1. PACS 2008 Unit: Atomic Structures Mr. Nylen Pulaski Academy High School 2008

2. The main sub-atomic particles ParticleChargeMassSymbolLocation Proton11 amuH +, or +Nucleus Neutron01 amuNucleus Electron0 amue -, or -Outer shell PACS 2008

3. Atomic Mass Mass of the atom – made up mostly of mass of protons and neutrons Mass of the atom – made up mostly of mass of protons and neutrons Measured in Atomic Mass Units Measured in Atomic Mass Units 1 amu = 1/12 the mass of 1 amu = 1/12 the mass of a Carbon-12 atom (the standard for all relative atomic masses) PACS 2008

4. Atomic Mass (A) Since a proton = 1 amu, and a neutron = 1 amu (or u), atomic mass also represents the number of protons and neutrons in the nucleus Since a proton = 1 amu, and a neutron = 1 amu (or u), atomic mass also represents the number of protons and neutrons in the nucleus Electrons have negligible weight and aren’t factored in to atomic mass Electrons have negligible weight and aren’t factored in to atomic mass PACS 2008

5. Atomic Number (Z) Represents the charge in the nucleus Represents the charge in the nucleus For atoms this means Z = the number of protons in the nucleus For atoms this means Z = the number of protons in the nucleus This is what makes an atom of an element different compared to other elements This is what makes an atom of an element different compared to other elements PACS 2008

6. Isotopes Atoms of the same element (w/same # of protons and same charge) BUT different number of neutrons (therefore different atomic mass) Atoms of the same element (w/same # of protons and same charge) BUT different number of neutrons (therefore different atomic mass) Ex. The 3 naturally occuring isotopes of CARBON Ex. The 3 naturally occuring isotopes of CARBON Carbon 12, Carbon 13, Carbon 14 Carbon 12, Carbon 13, Carbon 14 PACS 2008

7. Isotopes of Hydrogen Hydrogen usually has 1 proton, and an atomic mass of ~1 Hydrogen usually has 1 proton, and an atomic mass of ~1 Another isotope of Hydrogen has an atomic mass of ~2 Another isotope of Hydrogen has an atomic mass of ~2 How many protons must this isotope have? How many protons must this isotope have? How many neutrons must this isotope have? How many neutrons must this isotope have? PACS 2008

8. Ions - SUMMARY Never change # of protons Never change # of protons Charge comes from # electrons Charge comes from # electrons If electrons = protons, charge is 0 If electrons = protons, charge is 0 If electrons > protons, charge is negative If electrons > protons, charge is negative If electrons < protons, charge is positive If electrons < protons, charge is positive Neutrons are used to make up difference in atomic mass ONLY (they have no charge) Neutrons are used to make up difference in atomic mass ONLY (they have no charge) PACS 2008

9. Page 8, Weighted Atomic Mass Atomic mass shown in periodic table is a weighted average of the masses of the naturally occurring isotopes of the element. Atomic mass shown in periodic table is a weighted average of the masses of the naturally occurring isotopes of the element. This is why hydrogen has a mass of 1.00074 This is why hydrogen has a mass of 1.00074 PACS 2008

10. Weighted Atomic Mass An element has three isotopes (different number of neutrons). What is the weighted atomic mass of the element? An element has three isotopes (different number of neutrons). What is the weighted atomic mass of the element? PACS 2008 Isotope% abundance in nature Fractional AbundanceProduct Carbon 1298.9%12 * (.989) = Carbon 131.05%13 * (.0105) = Carbon 14.05%14 * (.0005) = Weighted Atomic Mass:

11. Weighted Atomic Mass (K) PACS 2008 Isotope% abundance in nature Fractional AbundanceProduct K- 3993.12% K- 406.88% Weighted Atomic Mass:

12. Models of the atom Dalton’s Indivisible Atom Dalton’s Indivisible Atom J.J. Thomson’s Plum Pudding Model J.J. Thomson’s Plum Pudding Model Rutherford’s Solar System Model Rutherford’s Solar System Model PACS 2008

13. Models of the Atom Page 36 in notes Thomson – plum pudding Thomson – plum pudding Electrons are even distributed through a positive body Electrons are even distributed through a positive body Rutherford Rutherford Established that the atom is mostly empty space with a positive massive center Established that the atom is mostly empty space with a positive massive center PACS 2008

14. Light as a Wave – Electromagnetic Radiation Visible light is energy that travels in the form of an electromagnetic wave Visible light is energy that travels in the form of an electromagnetic wave We can use a sine wave drawing as a model of an electromagnetic wave. We can use a sine wave drawing as a model of an electromagnetic wave. Wavelength = λ Wavelength = λ PACS 2008 crest wavelength crest wavelength

15. Light as a Wave Frequency – The number of crests passing a point each second. Units = 1/seconds (Hertz, Hz) Frequency – The number of crests passing a point each second. Units = 1/seconds (Hertz, Hz) Speed = 3x10 8 m/s (This is the speed of light) Speed = 3x10 8 m/s (This is the speed of light) c = f λ c = f λ c = speed of light, f = frequency, λ = wavelength c = speed of light, f = frequency, λ = wavelength PACS 2008

16. Electromagnetic Spectrum PACS 2008

17. Emission Spectra Review page 33 - 34 in notes PACS 2008

18. Bohr Model of the Atom Applied Quantum Theory to the Atom Energy is absorbed and emitted by atoms in discrete amounts Electrons may only be located in specific orbits Electrons possess definite amounts of energy

19. Bohr Model Electrons arrange themselves in specified energy orbits around nucleus Electrons fill lower energy levels first Arrangement of electrons equals electron configuration Outermost Principal Energy Level

20. Principal Energy Levels K shell (holds 2 electrons) L shell (holds 8 electrons) M shell (holds 18 electrons) N shell (holds 36 electrons) If electrons absorb exactly the difference between 2 orbits, they will “jump up” This is an all or nothing proposition This jumping orbital change causes emission spectra

21. Excited State Very unstable Very unstable Electrons want to fall back to ground state Electrons want to fall back to ground state Energy is released when electrons fall back Energy is released when electrons fall back In the form of electromagnetic radiation In the form of electromagnetic radiation These can be in visible These can be in visible range (photons) range (photons) Each jump represents EMR frequence of energy Each jump represents EMR frequence of energy PACS 2008

22. Electron Configurations Add up # electrons Add up # electrons Match to element on periodic table Match to element on periodic table See if electron config. Matches that on periodic table (if so, it is in ground state) See if electron config. Matches that on periodic table (if so, it is in ground state) If no, then it is in excited state If no, then it is in excited state PACS 2008 Example: 12 Mg Example: 12 Mg Ground = 2-8-2 Ground = 2-8-2 Excited = 2-7-3, or 1-8-3, or 1-7-4 Excited = 2-7-3, or 1-8-3, or 1-7-4

23. Page 35 - Review PACS 2008

24. Quantum Mechanical Model of the Atom Incorporated findings that electrons behave like waves and particles Incorporated findings that electrons behave like waves and particles Electrons do not move in fixed orbits, they move in areas called orbitals Electrons do not move in fixed orbits, they move in areas called orbitals Orbital = region of space where an electron of a certain energy is MOST LIKELY to be found Orbital = region of space where an electron of a certain energy is MOST LIKELY to be found 2-8-1 means there are 3 orbitals 2-8-1 means there are 3 orbitals There is 1 electron in the outermost principal energy level There is 1 electron in the outermost principal energy level PACS 2008

25. Page 37 - 43 Work in your lab groups Work in your lab groups Make sure you understand every question Make sure you understand every question If you don’t, ASK! If you don’t, ASK! This will be the regular bonus for the exam This will be the regular bonus for the exam PACS 2008

26. Homework Review Book p. 17 Review Book p. 17 Questions 15-30 Questions 15-30 PACS 2008