Chapt4 2, 4-3

Chapter 4Chapter 4

Atoms and their structureAtoms and their structure

Idea of the atomIdea of the atom Original idea Ancient Greece (400 B.C.)Original idea Ancient Greece (400 B.C.) Democritus, Leucippus and Aristotle- Greek Democritus, Leucippus and Aristotle- Greek

philosophers.philosophers.

History of the atomHistory of the atom Late 1700’s - John Dalton- England.Late 1700’s - John Dalton- England. Teacher- summarized results of his Teacher- summarized results of his

experiments and those of others.experiments and those of others. Elements substances that can’t be Elements substances that can’t be

broken downbroken down In Dalton’s Atomic Theory - combined In Dalton’s Atomic Theory - combined

idea of elements with that of atoms.idea of elements with that of atoms.

Dalton’s Atomic TheoryDalton’s Atomic Theory All All mattermatter is made of tiny is made of tiny indivisibleindivisible

particles called atoms.particles called atoms. Atoms of the same element are identical, Atoms of the same element are identical,

those of different atoms are different.those of different atoms are different. Atoms of different elements combine in Atoms of different elements combine in

whole number ratios to form compounds.whole number ratios to form compounds.

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

Parts of AtomsParts of Atoms J. J. Thomson - English physicist. 1897J. J. Thomson - English physicist. 1897 Made a piece of equipment called a Made a piece of equipment called a

cathode ray tube.cathode ray tube. It is a vacuum tube - all the air has been It is a vacuum tube - all the air has been

pumped out.pumped out. A limited amount of other gases are put A limited amount of other gases are put

inin

Thomson’s ExperimentThomson’s Experiment

Voltage source

+-

Metal Disks

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


Voltage source

+-

Voltage source


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

+

-

Thomson’s ExperimentThomson’s Experiment Used many different metals and gasesUsed many different metals and gases Beam was always the sameBeam was always the same By the amount it bent he could find the By the amount it bent he could find the

ratio of charge to massratio of charge to mass Was the same with every materialWas the same with every material Same type of piece in every kind of Same type of piece in every kind of

atomatom

Thomsom’s ModelThomsom’s Model Found the electron.Found the electron. Couldn’t find Couldn’t find

positive (for a while).positive (for a while). Said the atom was Said the atom was

like plum pudding.like plum pudding. A bunch of positive A bunch of positive

stuff, with the stuff, with the electrons able to be electrons able to be removed.removed.

Rutherford’s experimentRutherford’s experiment When the alpha particles hit a florescent When the alpha particles hit a florescent

screen, it glows.screen, it glows. Here’s what it looked like (pg 72)Here’s what it looked like (pg 72)

Lead block

Uranium

Gold Foil

Flourescent Screen

He ExpectedHe Expected The alpha particles to pass through The alpha particles to pass through

without changing direction very much.without changing direction very much. Because…Because… The positive charges were spread out The positive charges were spread out

evenly. Alone they were not enough to evenly. Alone they were not enough to stop the alpha particles.stop the alpha particles.

What he expected

Because, he thought the mass was evenly distributed in the atom

What he got

How he explained it

+

Atom is mostly empty.Atom is mostly empty. Small dense,Small dense,

positive piecepositive piece at at center.center.

Alpha particles Alpha particles are deflected byare deflected by

it if they get close it if they get close enough. enough.

Modern ViewModern View The atom is mostly The atom is mostly

empty space.empty space. Has two regions.Has two regions.

– NucleusNucleus--– Electron cloud-Electron cloud-

Subatomic particlesSubatomic particles

Electron

Proton

Neutron

Name Symbol ChargeRelative mass

Actual mass (g)

e-

p+

n0

-1

+1

0

1/1840

1

1

9.11 x 10-28

1.67 x 10-24

1.67 x 10-24

Structure of the AtomStructure of the Atom There are two regions.There are two regions.

1. The nucleus- 1. The nucleus- contains protons and contains protons and neutrons.neutrons.» Positive charge.Positive charge.» Almost all the mass.Almost all the mass.

2. Electron cloud- 2. Electron cloud- most of the volume most of the volume of an atom (empty space).of an atom (empty space).» The region where the electron can be foundThe region where the electron can be found..

Counting the ParticlesCounting the ParticlesAtomic Number

Atomic Mass

Atomic Number Atomic Number = number of protons (# p)= number of protons (# p) # of protons determines kind of atom.# of protons determines kind of atom. Helps find the atom in the periodic tableHelps find the atom in the periodic table In neutral atom, atomic number = # of eIn neutral atom, atomic number = # of e

Atomic mass - Atomic mass - avg mass of all isotopes of the atomavg mass of all isotopes of the atom Mass Number = Mass Number = (rounded atomic mass) # p + # n(rounded atomic mass) # p + # n

All the things with mass.All the things with mass. NOT on the periodic tableNOT on the periodic table

SymbolsSymbols if an element has an atomic if an element has an atomic

number of 34 and a mass number number of 34 and a mass number of 79 what is the of 79 what is the

–number of protonsnumber of protons

–number of neutronsnumber of neutrons

–number of electronsnumber of electrons– NameName

IsotopesIsotopes Dalton was wrong.Dalton was wrong. Atoms of the same element not Atoms of the same element not

identical, may have different masses.identical, may have different masses. called called isotopes – isotopes – different number of different number of

neutronsneutrons . . Do isotopes of an element have the Do isotopes of an element have the

same number of protons? Electrons?same number of protons? Electrons?

Nuclear SymbolsNuclear Symbols Contain the symbol of the element, the Contain the symbol of the element, the

mass number and the atomic number.mass number and the atomic number.

X Massnumber

Atomicnumber

Naming IsotopesNaming Isotopes Can also be represented as follows:Can also be represented as follows:

Put the mass number after the name Put the mass number after the name of the element.of the element.

carbon- 12 carbon- 12 carbon -14carbon -14 uranium-235uranium-235

SymbolsSymbols Find the Find the

– number of protonsnumber of protons

– number of neutronsnumber of neutrons

– number of electronsnumber of electrons

– Atomic numberAtomic number

– Mass NumberMass Number

– NameName

Na2411

SymbolsSymbols Find the Find the


–number of neutronsnumber of neutrons

–number of electronsnumber of electrons

–Atomic numberAtomic number

–Mass NumberMass Number– NameName

Br80 35

SymbolsSymbols if an element has 91 protons and if an element has 91 protons and

140 neutrons what is the 140 neutrons what is the


–Mass numberMass number

–number of electronsnumber of electrons

–Complete symbolComplete symbol– NameName

SymbolsSymbols if an element has 78 electrons and if an element has 78 electrons and

117 neutrons what is the 117 neutrons what is the


–Mass numberMass number


–Complete symbolComplete symbol– NameName

Measuring Atomic MassMeasuring Atomic Mass Atomic mass – average mass of isotopes in an Atomic mass – average mass of isotopes in an

elementelement Unit is the Unit is the Atomic Mass Unit Atomic Mass Unit (amu)(amu) 1 amu = One twelfth the mass of a carbon-12 1 amu = One twelfth the mass of a carbon-12

atom. atom. 1 amu ~ mass of p1 amu ~ mass of p++

and nand n00

Mass of isotopes notMass of isotopes not

Exact (Exact (silicon-30 29.974 amu)silicon-30 29.974 amu)

Calculating Atomic MassCalculating Atomic Mass Atomic mass:Atomic mass:

Atomic mass = (mAtomic mass = (m11* %* %11) + (m) + (m22* %* %22)+ (m)+ (mnn* %* %nn))

mm11 = mass of Isotope 1 = mass of Isotope 1

%%1 1 = abundance or percent of isotope 1 MUST = abundance or percent of isotope 1 MUST

BE IN DECIMAL BE IN DECIMAL Use for as many isotopes in an element.Use for as many isotopes in an element.

Atomic MassAtomic Mass Calculate the atomic mass of copper if Calculate the atomic mass of copper if

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

Atomic MassAtomic Mass Magnesium has three isotopesMagnesium has three isotopes. . 78.99%78.99%

magnesium 24 magnesium 24 with a mass of with a mass of 23.985023.9850 amu, amu, 10.00% magnesium 25 10.00% magnesium 25 with a mass of with a mass of 24.9858 amu24.9858 amu, and the , and the rest magnesium 25 rest magnesium 25 with a mass of with a mass of 25.9826 amu25.9826 amu. What is the . What is the atomic mass of magnesium?atomic mass of magnesium?

Atomic MassAtomic Mass Is not a whole number because it is an Is not a whole number because it is an

average. average. are the decimal numbers on the periodic are the decimal numbers on the periodic

table.table.

Chapt4 2, 4-3

Technology

Transcript of Chapt4 2, 4-3