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Relative atomic mass The relative atomic mass of an element (Ar) is the average mass of an atom of the element, taking into account all of its isotopes and their relative abundance, compared to one atom of carbon-12 The atom 0 atomos – Greek word meaning “indivisible” 0 Elements are made up of atoms 0 Atoms 0 Are the smallest unit of an element 0 Are made up of subatomic particles 0 Cannot be broken down by chemical reactions 0 All matter is built from ~100 elements The atom If you grind down gold into dust, each dust particle still has the properties of gold! With the right equipment you could keep grinding until you reach a particle that can not be divided any further and still retains the properties of gold– the atom! Scanning Tunneling Microscope Sub-atomic particles Relative charge + Location Notes Proton Relative mass 1 Nucleus = Atomic # • Defines type of atom • Makes up part of atomic mass Electron 0.0005 - Electron cloud = Atomic # in a neutral atom Neutron 1 0 Nucleus • Makes up part of atomic mass Particle Notation Atomic Mass Number Atomic Number Definitions 0 Atomic number (Z): Tells us the type of element 0 Defined by the number of protons 0 Mass number (A): The number of protons + neutrons 0 The mass of the atom is centered in the nucleus Atomic Number (Z) 0 Z = The number of protons 0 This number is unique for each element 0 This number never varies… Carbon always has 6 protons Atomic Number (Z) 0 Carbon has 6 protons 0 The atom is neutral 0 How many electrons does it have? Ions 0 An atom that has gained or lost electrons 0 Cation- An ion with a positive charge 0Atom has lost electrons 0 Anion- An ion with a negative charge 0Atom has gained electrons Ions 0 Determine the number of electrons present in an oxygen ion that has a negative 2 charge (O-2) 0 Z = the # of protons = 8 0 In a neutral atom, oxygen has 8 protons (8 negative charges to balance the 8 positive charges that the protons carry) 0 the -2 charge indicates that we have 2 more negative charges (therefore 2 more electrons) 0 10 total electrons Atomic Mass Number 0 If the relative mass of a protons and neutrons is 1, why is the atomic mass = 12.01? 0 Different kinds of carbon exist! 0 Average atomic mass is the average of all types of carbon that exist Isotopes 0 Isotopes- atoms of the same element with different numbers of neutrons 0 They still have the same # of protons! Z is always the same 0 The number of neutrons can vary 0 Same chemical properties Isotopes 0 Isotopes are identified by their mass #: Subatomic Particles Potassium- 39 Potassium-40 Potassium-41 Protons 19 19 19 Neutrons 20 21 22 Electrons 19 19 19 The differing masses leads to different physical properties (bp & mp) Isotopes 0 The relative abundance of each isotope is constant Subatomic Particles Potassium- 39 Potassium-40 Potassium-41 Protons 19 19 19 Neutrons 20 21 22 Electrons 19 19 19 Calculating Atomic Mass 0 Weighted average atomic mass = sum of all mass contributions 0 Mass Contribution = (Atomic Mass)(Percent Abundance) Calculating Atomic Mass 0 Boron has two naturally occurring isotopes: boron-10 (abundance 19.8%, mass = 10.013 amu) and boron-11 (abundance 80.2%, mass = 11.009 amu). Calculate the atomic mass of boron. Mass contributions: Boron-10 (10.013)(.198)= 1.98 Boron-11 (11.009)(.802)= 8.83 Weighted average atomic mass: 1.98 + 8.83 = 10.81 amu Announcements 0 Turn in take home test – Today 0 Turn in % correct – Today 0 Turn in solution labs if you haven’t already 0 Atomic Structure Quiz- turn in work 0 Field trip – tomorrow 0 Report to cafeteria before the 1st bell 0 Bring lunch or buy from cafeteria lunch 11-12pm 0 Sunny 70 degrees…. Bring appropriate clothing…wear clothes that can get dirty…wear tennis shoes 0 Take pre-survey – check edmodo 0 Presentation dates 22nd (1-3) 23rd (4-6) in F108 at 11:50 0 IJournal #10 by Wednesday 0 Finish packet by Thursday Radioisotopes 0 The stability of the nucleus depends on a balance between protons and neutrons 0 If there are too many or too few neutrons, changes will occur to the nucleus to create a more stable environment 0 These changes give out radiation in the form of 0 Alpha particles 0 Beta particles 0 Gamma rays 0 Nuclear Reaction: a reaction that involves a change to an atoms nucleus 0 A change to an atoms nucleus changes its identity 0 Radioactive atoms undergo changes that alter their identities 0 Radioactivity is a process that emits radiation 0 Tracers used to detect structure and function of organs 0 Medical Diagnosis – PET scan 0 Cancer treatment 0 Food preservation 0 Sensors in Smoke Detectors 0 Nuclear fuel for power plants 0 Detected with a Geiger Counter. (When ions strike the cylinder of the Geiger counter, it emits an audible click.) 0 Dosimeter – measures the total amount of radiation that a person has received. 0 Usually is worn like a badge. 0 The film is later developed and the exposure to radiation can be measured. α 0 Composition: Alpha particles 0 Charge: +2 0 Radiation: Helium Nuclei 0 Penetrating Power: Blocked by paper 0 Cannot penetrate skin, not dangerous 4He 2 α 4He 2 0 Helium nucleus released by nucleus 0 Mass decreases by 4 0 Atomic number decreases by 2 α 4He 2 U Th He 238 234 4 92 90 2 0 Uranium has changed into a new element: Thorium 0 Alpha particle is released β Composition: Beta Particles Radiation: Electrons 0 1 e Charge: -1 Penetrating Power: Blocked by metal foil, more dangerous 0 β 1 e 0 Neutron changes into a proton 0 Electron released (do not need to worry about the mechanism of how this happens) 0 Mass unchanged (the mass of a neutron is roughly equal to the mass of a proton) 0 Atomic number increases by 1 β 0 1 14 6 e C 7 N e 14 0 Carbon is changed into nitrogen 0 Atomic # increases 0 1 γ Composition: Electromagnetic Radiation (Rays) Radiation: Photons Charge: Neutral Penetrating Power: not completely blocked by lead or concrete – dangerous! γ 0 Pure energy released from nucleus 0 Mass unaffected 0 Atomic number unaffected γ 87 87 Sr* Sr 38 38 0 Pure energy released from nucleus 0 No new element formed 0 Protons and neutrons change relative positions in the nucleus Carbon-14 dating 0 14C has 8 neutrons (too many to be stable) 0 The atom can become stable by beta decay 0 1 neutron will be changed into a proton 0 1 electron will be ejected 14 6 C 7 N e 14 0 1 0 Carbon dating: 0 Used to measure the age of artifacts that were once part of a living organism 0 Every 5730 years the 14C to 12C ratio falls by 50% (1 half life) after a living organism dies • Can determine the age of organic matter with 14C (Up to 45,000 yrs) Cobalt- 60 0 Radiation therapy (radiotherapy) – the treatment of cancer with radiation 0 Emits gamma rays 0 Protons and neutrons change positions in nucleus 0 Damages normal and malignant cells 0 Knocks off electrons making it impossible for cells to grow Iodine-131 0 Used as a medical tracer 0 Iodine is an essential element that enables the thyroid gland to produce thyroid hormones 0 Radioisotopes travel through the body just like the isotopes that are naturally in our body (same chemical properties) 0 Positions in the body can be monitored by detecting radiation levels 0 Emits beta particles and gamma rays 0 Short half life of 8 days – quickly eliminated from body Iodine-125 0 Treatment of prostate cancer 0 Inserted into gland (isolated treatment) 0 Emits beta radiation 0 Longer half life of 80 days Mass Spectrometer 0 Sample introduction 0 Direct insertion 0 MALDI plates commonly used 0 Direct injection 0 If already in gaseous state Mass Spectrometer 0 Vaporization0 Sample vaporized (if not already in gaseous state) 0 Allows individual atoms to be analyzed 0 Ionization0 atoms hit with high energy electrons 0 electrons knocked out 0 produces positively charged ions 0 no effect on mass X(g) + e- X+(g) + 2e- Mass Spectrometer 0 Acceleration 0 Positive ions attracted to negatively charged plates in machine 0 The ions accelerate due to electrical field Mass Spectrometer 0 Deflection 0 positive ions deflected by a magnetic field 0 cause position changes 0 Amount of deflection based on charge/mass ratio: 0 ions with smaller mass are deflected more than heavier ions 0 ions with higher charges are deflected more than lower charges Mass Spectrometer 0 Detection 0 Positive ions are detected and sent to a recorder 0 Strength of signal dependent on the number of ions with a particular charge/mass ratio Uncharged particles removed by vacuum pump Mass Spectrometer 0 Relative atomic mass 0 Real mass numbers are very difficult to use 0 Relative masses provide a frame of reference with more straight forward numbers 0 Carbon-12 isotope 0 Common element (in all living things) 0 Solid 0 Easy to transport and store 0 Chosen as the standard in 1961 0 Given a relative mass of exactly 12 Mass Spectra/Spectrum 0 X axis- mass/charge (m/z) ratio 0 m/z ratio- always assume +1 charge 0 Y axis- % abundance Mass Spectra/Spectrum 0 Mass Spectra for Boron: 0 100 ions have a mass of 11 0 23 ions have a mass of 10 0 Total ions in sample: 123 0 Relative atomic mass: 0 81.3% have a mass of 11 0 18.7% have a mass of 10 0 (.813)(11) + (.187)(10) = 0Ar = 10.81 Electromagnetic Spectrum c = ʄ λ c = 3 x 108 m s-1 All waves travel at the same speed – can be distinguished by different wavelengths (λ) Electromagnetic Spectrum Wavelengths are measured peak to peak Frequency is the # of waves in a given period Line Spectra ΔEelectron= Ephoton 0 Line spectrums act like fingerprints to identify elements 0 Electrons absorb energy and move into an excited state 0 The excited state is very unstable, so the electrons fall back to their ground state or lowest energy level. 0 Energy is then lost by the electron in the form of photons (light) Hydrogen Spectra Convergence Equations c=ʄλ E = hf c = 3 x 108 m s-1 h = 6.63 x 10-34 J.s h = planks constant c= speed of light Energy levels Ionization energy: - minimum energy needed to remove an e- from its ground state Types of transitions Electron Arrangements 0 Need to be able to write electron arrangements for atoms through Z= 20 (Calcium) 0 Simpler than the method you learned in honors chem! Energy level # e- it can hold n= 1 n= 2 n= 3 n= 4 2 8 8 8 Z= 20 Ca e- arrangement: 2, 8, 8, 2 Energy levels are separated by commas & # of e- are shown Z= 12 Mg e- arrangement: 2, 8, 2 Z= 5 B e- arrangement: 2, 3 Z= 1 H e- arrangement: 1 e- arrangements 0 Valence electrons electrons in outermost energy level 0 Easiest to remove = lowest ionization energy Z= 5 B e- arrangement: 2, 3 3 valence e- Z= 12 Mg e- arrangement: 2, 8, 2 2 valence e- Z= 20 Ca e- arrangement: 2, 8, 8, 2 2 valence e- Z= 1 H e- arrangement: 1 1 valence e-