What is a Chemical Bond? The chemical attraction between elements which holds 2 or more atoms together with a chemical force

What is a Chemical Bond? The bond is determined by the electron arrangement in the outer level or valence level Oxidation tells how many electrons an element will gain, lose, or share and it is based on the valence number

What is a Chemical Bond? A stable arrangement has 2 or 8 electrons in the outer level. (Ex. Helium - 2, Xenon - 8) Called - the Octet Rule All atoms desire to have 8 electrons in their outer shell (except Hydrogen and Helium who want 2)

Types of Bonds: Covalent Bonds Occur when two atoms share electrons between outer energy levels When elements in the 13, 14, & 15 (3,4 and 5) families bond with each other When any element bonds to hydrogen

Types of Bonds – covalent (cont) Properties: can be broken easily have low melting points strong odors change states easily occur when an element bonds with itself ex.O2. called a diatomic bond

Covalent bond H + O H2O Electrons are shared

Types of Bonds -Ionic Bonds When a metal transfers an electron to a nonmetal A metal becomes positively charged more protons than electrons A nonmetal becomes negatively charged more electrons than protons Families 1,2, 16, & 17 bond ionically and the Transition Metals (3-12)

Types of Bonds - Ionic Bonds (cont) Properties: Conduct electricity Very strong bonds due to electrical attraction Ions are arranged in regular repeating pattern called a crystal lattice: +-+-+-+-+- -+-+-+-+-+

Ionic Bond Na + Cl NaCl Electron is transferred

Formulas and Equations Formulas are used to represent a chemical reaction in the form of an equation is an equal sign – called yield The elements and compounds on the left of the are called the reactants The elements and compounds on the right of the are called the products

Formulas and Equations - cont Subscript tells number of atoms of an element (Ex. H2O – the 2 tells you that there are 2 H atoms) Coefficients tell how many molecules are present (Ex. 3H2O – the 3 tells you that there are 3 water molecules with 2 H and 1 O each for a total of 6 H and 3 O)

Formula Writing Rules Find the oxidation number Put the oxidation numbers as superscripts above each element Cross the oxidation numbers, drop the signs and write the numbers as subscripts If it is multiple atoms in ( ) it is called a polyatomic ion. (CO3)2- Make no changes inside the ( ). Apply the same rules to it as a whole.

Na1+ O2- Parts of a formula There is a 2:1 ratio for Na:O Superscript Na2O 2Na2O Superscript There is a 2:1 ratio for Na:O No number means 1 Subscript Coefficient

Formula Writing - cont Most transition elements have so many electrons they are polyvalent. You can’t look at the periodic table to determine which oxidation number to use, so it will be given to you. Example – Fe2+ Ferrous/Iron II or Fe3+ Ferric/Iron III

Naming Rules for Binary Ionic Compounds If there are only 2 elements Keep the metal name Take the nonmetal (second element) drop the last syllable (the ending) and add ide NaCl – Sodium Chloride If the second part of the compound is a polyatomic ion, make no changes and write the words as written. Ca(CO3) – Calcium Carbonate

Naming Rules for Binary Covalent Compounds If there is only one atom just use the name with no prefix for the first element If there is more than one atom use the prefix that indicates the number (di, tri, etc.) For the second element use a prefix (mono, di, tri, etc.) drop the final syllable and add ide CO2 – Carbon Dioxide N2O – Dinitrogen Monoxide

Equations 2H2 + O2 -----> 2H2O It takes lots of energy to bond chemically so elements must use their energy efficiently. A chemical equation tells the story of a chemical reaction Reactants are starting substances. Products are the new substances.

Equations The large numbers in front of some of the formulas are called Coefficients These numbers are used to balance the equation because chemical reactions must obey the Law of Conservation of Matter The number of atoms of each element on both sides of the equation must be the same because matter cannot be created nor destroyed.

Balancing Act When balancing the equations, the only numbers that can be changed are the COEFFICIENTS. Remember that subscripts must never be changed in order to balance and equation.

Law of Conservation of Matter States that matter is not CREATED or destroyed, it only changes FORMS. In a chemical reaction this means that all the atoms present at the START of the reaction are present at the end.

Law of Conservation of Matter In a OPEN system, matter can enter from or escape to the surroundings. Open beaker, flask, test tube, outside In a CLOSED system, matter is not allowed to enter or leave. Ziplock bag, balloon over a test tube, cap on a bottle.

Types of Reactions In a chemical reaction, atoms are rearranged & changed in specific ways. Synthesis- 2 or more simple substances combine to form one more complex substance Fe + O2 FeO2 (rust) HINT: only one product on right side of arrow

Synthesis

Types of Reactions Decomposition occurs when one complex reactant breaks down into simpler products. Examples: H2O2----> H2 + O 2 KClO3-----> KCl + O3 HINT: only 1 reactant on left side of arrow

Decomposition

Types of Reactions Single Displacement- one element reacts with a compound and the element becomes a part of a compound. Al+ CuCl2 -----> Cu + AlCl3 HINT: element + compound  new element + new compound

Single Displacement

Types of Reactions Double Displacement- 2 compounds react and form 2 NEW compounds NaCl + HOH----> HCl + NaOH HINT: compound + compound  new compound + new compound

Double Displacement

Law of Conservation of Energy Energy can neither be created nor destroyed. It can only change forms. If energy is lost or released it is called EXOTHERMIC. The energy is Exiting the reaction examples: combustion and burning If energy is absorbed, it is called ENDOTHERMIC. The temperature decreases examples: yeast in dough absorbs heat and air expands causing it to rise.

Reaction Rates A rate describes how quickly reactants change to products. Collision theory states that for molecules to react they must collide at proper angles.

Reaction Rates The rate is effected by 4 factors: 1) Temperature 2) Concentration 3) Surface Area- grind up or make particles smaller 4) Catalyst speed up the reaction & do not effect the products while Inhibitors slow down the reaction. Ex. food preservatives