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