CHAPTER 5 OUTLINE
ATOMIC STRUCTURE AND THE PERIODIC TABLE
I. Atoms
A. Early Models of the Atom
1. Democritus Abdera (4 B.C.)
a. Matter is composed of particles called "atoms"
2. John Dalton (app. 1800)
a. Dalton's atomic theory
1. All elements are composed of tiny invisible & indivisible particles called atoms
2. Atoms of the same element are identical and different from all other elements
3. Atoms can physically mix or chemically combine in simple whole number ratios
4. Chemical reactions occur when atoms are separated, joined, or rearranged
B. Just How Small is an Atom?
1. Atom -- smallest part on an element that still has the properties of the element
a. One copper penny has 2.4 X 1022 atoms
b. "Seen" with a scanning tunneling microscope (electron microscope)
II. Structure of the Nuclear Atom (subatomic particles)
A. Electrons
1. Negatively charged particles
2. Discovered by J. J. Thomson in 1897
a. Cathode Ray Tube experiment
b. Found that cathode rays were attracted to a positively charged metal plate
1. Rays must be negatively charged particles
3. Amount of charge and mass determined by Robert A. Millikan in 1916
a. Charge = -1
b. Mass = 1/1840 of one Hydrogen atom
B. Protons and Neutrons
1. Protons - Positively charged particles
a. Discovered by E. Goldstein in 1886
b. Charge = +1
c. Mass = 1840 times mass of electron (mass of Hydrogen atom)
2. Neutron - Neutrally charged particles
a. Discovered by James Chadwick in 1932
b. Charge = 0
c. Mass = same as Proton
Particle Symbol Relative Electrical Relative Mass Actual Mass
Charge (g)
Electron e- -1 1/1840 9.11 X 10-28
Proton p+ +1 1 1.67 X 10-24
Neutron n 0 1 1.67 X 10-24
C. The Atomic Nucleus
1. Ernest Rutherford's gold foil experiment in 1911
a. Atoms are mostly empty space with a dense, tiny center with all the positive charge
2. Nucleus -- central core with all protons and neutrons
a. If atom is size of a football stadium, then the nucleus would a marble on the 50-yard line
III. Distinguishing Between Atoms
A. Atomic number -- number of protons in the nucleus
1. Used to distinguish atoms and elements
2. # protons = # electrons since atoms are electrically neutral
B. Mass number -- number of protons and neutrons
1. # neutrons = mass number - number of protons (atomic number)
2. Shorthand notation -- symbol, atomic number (subscript in front), mass number (superscript in front)
3. Designate atoms (Helium-4)
C. Isotopes -- atoms with same number of protons, but different numbers of neutrons (different mass #)
1. Same chemical properties (based on p+ and e-)
Ex. -- Hydrogen, Deuterium, Tritium
Hydrogen-1, Hydrogen-2, Hydrogen-3
1 proton each
0 neutron, 1 neutron, 2 neutrons respectively
D. Atomic mass
1. Mass of atoms are too small to really be useful
2. Developed amu
a. Atomic Mass Unit (amu) -- 1/12th the mass of Carbon-12 (reference isotope)
b. 1 proton = 1 amu = 1 neutron
3. Elements are found naturally as mixtures of their different isotopes
a. Atomic mass is based on the abundance (%) of each isotope
4. Atomic Mass -- weighted average mass of all the atoms for a given element
IV. The Periodic Table: Organizing the Elements
A. Development of the Periodic Table
1. 70 elements discovered in mid-1800's
2. Dmitri Mendeleev listed elements in order of atomic mass, then grouped them by similar properties
a. Left spaces for missing unknown elements
3. Periodic Table -- an arrangement of the elements according to similarities in their properties
4. 1913, Henry Moseley determined the atomic number of elements
a. Arranged elements by atomic #
b. Modern periodic table
B. The Modern Periodic Table
1. 114 elements known
2. Arranged by increasing atomic # from left to right
3. Periods -- horizontal rows
a. 7 in the table
b. Properties vary as you move through a period, but repeat in the next period
c. Periodic Law -- when elements are arranged by atomic #, there is a periodic repetition in their physical and chemical properties
1. Elements in the same column have similar properties
4. Group/Families -- vertical columns
a. Alkali Metals - group 1A (1)
b. Alkaline Earth Metals - group 2A (2)
c. Transition Metals - groups 3B - 2B (3-12)
d. Inner Transition Metals - Lanthanide and Actinide Series
e. Other Metals - groups 3A - 6A (13-16) (below staircase line)
f. Nonmetals - groups 3A - 6A (13-16) (above staircase line)
g. Halogens - group 7A (17)
h. Noble gases - group 8A (0 or 18)
5. Two categories of the table
a. Metals - left of the staircase line
b. Nonmetals - right of the staircase line
c. Metalloids - on or below the staircase line
1. Have both metal and nonmetal properties
Outline based upon:
Matta, M. S., Staley, D. D., Waterman, E. L., & Wilbraham, A. C. (2000). Chemistry, Addison-Wesley. (5th ed.). Menlo Park, CA: Prentice Hall, pp. 107-126
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