Early Atomic Theory Atoms, Molecules, and Ions Preparation for College Chemistry Luis Avila Columbia...
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Transcript of Early Atomic Theory Atoms, Molecules, and Ions Preparation for College Chemistry Luis Avila Columbia...
Early Atomic Theory
Atoms, Molecules, and Ions
Preparation for College ChemistryLuis AvilaColumbia UniversityDepartment of Chemistry
Atoms
Isotopes
Atomic theory
Components of the Atom
Atomic Number
Mass Number
•Nature consists solely of an infinite number of indivisible particles, having shape, size, impenetrability, and no further properties. These particles move through an otherwise empty space.
440 BC
LEUCIPUS of Miletus and his disciple DEMOCRITUS of Abdera:
470 BC
PLATO and ARISTOTLE reinforces:
•Matter is composed of four elements: EARTH, AIR, WATER, FIRE
384 - 270 BC
EMPEDOCLES: •Matter is composed of four elements: EARTH, AIR, WATER, FIRE
•The shape, size, location, and movement of these particles make up literally all of the qualities, relations, and other features of the natural world.
Atomic Theory. Early Thoughts
1500’s
FRANCIS BACON:
1500’s
ROBERT BOYLE and ISAAC NEWTON:
•Used atomic concepts to interpret physical phenomena.
17th Century
GALILEO GALILEI:
•Appearance of a new substance through chemical change involves rearrangement of parts too small to be seen.
•Heat might be a form of motion of small particles.
Dalton’s Model of the Atom
1. Elements consist of tiny particles called atoms.
2. Atoms of the same element are alike in mass and size.
3. Atoms of different elements differ in mass and size.
4. Chemical compounds form by the union of two or more atoms of different elements.
5. Atoms combine to form compounds in simple numerical ratios, such as 1:2, 2:3, etc.
6. Atoms of two elements may combine in different ratios to form more than one compound.
1803 - 1810
Consequences of Dalton’s Law
The Law of conservation of Mass:
The Law of Constant Composition:
The Law of Multiple Proportions:
“There is no detectable change in mass in an ordinary chemical rxn.”
“A compound always contains the same elements in the same proportions by mass.”
“The masses of one element that combine with a fixed mass of the second element are in a ratio of small whole numbers.”
Composition of Compounds
Percent H
Percent O
Atomic Composition
WaterHydrogen Peroxide
11.2
88.8
5.9
94.1
2H + 1O 2H + 2 O
A compound always contains two or more elements combinedin a definite proportion by mass.
Atoms of two or more elements may combine in different ratiosto produce more than one compound.
Careful experimentation lead Proust to demonstrate
H2 + Cl22HCl
H2SO4 + 2NaCl 2HCl + Na2SO4
Proportions by mass of elementsin a compound VARY OVER A CERTAIN RANGE
Proportions by mass of elements in a compound ARE FIXED. VARIATIONS ARE DUE TO IMPURITIES.
Claude Berthollet: Joseph Proust:
THE LAW OF DEFINITE PROPORTIONS (CONSTANT COMPOSITION):
“The proportions by mass of the elements in a compound ARE FIXED, and do not depend on its mode of preparation.”
Wüstite, an iron oxide whose simplest formula is FeO, with 77.73%Fe.
All gaseous compounds OBEY THE LAW OF DEFINITE PROPORTIONS.
Certain SOLIDS are exceptions of the Law of Constant Composition: NON STOICHIOMETRIC COMPOUNDS (BERTHOLLIDES)
Its composition truly ranges from Fe0.95O (76.8% Fe) to
Fe0.85O (74.8% Fe) depending of the method of
preparation.
The composition of a compound is shown by its CHEMICAL FORMULA.
C + O2 A
C + O2 B
CHEMICAL ANALYSIS:
If A is CO then B = CO2
For a FIXED mass of C the ratio of O in A and B is:
If A is CO2 then B is C2O4
Let’s take the elements C and O:
(1.000 g C and 1.333 g O)
(1.000 g C and 2.667 g O)
1.333 : 2.667 or 1: 2
We are unable to say which one is the right formula, but we know the ratio C : O
is the QUOTIENT OF INTEGERS.
As + S A
As + S B
0.4820.642
= 2 : 3
If A is As2S2 then B = As2S3
CHEMICAL ANALYSIS:For Arsenic and Sulfur:
(1.000 g As and 0.482 g S)
(1.000 g As and 0.642 g S)
For a FIXED mass of As the ratio of S in A and B is:
Certain substances when dissolved in water can conduct an electric current.
ANIONS: NEGATIVE IONS that “travel to the ANODE (positive electrode).
There must be some FUNDAMENTAL unit of electricity associatedwith atoms: ELECTRON.
MICHAEL FARADAY:
SVANTE ARRHENIUS:
Water is not necessary IONIC SUBSTANCES conduct electricity when melted.
CATIONS: POSITIVE IONS, they “travel” to the CATHODE (negative electrode)
G. J. STONEY:1891
1887
1830’s
Cathode rays are ELECTRONS (e-) particles with a negative charge.
1897
The first sub-atomic particle
J.J Thomson Discovered the Electron
1913
ERNEST RUTHERFORD and HANS GEIGER with the apparatus for counting alpha particles
Manchester, 1912
"It was as though you had fired a fifteen-inch shell at a piece of tissue paper and it had bounced back and
hit you."
The Nuclear Atom
The Nuclear Atom
np
Electron region
Nucleus
Arrangement of Subatomic Particles
Particle Location Relative Charge Relative Mass (amu)
proton Nucleus +1 1.00728
neutron Nucleus 0 1.00867
electron Outside nucleus
-1 0.00055
Properties of Subatomic Particles
Atomic Number, Z
Equals number of protons in nucleus
Equals number of electrons in neutral atom
Characteristic of a particular element
Location of the element in the Periodic Chart
Mass Number, A
A = number of protons + number of neutrons
Atoms of the same element can differ in mass number
Isotope # Protons # Neutrons Z A Symbol
Carbon-12 6 6 6 12
Carbon-14 6 8 6 14
€
612C
€
614C
11H 1
2H13H
ZAENuclei Representation
A - Z = number of neutrons
For light (Z < 20) isotopes the stable ratio is 1.0; with heavier isotopes it increases to 1.5. There are no stable isotopes for elements of Z > 83 (Bi).
Too heavyemission
Precise determination of the masses of individual atoms
Meaning of Atomic Masses• Give relative masses of atoms based on C–12 scale. • The Most common isotope of carbon is assigned an atomic mass of 12 amu.• The amu is defined as 1/12 of the mass of one neutral carbon atom
1amu=1dalton=112
12g612C
mol612C
×1mol6
12C6.0221×1023atoms6
12C
⎛
⎝ ⎜ ⎞
⎠ ⎟=1.66054 ×10−24 g/ atom6
12C
A nickel atom is 58.69 / 40.08 = 1.464 times as heavy as a calcium ion
It is 58.69 / 10.81 = 5.29 times as heavy as a boron ion
element B Ca Niatomic mass 10.81 amu 40.08 amu 59.61 amu
Meaning of Atomic Masses
Isotope Atomic Mass PercentNe-20 20.00 amu 90.92Ne-21 21.00 amu 0.26Ne-22 22.00 amu 8.82
Isotope Atomic Mass PercentNe-20 20.00 amu 90.92Ne-21 21.00 amu 0.26Ne-22 22.00 amu 8.82
A.M.=(A.M.isotope1 ×%
100+A.M.isotope2 ×
%100
+...A.M.=(A.M.isotope1 ×%
100+A.M.isotope2 ×
%100
+...
Atomic Mass from Isotopic Composition
Atomic Mass from Isotopic Composition
20.00 (0.9092) +21.00 (0.0026)22.00 (0.0882)
20.18 amu
A.M. Ne = 20.18g/mol
SystemOrgan Tissue
Macromolecule
CellOrganelle
Protons
Neutrons
Atom
Levels of Organization
Organism
Object
Leptons
Quarks,... http://www.rhic.bnl.gov/
Molecule
Electrons
Molecules
Types of Formulas
Composition
Composition
Usually made up of nonmetal atoms
Held together by covalent bonds
Types of Formulas
Empirical
Molecular
Structural
CH3
C2H6
C
H
H
CH
H
H
H
Ions
Formation of Monatomic Ions
Charges of Monatomic Ions
Polyatomic Ions
Formulas
Formation of Monatomic Ions
Na atom (11p+,11e -)
F atom (9p+,9e -) + e -
Nucleus remains unchanged
Na+ ion (11p+,10e -) + e -
F - ion (9p+,10e -)
Polyatomic Ions
Names and formulas
General structure
Polyatomic Ions
Ammonium
O22-Mercury(I)
C2H3O2 -
Cations
NH4+
Anions
MnO4-
Hg2+2
Permanganate
Peroxide
Acetate
per- Hal -ate Hal -ate Hal -ite hypo-Hal -ite
XO4-
The prefixes and suffixes used to name oxyanions are related to the valence of the element contained in the formula
Ammonium hypochlorite
XO3- XO2
- XO-
Ex:
NH4ClO
Iron(III) periodate Fe(IO4)3
Mercury(I) iodite (Hg2)(IO2)2
Mercury(II) bromate Hg(BrO3)2
Potassium Permanganate
Potassium Manganate
KMnO4
KMnO3
Writing Ionic Compound Formulas
Apply principle of electrical neutrality
Anion peroxide oxide dichromate
Cation HCO3- O2
2- O2- Cr2O72-
AmmoniumNH4
+NH4HCO3 (NH4)2O2 (NH4)2O (NH4)2Cr2O7
Mercury(I)Hg2
2+Hg2(HCO3) 2 Hg2O2 Hg2O Hg2Cr2O7
SodiumNa+
NaHCO3 Na2O2 Na2O Na2Cr2O7
CalciumCa2+
Ca(HCO3) 2 CaO2 CaO Ca Cr2O7
Anion peroxide oxide dichromate
Cation HCO3- O2
2- O2- Cr2O72-
AmmoniumNH4
+NH4HCO3 (NH4)2O2 (NH4)2O (NH4)2Cr2O7
Mercury(I)Hg2
2+Hg2(HCO3) 2 Hg2O2 Hg2O Hg2Cr2O7
SodiumNa+
NaHCO3 Na2O2 Na2O Na2Cr2O7
CalciumCa2+
Ca(HCO3) 2 CaO2 CaO Ca Cr2O7
Ionic
Name cation followed by anion
For transition metals cations the charge is indicated by Roman numeral when using the Stock system
Na2SO4 sodium sulfate
Fe(NO3)3 iron (III) nitrate
NH4Br ammonium bromide
Binary Molecular Compounds
Use of Greek prefixes
SF6 sodium hexafluoride
N2O3 dinitrogen trioxide
H2O dihydrogen monoxide
Acids
• Binary Acids:–hydrochloric acid
• Oxoacids:–ate salt ic acid
• Examples:–HClO4 hyperchloric acid
–Ca(ClO4)2 calcium perchlorate
Binary Compounds
Metal/nonmetal
Metal withone type of cation
Hydrogen/nonmetalTwo nonmetals
Metal withvarying type
of cations
1. name metal2. name nonmetal
Determine chargeof cation
1. use roman numeral2. stem name of nonmetal, -ide
1. choose appropriate-ous or -ic endingon metal2. stem name ofmetal -ide
in water not in water
1. Hydrogen2. Name nonmetal
1. prefix hydro--suffix -ic
2. add word acid
prefix that indicate # atomsfor ea. element
Usually end in -ide