Chemical Building Blocks:Chemical Building Blocks: Atomic Theories, Models, and Atomic Theories, Models, and

Electronic StructureElectronic Structure

Outline1. A Brief History

Pre-atomic view of matter The Greek Idea Lavoisier: Conservation of Mass Proust: Definite Proportions Dalton: Atomic Theory

2. Electricity and the Atom3. X-rays and Radioactivity4. Atomic Models

Rutherford’s nuclear model Structure of the nucleus The Bohr model and electronic arrangement

5. The Quantum Model Electronic configuration Quantum numbers

Pre-Atomic View of MatterMatter was seen as

continuous, as the four Greek elements were.

No distinct divisions between fire, water, earth, air

Mixtures of the four gave the properties of being hot or cold, moist, or dry

EARLY THOUGHTS ON MATTER LEUCIPPUS: “There must

be tiny particles of water that could not be subdivided.” Observe the SAND.

DEMOCRITUS: Referred to these particles as atomos; Each atom was distinct in size and shape (eg. Water as round balls, Fire as sharp)

EARLY THOUGHTS ON MATTER

ARISTOTLE: Matter was continuous, not atomistic

Five centuries after, the Roman LUCRETIUS wrote a poem, “On the Nature of Things,” where strong arguments for the atomic nature were presented

Late 1600’s, ROBERT BOYLE publishes The Sceptical Chymist. Proper experimentation can show if theory is valid. Introduction of ELEMENT and COMPOUND

LAVOISIER: Conservation of Mass Antoine Laurent Lavoisier “When a chemical reaction is

carried out in a closed system, the total mass of the system is not changed.”

Red mercuric oxide Mercury + OXYGEN

1st to use systematic names; 1st chem bk. ; “father”

Experiments with burning coal (combustion), and breathing guinea pigs (respiration).

LAW: Matter is neither created nor destroyed in a chemical change. The total mass of the reaction products is always equal to the total mass of the reactants

We cannot create from nothing. Chemistry is about transformation.

Proust: Definite Proportions Joseph Louis Proust: Copper carbonate always had

the same composition LAW OF DEFINITE PROPORTIONS or CONSTANT

COMPOSITION: A compound always contains the same elements in certain definite proportions and in no other combinations.

J.J.Berzelius: Prepared an extensive list of atomic weights; Lead sulfide experiments

Henry Cavendish: 1783; Hydrogen gas + Oxygen gas Water

1800: Volta designed a powerful battery W.Nicholson and A.Carlisle would use to separate water into its elements.

Dalton: Law of Multiple Proportions Elements could

combine in in more than one set of proportions.

If elements A and B react to form two different compounds, the masses of B combined with a fixed mass of A, can be expressed as a ratio of small whole numbers

Dalton’s Atomic Theory1. Matter is composed of extremely small

particles called atoms.

2. All atoms of a given element are identical, having the same size, mass and chemical properties. The atoms of one element are different from the atoms of all other elements.

3. Compounds are composed of atoms of different elements combined in fixed proportions.

4. Chemical reactions only involve the rearrangement of atoms. Atoms are not created or destroyed in chemical reactions.

2

8 X2Y16 X 8 Y+

ELECTRICITY and the ATOM ELECTROLYSIS CATHODE RAY TUBES

William Crookes passed an electric current through a tube with air at low pressure. The tube has metal electrodes and the beam of current is seen as green fluorescence when it strikes the Zinc fluoride coated screen

J.J. Thomson, measured mass/charge of e-

(1906 Nobel Prize in Physics) 2.2

Thomson’s Experiment: M/C Were the rays beams of particles or did it

consist of energy, much like light? 1897: Joseph John Thomson Cathode rays are deflected in an electric

field. Attracted by POSITIVE, deflected by NEGATIVE.

Particles were the same regardless of the electrodes or gas.

What would he conclude, then?

Foundations of Atomic Theory

Law of Definite Proportions

The fact that a chemical compound contains the same elements in exactly the same proportions by mass regardless of the size of the sample or source of the compound.

Law of Multiple Proportions

If two or more different compounds are composed of the same two elements, then the ratio of the masses of the second element combined with a certain mass of the first elements is always a ratio of small whole numbers.

Law of Conservation of Mass

Mass is neither destroyed nor created during ordinary chemical reactions.

Law of Definite Proportions

+ +

Whether synthesized in the laboratory or obtained from

various natural sources, copper carbonate always has

the same composition.

Analysis of this compound led Proust to formulate

the law of definite proportions.

103 g ofcopper carbonate

53 g ofcopper

40 g of oxygen 10 g of carbon

Law of Multiple ProportionsJohn Dalton (1766 – 1844)

If two elements form more than one compound, the ratio of the second element that combines with 1 gram of the first element in each is a simple whole number.

e.g. H2O & H2O2

water hydrogen peroxideRatio of oxygen is 1:2 (an exact ratio)

Cathode Ray Tube

2.2

Plum-Pudding Model

Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 56

Thomson’s CalculationsCathode Ray Experiment

Thomson used magnetic and electric fields to measure and calculate the ratio of the cathode ray’s mass to its charge.

Magneticdeflection

charge ofray particle

magneticfield

length ofdeflection region

length of drift region

mass of rayparticle

velocity ofray particle

x x x

x=

Electricdeflection

charge ofray particle

electricfield

length ofdeflection region

length of drift region

mass of rayparticle

velocity ofray particle

x x x

x=

2

magnetic deflection

electric deflection

magnetic field

electric fieldx velocity=

ThomsonPAPER

e- charge = -1.60 x 10-19 C

Thomson’s charge/mass of e- = -1.76 x 108 C/g

e- mass = 9.10 x 10-28 g

Measured mass of e-

(1923 Nobel Prize in Physics)

ROENTGEN RAYS WILHELM CONRAD ROENTGEN

1895 Working in a darkroom on the glow

produced in certain substances by cathode rays

He noticed the glow also occurring on a chemically-treated piece of paper (even in next room). The “ray” could travel through walls!

When he waved his hand between the radiation source and the glowing paper, he could see the bones of his own hand on the paper.

X-RAYS

Discovery of Radioactivity ANTOINE HENRI BECQUEREL

1895 Studied fluorescence by

1. Wrap photographic film in black paper2. Place fluorescing crystals on top3. Place paper in strong sunlight

i. Like ordinary light: would not pass through paper

ii. Like X-rays: would pass and fog the film4. Work with URANIUM: always fogging the film!5. Perhaps, radiation coming from uranium was

unrelated to fluorescence but a characteristic of uranium.

MARIE SKLODOWSKA: coined the term “Radioactivity”: the spontaneous emission of radiation from certain unstable elements

The CURIES MARIE SKLODOWSKA

married PIERRE CURIE, a French Physicist and discover radioactive polonium and radium

1903 Nobel in Physics (Becquerel, Curie, Curie)

Marie Curie: 2nd Nobel prize in 1911

TYPES OF RADIOACTIVITY Three types of radiation emanated

from these radioactive elements, ERNEST RUTHERFORD, a New

Zealander, chose the names alpha, beta, and gamma for these. ALPHA: beams of positive particles

(identical to He2+ ions BETA: negatively-charged; identical to

cathode rays; therefore, an electron GAMMA: not deflected; penetrating; a

form of energy

(Uranium compound)

Health Effects of Ionizing Radiation

REM – roentgen equivalent manDegree of exposure

5-25:genetic damage. 50:alter white blood cells. 75-125: radiation

sickness.400: kill 50% of exposed

people500-600 :will kill almost

all exposed people.

How much time?

genetic damage in 18-90s

alteration of white blood cells in 3 minutes

radiation sickness in 5-8 minutes

death in 35-60 minutes.