Early Atomic Theories History Theories Scientists Models

What’s inside the box? How can you determine the identity of the items in the boxes?

Early History Democritus (Greek) –world is made up of:: empty space tiny particles (atomos) Aristotle (Greek) –world is composed of continuous matter (hyle) accepted until 17 th Century

John Dalton agreed with Newton and Boyle –atoms were the basis (no proof) English studied Lavoisier and Proust (both were French)

Lavoisier Chemical change in a closed system has equal mass before and after the change, matter is neither created nor destroyed –Law of Conservation of Mass

Proust Law of Definite Proportions –Specific substances always contain elements in the same ratio by mass example: H 2 O has a ratio of 1:8 (H:O)

Dalton’s Law Law of Multiple Proportions –certain elements can combine to form two or more different chemical compounds Hydrogen and Oxygen can to form water (1:8) and peroxide (1:16)

Dalton’s Atomic Theory All matter is composed of extremely small particles called atoms. Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties. (*) Atoms cannot be subdivided, created, or destroyed. (*)

Atomic Theory con’t Atoms of different elements can combine in simple, whole-number ratios to form chemical compounds. In chemical reactions, atoms are combined, separated, or rearranged.

What does the * mean? These tennets are no longer true today! –#2 because of isotopes –#3 because of subatomic particles

~1832: FARADAY:  PROPOSED EXISTANCE OF ELECTRON  PROPOSED ELECTRICITY WAS CARRIED BY CHARGED ATOMS ----IONS ~1879: CROOKES: INVENTED GAS DISCHARGE TUBE (CRT) RAY FROM - “POLE” (CATHODE) TO + “POLE (ANODE) 1895: ROENTGEN: CRT HIT TARGET, GET LOWER ENERGY EMISSIONS ---- X-RAYS 1896: BEQUEREL: DISCOVERED RADIOACTIVITY! 1897: JJ THOMPSON USED CRT AND EXPLORED NATURE OF THESE “RAYS”

Subatomic Particles: Electron J. J. Thomson (Eng) –cathode ray tube experiment proved that the atom is divisible –cathode (negative electrode) –anode (positive electrode)

ZnS - + NO CHARGE ON PLATES RAY DEFLECTED BY ELECTRIC & MAGNETIC FIELD NOT LIGHT; THEREFORE, PARTICLES 2. DEFLECTION TOWARD POSITIVE PLATE PARTICLES NEGATIVELY CHARGED 3. LARGE DEFLECTION DETERMINED CHARGE/MASS (q/m) RATIO q/m < 1/1000 THE MASS OF HYDROGEN ATOM!!!!

THOMPSON: “FOUND” FARADAY’S ELECTRON DETERMINED THE ATOM WAS NOT THE SMALLEST PARTICLE 1909: MILLIKEN DETERMINED THE EXACT CHARGE AND MASS OF THIS ELECTRON ALL DATA INTEGRAL VALUES OF SAME NUMBER q = -1.6 x C m = 9.1 x kg ABOUT 1/1800th OF THE HYDROGEN ATOM TODAY: x C x kg

Subatomic Particles: Electron Robert Milliken (USA) –Oil Drop Experiment first to measure the mass of an electron –9.109 x g first to measure the charge of an electron –(-1)

Subatomic Particles: The Nucleons What is a nucleon? –A nucleon is a particle that is found within the nucleus of an atom. What are the major nucleons? –Proton and the Neutron

Ernest Rutherford (New Zealand) Gold Foil Experiment –hit a thin piece of gold foil with a beam of alpha radiation (positively charged) some of the beam went through uninerrupted some of the beam was deflected to the side or totally reflected

RUTHERFORD’S “GOLD FOIL” EXPERIMENT ZnS COATED SCREEN GOLD FOIL STREAM OF  (ALPHA) PARTICLES 1. MOST PASS THRU UNDEFLECTED MOST OF ATOM VOLUME IS EMPTY SPACE 2. SOME POSITIVE  PARTICLES DEFLECTED SLIGHTLY NEAR COLLISIONS WITH MASSIVE, POSITIVELY CHARGED PARTICLE 3. 1 OF DEFLECT ACUTELY CROSS SECTION OF MASSIVE, POSITIVELY CHARGED PARTICLE IS 1/20000 th THAT OF ATOM RUTHERFORD FOUND THE NUCLEUS!!!

Rutherford’s Results Since the positively charged radiation was repelled in certain areas, there was evidence for a positive entity inside of the foil –Proton This led to the idea of a central core that is very dense (nucleus) Since some of the radiation passes through unharmed the foil must not be totally positive

ATOM MUST BE A VERY DENSE, POSTIVELY CHARGED NULCLEUS SURROUNDED BY VERY LIGHT, NEGATIVELY CHARGED ELECTRONS QUANDRY: HEAVY PROTON (+ CHARGE) IN NUCLEUS LIGHT ELECTRONS ON OUTSIDE COMBINED, ACCOUNT FOR ~ 1/2 THE ATOMIC MASS AND THE ATOM IS NEUTRAL! 1932: CHADWICK ISOLATED THE NEUTRON IN NUCLEUS O CHARGE MASS ~ SAME AS PROTON

Chadwick If the nucleus is the home of the majority of the mass, and the atom is electrically neutral there must be a neutral particle with a mass: neutron

Comparison of the Major Nucleons Proton –+1 Charge –Mass:1.673 x g –number of protons must equal the number of electrons for the atom to be neutral –p+–p+ Neutron –No charge –Mass:1.675 x g –no–no

What holds it all together? nuclear force holds the particles together in the nucleus

What are isotopes? Isotopes are atoms of the same element that have different masses (different numbers of neutrons).

What do the numbers mean? Atomic Number –Z–Z –number of protons Mass Number –A–A –number of protons plus the number of neutrons

Where do you find the numbers? Using the periodic table locate the symbol for the element that you are looking for. Inside the element’s square will be the numbers.

Writing Nuclides X Copper Oxygen Silver

The Isotopes of Hydrogen

How many electrons, protons, and neutrons are found in a copper atom of mass # 65? Z = protons therefore protons = 29 Protons = Electrons therefore electrons = 29 A - Z = neutrons so = 36, there are 36 neutrons Now try Oxygen and Calcium:

Ions Ions have charge due to an imbalance in the number of protons and electrons. Atoms can either gain or lose electrons. If they gain electrons the ion is negative, where is they lose electrons the charge is positive.

Try these: O 2- Ca 2+

Isotopes of Beanium Lab Purpose: to determine the average atomic mass of a new element called Beanium Beanium has 3 isotopes: white, brown, and speckled

If you are given a sample of Beanium, what do you need to know in order to calculate the average atomic mass. REMEMBER, that means the average mass of all three isotopes! Number of each type, mass of each type, and then total to get the average mass per atom (bean)

Data Table for Beanium Lab Type of Isotope Mass of Isotope (g) Number of Isotope Average Mass of Isotope % of Each Present White Brown Speckled Total100