Atomic Structure IB 1

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Model of the Atom The atom of Nitrogen Particles LocationChargeMass(u) ProtonNucleus + 1 NeutronNucleus 0 1 ElectronOrbits or Energy Levels _ 5 x 10 -4

Atomic number (Z) = number of protons in nucleus Mass number (A) = number of protons + number of neutrons in the nucleus X A Z U Mass Number Atomic Number Element Symbol

Questions Complete the following table:

Atoms x Ions Atoms are neutral because # protons = # electrons Ions are atoms that lost or gained electrons. 11 Na > 11 Na 1+ p=11 e=11 e=10 9 F > 9 F 1- p=9 e=9 e=10

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LecturePLUS Timberlake8 Isotopes Isotopes are atoms with the same number of protons, but different numbers of neutrons. Isotopes have identical chemical properties. Isotopes of Chlorine:Cl17 Cl - 35 Cl – 37 AM= u AM= u % % Abundance: % of that isotope in nature IMPORTANT: When the Atomic Mass of the isotope is not given, we can consider its Mass Number

LecturePLUS Timberlake9 Exercise: Naturally occurring carbon consists of three isotopes, 12 C, 13 C, and 14 C. State the number of protons, neutrons, and electrons in each of these carbon atoms. 12 C 13 C 14 C #P _______ _______ _______ #N _______ _______ _______ #E _______ _______ _______

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Calculating Molecular Mass A mass spectrum of chlorine shows there to be 25% 37 Cl and 75% 35 Cl. Calculate the relative atomic mass of chlorine in this sample. IMPORTANT: When the Atomic Mass of the isotope is not given, we can consider its Mass Number

Calculating Relative Molecular Mass A mass spectrum of chlorine shows there to be 25% 37 Cl and 75% 35 Cl. Calculate the relative atomic mass of chlorine in this sample. Solution: (0.25 x 37) + (0.75 x 35) = 35.5

Relative Atomic Mass (NO UNIT!!!) The relative atomic mass Ar, is the weighed average mass of its isotopes compared to one- twelfth of the mass of one atom of carbon-12. Carbon -12 is the standard of the atomic mass scale

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

Radioisotopes Many isotopes are radioactive once their nucleus breaks down spontaneously. Radioisotopes can occur naturally or be created artificially. The stability of a nucleus depends on the balance between the number of protons and neutrons. When the isotopes break down, the radioisotopes emit radiation: Gamma γ (high skin penetration) and alpha α ( can be stopped by a few centimeters of air.

Uses These radioisotopes have many uses: Generate energy in nuclear power stations Sterilize surgical instruments in hospitals Preserve food Fight crime Detect cracks in structural materials. Dating artifacts In medicine, treating and diagnosing illness.

Radioactive Isotopes read SG page 7 and CC page Co, radiotherapy I-131 and I-125 used as medical tracers. SG page 7

Carbon Dating, C - 14 The Qin Terracotta Warriors were discovered in China's province near in 1974 by six local farmers. Carbon dating with C-14 indicates that the ceiling was burned 2200 years ago.

Nov 11 P2

Half Life, t 1/2 Half-life is the time it takes for the amount of something to half due to decay. After 1 half-life, the amount of the original stuff decreases by half. After 2 half-lives, the amount of the original stuff decreases by a factor of 4. After 3 half-lives, the amount of the original stuff decreases by a factor of 8 The more unstable something is, the shorter the half-life.

Radioisotopes(radioactive decay) The radiation have different forms: Alpha particles,: emitted by nuclei with too many protons to be stable. They have 2 protons and 2 neutrons (the same as a helium nucleus). Stopped by a few sheets of paper

Beta particles: emitted by nuclei with too many neutrons. They are electrons ejected from the nucleus as a neutron decays. Stopped by a few mm of plastic or aluminum.

Gamma rays are a form of electromagnetic radiation.

Other Uses: Radioactive isotopes can occur naturally or be created artificially.Their uses include nuclear power generation( U- 235).

Mass Spectrometer l

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

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. 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.

Scale

Wave Properties of Matter Light or electromagnetic radiation may be viewed as a wave or as a stream of particles(photons) Light Electromagnetic energy at a particular wavelength λ has a frequency ν and energy E. c = λ ν and E = h ν Where c ( speed of light ) = 3×10 8 m/s)speed of light h (Planck's constant ) = × 10 −34 J·sPlanck's constant

Exercise 1.Suppose we have an electromagnetic wave of wavelength 400nm ( I nm = 1 x m) a)Calculate its frequency b)Calculate its energy 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 ? a)How much energy was released ?

Spectra Dispersion is the basis for the prism and its ability to spatially separate light into its wavelengths: rum_hydrogen_element_flame_t_page_3&from=search When radiation is separated into its different wavelengths, a spectrum is produced.

2.2.1 Describe and explain the difference between a continuous spectrum and a line spectrum. A continuous spectrum is created when white light is passed through a prism. This spectrum, like the rainbow produced when sunlight is dispersed by raindrops, contains all the wavelengths of visible light. In contrast,if the light from atoms with excited electrons is passed through a prism, an emission spectrum is formed. It consists of a number of coloured lines on a black background.It is called line spectra.

Emission spectra differs from a continuous in two ways: 1. It is made of separate lines(coloured if they are in the visible region ), it is discontinuous 2. The lines converge, becoming progressively closer as the energy of the emission lines increases(higher levels)

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Bohr Model of Hydrogen Atom Electrons in their shells can receive energy in the form of heat or electricity and jump to higher energy shells (promotion). They cannot remain at these higher levels (excited state) for very long and soon fall back to their original shell (ground state). When they fall back they have to lose the energy difference between the two shells.This loss of energy is performed by releasing electromagnetic energy in the form of infrared, visible light or ultraviolet radiation.

Hydrogen Spectrum & Series When the electron falls back to 1: Lines are in the UV region When the electron falls back to 2: Lines are visible region When the e falls back to 3: Lines are in the IR region

H spectrum The amount of energy released may be found by: ΔE = E 2 - E 1 = h f F = E 2 - E 1 / h The energy levels become more closely spaced until they converge at high energy.

Balmer Series of Hydrogen A series of emission in the visible part of the hydrogen spectrum that is due to transitions between the second state and higher energy states of the hydrogen atom. It is are named after their discoverer, the Swiss physicist Johann Balmer (1825–1898).emissionhydrogen spectrum

Hydrogen Spectrum

Line Spectra of Other Elements

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