A Review of Early Atomic Models, Periodic Table Development, and Nomenclature Atoms, Molecules & Ions
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 17th 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: H2O 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
PROPOSED EXISTANCE OF ELECTRON • PROPOSED ELECTRICITY WAS CARRIED • BY CHARGED ATOMS ----IONS ~1832: FARADAY: ~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 THOMSON 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 - + - + 1. 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!!!!
1.60219 x 10-19 C 9.10940 x 10-31 kg TODAY: “FOUND” FARADAY’S ELECTRON THOMSON: 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 10-19 C m = 9.1 x 10-31 kg ABOUT 1/1800th OF THE HYDROGEN ATOM
Subatomic Particles: Electron • Robert Millikan (USA) • Oil Drop Experiment • first to measure the mass of an electron • 9.109 x 10-28g • 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
ZnS COATED SCREEN STREAM OF a (ALPHA) PARTICLES GOLD FOIL 1911 -- RUTHERFORD’S “GOLD FOIL” EXPERIMENT 1. MOST PASS THRU UNDEFLECTED MOST OF ATOM VOLUME IS EMPTY SPACE 2. SOME POSITIVE a PARTICLES DEFLECTED SLIGHTLY NEAR COLLISIONS WITH MASSIVE, POSITIVELY CHARGED PARTICLE 3. 1 OF 20000 DEFLECT ACUTELY CROSS SECTION OF MASSIVE, POSITIVELY CHARGED PARTICLE IS 1/20000th 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 HEAVY PROTON (+ CHARGE) IN NUCLEUS QUANDRY: 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
Proton +1 Charge Mass:1.673 x 10-24g number of protons must equal the number of electrons for the atom to be neutral p+ Neutron No charge Mass:1.675 x 10-24g no Comparison of the Major Nucleons
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).
Atomic Number Z number of protons Mass Number A number of protons plus the number of neutrons What do the numbers mean?
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
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 65 - 29 = 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 (anion), where is they lose electrons the charge is positive (cation).
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: black, black-eyed pea, and speckled bean.
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)
Mass Spectrometer • A gaseous sample is introduced into the spectrometer and then it is bombarded by a stream of high-energy electrons. • Collisions between the electrons and the sample produce cations (usually 1+) • The positive beam passes through magnetic poles and bends, the more massive the sample the less the bend of the ray
Metals • Loose electrons (oxidation) to form ions that are positively charged (cations) • Good conductors (allow energy to flow through them) of heat and electricity • Have 3 or less valence electrons
Non-metals • Gain electrons (reduction) in order to form negatively charged ions (anions) • Good insulators (don’t allow heat or electricity to flow through them) • 4 or more valence electrons
Metalloids • Found on the periodic table along the “staircase” • Have properties of both metals and non-metals depending upon the particular situation • Also called the semi-metals
Molecules • An assembly of two or more atoms tightly bound together • Represented by a chemical formula (written as a collection of element symbols and subscripts to indicate the # of each element)
Monatomic vs. Diatomic • Some elements exist in nature as pairs of atoms: diatomic “H and the 7” • N O F • Br • Cl • I
Empirical Formula • Simplest, true formula of a compound • C2H8 can be simplified to CH4
Molecular Formula • The TRUE formula for the ratio of elements in a compound