1. ATOMIC STRUCTURE & PERIODIC TABLE
CHAPTER 5
ATOMIC STRUCTURE
& PERIODIC TABLE

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

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

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

5. 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

6. 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

7. 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

8. 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

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

10. CATHODE RAY TUBE

11. 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

12. DEFLECTION of CATHODE RAY

13. 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

14. 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

15. 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

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

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

18. 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

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

20. 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.

21. 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

22. 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

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

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

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

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

27. 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

28. 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.

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

30. 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.

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

32. 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.

33. 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.

34. 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.

35. 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

36. 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

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

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

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

40. THE MODERN PERIODIC TABLE
NON-METALS
HALOGENS
NOBLE GASES

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