Bohr, isotopes, and ions, Oh My!!

1. Bohr, isotopes, and ions, Oh My!!

2. How do we Draw Atoms? • Bohr Models • Lewis Dot Diagrams

3. How to draw a Bohr Model • Draw a nucleus & put protons and neutrons inside. • (may use a square shape so you don’t draw any electrons on it) • Remember the p=e in a neutral atom, so begin putting electrons on the energy levels until you use them all up. • Fill energy levels in order (can’t put any in 2nd shell until you’ve filled the first)

4. Drawing Bohr models, cont… Helpful hints: • Draw electrons at each of the four “corners”, then double up • Write the number of electrons you drew (in parentheses) on each energy level to help you keep track.

5. Electron configurations (Bohr Models)

6. But…that can be a pain… • Most of the time we only really care about the valence electrons • Valence Electrons- electrons in the outermost shell • Also the GROUP NUMBER!!!

7. Valence Electrons- • Find the number of valence electrons by counting over the rows (skipping transition metals) • See next slide

9. Valence Electrons are what react and bond!

10. How to draw a Lewis Dot Structure • Find the group # (top of the row on the PT) • Write the symbol. • Draw dots around the symbol equal to the group number (if group 2- draw two dots) • Place dots one at a time around the top, right, bottom and left side of the atom before you double any up.

11. How to draw a Lewis Dot Structure • Find the group # (top of the row on the PT) Let’s do Phosphorus • Write the symbol. P • Draw dots around the symbol equal to the group number (if group 2- draw two dots) • Place dots one at a time (clockwise) around the top, right, bottom and left side of the atom before you double any up.

12. Octet Rule- • Most atoms want to have 8 electrons in their outer shell.

13. Octet rule exceptions… • (octet rule=Most atoms want to have 8 electrons in their outer shell) • Helium- • What is its group number? • Why doesn’t it make sense to draw that many dots? • Because it is easier for it to fill that first shell which only needs two electrons • Other- Exceptions: • ___H__ , __Li___ , __Be___

14. Elements with a full outer shell naturally (Noble Gases)

15. Lewis Dot Structures

16. Atomic Mass Mystery… • Look at the average atomic mass for Oxygen. What does it say (exactly?) • 15.9999 • What is the mass number? • P + N = whole number • So what the heck!?!?! • Average of the actual isotopes’ mass numbers and abundance on Earth!!!

17. How can we change the mass of an element? • We can’t mess with protons, but what CAN we “mess with?” • Neutrons… • What would that change about the atom? • Changes the MASS • Get an ISOTOPE

18. Isotopes • Isotopes are different atoms of the same element that contain the same number of protons but different number of neutrons. • Examples • Cl-35 vs. Cl-37 17P 17P 18N 20N

19. How to write isotopes… • Mass/Hyphen Notation: • Especially important for a form of the isotope that is NOT the “usual” • Write the symbol, a dash, and the mass # for that isotope • Ex’s • C-14 • C-12

20. How to write isotopes… • Nuclear Symbol Notation • Includes the symbol, atomic #, and the mass # for that isotope • Ex’s 14 6 C Mass # Atomic # (=p)

21. What else CAN we “mess with?” • Already know…Neutrons… • Get an ISOTOPE, changes the mass • But what if I mess with Electrons… • What would that change about the atom? • Changes the CHARGE • Get an ION

22. Intro to Ions

23. How are these ions made? • Can you mess with protons? • Would messing with neutrons do anything to the charge? • What must you mess with??? • What charge does an electron have? • So what would happen to the atom if they LOSE one? Would they get more positive or more negative overall???

24. IONS • If you mess with the electrons you change the overall charge of the atom…an atom that is no longer neutral is called an ION. • Anion- has a negative charge • Means you added an electron! • Cation- has a positive charge • Means you lost an electron