1. Chemical Formulas

2. TEKS 8.5 D and 8.5 F
Recognize that chemical formulas are used to identify substances and determine the number of atoms of each element in chemical formulas containing subscripts.
Recognize whether a chemical equation containing coefficients is balanced or not and how that relates to the law of conservation of mass.
Recognize the importance of formulas and equations in representing chemical reactions– 1998 TEKS 8.9C

3. What do you know about chemical reactions, chemical formulas, and chemical equations?
Teacher can type answers in here.

4. Chemical Formulas

5. What is a chemical formula?
Chemical, or molecular, formulas are a concise way of expressing information about the atoms that constitute a particular chemical compound.
Wait…what?
It is an expression which states the number and type of atoms present in a molecule of a substance.

6. Do you know what the chemical formulas are for the following substances?

7. Water http://www.citizensadvice.co.uk/PageFiles/4356/Water2.jpg

8. Carbon dioxide

9. Sodium chloride or salt

10. Magnesium sulfate (AKA Epsom salt)
MgSO4

11. For something more complicated…. Glucose or sugar

12. Subscripts

13. Definition
A subscript is used to represent the number of each atom being represented.
They are only used when more than one atom is being represented. If only one atom is represented, there is no subscript.
In the formula for water, what is the subscript?
There is only one atom of Oxygen, so it does not have a subscript.
H2O
H2O
H = Hydrogen
O = Oxygen

14. N(CH3)3 Some exceptions exist
Usually the subscript just multiplies or shows the number of atoms of a single element. If the subscript exists outside of a set of parenthesis then it will multiply the atoms of all of the elements inside the parenthesis.
How many of each atom are there now?
Answer: Nitrogen-1, Carbon-3, Hydrogen-9
N(CH3)3
N = Nitrogen
C = Carbon
H = Hydrogen

15. Here are some molecules…

16. Answer: NH3 This substance is ammonia
In this image Hydrogen atoms are white and Nitrogen atom is red.
Write the chemical formula for this molecule.
Answer: NH3
This substance
is ammonia
O2 and H6

17. This substance is carbonate
In this image the Carbon atom is black and the Oxygen atoms are red.
Write the chemical formula for this molecule.
Answer: CO3
This substance is carbonate
None for C, O3

18. This substance is caffeine
In this image blue represents Nitrogen atoms, red represents Oxygen atoms, white represents Hydrogen atoms and black represents Carbon atoms.
Write the chemical formula for this molecule.
C8, O2, H10, N4
Answer: C8H10N4O2
This substance is caffeine

19. This substance is carbon monoxide
In this image the Carbon atom is blue and the Oxygen atom is red.
Write the chemical formula for this molecule.
Answer: CO
This substance is carbon monoxide
None for either

20. Write the chemical formula for this molecule.
A harder one:
In this image Nitrogen atoms are blue, the Platinum atom is grey, Chlorine atoms are green, and Hydrogen atoms are white.
Write the chemical formula for this molecule.
Answer: N2PtH6Cl2
N2, Pt, H6, Cl2

21. Coefficient

22. Definition
Coefficients appear on the left side of a chemical formula.
They are used to multiply all the atoms in a compound
In the following formula, which is the coefficient?
Earlier we learned that the subscript 2 meant that there were two Hydrogen atoms. The coefficient 7 means there are 7 times more.
How many Hydrogen atoms do we have?
How many Oxygen atoms?
7H2O
7H2O
Answers are 14, 7

23. Chemical Equations

24. 2H2+O22H2O Chemical Equations
representation of chemical reaction in equation: a representation, using chemical symbols in a form resembling a mathematical equation, of the process involved in a chemical reaction
This is an example of a chemical equation. The components on the left combine together to yield (represented by the arrow) the component on the right.
2H2+O22H2O

25. Yields

26. Definition
The quantity of a specified product obtained in a reaction or series of reactions, usually expressed as a percentage of the quantity that is theoretically obtainable

27. Product

28. 2H2+O22H2O 2H2+O22H2O Definition What is produced.
Which side represents the products?
They are found on the right side of a chemical equation.
2H2+O22H2O
2H2+O22H2O

29. Reactant

30. 2H2+O22H2O 2H2+O22H2O Definition The starting substances.
Which side represents the reactants?
They are found on the left side of a chemical equation.
2H2+O22H2O
2H2+O22H2O

31. Law of conservation of mass

32. There is only a rearrangement
Atoms are neither created, nor destroyed, during any chemical reaction.
This means that the same number of atoms that are present after a reaction are the same number of atoms that are present before a reaction.
There is only a rearrangement

33. Balancing chemical equations

34. Subscripts are never changed when balancing an equation

35. Step 1
Write out your “un-balanced” equation using formulas of reactants and products.
CH4+O2CO2+H2O

36. CH4+O2CO2+H2O C=1 C=1 H=4 H=2 O=2 O=3 Step 2 They are NOT equal
Count up the atoms in the products and reactants.
How many carbons, hydrogens, and oxygens are on each side? Are they equal?
CH4+O2CO2+H2O
C=1
H=4
O=2
C=1
H=2
O=3
They are NOT equal

37. CH4+O2CO2+H2O CH4+O2CO2+2H2O C=1 C=1 H=4 H=4 O=2 O=4 Step 3
Since our carbons are ok we will not mess with those now.
However, we have half the number of hydrogens in the products than we do in the reactants.
What do we need to add? Where do we add it?
CH4+O2CO2+H2O
CH4+O2CO2+2H2O
C=1
H=4
O=2
C=1
H=4
O=4
They are still NOT equal

38. CH4+2O2CO2+2H2O CH4+O2CO2+2H2O C=1 C=1 H=4 H=4 O=4 O=4 Step 4
Now we have half the number of Oxygens.
What do we need to add? Where do we need to add it? Is everything equal now?
CH4+2O2CO2+2H2O
CH4+O2CO2+2H2O
C=1
H=4
O=4
C=1
H=4
O=4
They ARE now balanced

39. Practice Time

40. 2H2+O22H2O
H2+O2H2O

41. Fe+Cl2FeCl3 2Fe+3Cl22FeCl3

42. Cu+AgNO3Cu(NO3)2+Ag
Cu+2AgNO3Cu(NO3)2+2Ag

43. Zn+2HClZnCl2+H2
Zn+HClZnCl2+H2

44. Pb(NO3)2+AlCl3PbCl2+Al(NO3)3