Atomic Structure

1. Atomic Structure Unit II—Part 3

2. What is an atom? • Atom: the smallest unit of matter that retains the identity of the substance • First proposed by Democritus around 420 B.C. • “Atomos” in Greek means indivisible

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

4. What’s in the Nucleus? • The nucleus contains 2 of the 3 Subatomic Particles: • Protons: positively (+) charged subatomic particles • Neutrons: neutrally ( ) charged subatomic particles

5. What’s in the Electron Cloud? • The 3rdSubatomic Particle resides outside of the nucleus in the electron cloud • Electron: the subatomic particle with a negative charge and relatively no mass

7. How do these particles interact? • Protons and neutrons live compacted in the tiny positively charged nucleus accounting for more than 99% of the mass of the atom • The negatively charged electrons are small and have a relatively small mass but occupy a large volume of space outside the nucleus

8. How do the subatomic particles balance each other? • In an atom: • The # of protons = the # of electrons • If 20 protons are present in an atom then 20 electrons are there to balance the overall charge of the atom—atoms are neutral • The neutrons have no charge; therefore they do not have to equal the number of protons or electrons

9. 8 Atomic Number Atomic Math Challenge O Element Symbol Oxygen Element Name 15.99 Atomic Mass

10. How do we know the number of subatomic particles in an atom? • Atomic number: this number indicates the number of protons in an atom • Ex: Hydrogen’s atomic number is 1 • So hydrogen has 1 proton • Ex: Carbon’s atomic number is 6 • So carbon has 6 protons **The number of protons identifies the atom. Ex. 2 protons = He, 29 protons = Cu

11. How do we know the number of subatomic particles in an atom? • Mass number: the number of protons and neutrons in the nucleus • Ex: Hydrogen can have a mass of 3. Since it has 1 proton it must have 2 neutrons • # of neutrons = mass # - atomic #

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

13. What about the electrons? • The electrons are equal to the number of protons • So e- = p+ = atomic # • Ex: He has a mass # of 4 and an atomic # of 2 • p+ = 2 • no = 2 • e- =2

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

16. Pass out the student worksheet from “The Atoms Family” Lesson Atomic Math Challenge at this time and complete in class

17. How exactly are the particles arranged? • Bohr Model of the atom: Reviewers think this could lead to misconceptions! All of the protons p+ and neutrons n are within the nucleus The 3rd energy ring can hold up to 18 e- The 1st energy ring can hold up to 2 e- The 4th energy ring and any after can hold up to 32 e- The 2nd energy ring can hold up to 8 e-

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

19. Bohr Model Practice Lithium Atomic # 3 Atomic Mass 7 Protons 3 Neutrons 4 Electrons 3 P+ = 3 N = 4 # Electrons 1st energy ring / level 2 2d energy ring / level 1 3d energy ring / level 4th energy ring / level

20. Bohr Model Practice Aluminum Atomic # Atomic Mass Protons Neutrons Electrons 13 27 13 P+ = 13 N = 14 14 13 # Electrons 1st energy ring / level 2d energy ring / level 3d energy ring / level 4th energy ring / level 2 8 3 none

21. Hand out the Bohr Model Practice worksheet and assign 8 different atoms for students to complete their models