Unit – Atomic Structure

http://www.chemactive.com/ib_chemistry_HL.html

The atom is the smallest particle of matter

• The atom of sodium can be identified by its number of protons!!!!!

• Look at the periodic table and find Na

Model of the Atom The atom of Nitrogen Particles

Location Charge Mass(u)

Proton Nucleus + 1

Neutron Nucleus 0 1

Electron Orbits or Energy Levels

_ 1/2000

Elemental Notation:

X

AN- Atomic Number AN = p = e

MN-Mass Number MN = p + n n = MN - AN

For example: p= e= n=

Examples

• What would be the notation for the atom given?

Complete the following:

C O Au ?

# p 6 79

# n 7 14

# e 8

MN 17 198

AN 11

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Isotopes

Isotopes are atoms with the same number of protons, but different

numbers of neutrons. Isotopes have identical chemical

properties.

Isotopes of Chlorine:

35Cl 37Cl17 17

Cl - 35 Cl – 37 AM=34.968852 AM=36.965903 75.77 % 24.23 %

Abundance: % of that isotope in natureIMPORTANT: When the Atomic Mass of the isotope is not given, we can consider

its Mass Number

AM =

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Exercise:

Naturally occurring carbon consists of three isotopes, 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of these carbon atoms.

12C 13C 14C 6 6 6

#P _______ _______ _______

#N _______ _______ _______

#E _______ _______ _______

Relative Atomic Mass(no units!!!!!!!)

a)Find the relative atomic mass of Chlorine considering that the two isotopes occur in the ratio 3:1

b) Find the relative atomic mass of oxygen.

Properties of Isotopes

• Isotopes of the same element have identical chemical properties but may slightly differ in physical properties.

Radioactive Isotopeshttp://chemactive.com/flash_spring/ib/use_of_radioisotopes.swf

read SG page 7 and CC page 27

• Many isotopes are radioactive once their nucleus breaks down spontaneously.

60Co => 60 Ni + βI-131 and I-135 used as

medical tracers

• There are three forms of radiation:

I. Alpha - α

II. Beta - β or 0 e

III.Gamma - γ

Carbon Dating

The Qin Terracotta Warriors were discovered in China's province near in 1974 by six local farmers. A flurry of national media surrounded the discovery, and excavations were soon begun. The figures were found to be part of a massive burial complex whose construction was ordered by the First Emperor of China, Qin Shihuangdi, when he ascended the

throne in 246 BC.

• Carbon dating with C-14 indicates that the ceiling was burned 2200 years ago.

Other Uses: Radioactive isotopes can occur naturally or be created

artificially.Their uses include nuclear power generation( U-235), crime detection, preservation of food,radiotherapy( Co-60) and treating and diagnosing illness( I-131).

Mass Spectrometer

• http://www.colby.edu/chemistry/OChem/demoindex.html#table

• http://www.magnet.fsu.edu/education/tutorials/java/massspectra/index.html

• This is an instrument used for measuring the exact masses of particles.

• It can be used on elements to determine the isotopic abundances and very accurate mass measurements or it can be used, on molecules to find out the nature of the molecule by looking at the fragmentation pattern of its destructive ionisation.

• It has several stages of operation that you must get famiiliar with (i.e. learn!):

• injection of the sample • vaporisation of the sample (if it's not

already gaseous) • ionisation of the sample • acceleration of the ions • deflection of the ions • detection of the ions

• The mass spectrometer is a device used to measure the mass of an atom by reading on a detecting screen the amount of deflection their +1 ions experience in a magnetic field: the smaller the deflection the larger the mass.

• More specifically, the mass of an atom is measured by comparing its deflection in the mass spectrometer to the deflection of the carbon-12 mass standard.

• For a sample of an element one can also count the number of atoms of each isotope that hit the detecting screen to obtain the fractional abundance of each isotope. The average atomic mass of the element that appears on the periodic table is then the weighted average of the isotope masses.

• zirconium-90 , 51.5%• zirconium-91 ,11.2%• zirconium-92, 17.1%• zirconium-94, 17.4%• zirconium-96, 2.8%

• Do questions 1&2 Course Companion page 30.

Electromagnetic Spectrum• Electromagnetic waves can travel through space or matter.

• The electromagnetic spectrum encompasses all possible wavelengths of radiation

Wave Properties of Matter• Light or electromagnetic radiation may be viewed in one

of two complementary ways: as a wave or as a stream of particles

• Electromagnetic energy at a particular wavelength λ has an associated frequency ν and energy E. These quantities are related according to the equations:

c = λ ν and E = h ν

Where c ( speed of light ) = 3×108 m/s) h (Planck's constant ) = 6.626 × 10−34 J·s

http://csep10.phys.utk.edu/astr162/lect/light/waves.html

Exercise1. Suppose we have an electromagnetic wave of wavelength

400nm.a)Calculate its frequency b)Calculate its energyc)

2. The yellow light given off by a sodium vapor lamp used for public lighting has a walength of 589 nm.

a) What is the frequency of radiation ?b) What is the amount of energy?

SpectraDispersion is the basis for the prism and its ability to

spatially separate light into its wavelengths:

http://csep10.phys.utk.edu/astr162/lect/light/dispersion.html

When radiation is separated into its different wavelengths, a spectrum is produced.

• Continuous spectrum: Rainbow of colors containing light of all wavelengths.

• Emission spectra: consists of a series of separate discrete lines, which become closer together(converge) towards the

high energy end of the spectrum.

The Bohr Model of the AtomProposal: Electrons travel in orbits around the nucleus of the atom and each orbit is in

a fixed energy level.

In each case the wavelength of the emitted or absorbed light is exactly such that the photon carries the energy difference between the two orbits.

Electron Excitation

• http://www.upscale.utoronto.ca/GeneralInterest/Harrison/BohrModel/Flash/BohrModel.html

Hydrogen Spectrum

The visible spectrum occurs when the electron falls to the second level.