1. Week 12 Test Review
Chemistry

2. Formula
Group of elements and numbers that all symbolize a compound or molecule
Example: H2O
H20

3. Subscripts
The small numbers in the formula that tell you how many atoms for a specific element
Example
H2O
2 Hydrogen atoms

4. Coefficients
The big numbers in formulas that tell you how many molecules
2H20
2 Molecules of water

5. Chemical Reaction
Change in matter that produces one or more NEW substances out of the same elements

6. Reactants
Compounds/elements that you begin with in a chemical equation

7. Products
NEW substances you end with after a chemical reaction happens

8. Conservation of Mass
Law that matter cannot be created or destroyed – this is why chemical equations have to be balanced
Reactants
Products

9. Balanced or Not Balanced?
Both the product and the reactant has to have the same number of each element in order to be balanced. This is to ensure the law of conservation of mass
CH4 + O2  CO2 + H4
Reactants
C (carbon) 1
H (hydrogen) 4
O (oxygen) 2
Products
C (carbon) 1
H (hydrogen) 4
O (oxygen) 2 ? ? ? ? ? ?
Balanced or Not Balanced?

10. Chemical Equation
Short, easier way to write a chemical reaction through the use of symbols and numbers

11. Label:
2H2 + O2  2H2O

12. 3 Molecules
3H2O2
3 Molecules
6 atoms of oxygen
X 2 = 6
(Atoms)

13. 2CO3
2 Molecules
2 molecules
6 atoms of oxygen
2 X 3 = 6
(Atoms)

14. Remember: if there is no subscript or coefficient, add an invisible 1
1 Molecules
NaCl
1 molecule
1 atom of chlorine
1 X 1 = 1
(Atoms)

15. ZnCl2
1 Molecules
1 molecule
2 atoms of chlorine
1 X 2 = 2
(Atoms)

16. N2 + O2  N2O Unbalanced Reactants Products Nitrogen – 2 Oxygen – 2

17. Balanced Cu + 2 AgN  CuN2 + 2 Ag Reactants Products Cu – 1 Ag – 2

18. 8Fe + S8  8FeS
Reactants
Products
Fe – 8
S – 8
S - 8
Balanced

19. Unbalanced I2 + Na2S2O3  NaI + Na2S4O6 Reactants Products I – 2 I – 1

20. Precipitate (solid) Formed
 4 signs of a chemical reaction:
Heat or light given off
Gas produced (example: bubbles)
Precipitate formed (solid formed)
Color change
The one thing that will happen EVERYTIME a chemical reaction occurs is a New Substance will be formed!
Temperature change
Color change
Precipitate (solid) Formed
Gas (bubbles)

21. A + B  AB 8Fe + S  8FeS Synthesis
Two or more substances come together to form 1 substance
A + B  AB
8Fe + S  8FeS

22. AB  A + B CaCO3  CaO2 + CO2 Decomposition
One substance breaks down into 2 or more parts
AB  A + B
CaCO3  CaO2 + CO2

23. Combustion
The product is always carbon dioxide and water
A + B  CO2 + H2O

24. AB + C  AC + B Cu + 2AgNO  Cu(NO3)2 + 2 Ag Single replacement
When a compound reacts with an element and replaces the element with one of its parts
AB + C  AC + B
Cu + 2AgNO  Cu(NO3)2  + 2 Ag

25. AB + CD  AD + CB ZnO + 2HCl  ZnCl2 + H20 Double replacement
When two compounds react and trade elements
AB + CD  AD + CB
ZnO + 2HCl  ZnCl2 + H20

26. Atomic mass: the mass of an atom
What is the atomic mass?
Atomic mass: the mass of an atom
Protons
+ Neutrons
Atomic Mass

27. What is the atomic number?
Atomic number: Element number used to show where on the periodic table the element is found. Also, it is the number of protons.
Atomic Number = Number of Protons

28. What are valence electrons?
Electrons in the outside energy level, used to determine reactivity of an atom

29. How can you find the number of neutrons?
Atomic Mass
Atomic Number (protons)
Neutrons

30. How do you know if an atom is neutral?
Protons (positive charges) = Electrons (negative charges)
If it has the same number of positive (protons) and negative (electron) charges
3 positive charges
3 negative charges
Remember: all elements on the periodic table are neutral!

34. How does an atom get charged?
Gains or loses electrons

35. Give up electrons
Give up electrons – Positive charge

36. Gain electrons
Gain electrons – negative charge

37. Overall charge of the nucleus?
Positive because of the protons
Positive charged nucleus

38. Overall charge of the electron cloud?
Negative because of the electrons
Negative charge electron cloud

39. What do valence electrons determine?
They determine how reactive an atom is
1 and 7 valence electrons – most reactive
8 valence electrons – least reactive

40. What information can be found if you know the Period of an element?
Number of energy levels

41. What information can be found if you know the group of an element?
Number of valence electrons
Remember to cover the one on the two digit numbers!

42. Most reactive groups
Group 1
Group 17

43. Least Reactive Group
Noble Gasses – Group 18