The AtomThe Atom

Chapter 4Chapter 4

I.I. History of the Atomic TheoryHistory of the Atomic TheoryA. DemocritusA. DemocritusB. AristotleB. AristotleC. LavoisierC. LavoisierD. ProustD. ProustE. DaltonE. DaltonF. Modern Atomic TheoryF. Modern Atomic Theory

II.II. History of Atomic StructureHistory of Atomic StructureA. ThomsonA. ThomsonB. MilikanB. MilikanC. RutherfordC. RutherfordD. BohrD. BohrE. ChadwickE. ChadwickF. Quantum AtomF. Quantum Atom

III.III. Subatomic ParticlesSubatomic ParticlesA. Atomic NumberA. Atomic NumberB. Mass Number and IsotopesB. Mass Number and IsotopesC. Electrons and IonsC. Electrons and IonsD. Nuclear and Hyphenation NotationD. Nuclear and Hyphenation NotationE. Average Atomic MassE. Average Atomic Mass

IV.IV. Weighing and Counting AtomsWeighing and Counting AtomsA. Mole AtomsA. Mole AtomsB. Mole MassB. Mole MassC. Mass AtomsC. Mass Atoms

I. History of the Atomic I. History of the Atomic TheoryTheory

Remember: a scientific theory Remember: a scientific theory explains behaviors and the ‘nature’ explains behaviors and the ‘nature’ of thingsof things

Theories can be revised when new Theories can be revised when new discoveries are madediscoveries are made

The theory describing the The theory describing the composition of matter has been composition of matter has been revised many timesrevised many times

A.A. Democritus (460-370 BC)Democritus (460-370 BC)1.Matter is made up of “atoms” 1.Matter is made up of “atoms”

that are solid, indivisible and that are solid, indivisible and indestructibleindestructible

2.Atoms constantly move in 2.Atoms constantly move in spacespace

3.Different atoms have different 3.Different atoms have different size and shape size and shape

4.Changes in matter result from 4.Changes in matter result from changes in the grouping of changes in the grouping of atoms atoms

5. Properties of matter result 5. Properties of matter result from size, shape and from size, shape and movementmovement

I. History of the Atomic TheoryI. History of the Atomic Theory

I. History of the Atomic I. History of the Atomic TheoryTheory

B. B. AristotleAristotle (384-322 BC ) & Others(384-322 BC ) & Others 1. Four kinds of matter1. Four kinds of matter a. Fire – Earth – Water – Aira. Fire – Earth – Water – Air 2. One kind of matter can transform 2. One kind of matter can transform into anotherinto another 3. Rejected idea of the “atom” (idea 3. Rejected idea of the “atom” (idea

then then ignored for almost 2000 years ignored for almost 2000 years 4. This theory was more popular and 4. This theory was more popular and it was easier to acceptit was easier to accept

Aristotle’s Theory of MatterAristotle’s Theory of Matter

C.C. Antoine Lavoisier (1770s)Antoine Lavoisier (1770s)

1. Experiment:1. Experiment: 2 Sn + O2 Sn + O22 2 SnO 2 SnO

tin oxygen tin (II) oxidetin oxygen tin (II) oxide

mass before reaction = mass after reactionmass before reaction = mass after reaction

2. 2. Law of Conservation of MassLaw of Conservation of Mass

a. Matter cannot be created or a. Matter cannot be created or destroyed (in a chemical or physical destroyed (in a chemical or physical change)change)

I. History of the Atomic TheoryI. History of the Atomic Theory

D.D. Joseph Proust (1779)Joseph Proust (1779)1. Develops 1. Develops Law of Definite Composition-Law of Definite Composition-

all samples of a specific substance all samples of a specific substance contain the same mass ratio of the contain the same mass ratio of the same elementssame elements

a. ex: all samples of COa. ex: all samples of CO22 contains 27.3% contains 27.3%

carbon and 72.7% oxygencarbon and 72.7% oxygen

b. therefore ‘elements’ are combiningb. therefore ‘elements’ are combining

in a whole number ratio – WHY????in a whole number ratio – WHY????

I. History of the Atomic I. History of the Atomic TheoryTheory

E.E. John Dalton (1803)John Dalton (1803)1. Develops 1. Develops Law of Multiple ProportionsLaw of Multiple Proportions a. describes the ratio of elements by mass a. describes the ratio of elements by mass

in two different compounds composed of in two different compounds composed of the same elementsthe same elements

2. Example: carbon monoxide carbon 2. Example: carbon monoxide carbon dioxidedioxide 1 part oxygen : 2 parts 1 part oxygen : 2 parts oxygenoxygen

*when compared to the same amount of *when compared to the same amount of carbon in each compoundcarbon in each compound

I. History of the Atomic Theory - I. History of the Atomic Theory - DaltonDalton

3. Dalton collects data and develops 3. Dalton collects data and develops his his

atomic theory in 1803atomic theory in 1803

I. History of the Atomic Theory- I. History of the Atomic Theory- DaltonDalton

4. Dalton’s Background4. Dalton’s Background

a.a. Dalton became a school teacher at Dalton became a school teacher at the age of 12 (he left school at age the age of 12 (he left school at age 11)11)

b.b. loved meteorology - pioneer in this loved meteorology - pioneer in this fieldfield

c.c. studied works of Democritus, Boyle studied works of Democritus, Boyle and Proustand Proust

d.d. Wrote Wrote New System of ChemicalNew System of Chemical PhilosophyPhilosophy in 1808 in 1808

1. Matter is made of small particles-atoms1. Matter is made of small particles-atoms2. Atoms of a given element are 2. Atoms of a given element are identicalidentical in in

size, mass, but differ from those of other size, mass, but differ from those of other elements*.elements*.

3. Atoms cannot be 3. Atoms cannot be subdividedsubdivided or or destroyed*destroyed*..( supports law of conservation of mass)( supports law of conservation of mass)4.Atoms combine in small whole number 4.Atoms combine in small whole number

ratios to form compounds. (def comp,Mult ratios to form compounds. (def comp,Mult prop)prop)

5. Atoms combine, separate, or rearrange in 5. Atoms combine, separate, or rearrange in chemical reactions.chemical reactions.

* Modified in Modern Atomic Theory* Modified in Modern Atomic Theory

5. Dalton’s Atomic Theory5. Dalton’s Atomic Theory

JUST A THEORY……. JUST A THEORY…….

But it lead to the But it lead to the

Modern Atomic Modern Atomic theorytheory

1.1. All matter is made up of small particles All matter is made up of small particles called atoms.called atoms.

2.2. Atoms of the same element have the Atoms of the same element have the same chemical properties while atoms same chemical properties while atoms of different elements have different of different elements have different properties properties

3.3. Not all atoms of an element have the Not all atoms of an element have the same mass, but they all have a definite same mass, but they all have a definite average mass which is characteristic. average mass which is characteristic. (isotopes)(isotopes)

F. Modern Atomic TheoryF. Modern Atomic Theory

4.4. Atoms of different elements Atoms of different elements combine to form compounds and combine to form compounds and each element in the compound each element in the compound loses its characteristic properties.loses its characteristic properties.

5.5. Atoms cannot be subdivided by Atoms cannot be subdivided by chemical or physical changes – only chemical or physical changes – only by nuclearby nuclear

changeschanges

F. Modern Atomic TheoryF. Modern Atomic Theory

I. History of the Atomic I. History of the Atomic TheoryTheory

18031803 18971897 19091909 19131913 19351935 TodayToday

solidsolid

particleparticleelectronelectron protonproton e- orbit e- orbit

nucleusnucleusneutronneutron Quantum Quantum

Atom Atom theorytheory

DaltonDalton ThomsonThomson RutherforRutherfordd

BohrBohr ChadwickChadwick SchrodingSchrodinger and er and othersothers

II.II. History of the Atomic History of the Atomic StructureStructureA. J.J. Thomson (1856-1940)A. J.J. Thomson (1856-1940)

J.J. Thomson (1887)J.J. Thomson (1887)

1.1. Experiments with cathode ray tubesExperiments with cathode ray tubes

a. atoms have (-) charged particles a. atoms have (-) charged particles

which are smaller than atomswhich are smaller than atoms

b. determined charge/mass ratio of b. determined charge/mass ratio of thethe

“ “electron”electron”

Voltage source

+-

Vacuum tube

Metal Disks

Voltage source

+-

Voltage source

+-

Voltage source

+-

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

+-

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

+-

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

+-

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 By adding an electric field

Voltage source

By adding an electric field By adding an electric field

+

-

Voltage source

By adding an electric field By adding an electric field

+

-

Voltage source

By adding an electric field By adding an electric field

+

-

Voltage source

By adding an electric field By adding an electric field

+

-

Voltage source

By adding an electric field By adding an electric field

+

-

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

+

-

Demonstration of the cathode ray Demonstration of the cathode ray experiment.experiment.

2.2. Thomson’s Model Thomson’s Model The Pudding Model The Pudding Model

a. electrons a. electrons presentpresent

b. atom is like b. atom is like plum pudding - plum pudding - bunch of positive bunch of positive stuff (pudding), stuff (pudding), with the electrons with the electrons suspended (plums) suspended (plums)

II.II. History of the Atomic History of the Atomic StructureStructure

B. B. Robert MilikanRobert Milikan (1868- (1868-1953) 1953)

1. 1. Oil Drop Experiment (1909) (1909)

a. Discovered mass and actual charge a. Discovered mass and actual charge of of

electron (-1)electron (-1)

b. Mass is 1/1840 the mass of a b. Mass is 1/1840 the mass of a hydrogen hydrogen

atomatom

1) e 1) e – – has a mass of 9.11 x 10has a mass of 9.11 x 10-28-28 g g

Oil DropOil Drop

So, at this point we know:So, at this point we know:

- - Atoms are divisible into smaller particles Atoms are divisible into smaller particles– Electrons are negatively chargedElectrons are negatively charged– The mass of an electron is very smallThe mass of an electron is very small

HOWEVER HOWEVER – Atoms should have a (+) portion to Atoms should have a (+) portion to

balancebalance

the negative partthe negative part

- Electrons are so small that some other - Electrons are so small that some other particles must account for massparticles must account for mass

II.II. History of the Atomic History of the Atomic Structure – Structure –

Summary thus farSummary thus far

C.C. Ernest RutherfordErnest Rutherford (1909) (1909)

1. Discovered the proton 1. Discovered the proton pp+ +

2. Received Nobel Prize in Chemistry2. Received Nobel Prize in Chemistry

3. 3. Gold Foil Experiment (Expectations) (Expectations)

a. Shot alpha particles at atoms of a. Shot alpha particles at atoms of goldgold

b. expected them to pass straight b. expected them to pass straight

throughthrough

II. History of the Atomic StructureII. History of the Atomic StructureErnest Rutherford (1871-Ernest Rutherford (1871-1937)1937)

Lead block

Uranium

Gold Foil

Florescent Screen

He thought this would happen:

According to Thomson Model

He thought the mass of the positive charge was evenly distributed in the atom

Here is what he observed:

4. 4. Gold Foil Experiment ResultsGold Foil Experiment Resultsa. a. Most Most positive alpha particles pass right positive alpha particles pass right

throughthrough

b. However, a few were deflectedb. However, a few were deflected

c. Rutherford reasoned that the positivec. Rutherford reasoned that the positive

alpha particle was deflected or repelledalpha particle was deflected or repelled

by a concentration of positive charge by a concentration of positive charge

The positive region accounts for The positive region accounts for deflectiondeflection

5. 5. Gold Foil Experiment ConclusionsGold Foil Experiment Conclusions a. the atom is mostly empty spacea. the atom is mostly empty space

b. the atom has a small, dense positive b. the atom has a small, dense positive centercenter

surrounded by electronssurrounded by electrons

Rutherford Model of the AtomRutherford Model of the Atom

At this point in 1909, we know:At this point in 1909, we know:– pp++ = 1.67 x 10 = 1.67 x 10-24-24 g g– ee-- = 9.11 x 10 = 9.11 x 10-28-28 g g – The charges are balance!The charges are balance!

But,But,– How are the electrons arranged?How are the electrons arranged?– There is still mass that is unaccounted There is still mass that is unaccounted

forfor

II. History of the Atomic II. History of the Atomic StructureStructure

D.D. Niels Bohr (1913)Niels Bohr (1913)1. Electrons orbit 1. Electrons orbit

nucleus in nucleus in predictablepredictable pathspaths

II. History of the Atomic StructureII. History of the Atomic Structure

E.E. Chadwick (1935)Chadwick (1935)1. Discovers neutron in 1. Discovers neutron in

nucleusnucleus

2. Neutron is neutral - 2. Neutron is neutral - does does

not have a charge nnot have a charge n00

3. Mass is 1.67 x 103. Mass is 1.67 x 10-24-24 g g

a. slightly greater than a. slightly greater than the mass of a protonthe mass of a proton

II.II. History of the Atomic History of the Atomic StructureStructureE. Chadwick (1891 – 1974)E. Chadwick (1891 – 1974)

F. The Quantum Atom TheoryF. The Quantum Atom Theory

1.1. The atom is mostly empty The atom is mostly empty

spacespace

2.2. Two regions:Two regions:aa. . NucleusNucleus- protons and neutrons- protons and neutrons

b.b. Electron cloud-Electron cloud- region where region where you have a 90% chance of you have a 90% chance of finding an electronfinding an electron

II. History of the Atomic StructureII. History of the Atomic Structure

Charges balancedCharges balanced Mass accounted forMass accounted for However – However –

what about thewhat about the

behavior of thebehavior of the

electrons? electrons?

II. History of the Atomic II. History of the Atomic StructureStructure