INTRO AND BACKGROUND: Measurement, Uncertainty, Matter, Periodicity, and Nomenclature. Accuracy vs. Precision. Rounding with Sig Figs

Transcription

1 INTRO AND BACKGROUND: Measurement, Uncertainty, Matter, Periodicity, and Nomenclature Accuracy vs. Precision ACCURACY Closeness to the true value PRECISION How close a series of measurements are to each other *Tools with MORE numbers after the decimal = MORE precise WHEN MAKING MEASUREMENTS, IT S GOOD TO HAVE BOTH!! Accuracy vs. Precision % Error Compare a measurement to its accepted value % ERROR EXPERIMENTAL VALUE ACCEPTED VALUE ACCEPTED VALUE 100 Sally found the mass of a 34.0 g sample to be 32.7 g. What is the % error in her measurements? 3.82% Significant Figures All the numbers that are certain in a measurement, including one that is uncertain SIG FIGS RULES: 1) All non zero digits are significant 2) Zeros between other sig figs count Ex: ) Zeros at the end before an implied decimal point don t count (if it s there then they do) Ex: / ) When a number is smaller than one, zeros before the first S.F. don t count Ex: ) Zeros after a decimal do count (once you have a S.F.) Ex: Rounding with Sig Figs If digit to the right is LESS than 5 LEAVE IT BE!! (Ex: with 3 Sig Figs would be 56.4) If digit to the right is GREATER than 5 ROUND UP!! (Ex: with 3 Sig Figs would be 67.4) If digit to the right EQUALS 5 GO FOR EVEN #s!! (Ex: with 3 Sig Figs would be 94.6, while with 3 Sig Figs would be 94.8) 1

2 Math with Sig Figs Multiplication and Division: Count SIG FIGS in each and use the LEAST amount in the answer! Ex: X 2.10 X 0.75 = CORRECT SIG FIGS = 4.8 Addition and Subtraction: Count DECIMAL PLACES in each and use the LEAST amount in the answer! Sig Fig Practice How many sig figs are in these numbers? 1) 91,600 2) Calculate and round using the appropriate rule: 3) = 4) (5.610) x (34.908) x (2.30) = Ex: ml 2.43 ml = ml CORRECT SIG FIGS = 1.03 ml Ex: 1,000 mm = 1 m (MILLI is SMALLER!) Prefixes M (mega) = 10 6 k (kilo) = 10 3 D (deka) = 10 1 d (deci) = 10-1 c (centi) = 10-2 m (milli) = 10-3 µ (micro) = 10-6 n (nano) = 10-9 Ex: 1 km = 1,000 m (KILO is LARGER!) Positive exponents are LARGER than the base unit, while negative are SMALLER!! Temperature Conversions Equations to know: -FAHRENHEIT TO CELSIUS C =.56 X (F 32) -CELSIUS TO FAHRENHEIT F = ( 1.8 X C ) CELSIUS TO KELVIN K = C Know the reverse as well! What is -14 C expressed in Kelvin? Conversion Factors Amounts can be expressed in different EQUAL ways SOME COMMON CONVERSIONS: Dimensional Analysis What is 5 km expressed in meters? 1 in = 2.54 cm 1 ft = 12 in 1 yd = 3 ft 1 mi = 5280 ft 1 m = 10 dm 1 m = 100 cm 1 m = 1000 mm 1000 m = 1 km 1 g = 10 dg 1 g = 100 cg 1 g = 1000 mg 1000 g = 1 kg 1 ml = 1 cm ml = 1 L 1 min = 60 s 1 hr = 60 min 1 day = 24 hr 365 days = 1 yr 5 km X 1000 m 1 km = 5,000 m In order to cancel a unit, one must be on the top and the other must be on the bottom (immediately write the top unit on the bottom for the conversion factor)!! REMEMBER THE UNITS ARE YOUR FRIENDS!! 2

3 Dimensional Analysis MORE EXAMPLES: a) 3.48 g to kg kg b) 12.3 L to ml 12,300 ml c) 66 mm to km km d) days to s 97,630 s Density Relationship of mass to volume D = Mass / Volume Units are g / ml or g / cm 3 INTENSIVE PROPERTY: amount of the substance does not affect it If density is given, mass or volume could be determined M = D x V V = M / D Practice Practice A piece of wood has a mass of 11.2 g and a volume of 23 ml. What is the density? A piece of wood has a density of 0.82 g/ml and a volume of L. What is the mass of the wood in mg? Mercury metal is poured into a graduated cylinder that holds 22.5 ml. The mercury used to fill the cylinder weighs kg. Calculate the density (in g/cm 3 ) of mercury. Aluminum has a density of 2.70 g/cm 3. What is the mass (in kg) of a cube with a side of 6.78 cm? How Does Something Float? Lower density items FLOAT on higher density items ice is less dense than water! Most wood is less dense than water Helium is less dense than air A ship is less dense than water Matter Anything that has mass and takes up space THREE STATES OF MATTER SOLID: definite shape, definite volume, high density, not easily compressed, slow moving particles LIQUID: indefinite shape, flows but has a definite volume, not easily compressed GAS: indefinite shape, indefinite volume (takes the shape of the container), low density, easily compressed, fast moving particles (VAPOR = gaseous state that is liquid or solid) 3

4 INTENSIVE PROPERTY Describing Matter Depends on the type of matter, NOT the amount EX: Hardness, density, color, melting point EXTENSIVE PROPERTY Depends on the amount of matter present Types of Properties PHYSICAL PROPERTY: quality observed or measured WITHOUT changing the substance s composition EX: state, color, melting point, density CHEMICAL PROPERTY: observed only if the substance undergoes a chemical change EX: ability to oxidize (rust), flammability, ability to ferment EX: Mass, volume, weight Types of Changes Mixture Physical blend of two or more components TWO TYPES: HOMOGENEOUS è uniform composition throughout PHYSICAL CHANGE: properties of the material may change, but NOT the composition (REVERSIBLE) EX: cutting, melting, boiling, freezing, crushing HETEROGENEOUS è NOT uniform in composition CHEMICAL CHANGE: the composition of the matter always changes (IRREVERSIBLE) EX: cooking food, photosynthesis, rusting Solution Homogeneous mixture in which one substance is dissolved in another SOLUTE: substance that is dissolved SOLVENT: substance doing the dissolving Solution Solute Solvent Lemonade Soda pop Ocean water INSOLUBLE: does NOT dissolve SOLUBLE: does dissolve SUGAR SUGAR SALT WATER WATER WATER Separating Mixtures Differences in PHYSICAL properties can be used to separate mixtures 1) DECANT: pour off one layer leaving behind another layer of a mixture (density) 2) FILTRATION: separates a solid from the liquid 3) MAGNET: removes substances that are magnetized (ex: iron filings) 4) CHROMATOGRAPHY: separates colors 5) DISTILLATION: uses a difference in boiling points of two substances to separate them 4

5 Distillation Apparatus Pure Substance Composition does NOT vary TWO TYPES: ELEMENT è simplest form of matter that has a unique set of properties (Ex: hydrogen, oxygen, gold, lead) COMPOUND è contains two or more elements CHEMICALLY combined in a fixed proportion (Ex: water, carbon dioxide, sugars) Reaction Laws LAW OF CONSERVATION OF ENERGY Energy can neither be created nor destroyed only changed from one form to another! LAW OF CONSERVATION OF MASS Mass can neither be created nor destroyed Total mass in the universe is constant! Periodic Law Properties of elements repeat when placed in order of INCREASING atomic number MOSELEY (1913) developed the Modern Periodic Table Arranged elements in order of increasing atomic number Reading the Table PERIOD: Row on the Periodic Table / Energy level GROUP: Column (families) with similar physical and chemical properties Metals Found on the left hand side and middle of the table About 80% of elements are in this class High luster (shiny) Good conductors of heat and electricity Typically solids at room temperature (except Hg) DUCTILE: can be drawn into wires MALLEABLE: hammered into thin sheets Three classes of elements on the Periodic Table High density and melting point Form cations (+) 5

6 Metals Nonmetals Found on the right hand side of the table No luster Poor conductors of heat and electricity Most (not all) are gases at room temp Low density and melting point Not malleable or ductile Brittle Tend to form anions (-) Nonmetals Metalloids Found along the staircase on the table Arsenic Poisoning (from H 2O) Have properties of both metals and nonmetals Ex: B, Si, Ge, As, Sb, Te, Po, and At Ion formation depends on their group Metalloids Periodic Table Groups 6

7 Why Are Families Similar? Ions Charged (+ or -) atoms Atoms in their elemental state are NEUTRAL (protons and electrons are EQUAL) Atoms can gain or lose electrons giving them a charge Ions have DIFFERENT number of protons and electrons Each family has the same number of VALENCE ELECTRONS (outermost electrons of an atom) which determines an element s properties All want EIGHT!! Cations Positively (+) charged ions Anions Negatively (-) charged ions MAGNESIUM BOINK! Atoms that LOSE electrons become cations (loss of negatively charged particles) Atoms that GAIN electrons become anions (more negatively charged particles) CHLORINE Formed from Metals Formed from Nonmetals Number of electrons lost determines the charge (1+, 2+, etc.) Number of electrons gained determines the charge (1-, 2-, etc.) BOINK! Mg 2+ Cl 1- What Determines the Charge? What Determines the Charge? LOCATION on the Periodic Table and VALENCE ELECTRONS!! Atoms want EIGHT electrons in their outer or highest energy level to be stable They want to be like a NOBLE GAS! So they GAIN or LOSE electrons to accomplish this... Whichever is EASIER!!!! 7

8 Factors Influencing Trends 1) Electron Energy Level: distance from the nucleus 2) Effective Nuclear Charge (Z eff ): # of protons influences the pull on the electrons Atomic Radius Half the distance between the nuclei of two atoms of the same element (aka ATOMIC SIZE) Trend: INCREASES down a column and DECREASES going across a row 3) Shielding Effect: valence electrons are shielded from the pull / charge of the nucleus by all the electrons in between + Atomic Radius Half the distance between the nuclei of two atoms of the same element (aka ATOMIC SIZE) H Li Group: Na As you go down a column, the number of e- and energy levels increase so the radius K INCREASES! Atomic Radius Half the distance between the nuclei of two atoms of the same element (aka ATOMIC SIZE) Row: As you go across a row, all e- are in the same energy level and the nuclear charge is larger, causing the outer e- to be held tighter so it DECREASES! Rb Na Mg Al Si P S Cl Ar Atomic Radius Half the distance between the nuclei of two atoms of the same element (aka ATOMIC SIZE) Ionic Radius Half the distance between two ions Trend: INCREASES down a column and DECREASES going across a row for cations and anions, but cations are SMALLER and anions are LARGER 8

9 Ionic Radius Half the distance between two ions Ionic Radius Half the distance between two ions Group: As you go down a column, the number of e- and energy levels increase so the radius INCREASES! Row: Cations are SMALLER because as e- are lost nuclear charge increases and holds tighter, while anions are LARGER because as e- are added nuclear charge decreases and does not hold as tight but each type still DECREASES as go across! Ionization Energy Amount of energy required to remove a valence electron from an atom Trend: DECREASES down a column and INCREASES going across a row Ionization Energy Amount of energy required to remove a valence electron from an atom Group: As you go down a column, more energy levels are added and the valence e- are more shielded from the pull of the nucleus, making it easier to pull off an e- so it DECREASES! Ionization Energy Amount of energy required to remove a valence electron from an atom Row: As you go across a row, the nuclear charge gets greater (holds e- tighter) and the orbital gets closer to being full which adds stability, making it harder to pull off an e- so it INCREASES! Ionization Energy Amount of energy required to remove a valence electron from an atom Watch for EXCEPTIONS like Be / B, N / O, etc... WHY do they occur? To remove a second e-, even MORE energy is required (gets harder to steal) so I.E. INCREASES with each electron removed! Number of valence e- can also be seen look for jumps in energy (Ex: Be) 9

10 Ionization Energy Amount of energy required to remove a valence electron from an atom Electronegativity Ability of an atom to attract electrons when the atom is in a compound Trend: DECREASES down a column and INCREASES going across a row Electronegativity Ability of an atom to attract electrons when the atom is in a compound Group: As you go down a column, more energy levels are added, making the valence e- farther from the nucleus and not held as tightly due to shielding so it DECREASES! Electronegativity Ability of an atom to attract electrons when the atom is in a compound Row: As you go across a row, metals are more likely to give up e- to form cations, while nonmetals want more e- to be stable, forming anions so it INCREASES! Electron Affinity Amount of energy released when an electron is added Metallic / Reactivity Trend: DECREASES down a column and INCREASES going across a row *MORE negative number = MORE energy released! Think in terms of electronegativity the stronger the attraction to an e-, the more energy is released! As you go down a group, the metallic character INCREASES as well as the reactivity of the elements Exception: Halogens As you go down the family reactivity DECREASES! Therefore, the most reactive element in the halogen family is Fluorine!! 10

11 Ionic Bond TRANSFER of electrons between atoms forming opposite charges which attract to each other Each atom achieves a noble gas configuration (full valence shell) Usually between a METAL and a NONMETAL Naming Ionic Compounds To name an IONIC compound, ask yourself this question first Is the METAL in the compound MULTICHARGED? (in the d-block including Pb and Sn, but NOT Zn or Ag) Formula Unit: lowest wholenumber ratio of ions in an ionic compound (ex: NaCl or MgCl2) Naming Ionic Compounds EXCEPTIONS: -All transition metals (d-block) are multicharged except Ag is always Ag1+ and Zn is always Zn2+ so no Roman numerals are needed -Pb and Sn behave like transition metals Naming Ionic Compounds If the answer is NO 1) Name the cation (metal) first remember it keeps its name 2) Then name the anion (nonmetal) ending in -ide Name the following compound: AlBr3 Aluminum bromide Naming Ionic Compounds If the answer is YES 1) Criss-cross the SUBSCRIPTS and make them the charges (metals = + / nonmetals = - ) 2) Check the charge on the anion (-) and see if it is correct if it is NOT, multiply the - charge by a # to get the correct charge and then multiply the + charge by the same # 3) Write the name of the metal with its charge in parentheses as a Roman numeral [I, II, III, IV] followed by the nonmetal with an ide ending Naming Ionic Compounds Name the following compound: Fe2O3 IRON IS A MULTI-CHARGE METAL!! Fe2O3 = Fe3+ O2- Iron (III) oxide Make sure charge on anion is correct!! Name the following compound: ZnCl2 11

12 Naming Ionic Compounds If the compound has a POLYATOMIC ION: 1) Follow all previous rules, but the polyatomic ions get to keep their name Name the following compound: KNO 3 Name the following compound: NH 4 Cl Naming Ionic Compounds If the compound is a HYDRATE (contains water) 1) Follow all previous rules 2) Attach the correct PREFIX to the word hydrate to indicate the amount of water molecules present put this right after the name PREFIX NUMBER PREFIX NUMBER Mono 1 Hexa 6 Di 2 Hepta 7 Tri 3 Octa 8 Tetra 4 Nona 9 Penta 5 Deca 10 Naming Ionic Compounds Name the following compound: CuSO 4 5H 2 O Name the following compound: Pb(ClO 4 ) 2 3H 2 O Ionic Compound Formulas Rules for writing formulas 1) Write the SYMBOL of each element or ion from the name (cation is always written first followed by the anion) 2) Determine the CHARGE on each -Multi-Charged: it s in the ( ) -Polyatomic: keeps its charge -Otherwise: get from the table 3) Criss-cross the charges and make them SUBSCRIPTS simplify (reduce), if possible Ionic Compound Formulas Write the formula for calcium chloride. Ca 2+ Cl - Ionic Compound Formulas If POLYATOMIC IONS are present 1) Follow all previous rules 2) Treat polyatomic ions as a whole put in parentheses when subscripts are used 2+ = 2- CaCl 2 Fe(OH) 3 12

13 Ionic Compound Formulas If the compound is a HYDRATE (contains water) 1) Follow all previous rules 2) Use the PREFIX in front of hydrate to indicate the number of water molecules... Write this after the name by adding #H 2 O Write the formula for iron (III) chloride hexahydrate. Covalent Bond SHARING of electrons between atoms to satisfy the octet rule Involves two NONMETALS Known as covalent or molecular compounds MOLECULE: group of atoms joined by a covalent bond DIATOMIC MOLECULES: elements that cannot exist as single atoms Ex: H 2, N 2, O 2, F 2, Cl 2, Br 2, and I 2 Naming Covalent Compounds Naming a covalent / molecular compound: 1) Write the name of the first element 2) Change the ending of the second element to ide 3) Add correct PREFIXES to each to indicate the number of atoms (no mono on FIRST element) PREFIX NUMBER PREFIX NUMBER Mono 1 Hexa 6 Di 2 Hepta 7 Tri 3 Octa 8 Tetra 4 Nona 9 Penta 5 Deca 10 Covalent Compound Formulas Rules for writing covalent / molecular formulas: 1) Write each element symbol from the name 2) Use PREFIX in the name to determine the subscript for each element DO NOT SIMPLIFY!!! Write the formula for dinitrogen pentoxide. Hydrocarbons Compounds made of carbon and hydrogen Organic compounds Three groups we will look at: Alkanes, Alkenes, and Alkynes Named with PREFIXES based on the number of carbon atoms present: PREFIX # OF C PREFIX # OF C Meth 1 Hex 6 Eth 2 Hept 7 Prop 3 Oct 8 But 4 Non 9 Pent 5 Dec 10 Alkanes Have the generic formula: C n H 2n+2 Contains all single bonds Naming: Use the correct prefix with ane ending Formula: Prefix determines how many carbons Do the math to determine the number of hydrogens Name the following compound: C 3 H 8 Write the formula for butane. 13

14 Alkenes Have the generic formula: C n H 2n Contains one double bond Naming: Use the correct prefix with ene ending Formula: Prefix determines how many carbons Do the math to determine the number of hydrogens Name the following compound: C 6 H 12 Alkynes Have the generic formula: C n H 2n-2 Contains one triple bond Naming: Use the correct prefix with yne ending Formula: Prefix determines how many carbons Do the math to determine the number of hydrogens Name the following compound: C 5 H 8 Write the formula for decene. Write the formula for octyne. Rules for naming acids: Naming Acids 1) Hydrogen atom connected to anion (-) that ends in ide then it is named hydro- root of the element- ic acid HCl H 2 S Rules for naming acids: Naming Acids 2) Hydrogen atom connected to a polyatomic ion ending with ite then it is named (root of the polyatomic ion)- ous acid HClO 2 HNO 2 Rules for naming acids: Naming Acids 3) Hydrogen atom connected to a polyatomic ion ending with ate then it is named (root of the polyatomic ion)- ic acid HClO 3 Acid Formulas Rules for writing formulas of acids: 1) Hydrogen (H+) usually written first 2) Name indicates the anion (-) in the formula 3) Write the charges for each symbol and criss-cross to get subscripts Sulfurous acid H 2 SO 4 14