Chemical Formulas

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 http://www.esc9.net/pages/uploaded_files/Grade%208%20Unit%204.pdf

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

Chemical Formulas

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. http://chemistry.about.com/od/chemistryglossary/g/Chemical-Formula-Definition.htm

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

Water http://www.citizensadvice.co.uk/PageFiles/4356/Water2.jpg http://i579.photobucket.com/albums/ss236/mrchaize/Molecules/640px-water_molecule_3dsvg1.png?t=1254780777 http://www.resourcesgraphics.com/images/H2o-shape-of-water-drops-vector-material2.jpg http://www.chemicalformula.org/basic-chemistry/chemical-formula

Carbon dioxide http://www.sciencedaily.com/images/2008/01/080103135757-large.jpg http://upload.wikimedia.org/wikipedia/commons/4/41/Carbon-dioxide-3D-vdW.png

Sodium chloride or salt http://myclfree.com/assets/images/no%20salt.jpg http://www.carlton.srsd119.ca/teachers/ddice/chemical/Molemass/images/Nacl.gif

Magnesium sulfate (AKA Epsom salt) MgSO4 http://www.aquariumplantfood.co.uk/24-65-thickbox/potassium-nitrate-500g.jpg http://www.chemicalregister.com/upload/cr/7487-88-9.png http://efektmm.pl/AMAZONIKA_MISTOW/MgSO4.JPG

For something more complicated…. Glucose or sugar http://library.thinkquest.org/11226/image/glucose.jpg http://rlv.zcache.com/a_spoonful_of_c6h12o6_helps_the_medicine_go_down_invitation-p1612898221686315162nbxn_210.jpg http://www.integrateddiabetes.com/webstore/media/ccp0/prodlg/dex%20tubes.jpg

Subscripts

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

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

Here are some molecules…

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

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

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

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

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

Coefficient

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

Chemical Equations

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 http://www.bing.com/Dictionary/search?q=define+chemical+equation&qpvt=what+is+a+chemical+equation&FORM=DTPDIA

Yields

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 http://dictionary.reference.com/browse/yield

Product

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 http://www.mikeblaber.org/oldwine/chm1045/notes/Stoich/Equation/Stoich01.htm

Reactant

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 http://www.mikeblaber.org/oldwine/chm1045/notes/Stoich/Equation/Stoich01.htm

Law of conservation of mass

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 http://www.mikeblaber.org/oldwine/chm1045/notes/Stoich/Equation/Stoich01.htm

Balancing chemical equations

Subscripts are never changed when balancing an equation

Step 1 Write out your “un-balanced” equation using formulas of reactants and products. CH4+O2CO2+H2O http://www.mikeblaber.org/oldwine/chm1045/notes/Stoich/Equation/Stoich01.htm

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

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

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

Practice Time

2H2+O22H2O H2+O2H2O http://www.mikeblaber.org/oldwine/chm1045/notes/Stoich/Equation/Stoich01.htm

Fe+Cl2FeCl3 2Fe+3Cl22FeCl3 http://www.files.chem.vt.edu/RVGS/ACT/notes/scripts/bal_eq1.html

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

Zn+2HClZnCl2+H2 Zn+HClZnCl2+H2

Pb(NO3)2+AlCl3PbCl2+Al(NO3)3