che 117a review and refresh. every substance is composed of atoms an atom is the smallest possible...

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

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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

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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 = giga = 109

M = mega = 106

k = kilo = 103

c = centi = 10-2

m = milli = 10-3

µ = micro = 10-6

n = nano = 10-9

p = 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

mph 106.71

ft 5280

mile 1

in 12

ft 1

cm 2.54

in 1

m 1

cm 100

hr 1

min 60

min 1

s 60

s

m1000.3

8

8

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

26 10154.71052.3 51052.2

5.1

125.61.4

6.5435.124.13 3.20

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

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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

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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

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Review and Refresh Example 4:

Write the chemical formula for the following compounds

C2H4Cl2 C4H8O2 C3H4O

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?

3434

34

NONH mol 0.206g 80.04

mol 1NONH g 16.5

g/mol 80.04NONH

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