Kevin



Welcome! Happy Birthday, Josh!  **Covalent Bond** - a chemical bond that involves sharing a pair of electrons between atoms in a molecule ([|wordnet.princeton.edu/perl/webwn])
 * Electronegativity** - the tendency of an atom or radical to attract electrons in the formation of an ionic bond ([|wordnet.princeton.edu/perl/webwn])



Covalent Bond Gizmo - 


 * Chemical Equations**

Their job: Depict the kind of reactants and products and their relative amounts in a reaction. 4Al (s) + 3 02 → 2Al2O3 (s)

The numbers in the front are called stoichiometric coefficients.

The letters (s), (g), and (l) are the physical states of compounds.

-chemical reactions occur when bonds between the outermost parts of atoms are formed or broken. -chemical reactions involve changes in matter, the making of new materials with new properties, and energy changes. -symbols represent elements, formulas describe compounds, chemical equations describe a chemical reaction.


 * Parts of Reaction Equation**

-Chemical equations show the conversion of reactants (the molecules shown on the left of the arrow) into products (the molecules shown on the right of the arrow). -A plus sign separates the molecules on the same side. -The arrow is read as “yields” -Example: C + O2 → CO2 -This reads “carbon plus oxygen react to yield carbon dioxide.”

Because of the principle of the conservation of matter, an equation must be balanced. It must have the same number of the same kind on both sides.


 * Balancing Equations**

-When balancing a chemical reaction, you may add coefficients in front of the compounds to balance the equation, but you may not change the subscripts.

4Al (s) + 3 02 → 2Al2O3 (s)

This equations means 4 Al atoms + 3 O2 Molecules produces 2 molecules of 2Al2O3 and/or 4 moles of Al + 3 moles of O2.


 * Steps to Balancing Equations**

There are four basic steps to balancing a chemical equation. 1) Write the correct formula for the reactants and the products. 2) Find the number of atoms for each element on the left side. Compare those against the number of atoms of the same element on the right side. 3) Determine where to place coefficients in front of formulas so that the left side has the same number of atoms as the right side for EACH element in order to balance equation. 4) Check your answer to see if: -The numbers of atoms on both sides of the equations are now balanced. -The coefficients are in the lowest possible whole number ratios. (reduced)


 * Some Suggestions to Help You**

Some helpful hints for balancing equations: ?-Take one element at a time, working left to right except for H and O. Save H or next to last, and O until last. -IF everything balances except for O, and there is no way to balance O with a whole number, double all the coefficients and try again. (Because O is diatomic as an element) -(Shortcut) Polyatomic ions that appear on both sides of the equations should be balanced as independent units

Example:

_2__H2(g) +__ __O2 (g) → 2 H2O(I)

1) Beryllium + Oxygen → BeO 2) Magnesium + Nitrogen → Mg+2 + N+3 → Mg3O2 3) Potassium + Chlorine → KCl

-A chemical change in which a single compound breaks down into 2 simpler compounds. -2HgO (s) → 2 Hg (l) + O2 (g)


 * Decomposition**

A chemical change in which a single compound breaks down into 2 simpler compounds.

2HgO (s) → 2Hg (l) + O2 (g) 2H2O (l) → 2H2 (g) + O2 (g)

Any time you have a compound with a carbonate in it, it decomposes the same way -XCO3 → XO + CO2


 * Single Replacement**

-A chemical change in which one element replaces a second element in a bond. -2K (s) + 2HOH (l) → 2KOH (aq) + H2 (g) -Zn (s) + Cu(NO3)2 (aq) → Cu(s) + Zn(NO3)2 (aq)

Zn + H2SO4 → ZnSO4 + H2 Cl2 +2 NaI → 2NaCl + I2 Ca + 2HOH → 2Ca(OH)2 + H2


 * Double Replacement**

-A chemical change involving an exchange of positive ions between 2 compounds.

Na2S (aq) + Cd(NO3)2 (aq) → CdS (s) + NaNO3 (aq)


 * Synthesis Reactions**

Synthesis – combining one or more elements or compounds to form a single product.

2 Mg (s) + O2 → 2MgO (s)

S (s) + O2 (g) → SO2 (g)


 * Acid – Base Reactions**

-The neutralizing of an acid with a hydroxide -Just like a double replacement reaction; can tell because water is formed as a product. - 2H3PO4 + 3Ca(OH)2 → 6HOH + Ca3(PO4)2


 * Combustion Reaction**

-Reaction involving the burning of an organic compound. -Will always form CO2 & H2O -C3H8 + 5HO2 → 3CO2 + 4H2O


 * Will a reaction really happen?**

-Using your Activity Series Chart -This uses electronegativity values to determine which element “owns” more of the electron. -If the single element is higher on Activity Series, it will form a new compound. This means it would “own” more of the electron.


 * Examples**

Br2 + KI → will happen because Br is higher than I Br2 + KCl → won’t happen because Cl is higher than Br


 * Double Replacement Reactions**

-When a DR happens one of the two products must be a g, s, or water. -Otherwise, the reaction won’t happen.

Ex.: Na3PO4 (aq) + 3KCl (aq) → 3NaCl (aq) + K3PO4 (aq) 1) Converting to liters when a gas is at STP (standard temperature & pressure): 22.4 L/ 1 mol

2) Converting to liters when the molarity is given (M = mol/L) be sure to keep the # with moles. ex: 6 mol/ 1 L

3) Converting to molecules or atoms: 6.022 x 10²³ molecules

4) Using density: g/mL 