Atomic Structure

1. Atomic Structure • The smallest part of an element is an ATOM • All atoms consist of subatomic particles: • Protons • Neutrons • Electrons

2. Nucleus • The “core” of the atom • Contains 99.9% of the mass of the atom • Protons and neutrons are found in the nucleus of an atom Mass Number = mass of the nucleus or mass of protons + neutrons

3. Protons • Positively charged particles • The number of protons identifies the element • 1 proton = 1 atomic mass unit (amu) # protons = Atomic Number (whole number)

4. Neutron • Neutral Particles • Found in the nucleus • 1 neutron = 1 amu # neutrons = Mass number – Atomic Number

5. Electrons • Negatively charged particles • Found in the electron cloud • Electrons have a very small mass, so we don’t even count it! • Electrons give atoms their chemical properties • Atoms are neutral so; # electrons = # protons

6. + + + + + + Mass Number • mass # = protons + neutrons • always a whole number • NOT on the Periodic Table! Neutron Electrons Nucleus e- Proton Nucleus e- e- e- e- Carbon-12 Neutrons 6 Protons 6 Electrons 6 e-

8. Shorthand Notation Mass number SYMBOL OF ELEMENT Atomic number

9. C 12 6 Mass # Atomic # Isotopes • Atoms of the same element with different mass numbers. • Different number of neutrons & different mass • Nuclear symbol: • Hyphen notation: carbon-12; carbon-13 Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

10. Neutron Nucleus Proton Proton + Nucleus + Neutron + + + Carbon-12 + + + + + + + Carbon-14 Isotopes Electrons Nucleus Electrons Neutrons 6 Protons 6 Electrons 6 Neutrons 8 Protons 6 Electrons 6 Nucleus

11. Lithium-7 Lithium-6 Neutron Neutron 3 p+ 3 n0 3 p+ 4 n0 + 2e– 1e– 2e– 1e– + + + + + Proton Proton Nucleus Nucleus 6Li 7Li Electrons Electrons Nucleus Nucleus Neutrons 3 Protons 3 Electrons 3 Neutrons 4 Protons 3 Electrons 3

12. 17 Cl 37 Cl 37 17 Isotopes • Chlorine-37 • atomic #: • mass #: • # of protons: • # of electrons: • # of neutrons: • 17 • 37 • 17 • 17 • 20 Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

13. Average Atomic Mass • weighted average of all isotopes on the Periodic Table • round to 2 decimal places Avg. Atomic Mass (mass)(%) + (mass)(%) = 100 Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

14. Calculating Average Atomic Mass You will be given the mass number and the Percent Abundance (how common the isotope is in nature) of the isotope Atomic mass = (% abundance in decimal form isotope1)(mass isotope1) + (%abundance in decimal form isotope2)(mass isotope2)

15. Average Atomic Mass • EX: Calculate the avg. atomic mass of oxygen if its abundance in nature is 99.76% 16O, 0.04% 17O, and 0.20% 18O. Avg. Atomic Mass (16)(99.76) + (17)(0.04) + (18)(0.20) 16.00 amu = = 100 Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

16. Example • Carbon has 6 protons and 6 neutrons, what is Carbon’s mass number? C-12 • An isotope of Carbon has 6 protons and 8 neutrons, what is carbon’s mass number? C-14 Remember the number of protons NEVER changes for an element!

17. Isotope Review • Same element different number of NEUTRONS • Different Mass number • Same Atomic number, therefore the same number of protons and electrons

18. Isotope Applications • Complete the read around the room station activity

19. Atomic Structure • ATOMS • Differ by number of protons • IONS • Differ by number of electrons • ISOTOPES • Differ by number of neutrons

20. Electrons • Electrons give elements their chemical properties • The arrangement of the electrons will determine how it reacts with other substances • Gain electron the atom becomes negative (anion) • Lose an electron the atom becomes positive (cation)

21. Humor Two atoms are walking down the street. One atom says to the other, “Hey! I think I lost an electron!” The other says, “Are you sure??” “Yes, I’m positive!” A neutron walks into a restaurant and orders a couple of sodas. As she is about to leave, she asks the waiter how much she owes. The waiter replies, “For you, No Charge!!!”

22. Electrons are found in the electron cloud The cloud has regions of space called energy levels • The first energy level holds 2 electrons • The second energy level holds 8 electrons. • The third energy level holds 18 electrons

24. Valence Electrons • Are found furthest from the nucleus • Dictate the physical and chemical properties of an element • Use the periodic table to determine the number of valence electrons. • All atoms want 8 valence electrons

26. Lewis Dot Diagram • A way to illustrate the number of valence electrons • Use one dot for each valence electron • Place the dot around each side of the symbol before pairing the electrons • The symbol represents the nucleus plus all the inner electrons for the element.

27. Examples H O N F Ne

29. Electrons and Light • Electrons are normally in the ground state • When the atom is given energy the electrons move to the excited state. • When the electrons lose this energy they fall back to the ground state and emit light. • Each element has a unique emission spectrum

32. Electromagnetic Spectrum • Electromagnetic Radiation – • A broad range of energetic emissions • made up of photons • Photons – bundles of energy • Travel like waves • Move at the speed of light = 3.0 x 108 m/s • Electromagnetic waves do not require a medium to move

34. Parts of the wave • Amplitude – the height of the wave • Wavelength – the distance between the two successive waves • Frequency – the number of waves that pass a given reference point per second

35. Wavelength = lamda unit is nanometer • Frequency = nu in units of 1/s or s-1

36. What is the difference between these waves?