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CHE 117A Review and Refresh Review and Refresh Every Substance is composed of atoms An atom is the smallest possible particle of a substance Atoms are extremely small Review and Refresh In most substances atoms combine to form molecules A molecule is a combination of two or more atoms held together in a specific shape by attractive forces Review and Refresh A substance that contains only one type of atom is called and element. O Oxygen Na Sodium Br Bromine Sn Tin Review and Refresh Elements combine to form compounds The relative amounts of the elements in a compound never change This ratio is shown in the chemical formula of the compound O2, H2O, CO, CH4 Review and Refresh Review and Refresh The elements can be grouped according to their physical and chemical properties Periodic table Metals on the left Nonmetals on the right Review and Refresh Review and Refresh Elements combine to form compounds which can exist in three different phases Solid, liquid, and gas Review and Refresh Changes between phases are physical changes The substance’s chemical nature remains the same Ice melting to water Water converting to steam Sugar dissolving in water Chemical changes involve one substance becoming another substance C burning in O2 to form CO2 Review and Refresh Scientific Notation 650,000,000 is 6.5108 0.0000000100 is 1.0010-8 Review and Refresh Units G M k c m µ n p = = = = = = = = giga = 109 mega = 106 kilo = 103 centi = 10-2 milli = 10-3 micro = 10-6 nano = 10-9 pico = 10-12 Review and Refresh Unit conversions Example 1: The speed of light is generally accepted to be 3.00108 m/s. What is the speed of light in mph? 1 mile = 5280 ft 2.54 cm = 1 in 3.00 108 m 60 s 60 min 100 cm 1 in 1 ft 1 mile s 1 min 1 hr 1m 2.54 cm 12 in 5280 ft 6.71108 mph Review and Refresh Three temperature scales °F, °C, K °F = 1.8°C + 32 K = °C + 273.15 Review and Refresh Precision describes the exactness of a measurement Accuracy describes how close a measurement is to the true value Review and Refresh Example 2: Significant Figures 3.52 10 7.154 10 2 6 6.125 1 .5 2.52 10 4.1 13.24 1.435 5.6 20.3 5 Review and Refresh Back to molecules… The chemical formula describes the composition of a substance for most elements, the formula is the chemical symbol seven diatomic elements: H2, N2, O2, F2, Cl2, Br2, I2 also, P4 and S8 Review and Refresh When to different elements combine to form a binary compound, the chemical formulas are written as follows Usually the element farther to the left on the periodic table is written first KCl, Al2O3, Mg3N2 Review and Refresh H is only written first when combined with elements from Groups 6 and 7 H2O, HCl NaH, B2H6, CH4 If the elements are in the same group, the lower element is written first SeO2, IF3 Review and Refresh Example 3: Write the correct chemical formulas for the following sulfur compounds Review and Refresh SO3 H2S SF4 S2F2 Review and Refresh Chemical formulas only give the ratio of elements in a compound they say nothing about the arrangement of the elements relative to each other Structural formulas give both Propane, C3H8 Review and Refresh Often two very different compounds have the same chemical formula C2H6O Review and Refresh We can also represent structural formula in 3D ball-and-stick model space-filling model Review and Refresh Review and Refresh We can simplify line structures even further C-H bonds are not drawn C is not labeled C always has 4 bonds Review and Refresh Review and Refresh Review and Refresh Review and Refresh Example 4: Write the chemical formula for the following compounds C2H4Cl2 C4 H8 O2 C3 H4 O Review and Refresh Naming Compounds: binary compounds Elements that appear first keep their name Second element is named with the root name plus –ide Use greek prefixes to represent number of atoms never use mono- for the first element Review and Refresh CO carbon monoxide NO2 nitrogen dioxide SO3 sulfur trioxide P4O10 tetraphosphorus pentoxide Review and Refresh Ionic compounds are named with the cation first and the anion second Memorize Table 3.5 NaCl sodium chloride NH4NO3 ammonium nitrate Review and Refresh If the compound has a transition metal then the charge of the metal is indicated in the name by a Roman numeral FeCl3 iron(III) chloride Cu2O copper(I) oxide Review and Refresh The mole a mole of any substance is equal to 6.0221023 (NA) items of that substance exactly like a dozen eggs Obviously we can’t count that many items so we count mole by mass Review and Refresh 12g of carbon-12 contains exactly one mole of atoms all other molar mass are based on this value the atomic mass on the periodic table is the mass in grams of one mole of the element Review and Refresh The molar mass of a compound is simply the sum of the atomic masses of the constituent elements Example 5: What are the molar masses (molecular weights) of NaCl and C3H8 58.44 g/mol and 44.10 g/mol Review and Refresh Example 6: How many moles of NH4NO3 are contained in 16.5 g of the compound? NH 4 NO3 80.04 g/mol 1 mol 16.5 g NH 4 NO3 0.206 mol NH 4 NO3 80.04 g Review and Refresh Suggested Problems Chapter 1 8, 10, 12, 26, 33, 34, 40, 41, 55, 61, 69, 87, 88, 98 Chapter 3 2, 5, 8, 9, 10, 15, 16, 24, 31, 35, 38, 41 – 43, 72, 81, 95, 101, 108