Chemistry Notes A molecule consists of two or more atoms of the same element, or different elements, that are chemically bonded together. The smallest part of a pure substance (element or compound) Ex. One molecule H 2 0 vs. a glass of water. Diatomic molecule - composed of two of the same atom Examples: H 2, N 2, O 2, Cl 2, Br 2 In the animation above, two nitrogen atoms (N + N = N 2 ) make one Nitrogen molecule. Two or more different types of atoms chemically bonded to each other Table Salt & Ammonia are examples of compounds Compounds have different properties than the elements it is made of. All compounds are molecules, but not all molecules are compounds (diatomic molecules are NOT compounds) Organic Compounds- compounds containing covalently bonded carbon. Example: C 6 H 12 O 6 (Glucose) T he rule of 8. Valence electrons are the electrons in the outermost energy level. You must know the number of valence electrons an atom has. W hen atoms chemically combine they try to end up with a full outermost energy level or 8 valence electrons by either gaining or losing electrons. T o meet this need: MM etals tend to lose (give away) electrons. NN onmetals tend to gain electrons. N ature seeks balance! Having a full outermost energy level is stable. T hats why the Noble Gases do not react. They already have a full outer level. The group (column) represents the number of valence electrons in the outer shell. The period (row) represents the number of energy levels in the atom. A Lewis dot diagram is a system to represent atoms and their valence electrons. Drawing Lewis Dot Structures: An ionic bond is a bond that forms when valence electrons are lost or gained (transferred). It is the bond formed between oppositely charged ions. Example: A lithium atom gives up an electron to a fluorine atom. The result is a positively charged lithium ion and a negatively charged fluoride ion. Other ionic bond examples. A metal bonded to a nonmetal (Groups 1 & 2 with Groups 6 & 7) Conducts electricity when dissolved in water or melted. High melting points. Solids at room temperature. A metallic bond is the attraction of free floating valence electrons. Metal atoms can bond to atoms of the same element, or to other metals. Electrons divide evenly among atoms- electron sea A metallic compound is a metal bonded to another metal. Metallic compounds have: High melting points Good conductors of heat and electricity Malleable and ductile Strong bonds Atoms arranged in a pattern A covalent bond is a chemical bond formed when atoms share valence electrons. Usually nonmetals with nonmetals. Elements that are close together on the periodic table are more likely to share electrons in a covalent bond than to transfer electrons. Hydrogen, Carbon, Nitrogen, and Oxygen usually form covalent bonds. Drawing covalent bonds.. Hydrogen has one unpaired electron. Two hydrogen atoms share their single electrons to form a pair. The shared pair of electrons is a single covalent bond, which holds the hydrogen molecule H 2 together. Drawing single covalent bonds. Some atoms may form stronger bonds by sharing more than one pair of electrons. A triple bond has three pairs of shared electrons and is stronger than a double bond. A double bond has two pairs of shared electrons and is stronger than a single bond. Drawing double & triple bonds. Drawing covalent bonds.. Hydrogen, Oxygen, Nitrogen, and Carbon make up 98% of all living things Every Hydrogen atom has 1 line connecting it to other atoms. Every Nitrogen atom has 3 lines connecting it to other atoms. Every Oxygen atom has 2 lines connecting it to other atoms. Every Carbon atom has 4 lines connecting it to other atoms. Do not conduct electricity in water. More flammable than ionic compounds. Softer than ionic compounds. Low melting and boiling points. Usually do not dissolve in water (not soluble) Information about the atoms that make up a molecule/compound Atoms will combine in specific rations due to the number of electrons shared or transferred. Example: The chemical formula for sucrose, C 12 H 22 O 11, includes all the atoms in one molecule. Step 1: Determine the elements to be used in the formula and their oxidation numbers Step 2 Solve by making the charge of one atom the subscript for the other. Mg +2 F -1 Mg +2 F -1 = MgF2F2 **If the subscript is 1, you do not need to write it. Try it: **If the subscript is 1, you do not need to write it. Sodium Chloride Calcium Fluoride Carbon Tetrachloride Aluminum Oxide Magnesium Oxide Carbon Dioxide A polymer is a covalent compound made up of many repeating units linked together in a chain. Analogy = Beaded Necklace A monomer is a single molecule that forms a link (beads) in a polymer chain (necklace). Examples of Polymers: Carbohydrates Plastics Proteins DNA Rubber Acids are substances that release a positively charged hydrogen ion, H +, in water. The strength of the acid depends on the concentration of H + ions. Acids are important in several body processes, including breaking down food in the stomach. Acids are also used in making many products, such as fertilizers, detergent, and cleaners. Sour Feel like water Conduct electricity React with metals Can neutralize a base Turn blue litmus paper red pH between 1-6 Acid Properties Bases are substances that produce negatively charged hydroxide ions (OH - ) when dissolved in water. Common bases include baking soda and cleaning agents. Base Properties Feel slippery Bitter taste Turn red litmus paper blue Dissolve fats, oils, and grease Neutralize acids to produce salt and water Conduct electricity Have a pH between 8-14 Acids and Bases pH is a numerical scale used to determine the strength or weakness of an acid or base. The pH scale runs from 0 to 14 Acids are below 7; strong acids are near 0. Bases are above 7; strong bases near Neutral solutions have a pH of 7. pH can be measured using different indicators: Litmus paper (red or blue) pH paper (pool test strips) Universal indicator (cabbage juice) pH meter A mixture is a combination of two or more substances that can be separated by physical means (i.e. filtering, evaporation, magnet, etc.) NO CHEMICAL BOND Solutions are also mixtures. Solutions are groups of molecules that are mixed up in a completely even distribution. Also called solution Uniform appearance Evenly mixed at the atomic level Ex: blood, milk, metal alloy, air Also called solution Uniform appearance Evenly mixed at the atomic level Ex: blood, milk, metal alloy, air Not evenly mixed Distinct substances Ex: granite, mixed nuts, salad, salad dressing Physical properties can be observed without changing the substance. Ex: phase of matter, color, taste, odor, shape, texture, density, melting point, boiling point, hardness, conductivity, malleability A chemical property is the ability or inability of a substance to combine with or change into one or more new substances (how a substance reacts with other substances). Examples of chemical properties include burning or rusting. Some substances do not react. Physical change: What the substance is made of does not change. Physical changes are reversible. Ex) Changing from one state to another Other Examples: Cutting a lawn, breaking glass, Melting ice Chemical change: Change one substance into a new substance. Chemical bonds are formed/rearranged New substances have different properties and compositions than the original substances. Usually chemical changes cannot be easily reversed. Property Changes If a substance reacts with another substance, it means there is an attraction between atoms. A Chemical Bond formed! Not easily separated. Evidence that a chemical change (reaction) has occurred Heat produced/absorbed Gas produced (bubbles/fizzing) Odor produced Electricity produced Light produced Precipitate produced (solid/solute coming out of solution) Color change (weakest evidence!) Chemical equations show that in chemical reactions, atoms rearrange, but no atoms are gained or lost. Reactants are the original substances in a chemical reaction and are placed on the left side. Products are the new substances in a chemical reaction and are placed on the right side. reactant + reactant product original substancesnew substance/s A subscript tells how many atoms of an element are in one molecule. A coefficient tells how many atoms, molecules, or formula units are in a reaction. NaHCO 3 + CH 3 COOHCO 2 + H 2 O + NaC 2 H 3 O 2 All chemical reactions must obey the Law of Conservation of Matter # of atoms on the left = # of atoms on the right Step 1Determine the correct symbols and formulas for reactants and products. Step 2 Write reactant symbols and formulas to the left of an arrow and product symbols and formulas to the right. Step 3 Count the number of each kind of atom on both sides. Step 4 Use coefficients to make the number of each kind of atom the same on both sides of the arrow. Step 5 Check to see that each kind of atom balances. CH 4 + O 2 CO 2 + H 2 O Reaction of methane: