4.2 The Structure of an Atom

1. 4.2 The Structure of an Atom

2. Atomic Structure • Atoms are composed of 2 regions: • Nucleus: center of atom that contains mass of atom • Electron cloud: region that surrounds nucleus that contains most of space in atom Nucleus Electron Cloud

3. What’s in the Nucleus? • Nucleus contains 2 of 3 subatomic particles: • Protons: subatomic particle w/ 1+ charge (p+) • Rutherford - 1911 • Neutrons: subatomic particle w/ no charge (no) • James Chadwick - 1932

4. What’s in the Electron Cloud? • The 3rd subatomic particle resides outside nucleus in electron cloud • Electron: subatomic particle w/ 1- charge (e-) and virtually no mass • JJ Thomson - 1897

5. How do these particles interact? • Protons and neutrons live compacted in tiny nucleus • most atom’s mass • electrons small and reside outside nucleus • small mass (2000 e- = 1 p+ or no) • occupy large volume of space outside nucleus Atoms

6. How do the subatomic particles balance each other? • In atoms: • protons = electrons • If 20 protons are present in atom then 20 electrons balance overall charge of atom—atoms are neutral • The neutrons have no charge; therefore they do not need to (and often times don’t) equal protons or electrons

7. How do we know the number of subatomic particles in an atom? • Atomic #: indicates # of protons in atom • Ex: Hydrogen’s atomic # is 1 • hydrogen has 1 proton • Ex: Carbon’s atomic # is 6 • carbon has 6 protons **Number of protons identifies element similar to how your fingerprint ID’s you. Ex. 2 protons = He, 29 protons = Cu ALWAYS!!

8. How do we know the number of subatomic particles in an atom? • Mass number: number of protons and neutrons in nucleus (p+ + no) • Ex: hydrogen can have a mass # of 3. Since it has 1 proton it must have 2 neutrons • # of neutrons = mass # - atomic #

9. What are Isotopes? • Atoms of same element with different # of neutrons • Same atomic # • Different mass # (b/c neutrons are different) • Ex. Carbon 12, Carbon 13, and Carbon 14 all naturally occurring isotopes of Carbon. • Each has 6 p+ and 6 e-, but each has different # of neutrons (therefore, different mass#)

10. Determining the number of protons and neutrons • Li has mass # of 7 and atomic # of 3 • Protons = 3 (same as atomic #) • Neutrons= 7-3 = 4 (mass # - atomic #) • Ne has a mass # of 20 and an atomic # of 10 • Protons = 10 • Neutrons = 20 - 10= 10

11. What about the electrons? • electrons are equal to protons • So e- = p+ = atomic # • Ex: He has mass # of 4 and atomic # of 2 • p+ = 2 • no = 2 • e- =2 Basic Atomic Structure 1:57

12. Determine the number of subatomic particles in the following: • Chlorine has a mass # of 35 and an atomic # of 17 • p+ = 17, no = 18, e- = 17 • Potassium has a mass # of 39 and an atomic # of 19 • P+ = 19, no = 20 e- = 19

13. Candy Atoms • Atom #1 - mass # of 5 and an atomic # of 3. • Atom #2 – 5 protons and 7 neutrons. • Atom #3 – Atomic # of 7 and 8 neutrons.

14. Candy Atoms • Atom #4 – mass # 18 and 9 electrons • Atom #5 – build your own candy atom using the candies that you have. You should be able to accurately determine: • Atomic # • Mass # • # of protons, neutrons, and electrons

15. 4.3 Modern Atomic Theory

16. Bohr Model of the Atom • Agreed with Rutherford • Small nucleus w/ lots of space • Devised planetary model • trying to show why e- were not sucked into p+ in nucleus of atom. • e- in specific energy levels

17. Misconceptions from the Bohr Model • Bohr model good for diagramming atoms and energy levels • e- do NOT move like planets in predictable orbits • Mathematics determine probable location of e-

18. Energy Levels • Possible energies e- can have • Like floors in hotel • Floor nearest nucleus - ground floor

19. The Electron Hotel • Levels nearer nucleus have lower energy (ground floor of hotel) • Electrons fill energy levels from inside - outside. (ground floor - top floor of Electron Hotel)

20. Electron distribution in an Atom Energy Level 3 3d 3p 3s ENERGY 2 2p 2s 1 1s NUCLEUS

21. Energy Levels • Can’t stand “in between” steps in hotel stairwell • e-’s can’t exist “in between” energy levels • Must absorb right amt of energy in order to move up energy levels • Must lose right amt to move down

22. Evidence of Energy Levels • Energy gains & loses can be measured • As e- drop orbitals, energy released in form of light/heat • Like in fireworks (2:34)

23. Electron Cloud Model • Electrons travel around nucleus in random orbits. • cannot predict location at any given moment. • Electrons travel so fast, they appear to form a “cloud” around nucleus. • Ex. - Airplane propeller

24. Atomic Orbitals • Rooms in “Electron Hotel” • Region of space where e- likely located • Each orbital can have 2 e- max • Denser region = higher probability

25. Electron Configuration • Arrangement of e-’s (occupants) in orbitals (rooms) • Each orbitals holds 2 e-’s max (1 double bed) • Stable when e-’s in orbitals w/ least energy • Ground state • i.e. Lithium (atomic # = 3) has 1st 2 e-’s in the 1st energy level (fills up 1 room w/ double bed) • 3rd e- goes to 2nd energy level

26. Electron Configuration • If Lithium absorbs enough energy, 3rd e- jumps energy levels • Excited state • Less stable (like gymnast on beam) • Eventually releases energy (often as light) • Returns to ground state

27. How exactly are the particles arranged? • Bohr Model of the atom: Electrons move in orbits at fixed distances from the nucleus (planetary model) All of the protons and the neutrons The 3rd ring can hold up to 18 e- The 1st ring can hold up to 2 e- The 4th ring and any after can hold up to 32 e- The 2nd ring can hold up to 8 e-

28. What does carbon look like? Mass # = 12 atomic # = 6 p+ = 6 no = 6 e- = 6 6 p and 6 n live in the nucleus

29. Drawing Atoms • Draw the following atoms in your notes: • 1. Beryllium has an atomic # of 4 and a mass # of 9

30. Beryllium Atom

31. Drawing Atoms • 2. Sodium has an atomic # of 11 and a mass # of 23

32. Sodium Atom