Counting Atoms

Elements, Atoms, Molecules, & Compounds Hydrogen is an element. Oxygen is an element. When 2 hydrogen atoms and one oxygen atom bond they make a molecule of water. Water is a compound made of 2 elements The formula for water is H2O

Element An element is a type of matter that is made of only one kind of atom. Sulfur is made of atoms that have 16 protons. No other element has an atom with 16 protons.

Atoms An atom is the smallest unit of structure for an element. Still maintains the properties of the element An atom of silver is shiny, conducts heat & electricity, reacts with acid, and is malleable. A proton from a silver atom does not have the properties of the element silver

A combination of two or more atoms bonded together. Molecule A combination of two or more atoms bonded together.

Compound A substance made of two or more different elements that are chemically combined. Involves the sharing, stealing, or giving up of valence electrons H2O Water is a compound

Chemical Formulas Chemical formulas show the number of atoms of each element are present. Each element in a chemical formula is identified by a capital letter. If an element’s symbol contains two letters, the second letter is lower case. Example: H2SO4 The elements in Sulfuric Acid Hydrogen Sulfur Oxygen

Molecules can be represented many ways: CH4 H2O Chemical Formula: H H Structural Formula: O Ball and Stick Model: Space Filling Model:

Subscripts Subscripts tell us how many atoms of each element are present. C12H22O11 There are 12 atoms of Carbon There are 22 atoms of Hydrogen There are 11 atoms of Oxygen If there is not a subscript listed, it is understood to be 1. Example: NaCl There is one atom of Sodium There is one atom of Chlorine

NaHCO3 HCl You Practice! Hydrogen – 1 Chlorine - 1 Sodium – 1 Carbon – 1 Oxygen -3 HCl Hydrogen – 1 Chlorine - 1

There are times you will see a chemical formula with parenthesis There are times you will see a chemical formula with parenthesis. The subscript after the parenthesis affects everything inside the parenthesis. Pb(NO3)2 So, in counting the atoms, you would have the following: Lead – 1 Oxygen - 6 Nitrogen -2

(NH4)3PO4 Mg(OH)2 You Practice!! Nitrogen – 3 Magnesium – 1 Hydrogen – 12 Phosphorus – 1 Oxygen – 4 Mg(OH)2 Magnesium – 1 Oxygen – 2 Hydrogen – 2

Coefficient A coefficient identifies how many molecules are present. 2H2SO4 This means there are 2 molecules of H2SO4. Counting the atoms: Hydrogen – 4 Sulfur – 2 Oxygen - 8

Coefficient A coefficient can also be used to tell us how many atoms are present. 2Mg This means there are 2 atoms of Mg. Counting the atoms: Mg = 2

3H3PO4 2H2O You Practice!! Hydrogen – 9 Hydrogen – 4 Phosphorus – 3 Oxygen - 12 2H2O Hydrogen – 4 Oxygen - 2

Got It????

Movin' On!!

2K + Cl2 2KCl Reactant Product Chemical Equations Chemical equations express what is happening in a chemical reaction using symbols. 2K + Cl2 2KCl Reactant Product yields

Law of Conservation of Mass In a chemical reaction, matter cannot be created or destroyed. It can only be changed. Therefore, the amount of matter in the reactants must equal the amount of matter in the products.

What does that mean?? The atoms contained in the reactants must be the same as the atoms in the products. Atoms can not be created or destroyed. The atoms CAN be rearranged into different molecules.

Oxygen is not equal on each side of the equation. Is the Law of Conservation of Mass supported by this chemical equation? H2 + O2 H2O Reactants Products H = 2 atoms H = 2 atoms O = 2 atoms O = 1 atom NO! Oxygen is not equal on each side of the equation.

So what do we do? 2H2 + O2 2H2O Reactants: Products: H = 4 H = 4 The chemical equation must be written according to the law. To do this we change the coefficients. We NEVER change a subscript or a formula! 2H2 + O2 2H2O Reactants: Products: H = 4 H = 4 O = 2 O = 2

Do I Need to Know How to Balance? NOT YET. You need to be able to recognize if the chemical reaction follows the law of conservation of mass. Na + O2 Na2O Mg + 2HCl MgCl2 + H2 NOT BALANCED BALANCED!

You Practice!!! NOT BALANCED BALANCED! BALANCED HgO Hg + O2 Hg = Hg = O = O = N2 + 3H2 2NH3 Zn + 2HCl ZnCl2 + H2 NOT BALANCED BALANCED! BALANCED

More Practice NOT BALANCED NOT BALANCED BALANCED K + Br2 2KBr 2Fe + O2 6Fe2O3 2Na + 2H2O 2NaOH + H2 NOT BALANCED BALANCED

Got It???

Balancing Chemical Equations H2 + O2 H2O H = 2 atoms H = 2 atoms O = 2 atoms O = 1 atoms How can we use coefficients to balance this equation?

Using a coefficient of 2 will balance oxygen. H2 + O2 2H2O Reactants: H = 2 Products: H = 4 O = 2 O = 2 Now the Oxygen is balanced but Hydrogen is not. What can be done to balance Hydrogen?

Adding a coefficient of 2 here will balance hydrogen. 2H2 + O2 2H2O H = 4 atoms H = 4 atoms O = 2 atoms O = 2 atoms Now it is balanced!!!

Now You Practice ___HgO ___Hg + ___O2 ___K + ___Br2 ___KBr Hg = Hg = O = O = ___K + ___Br2 ___KBr K = K = Br = Br =

___N2 + ___H2  ___NH3 C = C= H = H = O = O = Balance two more… N = N = H = H = ___C2H6 + ___O2  ___CO2 +___H2O C = C= H = H = O = O =