Chemical Bonds and Equations Physical Science

Why do atoms form chemical bonds? Question: Why do atoms form chemical bonds?

Types of Chemical Bonds-11/18/14 Compound- substance made of the combined atoms of two or more elements Chemical formula- tells what elements a compound contains and the exact number of the atoms of these elements

Some Common Compounds Vinegar Acetic acid HC2H3O2 Sand Silicon dioxide SiO2 Stomach Acid Hydrochloric acid HCl Cane Sugar Sucrose C12H2208 Atoms form compounds to become chemically stable. An atom is chemically stable when the outer energy level is complete, or full.

* ION- positive or negatively charged atom Chemical bond- force that holds together the atoms in a substance * ION- positive or negatively charged atom Ionic Bond Covalent Bond Loses or gains electrons Attraction between opposite charges of ions Between metal & nonmetal Shares electrons Can form multiple bonds Between a nonmetal and a nonmetal

Ionic and Covalent Bonding

What would a chemist name the compound CuCl? Question: What would a chemist name the compound CuCl?

Writing Formulas & Naming Compounds -11/20/14 Binary compound- compound composed of two elements Oxidation number- positive or negative number which indicates how many electrons an element has gained, lost or shared when bonding with another atom *When writing formulas for binary ionic compounds, it is important to remember that compounds formed have a net charge of zero.

Polyatomic ions- a positively or negatively charged covalent bonded group of atoms *The prefix poly means “many,” so the term polyatomic means “having many atoms” Polyatomic Ions Charge Name Formula 1+ Ammonium NH4+ 1− Acetate C2H3O2− Chlorate ClO3− Hydroxide OH− Nitrate NO3− 2− Carbonate CO32− Sulfate SO42− 3− Phosphate PO43−

Prefixes for Binary Covalent Compounds Hydrate- compound that has water chemically attached to its ions and written into its chemical formula. Covalent compounds can form more than one compound with each other. Scientists use Greek prefixes to indicate # of atoms of each element in binary compound. Prefixes for Binary Covalent Compounds # of Atoms 1 2 3 4 5 6 7 8 Prefix Mono- Di- Tri- Tetra- Penta- Hexa- Hepta- Octa-

Why do chemical equations need to be balanced? Question: Why do chemical equations need to be balanced?

Chemical Reactions -12/2/14 Chemical reaction- a reaction in which one or more substances are changed to new substances Reactants- substances that are about to react Products- new substances produced Law of Conservation of Mass- total starting mass of all reactants equals the total final mass of all products. Reactants Produce Products

Chemical equation- uses chemical formulas and symbols to describe a chemical reaction and the product it produces Symbol Meaning  Produces/yields (aq) Aqueous (solid dissolved in H2O) + plus Heat Reactants heated (s) solid Light Reactants exposed to light (l) liquid Elect Electric current applied to reactants (g) gas

*Review: Coefficients- numbers which represent the number of units of each substance in a reaction Subscripts- numbers which represent the number of atoms in a molecule of a particular elements

Balancing Chemical Equations-12/9/14 Balanced chemical equations- have the same number of atoms of each element on both sides of equation *When balancing chemical equations NEVER change the subscripts, instead change the coefficient in front of the compounds needing to be balanced.

Steps to Balancing a Chemical Equation Write a chemical equation for the reaction using formulas and symbols—make sure reactants are on left side and products on right. Count the atoms in reactants and products. Choose coefficients that balance the equation.  Hint: Generally if there is an even # of an element on one side and an odd on the other side, place a 2 in front of compound containing odd number of atoms. Recheck the numbers of each atom on both sides of equation and adjust coefficients if necessary— remember NEVER change subscripts.

Example: Video: https://www.youtube.com/watch?v=Q4WWiAm3nPM

What happens to chemical bonds during energy exchanges? Question: What happens to chemical bonds during energy exchanges?

Chemical Reaction Types-12/9/14 Synthesis reaction – reaction where two or more substances combine to form another substance A + B  AB Decomposition reaction – reaction where one substance breaks down or decomposes into two or more simpler substances AB  A + B

Single displacement reaction- reaction in which one element replaced another in a compound. A + BC  AC +B or A + BC  AB +C Double-displacement reaction- reaction that results in a precipitate, water or gas when a positive ion of one compound swaps with another positive ion of another compound AB + CD  AC + BD

Chemical reactions involve energy exchange Exothermic Reactions Endothermic Reactions Reaction in which energy is released in form of heat Ex. Burning wood, fireworks, elephant’s toothpaste Reaction in which heat energy is absorbed Ex. Chemical ice packs, photosynthesis Catalyst- speeds up a chemical reaction without itself being permanently changed Inhibitor- prevents or slows a chemical reaction or interferes with the catalyst