Chapter 4Chapter 4““Atomic StructureAtomic Structure””

Introduction to the Introduction to the Atom and Atomic Atom and Atomic

ModelsModels

DEMOCRITUSDEMOCRITUS400 BC400 BC

Ancient philosopher: Father of the AtomAncient philosopher: Father of the Atom

Democritus believed all things consisted of tiny indivisible units.

He called these tiny units he called atomos. The Greek word

for “can not be cut” or “indivisible”

John DaltonJohn Dalton (1799) (1799) Developed what is considered to Developed what is considered to be the 1be the 1stst Atomic Theory Atomic Theory

Was born into a modest Quaker Was born into a modest Quaker family in England family in England

Began lecturing in public at the age Began lecturing in public at the age of 12of 12

DaltonDalton’’s Model (1799)s Model (1799)

Dalton's modelDalton's model was that the atoms were tiny, was that the atoms were tiny, indivisible, indestructible particles and that each one indivisible, indestructible particles and that each one had a certain mass, size, and chemical behavior that had a certain mass, size, and chemical behavior that was determined by what kind of element they were.was determined by what kind of element they were.

DaltonDalton’’s Models Model

Dalton’s model of the atom was similar to a tiny billiard ball.

Dalton’s model of the atom was solid and had no internal structure.

DaltonDalton’’s Atomic Theorys Atomic Theory elements consisted of tiny particles called elements consisted of tiny particles called

atomsatoms.. all atoms of an element are identicalall atoms of an element are identical atoms of each element are different from one atoms of each element are different from one

anotheranother; ; they have different massesthey have different masses.. compounds consisted of atoms of different compounds consisted of atoms of different

elements combined togetherelements combined together.. chemical reactions involved the rearrangement of chemical reactions involved the rearrangement of

combinations of those atomscombinations of those atoms..

Flaws in DaltonFlaws in Dalton’’s s ModelModel

DaltonDalton’’s falsely believed that the s falsely believed that the atom was the most fundamental atom was the most fundamental particle.particle.

We now know the atom is made up of We now know the atom is made up of even smaller particles we call the even smaller particles we call the proton, neutron and electron. proton, neutron and electron.

DaltonDalton’’s theory could also not s theory could also not account for the formation of ions account for the formation of ions (charged particles) (charged particles)

Daltons Atomic Model Daltons Atomic Model SummarySummary

Called: Billiard Ball ModelCalled: Billiard Ball Model Could account forCould account for

Atoms of different atomic masses Atoms of different atomic masses Elements were tiny particlesElements were tiny particles

Could NOT account forCould NOT account forThough atom was smallest particleThough atom was smallest particleDid not have an internal structureDid not have an internal structureThe formation of charged particlesThe formation of charged particles

John J. Thomson (1897)John J. Thomson (1897) Discovered the electron Discovered the electron

using the Cathod Ray Tube using the Cathod Ray Tube (CRT)(CRT)

Thomson found that the Thomson found that the beam of charge in the CRT beam of charge in the CRT was attracted to the was attracted to the positive end of a magnet positive end of a magnet and repelled by the and repelled by the negative end. negative end.

ThomsonThomson’’s Hypothesiss Hypothesis Concluded that the cathode beam was a stream Concluded that the cathode beam was a stream

of negative particles (electrons). of negative particles (electrons).

He tested several cathode materials and found He tested several cathode materials and found that all of them produced the same result. that all of them produced the same result.

He also found that the charge to mass ratio was He also found that the charge to mass ratio was the same for all electrons regardless of the the same for all electrons regardless of the material used in the cathode or the gas in the material used in the cathode or the gas in the tube. tube.

Thomson concluded that electrons must be part Thomson concluded that electrons must be part of all atoms. of all atoms.

ThomsonThomson’’s atomic model s atomic model Called the Called the ““plum-puddingplum-pudding”” it was the it was the

most popular and most wildly most popular and most wildly accepted model of the time. accepted model of the time.

Thompsons atomic model Thompsons atomic model could account for…..could account for…..

the atom having an the atom having an internal structureinternal structure

Light given off by Light given off by atoms atoms

Atom with different Atom with different atomic massesatomic masses

Thompsons atomic model Thompsons atomic model could NOT account for…..could NOT account for…..

Empty space (had Empty space (had atom filled with atom filled with positive pudding)positive pudding)

Formation of ionsFormation of ions

Gold Foil ExperimentGold Foil Experiment Conducted by students of Conducted by students of

Rutherford.Rutherford.

Proved that all atoms had a tiny, Proved that all atoms had a tiny, positively charged center.positively charged center.

Confirmed that atomConfirmed that atom’’s were mostly s were mostly empty space. empty space.

Rutherford ~ early Rutherford ~ early 1900s1900s

α-particle interaction with matter α-particle interaction with matter studied in gold foil experimentstudied in gold foil experiment

Rutherford's Nuclear Rutherford's Nuclear ModelModel

1. The atom contains a tiny dense center 1. The atom contains a tiny dense center the volume is about 1/10 trillionth the the volume is about 1/10 trillionth the

volume of the atom volume of the atom 2. The nucleus is essentially the entire 2. The nucleus is essentially the entire

mass of the atommass of the atom 3. The nucleus is positively charged3. The nucleus is positively charged

the amount of positive charge of the the amount of positive charge of the nucleus balances the negative charge of the nucleus balances the negative charge of the electrons electrons

4. The electrons move around in the 4. The electrons move around in the empty space of the atom surrounding the empty space of the atom surrounding the nucleusnucleus

RutherfordRutherford’’s atomic model s atomic model (1911)(1911)

Could account for:Could account for: Empty spaceEmpty space IonsIons Internal structure Internal structure Light given off when Light given off when

heated to high heated to high temperature.temperature.

Could not account Could not account for:for: StabilityStability

Philipp Lenard (1903)Philipp Lenard (1903) Aluminum foil experimentAluminum foil experiment

Lenard found that a beam of electrons Lenard found that a beam of electrons was able to pass through a sheet of Al was able to pass through a sheet of Al foil with almost no deflection. foil with almost no deflection.

Lenard correctly concluded that the Lenard correctly concluded that the majority of an atommajority of an atom’’s volume is empty s volume is empty space. space.

LenardLenard’’s atomic model s atomic model LenardLenard’’s model was s model was

composed of composed of dynamids. dynamids. Lenard calculated the size Lenard calculated the size

of a dynamid based on his of a dynamid based on his experimental results and experimental results and found it to be 1 billionth found it to be 1 billionth (1(1//1,000,000,000) the size 1,000,000,000) the size of the atom. of the atom.

LenardLenard’’s model could s model could account for:account for:

Different atomic masses (based on the Different atomic masses (based on the number of number of ““dynamidsdynamids””). ).

The internal structure of an atom The internal structure of an atom

The fact that most of the atom was The fact that most of the atom was empty space. empty space.

Flaws in LenardFlaws in Lenard’’s models model Formation of Ions (gaining or losing Formation of Ions (gaining or losing

charge)charge)

The light given off by materials when The light given off by materials when heated to a high temperature. heated to a high temperature.

• First to present an atomic model close to the presently accepted model.

• He came up with his model in 1903.

Hantaro Nagaoka

NagokaNagoka’’s Models Model NagokaNagoka’’s model of the atom was s model of the atom was

unstable.unstable.

According to the laws of planetary According to the laws of planetary motion, the atom would collapse over motion, the atom would collapse over time. time.

Planetary modelPlanetary model Planetary model used to explain Planetary model used to explain

electrons moving around the tiny, electrons moving around the tiny, but dense nucleusbut dense nucleus

Nucleus containsNucleus contains Protons- existence proposed in 1900s Protons- existence proposed in 1900s Neutrons- existence proposed in 1930sNeutrons- existence proposed in 1930s

Successes of NagokaSuccesses of Nagoka’’s s modelmodel

Atoms were able to Atoms were able to give off electrons to give off electrons to form ions. form ions.

Accounted for the Accounted for the experimental fact experimental fact that atomthat atom’’s were s were mostly empty spacemostly empty space

Explained different Explained different atomic weights. atomic weights.

Explained the light Explained the light given off when heated given off when heated to high temperatures. to high temperatures.

BohrBohr Questioned Questioned ‘‘planetary modelplanetary model’’ of atom of atom

Electrons located in specific levels from Electrons located in specific levels from nucleus (discontinuous model)nucleus (discontinuous model)

Proposed electron cloud model based Proposed electron cloud model based on evidence collected with H on evidence collected with H emission spectraemission spectra

BohrBohr’’s Atomic Model s Atomic Model (1913)(1913)

Bohr was a student of Rutherford. Bohr was a student of Rutherford.

Improved RutherfordImproved Rutherford’’s model by proposing s model by proposing electrons are found only in specific fixed electrons are found only in specific fixed orbits. orbits.

These orbits have fixed levels of energyThese orbits have fixed levels of energy

This explained how electrons could give off This explained how electrons could give off light (gain or lose energy) light (gain or lose energy)

BOHR MODELBOHR MODEL Electrons are placed in energy levels Electrons are placed in energy levels

surrounding the nucleussurrounding the nucleus

Nucleus

(p+ & n0) 2e-

8e-

8e-

BohrBohr’’s Atomic Models Atomic Model Could account forCould account for

Internal structureInternal structure Atoms of different massesAtoms of different masses Atom being mostly empty spaceAtom being mostly empty space Light given offLight given off Formation of positive ionsFormation of positive ions

FlawsFlaws Only really worked for HydrogenOnly really worked for Hydrogen

Chadwick (1932)Chadwick (1932) Discovered the neutron by bombarding Discovered the neutron by bombarding

Be with beta radiation. Be with beta radiation.

Nuclear fission released a neutron. Nuclear fission released a neutron.

chartchart

ReviewReview Describe each of the 6 different Describe each of the 6 different

atomic models. Give theatomic models. Give the Scientist NameScientist Name Name of modelName of model What they could account forWhat they could account for What they could not account for (flaws)What they could not account for (flaws)

Subatomic particle Subatomic particle summarysummary

Particle Discovery by

Year experiment

Proton Rutherford 1911

Gold Foil Experiment

Electron

Thompson 1887

The response of cathode ray tube to a magnetic and electric fields

Neutrons

Chadwich 1932

Bombarded Be with beta radiation and a neutron was released

Subatomic ParticlesSubatomic Particles

ElectronProtonNeutron

Name

Symbol

Charge

Relative mass

Actual mass (g)

e-

p+

n0

-1

+10

1/1840

1

1

9.11 x 10-28

1.67 x 10-24

1.67 x 10-24

Subatomic Particles Subatomic Particles (cont.)(cont.)

All atoms of an element have the All atoms of an element have the same # of protonssame # of protons protons identify an atom protons identify an atom atomic # atomic #

Atoms are electrically neutralAtoms are electrically neutral #p = #e#p = #e--

Only neutrons and protons contribute Only neutrons and protons contribute to an atoms massto an atoms mass

#n + #p = atomic mass#n + #p = atomic mass

ISOTOPESISOTOPES= = atoms with the same atoms with the same

number of protons number of protons but DIFFERENT but DIFFERENT numbers of neutronsnumbers of neutrons

Mass Number

Atomic Number

Element Symbol

Ex. Ex. Na-23 or Sodium-23 orNa-23 or Sodium-23 or 23 23 Na or Na or 2323NaNa

C-14 or Carbon-14 or C-14 or Carbon-14 or 1414C or C or 1414CCB-10 or Boron-10 or B-10 or Boron-10 or 1010B or B or 1010BB

11

6

5

Isotope PracticeIsotope PracticeElement hasElement hasa.a.6 p+, 8 n and 6 e-6 p+, 8 n and 6 e-b.b.6 p+, 6 n and 6 e-6 p+, 6 n and 6 e-c.c.19 p+, 21 n and 10 19 p+, 21 n and 10 e-e-d.d.__p+, __ n and __ e-__p+, __ n and __ e-e.e.__p+, __ n and __ e- __p+, __ n and __ e-

SymbolSymbola.a...b.b...c.c...d.d.Cu-65Cu-65e.e.H-2H-2

IonsIons Ion Ion is an atom that has gained or lost one is an atom that has gained or lost one

or more electrons and now has a chargeor more electrons and now has a charge Metals always lose electrons to form Metals always lose electrons to form

POSITIVE ionsPOSITIVE ions Non-metals always gain electrons to form Non-metals always gain electrons to form

NEGATIVE ionsNEGATIVE ions The charge of the element is show on the The charge of the element is show on the

right side of the symbol as a super scriptright side of the symbol as a super script Example: NaExample: Na+1+1, Zn, Zn+1+1, S, S-2-2, N, N-3-3

Ions practiceIons practiceElementElement

CaCa+2+2

BrBr-1-1

AlAl+3+3

II-1-1

Number of Number of electronselectrons????????

D. Average Atomic MassD. Average Atomic Mass

weighted average of all isotopesweighted average of all isotopes on the Periodic Tableon the Periodic Table round to 2 decimal placesround to 2 decimal places

D. Average Atomic MassD. Average Atomic Mass

EXEX: Calculate the avg. atomic mass of oxygen : Calculate the avg. atomic mass of oxygen if its abundance in nature is 99.76% if its abundance in nature is 99.76% 1616O, O, 0.04% 0.04% 1717O, and 0.20% O, and 0.20% 1818O.O.

D. Average Atomic MassD. Average Atomic Mass

EXEX: Find chlorine: Find chlorine’’s average atomic mass s average atomic mass if approximately 8 of every 10 atoms are if approximately 8 of every 10 atoms are chlorine-35 and 2 are chlorine-37.chlorine-35 and 2 are chlorine-37.