1. Chemistry in the Community Week of October 20, 2014

2. Learning Objectives After studying students will be able to: Apply the shell model of the atom to chemical bonding. Distinguish between an atom and an ion. Predict the formula of an ionic compound using the periodic table. Distinguish between ionic and covalent bonds. Understand how some molecules are polar. Understand how the polarity of molecules affects macroscopic properties.

3. Metals vs. Non-Metals; Dot Diagrams; Ions Metals versus Non-Metals (a little poem to help you remember). Metals are on the left side. Non-metals on the right. Metals tend to lose electrons. Non-metals gain them on sight.

4. Metals versus Non-Metals The dividing line is the red or bold black line from between Boron and Aluminum down and to the right. Everything to the left is a metal: to the right, non-metal. One exception (don’t ya just hate that?!) is hydrogen – a non-metal. Sodium (Na) is a metal. Oxygen is a non-metal.

5. Using your Periodic Table – YOU MAKE THE CALL Metal or Non-Metal? Potassium:________ Bromine:_________ Beryllium:________ Helium:__________ Fluorine:_________ Hydrogen:________ Silver:___________ Nitrogen:________

6. LEWIS DOT DIAGRAMS Dot Diagrams, sometimes called Lewis Dot Diagrams after the scientist who came up with the idea, visually represent an atom’s valence electrons. We use Dot Diagrams to help us understand, and even predict, how elements will combine! Ne Neon has 8 valence electrons (in the right hand column). Neon has no unoccupied spaces. It is full. There is an order as to how we fill in the dots, but when you read up on it, a few folks have their own way of mapping them out. We are going to learn it this way…. (Next Slide!)

7. Make sure you get this in your notebook! Ne 1 2 3 4 5 6 7 8

8. So let’s look at a few…. See what I mean about the order of the dots…. What do you notice about this pattern?????

9. Draw the Dot Diagrams for the following elements….. Beryllium Sodium Helium Carbon Boron

10. Section 18.2 Atoms can loose or gain electrons to become ions Well….. remember that….. Electrons are negatively charged and protons are positively charged. If you change the number of protons you change the element. If you change the number of neutrons you change the isotope. If you change the number of electrons you change the ion. This is why it matters…..

13. What’s an ion you ask? - An Ion is any atom with a net electric charge. Atoms can Lose or Gain Electrons to become Ions. Elements to the left of the periodic table tend to form positively charged ions. Elements to the right tend to form negatively charged ions. The number of electrons lost or gained is a function of the atomic group. An ion is an atom with a net charge; that has gained or lost electrons.

14. Isn’t it ionic that….. When the numbers of protons and the electrons in an atom are equal, the charges balance and the atom is electrically neutral. BUT WHEN IT DOESN’T …

16. More “ionic-ness”… Atoms in group 1 of the periodic table tend to lose an electron to become an ion with a net positive charge. Atoms in group 17 of the periodic table tend to gain an electron to become an ion with a net negative charge. http://www.youtube.com/watch?v=rwRtfrgJL5E http://www.youtube.com/watch?v=WaPxTAeW5e8

17. http://www.youtube.com/watch?v=BCYrNU-7SfA http://www.youtube.com/watch?v=1cqauZq4uYM

18. Sec. 18.3 IONIC BONDS RESULT FROM A TRANSFER OF ELECTRONS Ionic bond: The electric force of attraction between two oppositely charged ions. Ionic compound: Consists of a chemical compound that is made up of ions.

19. QUESTION What can happen when you place an atom that tends to give up an electron close to an atom that tends to gain one?

20. ANSWER An electron from the atom that tends to give up an electron may jump to the atom that tends to gain one.

21. Na + and Cl – What do you notice about these two? What happens then? What type of compound is this called?

22. Na + and Cl – They have opposite charges. Opposites attract. Ionic compound.

23. Let’s look at something more complicated… Ca 2+ and F 1– What do we know? Ca is Calcium, it is in period 4, it is in group 2, it has two valence electrons – in other words, it has two electrons it can give away. Fl is Fluorine, it is in period 2, it is in group 1 7, it has seven electrons in its outermost shell – it only needs one more to meet the octet rule.

24. So…. (Ca 2+) and (F 1–) What compound would this form…..draw an electron dot diagram (Lewis Dot Diagram, dot diagram – they all mean the same thing) if you need it to figure it out OR Do the math…. How many negatives to you need to neutralize the positive?

25. Al 2 O 3 What is the aluminum ion in the ionic compound aluminum oxide? This is really a TRICK QUESTION!!!!! What do we know? There are two Al atoms to three O atoms. Al has 3 valence electrons so that makes it Al 3+ ion because it has three electrons to give away!!!!!

26. Al 2 O 3 What is the oxygen ion in the ionic compound aluminum oxide? This is really a TRICK QUESTION!!!!! What do we know? I bet you’ve figured this out….right…. Oxygen has 6 valence electrons so that means it has room for 2 more, right O 2−

27. Quick Review Ca 2+ Chemical Symbol Charge 2 lost electrons, in other words, it has two it can give away. Just a point of clarification….if Calcium gives away its two electrons it will have more protons (+) than electrons (-) which will make it a positive ion. How can I tell how many electrons an ion has? Look at the formula: Ca 2+ How many protons does Calcium have? (Atomic number….20) NOW: 20 (Ca) – e (electrons) = +2 20=2 + e (electrons) 20-2= e (electrons) e = 18

28. Now you try one on your own…… How many electrons does N 3- have? Well, how many protons does N (nitrogen) have?______ Atomic number – electrons = -3 7 – e = -3 e = 10

29. DID YOU KNOW THAT….. There are anions and cations…… Can you tell which is which….? Ca 2+ and F 1– Let’s make a decision….. If you think….

30. Let’s look at it… Neutral atoms have an equal number of protons and electrons. A neutral atom has a net electrical charge of zero. Why would atoms gain or lose electrons? To fulfill the octet rule and end up with a full outer shell of electrons. Metals will lose electrons and make positive ions (cations). Non-metals will gain electrons and make negative ions (anions).

31. Definition worth having…… Cations cough up electrons - Lose electrons (+ ion). CATIONS are POSTIVE IONS BECAUSE THEY HAVE LOST SOME OF THEIR NEGATIVE ELECTRONS!!!! (METALS fall into this category!) ==== + + + + + + + I am soooo positive!

32. Another Definition worth having Anions accept electrons - Gain electrons (- ion). REMEMBER if you gain negative electrons you become more negative!!!! NON-METALS tend to be in this category. Let me put it this way = when you hang out with negative people you tend to become more negative…… The more electrons you take on, the more negative you become.