ATOMIC STRUCTURE & PERIODIC TABLE CHAPTER 5 ATOMIC STRUCTURE & PERIODIC TABLE

ATOMIC STRUCTURE DEMOCRITUS ATOMIST SCHOOL of THOUGHT TEACHER, 4th Century BC ATOMIST SCHOOL of THOUGHT

ATOMIC STRUCTURE MATTER ATOMS TINY PARTCLES CALLED ATOMS FUNDAMENTAL UNITS OF MATTER INVISIBLE INDESTRUCTABLE

ATOMIC STRUCTURE JOHN DALTON (1766-1844) ENGLISH SCHOOL TEACHER STUDIED ELEMENTAL RATIOS IN CHEMICAL REACTIONS DALTON’S ATOMIC THEORY

ATOMIC STRUCTURE DALTON’S ATOMIC THEORY ELEMENTS ARE COMPOSED OF SUBMICROSCOPIC INDIVISIBLE PARTICLES – ATOMS ATOMS OF THE SAME ELEMENT ARE IDENTICAL ATOMS OF ANY 1 ELEMENT ARE DIFFERENT FROM ATOMS OF ANY OTHER ELEMENT

ATOMIC STRUCTURE DALTON’S ATOMIC THEORY ATOMS OF DIFFERENT ELEMENTS CAN MIX TOGETHER or CHEMICALLY COMBINE TO FORM COMPOUNDS IN SIMPLE WHOLE NUMBER RATIOS CHEMICAL REACTIONS OCCUR WHEN ATOMS ARE SEPARATED, JOINED OR REARRANGED

ATOMIC STRUCTURE DALTON’S ATOMIC THEORY ATOMS OF ONE ELEMENT ARE NEVER CHANGED INTO ATOMS OF ANTOHER ELEMENT AS A RESULT OF A CHEMICAL REACTION TODAY, MUCH OF THEORY STILL VALID EXCEPT THAT ATOMS ARE NOT INDIVISIBLE

THE ATOM SMALLEST PARTICLE OF AN ELEMENT THAT RETAINS THE ELEMENT’S PROPERTIES THE ATOM’S SIZE IF YOU PLACED 100,000,000 COPPER ATOMS SIDE BY SIDE, THE LINE WOULD BE 1 cm LONG

J. J. THOMSON ENGLISH PHYSICIST 1897 – DISCOVERED ELECTRONS NEGATIVELY CHARGE SUBATOMIC PARTICLES EXPERIMENTS USED FLOW OF ELECTRIC CURRENT THROUGH GASES

CATHODE RAY TUBE

CATHODE RAY TUBE CATHODE RAYS WERE ATTRACTED TO POSITIVELY CHARGED METAL PLATES NEGATIVELY CHARGED PLATES REPELLED THE RAY IF LIKE CHARGES REPEL AND OPPOSITE CHARGES ATTRACT, RAY IS MADE UP OF NEGATIVE CHARGED PARTICLES, i.e. ELECTRONS

DEFLECTION of CATHODE RAY

CATHODE RAY CATHODE RAY PRODUCTION WAS INDEPENDENT OF TYPE OF GAS ELECTRON PARTICLES WERE PART OF EVERY ATOM DETERMINED ELECTRON MASS WAS 1/2000 THE MASS OF A HYDROGEN ATOM

MATTER AND ELECTRIC CHARGE ATOMS HAVE NO NET CHARGE CHARGES ARE CARRIED BY PARTICLES OF MATTER CHARGES ALWAYS EXIST IN WHOLE NUMBER MULTIPLES OF A SINGLE BASIC UNIT WHEN AN EQUAL NUMBER OF NEGATIVE CHARGES COMBINE WITH AN EQUAL NUMBER OF POSITIVE CHARGES, THE PARTICLE HAS NO NET CHARGE

PROTONS A POSITIVELY CHARGED PARTICLE MUST BE PRESENT TO BALANCE EACH NEGATIVELY CHARGED ELECTRON EVIDENCE OF THESE PARTICLES WERE PRESENTED BY E. GOLDSTEIN IN 1886 OBSERVED A RAY TRAVELING IN THE OPPOSITE DIRECTION OF THE CATHODE RAY – CANAL RAY CANAL RAY MADE UP OF POSITIVE PARTICLES - PROTONS

THE NEUTRON IN 1932, JAMES CHADWICK (English physicist 1891-1974) CONFIRMED THE EXISTENCE OF ANOTHER SUB-ATOMIC PARTICLE – NEUTRON NEUTRONS HAVE MASS SIMILAR TO PROTONS, BUT NO CHARGE

THE ATOMIC NUCLEUS BECAUSE OF SMALL SIZE, ATOM WAS DIFICULT TO STUDY ORIGINALLY BELIEVED THAT POSITIOVE AND NEGATIVE CHARGES WERE DISTRIBUTED EVENLY THROUGHOUT ATOM

THE ATOMIC NUCLEUS ERNEST RUTHERFORD (1871-1937) University of Manchester, England TESTED THEORY OF ATOMIC STRUCTURE BOMBARDED GOLD FOIL WITH ALPHA PARTICLE BEAM IF POSITIVE CHARGE EVENLY SPREAD IN ATOM, BEAM SHOULD PASS THROUGH

RUTHERFORD’S EXPERIMENT Rutherford and coworkers aimed a beam of alpha particles at a sheet of gold foil surrounded by a florescent screen.

RUTHERFORD’S EXPERIMENT Most particles passed through with no deflection, while some were highly deflected Rutherford concluded that most particles passed through because the atom is mostly empty space.

RUTHERFORD’S EXPERIMENT CONCLUDED THAT ALL OF POSITIVE CHARGE AND MOST OF ATOM’S MASS ARE CONCENTRATED IN A SMALL CORE THIS REGION WOULD HAVE A POSITIVE CHARGE CAPABLE OF DEFLECTING BEAM THIS REGION WAS CALLED THE NUCLEUS

DISTINGUISHING ATOMS ATOMIC NUMBER UNIQUE FOR EACH ELEMENT EQUALS THE NUMBER OF PROTONS IN THE ELEMENT’S ATOM NUMBER OF PROTONS MUST EQUAL NUMBER OF ELECTRONS FOR NEUTRAL ATOM

DISTINGUISHING ATOMS ATOMIC MASS NUMBER MASS IS CONCENTRATED IN THE NUCLEUS DEPENDS ON THE NUMBER OF PROTONS & NEUTRONS

DISTINGUISHING ATOMS Element Symbol Atomic # Mass # # of Neutrons Nitrogen-15 Neon-22 Beryllium-9

DISTINGUISHING ATOMS ISOTOPES CHEMICALLY ALIKE EQUAL NUMBER OF PROTONS & ELECTRONS DIFFERENT NUMBER OF NEUTRONS DIFFERENT MASS NUMBER CHEMICALLY ALIKE

DISTINGUISHING ATOMS Atomic Mass Mass of proton or neutron is small (1.67 x 10-24 g) Mass of electron is negligible in comparison (9.11 x 10-28 g) The mass of even the largest atom is incredibly small

DISTINGUISHING ATOMS Compare relative mass using a reference isotope as a standard Isotope C-12 assigned a mass of 12 amu Atomic mass unit (amu) defined as one-twelfth the mass of carbon-12

DISTINGUISHING ATOMS If atomic mass is determined by the number of protons and electrons, why isn’t the mass of an element a whole number? Most elements occur as a mixture of two or more isotopes.

DISTINGUISHING ATOMS The atomic mass of an element is a weighted average mass of the atoms in a naturally occurring sample of the element.

DISTINGUISHING ATOMS You can calculate the atomic mass if you know three values: The number of stable isotopes of the element. The mass of each isotope. The natural percent abundance of each isotope.

MASS DEFECT Calculate the mass defect of a chlorine-35 atom. The actual mass of chlorine-35 is 5.81 x 10-23 grams e = 9.11 x 10-28 g p = 1.67 x 10-24 g n = 1.67 x 10-24 g

THE PERIODIC TABLE Dmitri Mendeleev (1834-1907) Russian chemist Listed elements in columns in order of increasing atomic mass. Arranged columns so that elements with similar properties were side by side.

THE PERIODIC TABLE Medeleev left blank spaces where there were no known elements with the appropriate properties or mass. Predicted the properties of the missing elements.

THE PERIODIC TABLE Henry Mosely (1887-1915) British Physicist Determined the atomic number of the atoms of the elements. Arranged elements in table by atomic number instead of mass.

THE MODERN PERIODIC TABLE Each horizontal row is a period Seven periods From 2 to 32 elements in a period Properties of the elements change as you move across a period. This pattern repeats from period to period The Periodic Law

THE MODERN PERIODIC TABLE Each column is a group or family Elements in a group have similar physical and chemical properties Groups are identified by a number and the letter A or B Group A are the representative elements Group A can be divided into three broad classes

THE MODERN PERIODIC TABLE METALS HIGH ELECTRICAL CONDUCTIVITY HIGH LUSTER DUCTILE MALLEABLE

THE MODERN PERIODIC TABLE METALS ALKALI METALS ALKALINE EARTH METALS TRANSITION METALS INNER TRANSITION METALS

THE MODERN PERIODIC TABLE NON-METALS POOR ELECTRICAL CONDUCTIVITY NON-LUSTRIOUS

THE MODERN PERIODIC TABLE NON-METALS HALOGENS NOBLE GASES

THE MODERN PERIODIC TABLE METALLOIDS Elements with properties that are intermediate between those of metals and non-metals.