atom.of an atom.

# of Neutrons=Mass# - # of Neutrons=Mass# - Atomic#Atomic#

Can vary for atoms of the Can vary for atoms of the same element.same element.

1919

BoronBoronThe atomic number of boron is The atomic number of boron is

5.5.The mass number of boron is 11.The mass number of boron is 11.The number of protons and The number of protons and

electrons are equal to the electrons are equal to the atomic number.atomic number.

2020

BoronBoronAtomic Number

Mass Number

Element Symbol

2121

BoronBoronElectrons = 5Electrons = 5Protons = 5Protons = 5Neutrons = 11 – 5 = 6Neutrons = 11 – 5 = 6

2222

CopperCopperHow many protons, How many protons,

neutrons, and electrons neutrons, and electrons are present in copper are present in copper which has an atomic which has an atomic number of 29 and a mass number of 29 and a mass number of 64?number of 64?

2323

CopperCopperElectrons = 29Electrons = 29Protons = 29Protons = 29Neutrons = 35Neutrons = 35

2424

Atomic StructureAtomic Structure

Atomic and Atomic and mass mass numbers can numbers can be written be written beside the beside the elements elements symbolsymbol

9944BeBe

Mass Number

Atomic Number

2525

Concept CheckConcept Check

What three subatomic What three subatomic particles are important to particles are important to chemistry and what are chemistry and what are their electrical charges?their electrical charges?

2626

IsotopesIsotopes

Isotope – An atom that has Isotope – An atom that has the same # of protons as the same # of protons as other atoms of the same other atoms of the same element but has a diff. # element but has a diff. # of neutronsof neutrons

Many elements exist as Many elements exist as mixtures of isotopes.mixtures of isotopes.

2727

Lead IsotopesLead Isotopes

NameName # of # of NeutronNeutronss

Mass Mass (amu)(amu)

Amt Amt (%)(%)

Lead - Lead - 204204

122122 203.97203.9733

1.41.4

-206-206 124124 205.97205.9744

24.124.1

-207-207 125125 206.97206.9766

22.122.1

-208-208 126126 207.97207.9777

52.452.4

2828

RadioisotopesRadioisotopesSome elements have only Some elements have only

one stable isotope and will one stable isotope and will degrade and are called degrade and are called radioisotopes.radioisotopes.

Unstable nuclear Unstable nuclear configurations.configurations.

Unstable atoms that undergo Unstable atoms that undergo radioactive decay.radioactive decay.

2929

Unstable in NatureUnstable in Nature

Some elements have no Some elements have no stable isotopes.stable isotopes.

Technetium has no stable Technetium has no stable nucleus.nucleus.

Was the first element to be Was the first element to be made artificially in a made artificially in a laboratory.laboratory.

3030

Section ReviewSection Review

Complete numbers 1-6 Complete numbers 1-6 in the section review on in the section review on page 89.page 89.