Atomic Structure IB 1

1
Atomic StructureIB 1

2
Sites

• http//ibchem.com/IB/ibnotes/brief/ato-sl.htmato
• http//www.chemactive.com/ib_chemistry_HL.html

3
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 _ 5 x 10-4
4
Atomic number (Z) number of protons in
nucleus Mass number (A) number of protons
number of neutrons in the nucleus

5
Questions

• Complete the following table

6
Atoms x Ions

• Atoms are neutral because protons
  electrons
• Ions are atoms that lost or gained electrons.
• 11 Na ---------- gt 11 Na 1
• p11
  p11
• e11
  e10
• 9 F ------------ gt 9 F 1-
• p9
  p9
• e9
  e10

7
IB
8
Isotopes

• Isotopes are atoms with the same number of
  protons, but different numbers of neutrons.
  Isotopes have identical chemical properties.
• Isotopes of Chlorine
• Cl Cl
• 17 17
• Cl - 35
  Cl 37
• AM34.968852u
  AM36.965903u
• 75.77
  24.23
• Abundance of that isotope in nature
• IMPORTANT When the Atomic Mass of the isotope is
  not given, we can consider its Mass Number

9
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 _______ _______
  _______

10
IB
11
Calculating Molecular Mass

• A mass spectrum of chlorine shows there to be 25
  37Cl and 75 35Cl. 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

12
Calculating Relative Molecular Mass

• A mass spectrum of chlorine shows there to be 25
  37Cl and 75 35Cl. Calculate the relative atomic
  mass of chlorine in this sample.
• Solution
• (0.25 x 37) (0.75 x 35) 35.5

13
(No Transcript)
14
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

15
Properties of Isotopes

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

16
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 ? (high skin penetration) and alpha
  a ( can be stopped by a few centimeters of air.

17
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.

18
Radioactive Isotopeshttp//chemactive.com/flash_
spring/ib/use_of_radioisotopes.swfread SG page 7
and CC page 27

• 60Co , radiotherapy
• I-131 and I-125 used as medical tracers.

• SG page 7

19
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.

20
Nov 11 P2
21
(No Transcript)
22
Half Life, t 1/2

• http//mcat-review.org/atomic-nuclear-structure.ph
  p
• 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.

23
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

24

• 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.

25

• Gamma rays are a form of electromagnetic
  radiation.

26
Other Uses

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

27
Mass Spectrometer

• http//www.colby.edu/chemistry/OChem/demoindex.htm
  l
• http//ibchem.com/IB/ibnotes/brief/ato-sl.htmato
• l

28

• 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

29

• 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 12 Course Companion page 30.

30
Electromagnetic Spectrum

• Electromagnetic waves can travel through space or
  matter.
• The electromagnetic spectrum encompasses all
  possible wavelengths of radiation.

31
Scale
32
Wave Properties of Matter

• Light or electromagnetic radiation may be viewed
  as a wave or as a stream of particles(photons)
• Electromagnetic energy at a particular wavelength
  ? has a frequency ? and energy E.
• c ? ? and E h ?
• Where
• c ( speed of light ) 3108 m/s)
• h (Planck's constant ) 6.626 10-34 Js
• http//www.kentchemistry.com/links/AtomicStructure
  /PlanckQuantized.htm

33
Exercise

• Suppose we have an electromagnetic wave of
  wavelength 400nm ( I nm 1 x 10-9 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.
• What is the frequency of radiation ?
• How much energy was released ?

34
(No Transcript)
35
Spectra

• Dispersion is the basis for the prism and its
  ability to spatially separate light into its
  wavelengths
• http//yteach.com/page.php/resources/view_all?idl
  ine_spectra_light_electromagnetic_spectrum_hydroge
  n_element_flame_t_page_3fromsearch
• When radiation is separated into its different
  wavelengths, a spectrum is produced.

36
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.

37

• 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)

38
IB Question
39

• http//www.mhhe.com/physsci/chemistry/essentialche
  mistry/flash/linesp16.swf

40
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.
• http//science.sbcc.edu/physics/solar/sciencesegme
  nt/bohratom.swf

41
(No Transcript)
42
(No Transcript)
43
Hydrogen Spectrum Series

• http//www.youtube.com/watch?v6rHerkru60E
• http//hyperphysics.phy-astr.gsu.edu/hbase/hyde.ht
  ml
• 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

44
H spectrum

• The amount of energy released may be found by
• ?E E2 - E1 h f
• F E2 - E1 / h
• The energy levels become more
• closely spaced until they converge
• at high energy.

45
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
  (18251898).

46
Hydrogen Spectrum
47
Line Spectra of Other Elements
48

• http//www.trschools.com/staff/g/cgirtain/Sodium_e
  mission.htm