1. Chemical Reactions
2/2018

2. Atoms are the building blocks for everything
Elements are made of atoms
Compounds are made of elements

3. Chemical Reactions
Let's start with the idea of a reaction. In chemistry, a reaction happens when two or more molecules interact and something happens.

4. There are a few key points you should know about chemical reactions.
1. A chemical change must occur. You start with one compound and turn it into another.
2. A reaction could include ions, molecules, or pure atoms. A reaction can happen with anything, just as long as a chemical change occurs (not a physical one).

5. Compounds
A substance formed from elements, but it does not have the same characteristics as the individual elements
Ex. Iron oxide (rust)

6. Review

7. Chemical Formulas
Chemists us chemical formulas to represent the composition (make-up) of the elements in compounds
A short-hand (text message) way of writing a chemical compound
NaCl- salt or Sodium Cloride
H20- water

8. Electron shells Atomic number = number of Electrons
Electrons vary in the amount of energy they possess, and they occur at certain energy levels or electron shells.
Electron shells determine how an atom behaves when it encounters other atoms

9. Electrons are placed in shells according to rules:
The 1st shell can hold up to two electrons,
and each shell thereafter can hold up to 8 electrons.

10. Valence
An atom is stable when it has 8 electrons in its outer shell. This makes them “fat and happy”

11. Electron Dot Structures
Symbols of atoms with dots to represent the valence-shell electrons
H He:
          
Li Be  B   C   N   O  : F  :Ne :
       
          
Na Mg  Al  Si  P S :Cl  :Ar :
       

12. Why are electrons important?
Elements have different electron configurations
different electron configurations mean different levels of bonding
The configuration determines how it bonds with other elements

13. Chemical Bond
When an element comes together or combines with another element to form a compound
An attempt to fill outer shell (make it fat and happy) with 8 electrons

14. Types of Bonds
Ionic- giving or receiving of electrons to another element
Covalent- sharing of electrons in the outer shell (valence). Covalent bonds form molecules

15. IONIC BOND bond formed between two ions by the transfer of electrons- metals combine with nonmetals

16. Ions
Formed when electrons (-) are given away from element resulting in a positive charge, because the number of protons (+) is greater than the number of electrons (-) in the atom
Positive ions are called cations

17. Ions
Formed when electrons (-) are received from an element resulting in a negative charge, because the number of protons (+) is less than the number of electrons (-) in the atom
Negative ions are called anions.

18. Formation of Ions from Metals
Ionic compounds result when metals react with nonmetals
Metals lose electrons to match the number of valence electrons of their nearest noble gas
Positive ions form when the number of electrons are less than the number of protons
Group 1 metals  ion 1+
Group 2 metals  ion 2+
Group 3A (13) metals  ion 3+

19. Ions from Nonmetal Ions
In ionic compounds, nonmetals in 15, 16, and 17 gain electrons from metals
Nonmetals add electrons to achieve the octet (8) arrangement
Negative ions form when the number of electrons are more than the number of protons
Group 5(15) nonmetals  ion 1-
Group 6 (16) nonmetals  ion 2-
Group 7 (17) nonmetals  ion 3-

21. Learning Check Give the ionic charge for each of the following:
A. 12 p+ and 10 e-
1) 0 2) 2+ 3) 2-
B. 50p+ and 46 e-
1) 2+ 2) 4+ 3) 4-
C. 15 p+ and 18e-
1) ) 3- 3) 5-

22. COVALENT BOND bond formed by the sharing of electrons

23. Covalent Bond
Between nonmetallic elements of similar electronegativity.
Formed by sharing electron pairs
Examples; O2, CO2, C2H6, H2O, SiC

24. Covalent Bonds

25. Chemical Change
Change from one substance to another
Burning paper

26. Physical Change
Change is physical or outward appearance. Does not change chemical make-up
Wrinkled paper

27. Reactants the elements or compounds that are put together to form a chemical change
Na + Cl  NaCl
reactants

28. Products- the end result of reactants coming together Na + Cl  NaCl

29. Chemical Reactions Types
Endothermic-energy absorbed
Exothermic- energy is released

30. Rates of Reactions Catalyst- speeds up a chemical reaction
Inhibitor- slows down a chemical reaction (takes longer)

31. Law of Conservation of Mass
“In an ordinary chemical reaction, matter is neither created nor destroyed.”
This means that you have neither gained nor lost any atoms during the reaction. They may be combined differently, but they’re still there.

32. Law of Conservation of Mass
The mass of the products must equal the mass of the reactants (what I put into a reaction, I must get out)
Mass is neither created or destroyed.

33. If the product has a mass less than the reactants what happed
If the product has a mass less than the reactants what happed? Was their a gas, smoke or other byproducts?
Example Burning paper- does the burnt paper (ashes) weigh as much as the original piece? Why?

35. Mass of Smoke =7 g

36. How to Balance Equations
Draw boxes around all the chemical formulas.
Make a Chemical Inventory (Look at the subscripts next to each atom to find the number of atoms in the equation.)

37. Write numbers in front of each of the boxes (coefficient) until the inventory for each element is the same both before and after the reaction.
Multiply the coefficient
Never change subscripts
Try to leave single elements for last
Whenever you change a number, make sure to update the inventory - otherwise, you run the risk of balancing it incorrectly. When all the numbers in the inventory balance, then the equation can balance

39. Finished
Since both sides of the inventory match, the equation is now balanced!  All other equations will balance in exactly the same way, though it might take a few more steps in some cases.

40. Some practice problems:
__NaCl + __BeF2 --> __NaF + __BeCl2
2. __FeCl3 + _Be3(PO4)2 --> _BeCl2 + _FePO4
3. __AgNO3 + _LiOH --> _AgOH + __LiNO3
4. __CH4 + __O2 --> __CO2 + __H2O
5. __Mg + __Mn2O3 --> __MgO + __Mn

41. Solutions 2 NaCl + 1 BeF2 --> 2 NaF + 1 BeCl2
2 FeCl3 + 1 Be3(PO4)2 --> 3 BeCl2 + 2 FePO4
1 AgNO3 + 1 LiOH --> 1 AgOH + 1 LiNO3
1 CH4+ 2 O2 --> 1 CO2 + 2 H2O
3 Mg + 1 Mn2O3 --> 3 MgO + 2 Mn

42. Practice at home