chapter 2: atoms, molecules, and ions the atomic theory of matter democritus (460-371 bc): matter...
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Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
The Atomic Theory of Matter
Democritus (460-371 BC):
• matter consists of atomswhich are solid particles(a-tomos = un-cuttable)
• Democritus' ideas were ignored for the next 2000 years
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
The Atomic Theory of Matter
John Dalton (1766-1844): •Elements are made of tiny particles called atoms
• atoms of different elementscan combine to form compounds
• atoms are not created nor destroyed in chemical processes
• all atoms of one element are identical
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
The Atomic Theory of Matter
Dalton’s Atomic Theory explained..
… The Law of Constant Composition
… The Law of Conservation of Mass
… The Law of Multiple Proportions
[in one compound, number and kind of atoms is constant]
[total mass before reaction = total mass after reaction]
[If two elements form more than one compound, the ratios of the masses of the second element which combine with a fixed mass of the first element will be ratios of small whole numbers]
The Law of Multiple Proportions:
12 g carbon + 16 g oxygen => CO
12 g carbon + 32 g oxygen => CO2
32 g : 16 g = 2 : 1
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
The Atomic Theory of Matter
HW: 8
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
The Discovery of Atomic Structure
J.J. Thomson (1856-1940): • discovered the electron
• electron: negatively chargedparticles of very small mass
• atoms of all elements containelectrons
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Cathode Ray Tube_
+
e-
HV
chargemass
= 1.76×108 coulombsg
e-
Determination of charge to mass ratio:
The Discovery of Atomic Structure
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
J.J Thomson's originalCathode Ray Tube
The Discovery of Atomic Structure
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
R. Millikan (1868-1953):
• measured electron charge
electron charge = 1.60×10−19 C
The Discovery of Atomic Structure
electron mass = 1.60×10−19 C
1.76×108C / g= 9.10×1028 g
-
HW: 14a,b
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Electrons are negatively charged but atoms as a whole are neutral.
+
Rutherford's Model:
"smeared-out" positive charge
J.J. Thomson's Model: “Plum Pudding Model”
The Discovery of Atomic Structure
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
The Discovery of Atomic Structure
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
+
Rutherford's Model:
The Discovery of Atomic Structure
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Ernest Rutherford (1871-1937):
• Rutherford concluded that
(a) the atom has a positive charge concentrated in the nucleus
(b) the electrons orbit around the positive nucleus
(c) that the atom is mostly emptyspace
The Discovery of Atomic Structure
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
More evidence for atomic substructure:• some substances spontaneously break down intosmaller particles (radioactivity)
• -particles (heavy, +2 charge)• -particles (small mass, -1 charge)• -rays (electromagnetic radiation => no mass, no charge)
The Discovery of Atomic Structure
HW: 12
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
The nucleus is structured:
PROTONS: positively charged (+1)
NEUTRONS: no charge
The Modern View of Atomic Structure
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
The mass of an atom is concentrated in its nucleus:
•proton: 1 atomic mass unit (1amu) +1
•neutron: 1 amu 0
•electron: negligible mass -1 (5.486 x 10-4 amu) (1.6 x 10-19C)
MASS Charge
The Modern View of Atomic Structure
1 amu = 1.66054 x 10-24 g
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Elements differ in their number of protons:
Hydrogen:1 proton
H1
the atomic number counts the number of protons
1
the mass number counts protons and neutrons
Helium:2 protons
2 neutrons
He
Lithium:3 protons
4 neutrons
Li
Beryllium:4 protons
5 neutrons
Be
The Modern View of Atomic Structure
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
The Modern View of Atomic Structure
How about the neutrons?
• an element is defined by the number of protons
• atoms of one element can exist in different 'versions' :
all atoms must still have the same number of protons
but they may have a different number of neutrons
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
The Modern View of Atomic Structure
H1
1H3
1H2
1
Hydrogen or Protium
Deuterium Tritium
Isotopes of an element:
same number of protons but different number of neutrons
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Average Atomic Mass = Atomic Weight
Average Mass = fraction of heavy x mass of heavy + fraction of light x mass of light
= 3/4 x 70amu + 1/4 x 30amu
= 0.75 x 70amu + 0.25 x 30amu = 60amu75% 25%
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Average Atomic Mass = Atomic Weight
Si naturally occurs in three isotopes:
92.2% of 28Si (27.98 amu)4.7%of 29Si (28.98 amu)3.1%of 30Si (29.97 amu)
what is the atomic weight of Si?
HW: 33a
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Periodic Table
● Elements are sorted according to atomic number
C6
12.01
Atomic Number
Atomic weight
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Hydrogen:1 proton
H11
Helium:2 protons
2 neutrons
He24
Lithium:3 protons
4 neutrons
Li37
Beryllium:4 protons
5 neutrons
Be49
How can you tell how many electrons an element has?
HW: 23
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Periodic Table
● Elements with similar properties fall in vertical groups
● A row in the periodic table is called a period
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Periodic Table
● Most elements are metals
Alkali Metals
Alkaline Earth Metals
Noble Gases
Halogens
I A II A
III A IV A VA VI A VIIA
VIII A
Transition metals
HW: 37
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Molecules and Molecular Compounds
● Some elements exist as diatomic molecules at room temp.
H2 N
2 O
2 F
2 Cl
2Br
2 I
2
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Molecules and Molecular Compounds
The periodic table helps predict how elements combine
Empirical Formulas Molecular Formulas
● Only gives relative number of atoms in compound
● Subscripts are smallestwhole-number ratios
● Show actual number and types of atoms in a molecule
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Hydrogen peroxide
Empirical Formulas Molecular Formulas
H2O
2
Butane
C4H
10
Propane
C3H
8
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Drawing Molecules: methane
Space-filling model
Ball-and-Stick model
Structural formula
Perspectivedrawing
HW: 45
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Ions and Ionic Compounds
Ions are formed when a neutral atom
- gains electrons or- loses electrons
Li Li+
e-
Cation
BrBr
-Anion
e-
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
● Metals tend to form Cations
Which Elements form Anions, which Cations?
● Nonmetals tend to form Anions
Alkali Metals
Alkaline Earth Metals
Noble Gases
Halogens
I A II A
III A IV A VA VI A VIIA
VIII A
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
How can you tell how many electrons an element will gain/lose?
NOBLE GASES
● Atoms tend to gain/lose the number of electrons neededto achieve the electron configuration of the closest noble gas
X1
NbX
2
X3
Na
Nc
Nd
Ne
Nf
X4
● Metals tend to form Cations● Nonmetals tend to form Anions
HW: 49,50
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Li Li+
e-
Cation
BrBr
-Anion
Cations and Anions can combine to from Ionic Compounds
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Cations and Anions can combine to from Ionic Compounds
Ionic Crystal – not a discrete molecule
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Empirical Formulas for Ionic Compounds:
(A) determine charge of ions formed
(B) add ions so that compound is neutral overall
Na, O =>
Na2O
Al, O =>
Al2O
3
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
LiBr
MgCl2
Li, Br => Mg, Cl =>
HW: 51,53
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Empirical Formulas for Ionic Compounds:
Mg2+ MgCl
2
Al O3+ 2-Al
2O
3
O 2-
Ca2+
CaO
Cl-1
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Naming Ionic Compounds: cations come first
(Ia) Monoatomic Cations:
● Metal cations keep the name of the element:
Na+ sodium ion Li+ Lithium ion Zn2+ Zinc ion
● If a metal can form different kinds of cations (transition metals),the charge is indicated by a Roman Numeral:
Fe2+ Iron(II) ionFe3+ Iron(III) ionCo2+ Cobalt(II) ion
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Naming Ionic Compounds
(Ib) Cations formed from Nonmetals:
● end in -ium:
NH4+ ammonium ion H
3O+ Hydronium ion
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Naming Ionic Compounds
(IIa) Monoatomic and Simple Polyatomic Anions
● Are derived from the element name by replacing the ending with -ide
N3- Nitride ion
O2- Oxide ion CN-
OH- Hydroxide ion
Cyanide ion
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Naming Ionic Compounds
(IIb) Oxyanions (polyatomic anions containing oxygen)
● The most common oxyanion of an element ends in -ate● One more oxygen: per-.....-ate● One fewer oxygen: -ite● Two fewer oxygen: hypo-.....-ite
Chlorate ClO3-
Perchlorate ClO4-
Chlorite ClO2-
Hypochlorite ClO-
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Naming Ionic Compounds
(IIb) Oxyanions (polyatomic anions containing oxygen)
● The most common oxyanion of an element ends in -ate● One more oxygen: per-.....-ate● One fewer oxygen: -ite● Two fewer oxygen: hypo-.....-ite
Sulfate SO42-
Sulfite SO32-
Hyposulfite SO22-
[ Persulfate SO52-, S
2O
82-
]
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Naming Ionic Compounds
Common Oxyanions:
SulfateSO
42-
Phosphate PO
43-
ChlorateClO
3-
BromateBrO
3-
IodateIO
3-
Nitrate NO
3-
Carbonate CO
32-
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Naming Ionic Compounds
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Naming Ionic Compounds
You must know these!
HCO3
-Hydrogen carbonate ionor Bicarbonate ion
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Naming Ionic Compounds: chemical formula → name
Identify the ions
Cation Anion
Transition metal ?Element name
Element name and charge in
Roman numerals
Group 1A, 2A, 3A metal?
Nonmetal ion?
-ide
monoatomic orsimple polyatomic
anion? oxyanion?
per ... ate... ate... ite
hypo ... itee.g. Ammonium
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Naming Ionic Compounds: chemical formula → name
MgSO4
FeCl3
NaClO
NH4OH
HW: 60,96
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Naming Ionic Compounds: name → chemical formula
Fe(II) chloride
Potassium cyanide
Magnesium hydroxide
Sodium sulfite
HW: 61
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Naming Molecular Compounds
ClO2
does not dissociate into ions!
Metal cations + Nonmetal anions => ionic compoundsNonmetal cations + Nonmetal anions => ionic compounds(e.g. NH
4+)
Nonmetal + Nonmetal => molecular compounds
Before you start naming, determine what kind of compound you have!
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Naming Binary Molecular Compounds
ClO2
● Name of the element farther to the left in the P.T. comes first- except oxygen, which is usually named last
● If both element are from the same group, the heavier one is named first
● The second element is given an -ide ending
● Greek prefixes indicate number of atoms of each element involved
Chlorine dioxide
[mono-, di-, tri-, tetra-, penta-, hexa-, hepta-, octa-, nona- , deca-]
[mono-prefix is never used with 1st element]
Chapter 2: Atoms, Molecules, and IonsChapter 2: Atoms, Molecules, and Ions
Naming Compounds
NiO 1) Ionic or molecular?
2 a) Ionic: what are the ions? b) molecular: how many atoms?
SO
KMnO4
BF3