1. Balancing Chemical Equations Chemical Bonds & Reactions

2. Let’s Bond H2H2 molecule A molecule is formed when two or more atoms are bonded together.

3. Chemical Bonds are formed when atoms gain, lose or share valence electrons. outer level middle Valence electrons are like the outer level of skydivers in this formation… it’s much easier for them to pull away than it is for the skydivers in the middle. It’s also easier for a new skydiver (electron) to join the outer level of the formation than it is to move into the middle of the formation.

4. sharing electronscovalent bond When atoms come together by sharing electrons, the bond is a covalent bond. Water - A Most Important Molecule covalent bonding Note how covalent bonding fills all outer electron levels; oxygen has 8 valence electrons, and the hydrogens both have 2. By sharing their electrons, everybody is happy! Water is one of the most stable molecules around.

5. covalent bonds. The electron dot diagrams on the right show molecules with covalent bonds.

6. Ion Formation Ion Formation: one atom gives electrons, one atom takes electrons Sodium gives a single electron to chlorine to complete its outer electron shell. Chlorine is happy to take it.  ionatom or molecule with a positive or negative chargesodium Na+.chlorine Cl-.  An ion is an atom or molecule with a positive or negative charge. Since sodium loses one electron, it has a positive charge of +1, written as Na+. Since chlorine gains one electron, it has a negative charge of -1, written as Cl-.  ionic bond.  The type of chemical bond formed in this way is called an ionic bond. ion formation The result is ion formation.

7. Ions and Ion Formation

8. Ionic Bonds Two oppositely charged ions are attracted to each other, and bond together. ionic bond This type of chemical bond is an ionic bond. Salts Salts are solids held together by ionic bonds. Group 1 (Alkali metals) 1 valence electron Group 17 (Halogens), short 1 valence electron Elements in Group 1 (Alkali metals) all have 1 valence electron, so they bond easily with elements in Group 17 (Halogens), which are short 1 valence electron.

9. Why do Group 1 and Group 17 react so easily with one another? Alkali metals 1 valence electron they want to get rid of. Halogensall short 1 valence electron, and want to gain one The answer lies in the valence electrons. The Alkali metals in Group 1 all have 1 valence electron they want to get rid of. The Halogens in Group 17 are all short 1 valence electron, and want to gain one to fill their outer electron level. Each group has what the other needs. Result: 2 happy atoms.

10. Sodium mixing with chlorine http://www.yout ube.com/watch? v=2mzDwgyk6 QM&NR= 1

11. The Parts of a Chemical Reaction Reactantsingredients in a chemical reaction; substances that you start with Reactants: ingredients in a chemical reaction; substances that you start with Productsnew substances formed in a chemical reaction (what you end up with) Products: new substances formed in a chemical reaction (what you end up with) Example : Photosynthesis carbon dioxide + water sugar + oxygen reactants products sunlight The arrow stands for “becomes”

12. There are 4 types of chemical reactions: 1. SYNTHESIS : A + B ---> AB Two elements combine to form a compound. 2. DECOMPOSITION : AB ---> A + B A compound breaks down to form simpler substances. SINGLE REPLACEMENTA + BC ---> AC + B 3. SINGLE REPLACEMENTA + BC ---> AC + B One element replaces another in a compound. 4. DOUBLE REPLACEMENTAB + CD ---> AC + BD Two elements replace each other, forming two new compounds. CHEMICAL REACTIONS

13. Let’s look at the 4 types of chemical reactions in another way… 1.Synthesis reaction (putting together a compound) + 2. Decomposition Reaction (breaking down a compound) + 3. Single Replacement Reaction (1 atom switches places) ++ 4. Double Replacement Reaction (2 atoms switch places) ++ 4 types of chemical reactions

14. Or, we could use relationships to visualize the 4 types of reactions…. 1. Synthesis (Hook-up) + 2. Decomposition (Break-up) + 3. Single Replacement (change 1 partner) ++ 4. Double Replacement (change 2 partners) ++ relationships

15. The Law of Conservation of Mass “During a physical or chemical change, matter is neither created nor destroyed.” The Law of Conservation of Mass states: “During a physical or chemical change, matter is neither created nor destroyed.” during a chemical reaction atoms on the left equal the atoms on the right This means that during a chemical reaction, the atoms on the left side of the arrow must balance or equal the atoms on the right side of the arrow. 4 H atoms 2 O atoms 4 H atoms 2 O atoms WRONG WRONG This one is CORRECT! Balancing Chemical Equations

16. _____H 3 PO 4 + _____KOH => _____K 3 PO 4 + _____H 2 O _____K + _____B 2 O 3 => _____K 2 O + ____B _____HCl + _______NaOH =>_______NaCl + _______H 2 ______Na + _______NaNO 3 => _______Na 2 O + ______N 2 _____C + _____S 8 => _____CS 2 Practice Balancing These Equations

17. ___2__H 3 PO 4 + __6__KOH => ___2__K 3 PO 4 + ___6__H 2 O __6___K + _____B 2 O 3 => ___3__K 2 O + __2__B _____HCl + _____NaOH =>_______NaCl + ______H 2 O _____HCl + _____NaOH =>_______NaCl + ______H 2 O Already balanced ___10__Na + ___2__NaNO 3 => ___6___Na 2 O + ______N 2 ___10__Na + ___2__NaNO 3 => ___6___Na 2 O + ______N 2 __4___C + _____S 8 => ___4__CS 2 ANSWERS