Ch. 4: Atoms/Atomic Theory. Atoms Definition - the smallest particle that has the properties of an element, basic unit of matter 119 distinct atoms as.

Ch. 4: Atoms/Atomic Theory

Atoms

• Definition- the smallest particle that has the properties of an element, basic unit of matter

•119 distinct atoms as of 1999, form elements

Atomic Symbols

- each element has its own name, accompanied by a symbol

- usually one/two letters (first one is always capitalized)

ex. Iron: Fe- Fe represents 1 atom of iron, - 2Fe represents 2 atoms of iron etc…

- can also be written as Fe2

HistoryHistory

DemocritusDemocritus named the most basic named the most basic

particleparticle atom- means “atom- means “indivisibleindivisible””

AristotleAristotle didn’t believe in atomsdidn’t believe in atoms thought matter was thought matter was

continuouscontinuous

HistoryHistory

by 1700s, all chemists agreedby 1700s, all chemists agreed on the existence of atomson the existence of atoms that atoms combined to make that atoms combined to make

compoundscompounds

Still did not agree on whether Still did not agree on whether elements combined in the same ratio elements combined in the same ratio when making a compoundwhen making a compound

Law of Conservation of MassLaw of Conservation of Mass

massmass is neither is neither createdcreated or or destroyeddestroyed during regular during regular chemicalchemical or or physicalphysical changeschanges

Law of Definite ProportionsLaw of Definite Proportions

anyany amount of a compound contains amount of a compound contains the same element in the the same element in the same same proportionsproportions by mass by mass

No matter where the copper carbonate is used, it still has the same composition

Law of Multiple ProportionsLaw of Multiple Proportions applies when applies when 2 or more elements2 or more elements combine combine

to make to make more than onemore than one type of compound type of compound the the mass ratiosmass ratios of the second element of the second element

simplify to simplify to small whole numberssmall whole numbers

Dalton’s Atomic TheoryDalton’s Atomic Theory

1.1. All mass is made of All mass is made of atomsatoms

2.2. Atoms of same Atoms of same elementelement have the same have the same sizesize, , massmass, and , and propertiesproperties

3.3. Atoms can’t be Atoms can’t be subdividedsubdivided, , createdcreated or or destroyeddestroyed

4.4. Atoms of Atoms of differentdifferent elements combine in elements combine in whole number whole number ratiosratios to make compounds to make compounds

5.5. In chemical reactions, atoms are In chemical reactions, atoms are combinedcombined, , separatedseparated, and , and rearrangedrearranged..

Modern Atomic TheoryModern Atomic Theory

Some parts of Dalton’s theory were wrong:Some parts of Dalton’s theory were wrong: atoms are atoms are divisibledivisible into smaller particles into smaller particles

((subatomicsubatomic particles) particles) atoms of the same element atoms of the same element cancan have different have different

masses (masses (isotopesisotopes)) Most important parts of atomic theory:Most important parts of atomic theory:

all matter is made of atomsall matter is made of atoms atoms of different elements have different atoms of different elements have different

propertiesproperties

Structure of AtomStructure of Atom

Nucleus:Nucleus: contains contains protonsprotons

and and neutronsneutrons takes up very takes up very littlelittle

spacespace Electron Cloud:Electron Cloud:

contains contains electronselectrons takes up takes up mostmost of of

spacespace

Subatomic ParticlesSubatomic Particles

includes all particles inside atomincludes all particles inside atom protonproton electronelectron neutronneutron

charge on protons and electrons are charge on protons and electrons are equal but oppositeequal but opposite

to make an atom to make an atom neutralneutral, need equal , need equal numbers of numbers of protonsprotons and and electronselectrons

Subatomic ParticlesSubatomic Particles

number of protonsnumber of protons identifies the identifies the atom as a certain elementatom as a certain element

protons and neutrons are about protons and neutrons are about samesame size size

electrons are much smaller electrons are much smaller

Comparing Subatomic Comparing Subatomic ParticlesParticles

Discovery of ElectronDiscovery of Electron resulted from scientists passing resulted from scientists passing electric electric

currentcurrent through through gasesgases to test conductivity to test conductivity used used cathode-ray tubescathode-ray tubes noticed that when current was passed noticed that when current was passed

through a through a glowglow (or “ray”)(or “ray”) was produced was produced

Discovery of Discovery of ElectronElectron

Noted Qualities of Ray Produced:Noted Qualities of Ray Produced:

1.1. existedexisted- there was a shadow on the - there was a shadow on the glass when an object was placed glass when an object was placed insideinside

2.2. had had massmass- the paddle wheel placed - the paddle wheel placed inside, moved from one end to the inside, moved from one end to the other so something must have been other so something must have been “pushing” it“pushing” it

Discovery of ElectronDiscovery of Electron3.3. negatively chargednegatively charged- the rays behaved the - the rays behaved the

same way around a magnetic field as a same way around a magnetic field as a conducting wireconducting wire

4.4. negatively charged-negatively charged- were were repelledrepelled by a by a negatively charged objectnegatively charged object

Discovery of ElectronDiscovery of Electron

All of these led scientists All of these led scientists to believe there were to believe there were negatively charged negatively charged particles inside the particles inside the cathode raycathode ray

Discovery of ElectronDiscovery of Electron

J.J. Thomson (English 1897) did more J.J. Thomson (English 1897) did more experiments to actually make the experiments to actually make the discoverydiscovery

he found ratio of charge of this he found ratio of charge of this particle to this mass of the particleparticle to this mass of the particle

since the ratio stayed constant for since the ratio stayed constant for any metal that contained it, it must any metal that contained it, it must be the same in all of the metalsbe the same in all of the metals

Are electrons the only Are electrons the only particles?particles?

since atoms are neutral, something since atoms are neutral, something must balance the negative chargemust balance the negative charge

since an atom’s mass is so much since an atom’s mass is so much larger than the mass of its electrons, larger than the mass of its electrons, there must be other matter inside an there must be other matter inside an atomatom

Discovery of NucleusDiscovery of Nucleus Rutherford discovered the nucleus by Rutherford discovered the nucleus by

shooting alpha particles (have positive shooting alpha particles (have positive charge) at a very thin piece of gold foilcharge) at a very thin piece of gold foil

he predicted that the particles would go he predicted that the particles would go right through the foil at some small angleright through the foil at some small angle

Discovery of NucleusDiscovery of Nucleus

Discovery of NucleusDiscovery of Nucleus some particles (1/8000) bounced some particles (1/8000) bounced

back from the foilback from the foil this meant there must be a “powerful this meant there must be a “powerful

force” in the foil to hit particle backforce” in the foil to hit particle back

Predicted Results Actual Results

Discovery of NucleusDiscovery of NucleusCharacteristics of Characteristics of

““Powerful Force”:Powerful Force”:

1.1. dense-dense- since it was strong since it was strong enough to deflect particleenough to deflect particle

2.2. small-small- only 1/8000 hit the only 1/8000 hit the force dead on and bounced force dead on and bounced backback

3.3. positively charged-positively charged- since since there was a repulsion there was a repulsion between force and alpha between force and alpha particles particles

Atomic Math and Atomic Math and IsotopesIsotopes

Atomic NumberAtomic Number number of protons is the atomic # number of protons is the atomic # It is the identity of an element. It is the identity of an element. All atoms of the same element have the same All atoms of the same element have the same

atomic numberatomic number located above the symbol in the periodic tablelocated above the symbol in the periodic table order of the elements in the periodic tableorder of the elements in the periodic table

IsotopesIsotopes

atoms of the same element with atoms of the same element with different numbers of neutronsdifferent numbers of neutrons

most elements exist as a mixture of most elements exist as a mixture of isotopesisotopes

B. IsotopesB. Isotopes

© Addison-Wesley Publishing Company, Inc.

What do the Carbon isotopes below What do the Carbon isotopes below have in common? What is different have in common? What is different about them?about them?

Mass Number For IsotopesMass Number For Isotopes sum of particles in nucleussum of particles in nucleus A = #p + #nA = #p + #n

Hydrogen isotopes have special names:Hydrogen isotopes have special names: protiumprotium deuteriumdeuterium tritiumtritium

Designating IsotopesDesignating Isotopes Hyphen notation:Hyphen notation:

Name - mass numberName - mass number ex. Carbon – 13ex. Carbon – 13

Nuclear Symbol notation:Nuclear Symbol notation:

Symbolnpp

CEx 13

6 :

ExamplesExamples

1.1. 7 protons, 8 neutrons7 protons, 8 neutrons

Nitrogen-15Nitrogen-15

2.2. 17 electrons, 19 neutrons17 electrons, 19 neutrons

Chlorine- 36Chlorine- 36

N157

Cl3617

ExamplesExamples

3.3. Z=5, 6 neutronsZ=5, 6 neutrons

Boron- 11Boron- 11

3.3. A=75, 42 neutronsA=75, 42 neutrons

Arsenic- 75Arsenic- 75

B115

As7533

Ch. 3 AtomsCh. 3 Atoms

Average Atomic MassAverage Atomic Mass

ReviewReviewSubatomic ParticlesSubatomic Particles

POSITIVECHARG E

PROTONS

NEUTRALCHARG E

NEUTRON S

NUCLEU S

NEGATIVE CHARGE

ELECTRONS

ATO M

Most of the atom’s mass.Atomic Numberequals the # of...

equal in a neutral atom

A neutral atom contains 34 A neutral atom contains 34 electrons and has an A of electrons and has an A of

59. Write the nuclear 59. Write the nuclear symbol notation and symbol notation and

hyphen notation for this hyphen notation for this isotope. isotope.

Atomic MassAtomic Mass

DefinitionDefinition- mass of an atom in atomic mass - mass of an atom in atomic mass units (amu)units (amu)- atoms have very little mass- atoms have very little mass- equal to 1/12- equal to 1/12thth of the mass of carbon of the mass of carbon- often an average mass - often an average mass

- weighted mass- weighted massAMU or the Dalton (Da)AMU or the Dalton (Da)

- equal to - equal to 1.6605402 x 101.6605402 x 10-27-27 kg kg

Atomic Mass Cont.Atomic Mass Cont.

ex. 99% of all carbon atoms are ex. 99% of all carbon atoms are the isotope the isotope containing 6 neutrons, containing 6 neutrons, the remaining 1% is the the remaining 1% is the heavier heavier isotope containing 7 neutrons, which isotope containing 7 neutrons, which

raises the average mass of raises the average mass of carbon from carbon from 12.000 to 12.01112.000 to 12.011

Relative Atomic MassRelative Atomic Mass

since masses of atoms are so small, since masses of atoms are so small, it is more convenient to use relative it is more convenient to use relative atomic masses instead of real atomic masses instead of real massesmasses

to set up a scale, we have to pick to set up a scale, we have to pick one atom to be the standardone atom to be the standard

since 1961, the carbon-12 nuclide is since 1961, the carbon-12 nuclide is the standard and is assigned a mass the standard and is assigned a mass of exactly 12 amuof exactly 12 amu

Relative Atomic MassRelative Atomic Mass

atomic mass unit (amu)- one is atomic mass unit (amu)- one is exactly 1/12exactly 1/12thth of the mass of a of the mass of a carbon-12 atomcarbon-12 atom

mass of proton= 1.007276 amumass of proton= 1.007276 amu mass of neutron= 1.008665 amumass of neutron= 1.008665 amu mass of electron= 0.0005486 amu mass of electron= 0.0005486 amu

Relative Atomic MassRelative Atomic Mass

the mass number (A) and the relative the mass number (A) and the relative atomic mass are very close but not atomic mass are very close but not the same becausethe same because relative atomic mass includes electronsrelative atomic mass includes electrons the proton and neutron masses aren’t the proton and neutron masses aren’t

exactly 1 amuexactly 1 amu

Average Atomic MassAverage Atomic Mass

weighted relative atomic masses of weighted relative atomic masses of the isotopes of each elementthe isotopes of each element

each isotope has a known natural each isotope has a known natural occurrence (percentage of that occurrence (percentage of that elements’ atoms)elements’ atoms)

Calculating Average Atomic MassCalculating Average Atomic Mass

Naturally occurring copper consists Naturally occurring copper consists of:of: 69.71% copper-63 (62.929598 amu)69.71% copper-63 (62.929598 amu) 30.83% copper-65 (64.927793 amu)30.83% copper-65 (64.927793 amu)

(0.6971 x 62.929598)+(0.3083 x (0.6971 x 62.929598)+(0.3083 x 64.927793)64.927793)

=63.55 amu=63.55 amu

Calculating Average Atomic MassCalculating Average Atomic Mass

An element has three main isotopes An element has three main isotopes with the following percent with the following percent occurances:occurances: #1: 19.99244 amu, 90.51%#1: 19.99244 amu, 90.51% #2: 20.99395 amu, 0.27%#2: 20.99395 amu, 0.27% #3: 21.99138 amu, 9.22%#3: 21.99138 amu, 9.22%

Find the average atomic mass and Find the average atomic mass and determine the element.determine the element.

Calculating Average Atomic Calculating Average Atomic MassMass

amu17945.20

100

9.22)(21.99138 0.27)(20.99395x 90.51)(19.99244x

Neon