2.1 2 atom mass spectrometer student

7/27/2019 2.1 2 Atom Mass Spectrometer STUDENT

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S.MORRIS 2006


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HISTORY OF THE ATOM

460 BC Democritus develops the idea of atoms

he pounded up materials in his pestle and

mortar until he had reduced them to smaller

and smaller particles which he called

ATOMA

(greek for indivisible)


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HISTORY OF THE ATOM

1808 John Dalton

suggested that all matter was made up of

tiny spheres that were able to bounce around

with perfect elasticity and called them

ATOMS


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HISTORY OF THE ATOM

1898 Joseph John Thompson

found that atoms could sometimes eject a far

smaller negative particle which he called an

ELECTRON


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HISTORY OF THE ATOM

Thompson develops the idea that an atom was made up of

electrons scattered unevenly within an elastic sphere surrounded

by a soup of positive charge to balance the electron's charge

1904

like plums surrounded by pudding.

PLUM PUDDINGMODEL


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HISTORY OF THE ATOM

1910 Ernest Rutherford

oversaw Geiger and Marsden carrying out his

famous experiment.

they fired Helium nuclei at a piece of gold foil

which was only a few atoms thick.

they found that although most of them

passed through. About 1 in 10,000 hit


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HISTORY OF THE ATOM

gold foil

helium nuclei

They found that while most of the helium nuclei passed

through the foil, a small number were deflected and, to their

surprise, some helium nuclei bounced straight back.

helium nuclei


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HISTORY OF THE ATOM

Rutherfords new evidence allowed him to propose a more

detailed model with a central nucleus.

He suggested that the positive charge was all in a central

nucleus. With this holding the electrons in place by electrical

attraction

However, this was not the end of the story.


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HISTORY OF THE ATOM

1913 Niels Bohr

studied under Rutherford at the Victoria

University in Manchester.

Bohr refined Rutherford's idea by adding

that the electrons were in orbits. Rather

like planets orbiting the sun. With each

orbit only able to contain a set number of

electrons.


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Bohrs Atom

electrons in orbits

nucleus


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Marie Skodowska Curie

TWO Nobel Prizes

1903PHYSICS With

her husband for radiation

phenomena in Uraniumsalts

1911CHEMISTRY

On her own for

discovering theradioactive elements,

radium and polonium

The first person to win

TWO Nobel Prizes


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HELIUM ATOM

+

N

N

+

--

proton

electron

neutron

Shell

NOTE: THIS IS NOT TO SCALE. The nucleus is extremely small relativeto the space the electrons are moving in. And electrons do not move innice concentric rings.

POINT: THIS IS A MODEL that shows composition and relative position.


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SUBATOMIC PARTICLES

Particle

proton

neutron

electron

?

?

01

?

5X10-4

RelativeMass

RelativeCharge


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ATOMIC STRUCTURE

the number of protons in an atom

the number of protons andneutrons in an atom

He

4

2

number (A)

number (Z)

number of ________= number of protonsbut only for NEUTRAL atoms & compounds

if no CHARGE is shown, assume neutrality

number of _______= (atomic mass - number of protons)number of _________= atomic number


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Mass SpectrometerSeparates particles relative to MASS:CHARGE (m/z)

Used for:

Determining mass of particlesElemental composition of a compound

Chemical make-up of a sample


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1. sample is vaporized

2. sample is ionized by

an electron beam; ideally every

particle is 1+

3. sample is accelerated

by charged plates; ions move in a

beam trough the spectrometer tube

4. sample is deflected by

a magnetic field; MOMENTUM:

heavier particles resist change in

direction and bend LESS

5. particles of varied mass

detected; relative frequencies of each

is recorded

Mass Spectrometer


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Spectrometer Results

Relative abundance ofmolecules in sea water Br2


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Isotopes

All atoms of a certain element have the same , but they

may have different atoms of the same element that have different

numbers of neutrons; they have different A, atomic masses

12C is the atomic mass standard

12C is set at EXACTLY 12 atomic mass units (amu)

so, 1 amu = 1/12 the mass of12C1 amu = 1 dalton (Da)

isotopic mass so how do we determine isotopic mass?

spectrometer finds mass ratio relative to

Aisotope = mass ratio X

What is the isotopic mass of a pure sample of an Si

isotope with a mass ratio of 2.331411?


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Spectrometry Problems

Rubidium has two common isotopes, 85Rb and 87Rb. Ifthe abundance of 85Rb is 72.2% and the abundance of

87Rb is 27.8%, what is the average atomic mass of

rubidium?


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Uranium has three common isotopes. If the abundance of

234U is 0.01%, the abundance of 235U is 0.71%, and theabundance of 238U is 99.28%, what is the average atomic

mass of uranium?



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Titanium has five common isotopes: 46Ti (8.0%), 47Ti (7.8%),48Ti (73.4%), 49Ti (5.5%), 50Ti (5.3%). What is the average

atomic mass of titanium?



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Isotopic Properties

All isotopes of a given element have nearly identical

chemical behavior

(i.e. bonds involving lighter isotopes may break easier)

Physical characteristics may vary between isotopes

of the same element relative to mass (momentum) mass/volume

molecules of liquid separate to gas form

molecules move to disorder

these varied physical properties can alter isotopic

proportions in nature (i.e. global distribution of heavy

water)


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Isotope Example Hydrogen has three isotopes:

1H protium

2H deuterium

3

H tritium

3H is RADIOACTIVE

In this case, it is Beta () decayOne neutron turns into a proton and a -particle

The proton stays, the -particle is emitted

3

H


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Uses of

Radioisotopes14C used for determining age of organic material

half life is ~5700 years

40

K-40

Arratios are used to date rockhalf life is ~1.25 billion years

makes food safer to eat, have a longer shelf life

60

Co and

137

Cs kill microorganisms, likeE. co li

125I and 131I for checking thyroid activity

60Co produce gamma rays to destroy targeted

cancer cells

2.1 2 atom mass spectrometer student

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