Chapter 4History and Atomic History and Atomic

StructureStructure

IDEAS:• He believed that matter was not divisible• He believed that matter was made up of tiny particles – atoms.• Properties of matter were due to the size and shape of the atoms.• Changes in matter were due to the grouping of atoms (not from changes within the atom)

PROBLEMS: • He could not experiment, therefore he could not validate his ideas. • (For example, he could not explain what held the atoms together)

IDEAS• Questioned the idea that atoms moved through empty space. • He rejected the idea of atoms.

PROBLEMS• Many people respected his ideas, therefore the atomic theory that was proposed 100 years earlier was rejected for the next 2000 years.

Obj. 1…Dalton’s Atomic TheoryObj. 1…Dalton’s Atomic Theory• Four postulates (1808)...Four postulates (1808)...

2. Atoms of the same element are identical...2. Atoms of the same element are identical...each element is uniqueeach element is unique

* proton, neutron and

electron

isotopes exist

*

• Much of this theory is still Much of this theory is still accepted, accepted, with with 2 exceptions exceptions

3. Atoms of different elements can physically 3. Atoms of different elements can physically mix ormix orchemically combine (compounds).chemically combine (compounds).

1. All elements are composed of tiny, indivisible 1. All elements are composed of tiny, indivisible particlesparticlescalled ‘atoms’.called ‘atoms’.

4. Chemical rxns. occur when atoms are4. Chemical rxns. occur when atoms areseparated, joined, or rearranged.separated, joined, or rearranged.

Obj. 2…Atomic ScientistsObj. 2…Atomic Scientists• J. J. ThomsonJ. J. Thomson discovered discovered electronselectrons (e-) in (e-) in 1897.1897.• He passed an electric current through a He passed an electric current through a glassglasstube filled with gas.tube filled with gas.

• He discovered that a beam of negative He discovered that a beam of negative chargeschargestraveled from the cathode (-) to the anode (+).traveled from the cathode (-) to the anode (+).

Obj. 2 cont...Obj. 2 cont...• E. GoldsteinE. Goldstein discovered positive particles in discovered positive particles in atomsatoms

in 1886.in 1886.

• He observed rays traveling in the opposite He observed rays traveling in the opposite direction ofdirection ofcathode rays.cathode rays.

• These particles were termed ‘ protons’ (pThese particles were termed ‘ protons’ (p++) by ) by ErnestErnestRutherford in 1920.Rutherford in 1920.

• His discovery was based on the fact thatHis discovery was based on the fact thatdifferent atoms’ atomic mass and atomic #different atoms’ atomic mass and atomic #(# of protons) were not adding up.(# of protons) were not adding up.

• James ChaddwickJames Chaddwick discovered discovered neutronsneutrons (n (n00))in 1932.in 1932.

Obj. 2 cont...Obj. 2 cont...

• all e- carry exactly one unit of negative charge.all e- carry exactly one unit of negative charge.

• mass of an e- is 1/1840 the mass of a hydrogen mass of an e- is 1/1840 the mass of a hydrogen atom (patom (p++).).

• Robert MillikanRobert Millikan furthered Thomson’s work by furthered Thomson’s work by describingdescribingthe electronthe electron more in depth. more in depth.

Obj. 3 and 4…The Bohr-Rutherford Obj. 3 and 4…The Bohr-Rutherford ModelModel

1. atoms are mostly space. 1. atoms are mostly space. (football arena)(football arena)

• Ernest Rutherford conducted the famous ‘gold Ernest Rutherford conducted the famous ‘gold foilfoilexperiment’ (1911) which concluded that:experiment’ (1911) which concluded that:

2. atoms have a solid nucleus at the2. atoms have a solid nucleus at the

centercenter which contains most of the mass.which contains most of the mass.

• This overturned the accepted ‘plum pudding This overturned the accepted ‘plum pudding model’ of themodel’ of thetime.time.

Obj. 3 and 4 cont...Obj. 3 and 4 cont...• The Gold Foil Experiment...The Gold Foil Experiment...

• Stats...Stats...

• 98% of particles went straight through 98% of particles went straight through (expected)(expected)

• 2% of particles deflected at large angles2% of particles deflected at large angles• 0.01% of particles deflected straight back 0.01% of particles deflected straight back (canon (canon balls & tissue!)balls & tissue!)

(BBs and cream cheese!)(BBs and cream cheese!)

Obj. 3 and 4 cont...Obj. 3 and 4 cont...

• The progression of the atom...The progression of the atom...

• Why don’t the (-) e- fall into the (+) Why don’t the (-) e- fall into the (+) nucleus?nucleus?

Plum Pudding Rutherford Rutherford-

BohrQuantum

• After Rutherford’s findings, Niels Bohr further After Rutherford’s findings, Niels Bohr further explainedexplainedthe atom by concentrating on the e- (1913).the atom by concentrating on the e- (1913).

• Bohr proposed that the e- travel on concentricBohr proposed that the e- travel on concentricorbits around the nucleus.orbits around the nucleus.

• Each orbit has a fixed energy (energy level) and Each orbit has a fixed energy (energy level) and e- do note- do notlose energy.lose energy.

Obj. 5…Subatomic ParticlesObj. 5…Subatomic Particles

PROPERTIES OF SUBATOMIC PROPERTIES OF SUBATOMIC PARTICLESPARTICLES

PARTICLPARTICLEE

SYMBOLSYMBOL ELECTRICAL ELECTRICAL CHARGECHARGE

RELATIVRELATIVE MASSE MASS

ACTUAL ACTUAL MASS MASS

(g)(g)

ElectroElectronn

ProtonProton

NeutroNeutronn

e-e-

pp++

nn00

-1-1

+1+1

00

1/18401/1840

11

11

9.11 x 109.11 x 10--

2828

1.67 x 101.67 x 10--

2424

1.67 x 1.67 x 1010-24-24

Obj. 6…Characteristics of Obj. 6…Characteristics of ElementsElements

K19

Potassium

39.098

atomic #

element symbol

element name

atomic mass

Obj. 6 cont...Obj. 6 cont...• Atomic Atomic ##:: # of p# of p++ in an atom in an atom

identifies identifies elementelement # p# p++ = # e- in neutral atom = # e- in neutral atom

(change atomic # = change of element).

** (+) charge = less e- than p** (+) charge = less e- than p++

** (-) charge = more e- than p** (-) charge = more e- than p++

• Atomic massAtomic mass::

mass of the nucleusmass of the nucleus

pp++ + n + n00

units are a.m.u. units are a.m.u. (atomic mass unit)(atomic mass unit)

(a.k.a. mass #)

Obj. 7…Atomic SymbolsObj. 7…Atomic Symbols• There are two ways to represent elements:There are two ways to represent elements:

• Symbol Form:Symbol Form:

## X ##

atomic mass

(# of p+)atomic #

element symbol

## Xatomic

mass element symbol

OROR

• Shorthand Form:Shorthand Form: name of element followed by atomic name of element followed by atomic mass.mass. • Ex...Ex...

Carbon - 14 Carbon - 14

Aluminum - Aluminum - 2727 Nitrogen - 14Nitrogen - 14

• You can find mass #, atomic #, # of nYou can find mass #, atomic #, # of n00, and # of , and # of e- withe- witheither notation!either notation!

Obj. 8…Atomic CalculationsObj. 8…Atomic Calculations• All mass of the atom is in the nucleus.All mass of the atom is in the nucleus. - only p- only p++ and n and n00 are in the are in the nucleus.nucleus. - if you know the mass of any atom, you can find - if you know the mass of any atom, you can find the # of nthe # of n00..

• Ex...Ex...

3131PP 1515

+1+1

electrical charge on atomelectrical charge on atom

element = _______________element = _______________

atomic mass = ___________atomic mass = ___________

atomic # = ______________atomic # = ______________ # of p# of p++ = _______________ = _______________

# of n# of n00 = _______________ = _______________

# of e# of e-- = _______________ = _______________

Phosphorus

31 a.m.u.s 15 15 16 14

Manganese - Manganese - 5555 symbol = ______________symbol = ______________

atomic mass = __________atomic mass = __________ atomic # = ____________atomic # = ____________ # of p# of p++ = ______________ = ______________ # of n# of n00 = ______________ = ______________

# of e# of e-- = ______________ = ______________

Mn 55 a.m.u.s 25 25 30 25

- if you know the # of n- if you know the # of n0 0 and the # of p+, you can find and the # of p+, you can find thethemass.mass.

Obj. 9…IsotopesObj. 9…Isotopes

- different # of - different # of nn0 0 !!!!!! • Three isotopes of Carbon:Three isotopes of Carbon:

Carbon - 14 Carbon - 14

Carbon - 12 Carbon - 12 Carbon - 13 Carbon - 13

(6p(6p++, 6n, 6n00) ) (6p(6p++, 7n, 7n00) ) (6p(6p++, 8n, 8n00) )

element of life element of life extremely extremely rare rare radioactive…carbon radioactive…carbon dating dating • Note: atomic # will Note: atomic # will NEVERNEVER change in change in

isotopes…isotopes…only mass and # of nonly mass and # of n00 do! do!

• Which of the following are isotopes of the same Which of the following are isotopes of the same element?element?

2222XX 1212

+3+3

2222XX 1010

2525XX 1010

-1-1 Neon - 20Neon - 20

Neon - 22Neon - 22

Fluorine - Fluorine - 2020

• IsotopesIsotopes: atoms of the : atoms of the same elementsame element with with different different atomicatomicmassesmasses..

Obj. 10…Average Mass of Obj. 10…Average Mass of IsotopesIsotopes• Isotopes are naturally occurring.Isotopes are naturally occurring.

• The mass # of an element (periodic table) is the The mass # of an element (periodic table) is the weightedweightedavg.avg. of all of all isotopes that exist in nature.isotopes that exist in nature.

- abundance of isotope is just as important - abundance of isotope is just as important as mass!as mass! • Ex...Ex...

Natural copper (Cu) consists of 2 Natural copper (Cu) consists of 2 isotopes ...isotopes ... Copper - 63 (mass = 62 .930 g/mole) Copper - 63 (mass = 62 .930 g/mole)

Copper - 65 (mass = 64 .930 g/mole) Copper - 65 (mass = 64 .930 g/mole) 69% 69%

31% 31%

• To calculate avg. To calculate avg. mass... mass... mass x abundance for each isotopemass x abundance for each isotopeStep 1 :Step 1 :

Step 2 :Step 2 :add the two values from step 1 togetheradd the two values from step 1 together

62 .93 x .69 = 62 .93 x .69 =

64 .93 x .31 = 64 .93 x .31 = 43.4243.42

20.1320.13

43.4243.4220.1320.13++

63.55 g/mole

Obj. 10 cont...Obj. 10 cont...

• Ex...Ex...

Three isotopes of Oxygen:Three isotopes of Oxygen:

Oxygen - 18 Oxygen - 18

Oxygen - 16 Oxygen - 16 Oxygen - 17 Oxygen - 17

• The avg. mass (from P.T.) is closest to 16, The avg. mass (from P.T.) is closest to 16, therefore, therefore, Oxygen-16 is the isotope that is most abundant Oxygen-16 is the isotope that is most abundant

in nature.in nature.

99 . 759%0.037%

0.204%

• The average mass of an element is closest to The average mass of an element is closest to the isotopethe isotopethat is mostthat is most plentiful in nature.plentiful in nature.