atomic structure and the mass spectrum.ppt

8/10/2019 atomic structure and the mass spectrum.ppt

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Lesson 1

The atom and mass spectrum


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Outline

Introduction of atom

Atomic number and mass number

Measuring the mass of an atom

Using data from a mass spectrum


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Classification of Matter


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Atomsare the building blocks of matter.

Eachelementis made of the same kind of atom.

Acompoundis made of two or more different kinds of atoms.

Classification of Matter


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Structure of atom


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Atom


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The atoms of an element all contain the same number of

protons

An atom is electrically neutral

Compare to the nuclear, the mass of electron is negligible

Atom


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Element

What make an atom of one element different from anatom of another element?


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Atomic numbers

Mass # = p+ + n0

Number of electrons = number of protons

Atomic numbers and weights


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Nuclide p+ n0 e- Mass #

Oxygen - 10

- 33 42

- 31 15

8 8 1818

Arsenic 75 33 75

Phosphorus 15 3116

Atomic numbers--Practice

1.2 Atomic numbers and weights


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Isotopes

Isotopesare atoms of the same elementwith different

masses.

Isotopes have different numbers of neutrons.



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Atomic mass

Whats the mass of single 12C and 13C?

20.088* 10-27kg


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Isotope Symbol Composition of

the nucleus

% in nature

Carbon-12 12C 6 protons

6 neutrons

98.89%


7 neutrons

1.11%


8 neutrons


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Relative atomic mass

The relative atomic mass(RAM, given the symbol Ar) is defined

as the average mass of its isotopescompared with one-twelfththe mass of acarbon-12atom.


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1.3 Measuring the mass of atoms

Isotope Symbol Composition ofthe nucleus

% in nature

Carbon-12 12C 6 protons6 neutrons

98.89%


7 neutrons

1.11%

Carbon-14 14C 6 protons8 neutrons


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Mass spectrometer


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1.3 Measur ing the mass of atoms

Finding the relative atomic mass


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35Cl-37Cl

37Cl-37Cl

35Cl-35Cl


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Practice

Whats the average atomic mass of silicon?

Ar(Si) = 25.76 + 1.45 + 0.9 = 28.11


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1.4 Using data from a mass spectrometer

Mass spectrometry and chickens

corn-fed chicken yellow dye foodVs

Test the 12C : 13C ratio!


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Radioactive dating

Radioactive decay takes place when unstable

nucleus break apart to become more stable.

The time taken for half of the atoms in a

sample of a radioisotope to decayis constant

for that particular isotope. The time is called

the half-life, t1/2


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Radioactive dating

The ratio of carbon-14 to carbon-12 falls over

time.


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Radioactive dating

21

2

1 tx

y

Where

y is the percentage of original carbon-14left in the sample

x is the time since organism died (years)


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Drug testing

Enhancing drugs would change the ratio of

testosterone to epitestosterone (T:E ratio)


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Mass spectrometers in space

Sending a mass spectrometer into space to

identify the different elements of a planet

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atomic structure and the mass spectrum.ppt