ATOMIC THEORY

Honors Chemistry

Chapters 3 & 4

Topics of Discussion• Summarize the Development of Atomic

Theory

• Examine Atomic Structure

Laws• Law of Conservation of Mass

• Law of Definite Proportions

• Law of Multiple Proportions

Laws

• Law of Conservation of MassMass is neither Destroyed nor Created during ordinary Chemical or Physical Reactions

Laws

• Law of Definite ProportionsA Chemical compound contains the same

elements

in exactly the same proportions, by Mass,

regardless of size of sample or source of compound

Laws

• Law of Multiple ProportionsIf 2 or more different compounds are composed

of the Same 2 Elements, then the ratio of the 2nd. element combined

with the a certain mass of the 1st. element is always

a ratio of small whole numbers

Development of Atomic Theory

• Democritus– Believed that matter was made up of atoms– Atoms were invisible particles– Atoms were indestructible particles– Lost out to Aristotle who stated that matter was

continuous

Development of Atomic Theory

• Dalton (1808)

• Explains the Laws of conservation of mass, definite proportion and multiple proportion– Elements are composed of extremely small

particles called atoms– Atoms of the same element are identical in size

mass and properties. Atoms of different elements differ in size. Mass and properties

Development of Atomic Theory

• Dalton (1808) cont.– Atoms cannot be subdivided, created, or

destroyed.– Atoms of different elements combine in simple

whole-number ratos to form chemical compounds

– In chemical reactions , atoms are combined, separated or rearranged

Development of Atomic Theory

• J.J. Thomson (1897)

• Discovers the electron – (mass and a high charge)

• Proposes the “Plum-Pudding“ model– Atom is neutral– Electrons embedded in a sphere of positive

charge

Development of Atomic Theory

• Rutherford (1911)

• Gold foil experiment

• Discovers that the atom has a nucleus– Extremely small– Extremely dense– Positive charge

• Electrons move around the nucleus

Gold Foil Experiment

Development of Atomic Theory

• Bohr (1913)• Electrons circle nucleus in specific circular

paths at fixed distances from the nucleus• Each electron orbit has a Specific Energy or

energy level• A Quantum of energy is required to move

from one orbit to the next• Works for Hydrogen only!

Development of Atomic Theory

• Millikan discovers electron charge and Mass of an electron (1909)

• Chadwick discovers Neutron (1932)

• De Broglie proposes particle wave behavior of Electron (1923)

• Schrödinger writes an equation to determine probability of electron location

Development of Atomic Theory

• Electron Cloud Model (present)

• Based on Schrödinger's wave equation

• Visual model of the probable locations of the electron in an atom

Development of Atomic Theory

Atomic Structure• Properties of sub-atomic particles

(proton, neutron, & electron)– Charge – Location in Atom

• Symbols

• A(mass number) & Z (atomic number)

Atomic Structure

• PROTON– Location

– Charge

– Symbol

Center of atom; nucleus area

Positive

p

ATOMIC NUMBER (Z) = number of protons in the atom

Atomic Structure

• Neutron– Location

– Charge

– Symbol

Center of atom; nucleus area

No charge (0)

n

To find the number of neutrons in an atom:

Mass number of the element – number of protons (atomic number) = A (number of neutrons

Atomic Structure

• Electron– Location

– Charge

– Symbol

In shells around the nucleus of the atom.

Negative

e

In a neutral atom, # of electrons = # of protons

Atomic Structure

Element-A # p+ #n0 #e-

Beryllium-9

Oxygen-16

Sulfur-32

4 5 4

8 8 8

16 16 16

Atomic Structure

• IONS

• Ions are charged particles.

• Atoms gain or lose ELECTRONS are ions.

• Lose e- --- more positive --- positive charge

• Gain e- --- more negative ---negative charge

• Na lose 1e- = Na1+ (11+ + 10- = 1+)

Atomic Structure

ION # p+ #e-

Cl1-

Mg2+

Fe3+

17 18

12 10

26 23

Atomic Structure

• Isotopes are:– Atoms of the same element – That have different masses

• Naturally occur or man made

Atomic Structure

• Practice:• 1. Element D has 6 protons and 7 neutrons.• Element F has 7 protons and 7 neutrons.• 2. Element J has 27 protons and 32 neutrons.• Element L has 27 protons and 33 neutrons.• 3. Element X has 17 protons and 18 neutrons.• Element Y has 18 protons and 17 neutrons.• 4. Element Q has 56 protons and 81 neutrons.• Element R has 56 protons and 82 neutrons.

Atomic Mass

• Average Atomic Mass– Weighted average– Of all naturally occurring isotopes

• This is the mass on the Periodic Table

• This is the mass we use for calculations

• Can you calculate a weighted average?

Atomic Mass

ISOTOPE % in Nature MASS

• Copper-63 69.17% 62.929599 amu

• Copper-65 30.83% 65.927793 amu

100.00%

Atomic Mass

ISOTOPE % in Nature MASS

Carbon-12 98.89% 12.000 amu

Carbon-13 1.11% 13.003 amu

100.00%