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Rules for Significant Figures All non-zero digits (1-9) are significant. Zeros between non-zero digits are significant. Ex: 3004 has 4 significant figs. Zeros to the left of the first non-zero digit are not significant. Ex: 0.004 has 1 significant fig. If a number ends in zeros to the right of the decimal point, those zeros are significant. Ex: The number 40.0 has 3 significant figures Multiplication and division, the result may have no more significant figures than the factor with the fewest number of significant figures. Example: 2.52 x (3 sig figs) (smallest) 1.003 (4 sig figs) = 2.52756 recorded to 2.53 = (3 sig. figs) Adding and subtracting: Add or subtract the numbers. The final answer can contain only as many decimal places as found in the measurement with the fewest number of decimal places. Example: 134.052 m + 1.23 m = 135.282 rounds to 135.28 (3 decimal places) (2 decimal places) (2 decimal places) ________________________smallest_________________________________________ Density (mass unit/volume unit) = Mass (unit) ÷ Volume (unit) ________________________________________________________________________ Specific heat (c) (units) = calories / (grams x C) or joules / (grams x C) Heat released (cal or J) = mass (g) x Specific heat (choose one unit above) x temp change (ºC) ________________________________________________________________________ Conversions: When converting units make sure the unit you are looking for is on top of the conversion fraction and the unit given is on the bottom of the conversion fraction so the units given can cancel. 1 dozen Example: 132 pencils = ________ dozen 132 pencils x ---------------- = 11 dozen 12 pencils Metric Conversions Units Length (Decreasing order) Kilo: 0.001 Km 1m Base unit: Centi: 100 cm 1000 mm Milli: 1,000,000 µm Micro: 1,000,000,000 nm Nano: Mass Volume 0.001 Kg 1g 100 cg 1000 mg 1,000,000 µg 1,000,000,000 ng 0.001 KL 1L 100 cL 1000 mL 1,000,000 µL 1,000,000,000 nL 3 1cm = 1 mL When choosing the ratios from the table above, one part of the ratio goes on top of the fraction and the other goes on the bottom. The ratio should be set up so that the top of the ratio should have the units that you are looking for and the bottom should be the units that you start with. Example: 2 mm = _______ cm Get from chart above 100 cm 2 mm ---------------- = 0.2 cm 1000 mm ________________________________________________________________________ Lewis / Electron-dot diagrams 1. Write symbol of element 2. Place the correct number of dots around the symbol (The number of dots equals the number of valance electrons or the group / roman number the element is in) 3. Spread out the dots before doubling up ● Aluminum = Group III ● Al ● ●● Nitrogen = Group V ● N ● ● ______________________________________________________________________________ Percent Error Formula Percent error = [Measured value – Accepted value] Accepted value x 100 Percent Composition Percent composition = (Mass of element x subscript) (mass of compound) x 100 Writing Formulas Ionic Compounds: oppositely charged ions. A metal and nonmetal(s) Binary Ionic Compounds Criss-cross to arrive at subscripts Ex: Sodium nitride = Na+1 and N -3 Na3N Ternary Ionic Compounds Aluminum hydroxide = Al+3 and (OH-1) switch numbers to get Al(OH)3 Binary Molecular (Covalent) Compounds: Prefixes (see chart below) become subscripts: Ex: Trinitrogen pentabromide N3Br5 Naming Compounds Binary Ionic: 1. One metal and nonmetal 2. If metal is from transitional group must use roman number if not just name metal 3. Nonmetal drops ending and adds “ide” Example: CaCl2 Calcium chloride Example: Cr2S3 Chromium (IIII) sulfide (Roman number is found as other subscript) Ternary Ionic Compounds 1. One metal and more than one nonmetal 2. If metal is from transitional group must use roman number if not just name 3. Nonmetal group gets name from polyatomic ion chart. Example: Ca(NO3)2 Calcium nitrate Example: Fe(OH)2 Iron (II) hydroxide (Roman number is found as other subscript) Binary Molecular (Covalent) Compounds: Both negative charged ions. Both non-metals (Use prefixes as subscripts) 1. Second nonmetal drops ending and adds “ide” Ex: N2O3 Dinitrogen trioxide Prefix Mon Di Tri Tetra Penta Number of atoms 1 2 3 4 5 Prefix Hexa Hepta Octa Nona Deca Number of atoms 6 7 8 9 10 Drawing Bohr diagrams 1. The number of protons and neutrons are place in the nucleus. 2. The electrons are placed in energy levels according to the maximum occupancy. (Fill each shell in numerical order until all electrons are used) Energy Level Maximum number of electrons 1 2 2 8 3 18 4 32 Ex: 18p+ 22 n0 Argon #18 ﴿ 2e﴿ ﴿ 8e﴿ ﴿ 8e﴿ Temperature Conversions using formulas 1. To change Celsius to Fahrenheit: Take the given temperature and multiply by 1.80 then press equal then add 32 then press equal. 2. To change Fahrenheit to Celsius: Take the given subtract 32 then press equal then multiply the number by 0.56 then press equal. 3. To change Celsius to Kelvin: Add 273 to the given temperature 4. To change Kelvin to Celsius: Subtract 273 from the given temperature. Types of Equations Combination: A + B AB Decomposition: AB A + B Single Replacement: A + BC AC + B A + BC BA + C Double Replacement: (A is metal) (A is a nonmetal) AB + CD AD + CB Complete Combustion: Incomplete Combustion: AB + O2 CO2 + H2O AB + O2 CO + H2O