CHE 117A 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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  O 2, H 2 O, CO, CH 4

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

 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 O 2 to form CO 2

Review and Refresh  Scientific Notation  650,000,000 is 6.5  10 8  is 1.00  10 -8

Review and Refresh  Units  G = giga = 10 9  M = mega = 10 6  k = kilo = 10 3  c = centi =  m = milli =  µ = micro =  n = nano =  p = pico =

Review and Refresh  Unit conversions  Example 1: The speed of light is generally accepted to be 3.00  10 8 m/s. What is the speed of light in mph?  1 mile = 5280 ft  2.54 cm = 1 in

Review and Refresh  Three temperature scales  °F, °C, K  °F = 1.8°C + 32  K = °C

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

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: H 2, N 2, O 2, F 2, Cl 2, Br 2, I 2  also, P 4 and S 8

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, Al 2 O 3, Mg 3 N 2

Review and Refresh  H is only written first when combined with elements from Groups 6 and 7  H 2 O, HCl  NaH, B 2 H 6, CH 4  If the elements are in the same group, the lower element is written first  SeO 2, IF 3

Review and Refresh  Example 3:  Write the correct chemical formulas for the following sulfur compounds

Review and Refresh SO 3 H2SH2SSF 4 S2F2S2F2

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, C 3 H 8

Review and Refresh  Often two very different compounds have the same chemical formula  C 2 H 6 O

Review and Refresh  We can also represent structural formula in 3D  ball-and-stick model  space-filling model

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

 Example 4:  Write the chemical formula for the following compounds C 2 H 4 Cl 2 C4H8O2C4H8O2 C3H4OC3H4O

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  NO 2  nitrogen dioxide  SO 3  sulfur trioxide  P 4 O 10  tetraphosphorus pentoxide

Review and Refresh  Ionic compounds are named with the cation first and the anion second  Memorize Table 3.5  NaCl  sodium chloride  NH 4 NO 3  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  FeCl 3  iron(III) chloride  Cu 2 O  copper(I) oxide

Review and Refresh  The mole  a mole of any substance is equal to  (N A ) 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 C 3 H 8  g/mol and g/mol

Review and Refresh  Example 6:  How many moles of NH 4 NO 3 are contained in 16.5 g of the compound?

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