Chap(1).ppt

Chapter 1: Chemistry
and the Atomic/Molecular
View of Matter
Chemistry: The Molecular Nature
of Matter, 6E
Brady/Jespersen/Hyslop

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E
1.2- Scientific Method
 Approach to gathering information &
formulating explanations.
 Scientists perform experiments in laboratories
under controlled conditions
1. Make observations/collect data
2. Law or Scientific Law
3. Hypothesis
4. Theory
2

Atomic Theory
 Most significant theoretical model of nature
Atoms
 Tiny submicroscopic particles
 Make up all chemical substances
 Make up everything in Macroscopic world
 Smallest particle that has all properties of given
element
 Composed of:
 Electrons
 Neutrons
 Protons
3

1.3- Matter & Its Classifications
Matter
 Anything that has mass & occupies space
Mass
 How much matter given object has
Weight
 Force with which object is attracted by gravity
Ex. Mass vs. Weight
Astronaut on moon & on earth
 Weight on moon = 1/6 weight on earth
 Same mass regardless of location
4

Matter
Chemical Reactions
 Transformations that alter chemical compositions
of substances
Decomposition
 Chemical reaction where 1 substance broken
down into 2 or more simpler substances
Ex.
5
Molten
sodium
chloride
Sodium metal Na
+
chlorine gas Cl2
Electric
current

Elements
 Substances that can’t be decomposed into simpler
materials by chemical reactions
 Substances composed of only 1 type of atom
H2 , O2 , Cl2 , Br2 , Na , Ca , Fe
 More complex substances composed of elements in various
combinations
6
diamond = carbon gold sulfur

Chemical Symbols for Elements
Chemical Symbol
 One or two letter symbol for each element name
 First letter capitalized, second letter lower case
Ex. C = carbon S = sulfur
Ca = calcium Ar = argon
Br = bromine H = hydrogen
Cl = chlorine O = oxygen
 Used to represent elements in chemical formulas
Ex. Water = H2O
Carbon dioxide = CO2
 Most based on English name
 Some based on Latin or German names
7

Chemical Symbols
English Name Chemical Symbol Latin Name
Sodium Na Natrium
Potassium K Kalium
Iron Fe Ferrum
Copper Cu Cuprum
Silver Ag Argentum
Gold Au Aurum
Mercury Hg Hydrargyrum
Antimony Sb Stibium
Tin Sn Stannium
Lead Pb Plumbum
Tungsten W Wolfram
(German)
8

Compound
 Formed from 2 or more atoms of different
elements
 Always combined in same fixed ratios by
mass
 Can be broken down into elements by some
chemical changes
Ex. Water decomposed to elemental hydrogen
& oxygen
Mass of oxygen =
8 × mass of hydrogen
9

Pure Substance vs. Mixture
Pure substances
 Elements and compounds / H2O, Na, N2, …
 Composition always same regardless of source
Mixture
 Can have variable compositions
 Made up of two or more substances
Ex. CO2 in water—varying amounts of “fizz” in soda
 2 broad categories of mixtures:
 Heterogeneous Mixtures
 Homogeneous Mixtures
10

Homogeneous Mixtures
 Same properties throughout sample
 Solution
 Thoroughly stirred homogeneous mixture
Ex.
 Liquid solution
 Sugar in water
 Salt in water
 Gas solution
 Air
 Contains nitrogen, oxygen, carbon
dioxide & other gases
 Solid solution
 US 5¢ coin – Metal Alloy
 Contains copper & nickel metals
11
Other examples
- Flour
- Milk powder
- Potable water
- Gasoline

Heterogeneous Mixtures
 2 or more regions of different properties
 Solution with multiple phases
 Separate layers
Ex.
 Salad dressing
 Oil & vinegar
 Ice & water
 Same composition
 2 different physical states
 Ether and water
 Soil
12

Physical Change
 No new substances formed
 Substance may change state or the proportions
Ex. Ice melting or water freezing
 Sugar or salt dissolving
 Melting of metals
 Condensation of vapor or evaporation of water
 Stirring iron filings & sulfur together
13

Chemical Change
or Chemical Reaction
 Formation of new substance or compound
 Involves changing chemical makeup of substances
 New substance has different physical properties
 Can’t be separated by physical means
Ex.
 Fool’s gold
 Compound containing sulfur & iron
 No longer has same physical properties
of free elements
 Can’t be separated using magnet
14

Learning Check:
Chemical Physical
Magnesium burns when heated
Magnesium metal tarnishes in air
Magnesium metal melts at 922 K
Grape Kool-aid lightens when
water is added
15
 For each of the following, determine if it
represents a Chemical or Physical Change:
X
X
X
X

Classification of Matter
16

Learning Check: Classification
Hot
Cocoa
Ice
(H2O)
White
Flour
Table
Salt
(NaCl)
Pure substance
Element
Compound
Molecule
Heterogeneous Mixture
Homogeneous Mixture
17
X
X
X
X X
X
X

1.5- Atoms and Molecules
Chemical Formulas
 Atoms combine to form more complex
substances
 Discrete particles
 Each composed of 2 or more atoms
Ex.
 Molecular oxygen, O2
 Carbon dioxide, CO2
 Ammonia, NH3
 Sucrose, C12H22O11
18

Chemical Formulas
 Specify composition of substance
 Chemical symbols
 Represent atoms of elements present
 Subscripts
 Given after chemical symbol
 Represents relative numbers of each type of atom
Ex.
Fe2O3 : iron & oxygen in 2:3 ratio
19

Chemical Formulas
Free Elements
 Element not combined with another in compounds
 Just use chemical symbol to represent
Ex. Iron Fe Neon Ne
Sodium Na Aluminum Al
Diatomic Molecule
 Molecules composed of 2 atoms each
 Many elements found in nature
Ex. Oxygen O2 Nitrogen N2
Hydrogen H2 Chlorine Cl2
20

Depicting Molecules
 Want to show:
 Order in which atoms are attached to each other
 3-dimensional shape of molecule
 Three ways of visualizing molecules:
1. Structural formula
2. Ball-and-Stick model
3. Space filling model
21

1. Structural Formulas
 Use to show how atoms are attached
 Atoms represented by chemical symbols
 Chemical bonds attaching atoms indicated by lines
22
H O H H C H
H
H
H2O
water
CH4
methane

3-D Representations of Molecules
 Use touching spheres to indicate molecules
 Different colors indicate different elements
 Relative size of spheres reflects differing sizes
of atoms
23
Hydrogen
molecule,
H2
Oxygen
molecule,
O2
Nitrogen
molecule
N2
Chlorine
molecule,
Cl2

2. “Ball-and-Stick” Model
 Spheres = atoms
 Sticks = bonds
24
Chloroform,
CHCl3
Methane,
CH4

3. “Space-Filling” Model
 Shows relative sizes of atoms
 Shows how atoms take up space in molecule
25
Chloroform, CHCl3
Methane
CH4
Water
H2O

More Complicated Molecules
 Sometimes formulas contain parentheses
 How do we translate into a structure?
Ex. Urea, CO(NH2)2
 Expands to CON2H4
 Atoms in parentheses appear twice
26
Ball-and-stick
model Space-filling model

Hydrates
 Crystals that contain water molecules
Ex. plaster: CaSO4∙2H2O calcium sulfate dihydrate
 Water is not tightly held
 Dehydration
 Removal of water by heating
 Remaining solid is anhydrous (without water)
27
Blue =
CuSO4 •5H2O
White =
CuSO4

Counting Atoms
1. Subscript following chemical symbol
indicates how many of that element are part
of the formula
 No subscript implies a subscript of 1.
2. Quantity in parentheses is repeated a
number of times equal to the subscript that
follows.
3. Raised dot in formula indicates that the
substance is a hydrate
 Number preceding H2O specifies how
many water molecules are present.
28

Counting Atoms
Ex. 1 (CH3)3COH
 Subscript 3 means 3 CH3 groups
So from(CH3)3, we get 3 × 1C = 3C
3 × 3H = 9H
#C = 3C + 1C = 4 C
#H = 9H + 1H = 10 H
#O = 1 O
Total # of atoms = 15 atoms
29

Counting Atoms
Ex. 2 CoCl2 · 6H2O
 The dot 6H2O means you multiple both H2 &
O by 6
 So there are:
#H 6 × 2 = 12 H
#O 6 × 1 = 6 O
#Co 1 × 1 = 1 Co
#Cl 2 × 1 = 2 Cl
Total # of atoms = 21 atoms
30

Your Turn!
a. Na2CO3
b. (NH4)2SO4
c. Mg3(PO4)2
d. CuSO4∙5H2O
e. (C2H5)2N2H2
31
a. ___Na, ___ C, ___ O
b. ___N, ___H, ___S, ___O
c. ___Mg, ___P, ___O
d. ___Cu, ___S, ___O, ___H
e. ___C, ___H, ___N
3
2 1
2 8 1 4
3 2 8
1 1 9 10
Count the number of each type of atom in the
chemical formula given below
4 12 2

1.6- Chemical Reactions
 When 1 or more substances
react to form 1 or more new
substances
Ex. Reaction of methane, CH4,
with oxygen, O2, to form
carbon dioxide, CO2, &
water, H2O.
Reactants = CH4 & O2
Products = CO2 & H2O
32

Chemical Equations
 Use chemical symbols & formulas to represent
reactants & products.
 Reactants on left hand side
 Products on right hand side
 Arrow () means “reacts to yield”
Ex. CH4 + 2O2  CO2 + 2H2O
 Coefficients
 Numbers in front of formulas
 Indicate how many of each type of
molecule reacted or formed
 Equation reads “methane & oxygen
react to yield carbon dioxide & water”
33

Conservation of Mass in Reactions
 Mass can neither be created nor destroyed
 This means that there are the same number of each
type of atom in reactants & in products of reaction
 If # of atoms same, then mass also same
34
CH4 + 2O2  CO2 + 2H2O
4 H + 4O + C = 4 H + 4O + C

Balanced Chemical Equation
Ex. 2C4H10 + 13O2  8CO2 + 10H2O
35
4 C & 10 H
per
molecule
2 O per
molecule
2 H & 1 O
per
molecule
1 C & 2 O
per
molecule

Balanced Chemical Equation
Ex. 2C4H10 + 13O2  8CO2 + 10H2O
36
2 molecules
of C4H10
13 molecules
of O2
10 molecules
of C4H10
8 molecules
of CO2
Coefficients
 Number in front of formulas
 Indicate number of molecules of each type
 Adjusted so # of each type of atom is
same on both sides of arrow
 Can change

Balanced Chemical Equations
 How do you determine if an equation is balanced?
 Count atoms
 Same number of each type on both sides of equation?
 If yes, then balanced
 If no, then unbalanced
Ex. 2C4H10 + 13O2  8CO2 + 10H2O
Reactants Products
2×4 = 8 C 8×1 = 8 C
2×10 = 20 H 10×2 = 20 H
13×2 = 26 O (8×2)+(10×1)= 26 O
37

Learning Check
Fe(OH)3 + 2 HNO3  Fe(NO3)3 + 2 H2O
 Not Balanced
 Only Fe has same number of atoms
on either side of arrow.
38
Reactants Products
Fe 1 1
3 + (2×3) = 9 (3×3) + 2 = 11
O
3 + 2 = 5 (2×2) = 4
H
2 3
N

Your Turn!
How many atoms of each element appear on
each side of the arrow in the following
equation?
4NH3 + 3O2 → 2N2 + 6H2O
39
Reactants Products
N (4 × 1) = 4 (2 × 2) = 4
O (3 × 2) = 6 (6 × 1) = 6
H (4 × 3) = 12 (6 × 2) = 12

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E 40
* All Review Questions are required
Focus On the following
1.5
1.11
1.12
1.14
1.29
1.32
1.33
1.41
1.48
1.53

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