Download Chapter 2

2/9/2012
Chapter 2
Atoms, Molecules, and Ions
Chapter 2
• Atomic Theory
– Model for atom and ions that works well for chemistry
• Molecules
– Combinations of atoms
– Ways of representing molecules: formulas and models
• Names and formulas
– Binary molecular compounds
– Ionic compounds
– Acids
• Organic compounds
– Brief introduction
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Atomic Theory
• Elements composed of small particles called atoms
– All atoms of a given element are identical
• What does experiment tell us about atoms?
Radioactivity
• Discovered in late
19th century
α-particles: positive (+2) and heavy
Β-particles: negative (-1) and light
γ-rays: energy
(now know: He nuclei)
(now know: electrons)
(Incredible Hulk)
Conclusion: atoms contain smaller particles
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Rutherford’s Experiment
What does this experiment tell us about the atom?
The Nuclear Atom
• Atoms contain a heavy core
• Called the nucleus of the atom
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Atomic Structure
• Our model: Atoms made of three particles
– Electrons (e-): light (1/2000 amu)
negative (-1)
+
– Protons (p ): heavy (1 amu)
positive (+1)
o
– Neutrons (n ): heavy (1 amu)
neutral
• Atoms are electrically neutral
– What does this imply about # electrons and # protons?
– Imply anything about neutrons?
Atomic and Mass Numbers
• Atomic Number (Z) : # protons in nucleus
– Characteristic of a given element
• Mass Number (A): #protons + # neutrons in nucleus
• Isotopes: atoms with same atomic number but
different mass numbers (AZX)
– Carbon isotopes:
– Oxygen isotopes:
12
16
6C
13
8O
17
6C
14
6C
8O
18
8O
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Ions
• Electrons can be added or removed from an atom or
molecule.
– Electrons added: negative ion
– Electrons removed: positive ion
(anion)
(cation)
• Examples:
– Li ion (1 electron removed)
– O ion (2 electrons added)
3 protons, 2 electrons +1
8 protons, 10 electrons -2
Molecules
• Two or more atoms held together by a chemical
bond.
– Examples: H2O, NH3, CH4
– Diatomic: two atoms in molecule (H2)
– Polyatomic: three or more atoms in molecule (H2O, O3)
• Chemical bond = shared electrons
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Molecular Compounds
• Made of molecules
• Usually formed between two nonmetals
– Right side of periodic table (except for H)
– CO2, BF3, PCl3, CH4, H2O, XeF4
Formulas for Molecules
• Molecular formula
– Shows exact number of atoms in molecule
• Simplest (empirical) formulas
– Shows simplest ratio of atoms in molecule
• Structural formulas
– Shows how atoms are bonded together
• Condensed structural and skeletal formulas
– Simplified structures in organic chemistry
• Molecular geometry
– Shows three dimensional structure (Chapter 10)
• Molecular models
– Help visualize three dimensional structure
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Molecular Formula
•
•
•
•
•
•
Shows actual number of atoms in molecule
H2 O
C2H4
(ethylene)
C27H46O (cholesterol)
O2
(oxygen)
O3
(ozone)
– Above two are allotropes
– Two different forms of same element
Simplest (Empirical) Formulas
• Simplest whole number ratio of atoms in molecule
• Example: Ethylene
– Molecular formula
– Simplest formula
C2H4
CH2
• Polymers
– Long chains
– Exact number atoms unknown
– Polyethylene (above): simplest formula = CH2
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Structural Formulas
• Show how atoms in molecule are bonded
Condensed Structural Formulas
• Simplified structural formulas
• Use subscripts for multiple atoms bonded to same
atom
– Subscripted atoms are bonded to element on left
– Organic: sometimes omit C-C bonds
represents
?
?
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Organic Chemistry
• Basic molecules: hydrocarbons (C, H)
• Few other elements involved: mainly O and N
• Regular bonding patterns for key elements
• H: 1 bond
C: 4 bonds
O: 2 bonds
N: 3 bonds
Skeletal Formulas
• Represent C atoms by angled junctions
• Use H atoms to give each C four bonds
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Skeletal Formulas
• What are the skeletal formulas for the following:
• What are the condensed structural and molecular
formula for this molecule?
Skeletal Formulas
• Why do this?
– Organic molecules can be huge
– Carbon backbone frequently not as important as noncarbon atoms
– Skeletal structures are compact and give most
important information
• Structure
• Functional groups (later in lecture)
Cholesterol
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Molecular Models
• Molecules are small and generally three-dimensiona
– Molecules seldom are flat !
• We frequently represent them with physical or
computer models.
Structural formula
Ball-and-stick
Space-filling
Molecular Models
• Computer models frequently generated using
– Experimental data (e.g., x-ray diffraction)
– Theoretical calculations
• Useful for visualizing three-dimensional structures
– Example: RasWin viewer (On USB drive)
– Ethanol
– Vitamin C
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Molecular Molecules
• Good example is model of DNA
• Difficult to visualize in two dimensions
– 3-D model more useful
–
http://www.umass.edu/molvis/tutorials/dna/dnapairs.htm
Ionic Compounds
• Ionic Compounds
– Made of positive and negative ions
• Charges must balance
– Model as a large stack of ions
• Ionic compounds usually formed between a metal
and a nonmetal
– Opposite sides of
periodic table
– NaCl, K2O, MgF2
– Can involve
polyatomic ions
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Polyatomic Ions
• Polyatomic ions: Ions that are made of two or more
atoms
– Hydroxide: OH– Phosphate: PO43– Ammonium: NH4+
• Table 2.3 in the text, p 61
• You should know the name, formula, and charge of the
ions
Polyatomic Ions
• Polyatomic Cations
– NH4+, mercury (I) Hg22+
• Polyatomic Anions
– CO32-, HCO3-, SO42-, HSO4-, PO43-, HPO42-, H2PO4(carbonate, hydrogen carbonate, etc.)
– NO3- (nitrate), NO2- (nitrite),
ClO4- (perchlorate), ClO3- (chlorate), ClO2- (chlorite)
SO32- (sulfite)
– CrO42-, Cr2O72-, MnO4– OH-, CN-, SCN-, O22-
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Ionic Compounds
•
•
•
•
Can involve polyatomic ions
Na2CO3
Hg2I2
(NH4)3PO4
Names and Formulas
• Vocabulary of chemistry
• We deal with MANY compounds
• Need a standard method for representing them with
names and formulas
• Will look at
– Binary molecular compounds
– Ionic compounds
• Introduce organic compounds
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Naming: Binary Molecular Compounds
• First element: same name as element
• Second element: “ide” suffix
• Greek prefixes tell the number of atoms present
(Table 2.4)
– 1: mono
– 2: di
– 3: tri
–
4: tetra
5: penta
6: hexa
7: hepta
8: octa
9: nona
10: deca
• Examples:
– CO -- carbon monoxide
CO2 -- carbon dioxide
Naming: Binary Molecular Compounds
• Question: What are the names or formulas of these
compounds?
– NO2
– Carbon tetrachloride
– P2O5
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Ionic Compounds
• Ionic compounds are arrays of
positive and negative ions.
– Model of sodium chloride
• The formulas for ionic compounds always are
simplest formulas.
– Simplest formula: simplest whole-number ratio of
elements
– Sodium chloride: NaCl
Formulas of Ionic Compounds
• Most of Table 2.3
in picture at right
• Compounds are electrically
neutral
• Question: What is formula of a compound of sodium
and oxygen?
• Question: What is formula of aluminum oxide?
• Question: What is formula of potassium phosphate?
(PO43-)
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Naming Ionic Compounds
• Cation Names
• If only one ion possible (Group 1A, IIA, Al):
– Cation name = element name
– Na+ = sodium
Ca2+ = calcium
• More than one ion (transition metals):
– Use Stock notation
– Roman numeral for charge
– Cu+ = copper(I)
Cu2+ = copper(II)
Naming Ionic Compounds
• Anion names
– Add “ide” to stem of element’s name (Table 2.3 Chang)
– Cl- = chloride
– O2- = oxide
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Naming Ionic Compounds
• Question: What are the names or formulas of the
following compounds?
–
–
–
–
–
–
–
KCl
calcium bromide
FeCl2
ammonium nitrate
Co(MnO4)2
Lead (II) sulfate
Potassium hydride
• Potassium ion always +1
Naming
• Step 1: Decide if compound is molecular or ionic
• Step 2: Use conventions we have discussed
• Examples
–
–
–
–
–
Aluminum sulfate
BF3
K 2O
Carbon monoxide
NaSCN
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Naming Acids
• Binary Acids
– HCl (aq)
– HF (aq)
hydrochloric acid
hydrofluoric acid
• Oxoacids
–
–
–
–
H2SO4
HNO3
HClO3
H3PO4
sulfuric acid
nitric acid
chloric acid
phosphoric acid
Naming Acids
• Often more than one oxoacid for a given element.
• Start with “ic” acid, such as chloric acid, HClO3
–
–
–
–
One more O
per... ic
The “ic” acid is here
One less O
... ous
Two less O hypo ... ous
HClO4 perchloric acid
HClO3 chloric acid
HClO2 chlorous acid
HClO hypochlorous acid
• Note: “per” and “hypo” acids don’t always exist
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Naming Oxoacid Anions
• …ous acid
• … ic acid
anion = ... ite
anion = … ate
• Examples:
–
–
–
–
ClO3ClO2ClOClO4-
Chlorate
Chlorite
Hypochlorite
Perchlorate
(HClO3 = chloric acid)
(HClO2 = chlorous acid)
(HClO = hypochlorous acid)
(HClO4 = perchloric acid)
Hydrates
• Specific number of water molecules attached
• Use Greek prefixes to specify number of waters
• CuSO4·5H2O copper(II) sulfate pentahydrate
CuSO4·5H2O
CuSO4
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Organic Compounds
• This is an introduction. Naming organics can be
complicated
• Alkanes: straight-chain hydrocarbons (CnH2n+2)
– CH4
– C2H6
– C3H8
methane
ethane
propane
• More in table 2.8
• I will not cover hydrocarbon naming on the exam
Functional Groups
• Give organic compounds their “personality”
• Know the functional groups below
• -OH
alcohol
• -NH2
amine
organic base
• -COOH
carboxyl
organic acid
• Aldehyde
• Ketone
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Functional Groups
• Acetic acid
• Methyl amine
CH3COOH
CH3NH2
• Alanine CH3CH(NH2)COOH
(an amino acid)
DNA
• DNA strands held together by interactions of
functional groups
– Hydrogen bonding (Chpt 11)
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Solubility
• Functional groups help us understand the solubility
of organic compounds
– Compounds similar to water (H-O-H) tend to dissolve in
water
– Contain –OH or –NH bonds
• Which of the following would you predict to be
water-soluble?
–
–
–
CH3CH2OH
CH3CH2CH3
Drug Metabolism
• Caffeine metabolism occurs
in the liver.
– cytochrome P450 oxidase
enzyme
• Adding –NH groups makes
compound more water
soluble
• Excreted in urine
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