chapter 4 atomic structure. defining the atom early models of the atom democritus – greek...
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Chapter 4
Atomic Structure
Defining the Atom
• Early Models of the Atom
• Democritus – Greek philosopher suggested the existence of the atom around 400 BC– Atoms are _____________________– Idea lacked ______________ support– Idea challenged by ________________
• Dalton – early 1800’s (2000 yrs. after Democritus)– Used experiments (Scientific Method)– Studied the nature of atoms & ratios in which
elements combine in chemical reactions– Dalton’s Atomic Theory: page 102
1 - All elements are composed of _____________________________________
4.1
• 2 - Atoms of the same element are _________. The atoms of any one element are ___________ from those of any other element.
4.1
• 3 - Atoms of different elements can _________mix together or can _______________________________________.
4.1
• 4 - Chemical reactions occur when atoms are _________________________. Atoms of one element are _____________________________________in a chemical reaction.
4.1
• Atoms are defined today as _____________________________________
• Atoms today are observable with scanning tunneling microscope
• Dalton’s work stimulated much scientific research into the structure of the atom
• Page 103, Section assessment # 1 to 7, skip 6
• READ pages 104, 105 summarize JJ Thomson’s use of cathode ray tube
Structure of the Nuclear Atom
• Subatomic Particles
• Electrons– JJ Thomson used cathode ray tube to
discover ___________, 1897– Figures 4.4, 4.5– Concluded that electrons must be parts of
atoms of all elements– Millikan – electron ___________________
• Protons – E Goldstein used cathode ray tube and found
rays traveling in opposite direction to cathode ray, 1886
– Concluded that rays were made of ____________________
– Protons have mass __________________
• Neutrons– _______________ confirmed the existence of
neutrons, 1932– Particle with ____ charge, mass equal to
___________
• Table 4.1 – Properties of Subatomic Particles
Subatomic Particles
• Table 4.1 summarizes the properties of electrons, protons, and neutrons.
4.2
• The Atomic Nucleus
• Scientists tried to answer the question, How are subatomic particles put together in the atom?
• JJ Thomson – the ‘plum pudding’ model:
The Atomic Nucleus
– Rutherford’s Gold-Foil Experiment• In 1911, Rutherford and his coworkers at the
University of Manchester, England, directed a narrow beam of alpha particles at a very thin sheet of gold foil.
4.2
• E Rutherford – student of Thomson– Gold foil experiment – figure 4.7– In the plum pudding model, alpha particles
should pass through the foil with slight deflections caused by the positive charge spread throughout the gold atoms
– Results showed that ____________________________________
• Rutherford’s new theory: – atom is mostly _______________– Positive charge is concentrated in small
region – ____________– Nuclear atom – small nucleus with protons
and neutrons; electrons occupy most of the volume
• Page 108, Section Assessment, # 8 -14
• Page 110, Vocabulary
Distinguishing Among Atoms
• Atomic Number– # of _____________– Identifies an atom– All atoms are neutral, therefore,
______________________________
– Table 4.2– Page 111, Practice Problems #15, 16
Atomic Number4.3
• Mass Number– Total # of ________ + _____________– # neutrons = ______ # - _________ #– Atomic notation
• 2 forms, page 111, last sentence
• Page 112, Sample Problem 4.1, Practice Problems # 17 & 18
Mass Number
• Au is the chemical symbol for gold.
4.3
for Sample Problem 4.1
• Isotopes– Same #______ but different # ________,
therefore, different ________ #– Figure 4.9– Isotopes of Hydrogen: page 113
• Page 113, Conceptual Problem 4.2, Practice Problems # 19 & 20
• Atomic Mass– Amu – atomic mass unit, unit that measures
mass of atoms and subatomic particles– 1 amu = 1/12 mass of carbon-12 ( mass of
carbon-12 is assigned to be 12 amu– Proton mass = neutron mass = 1 amu =
1.67 x 10-24 grams
– Electron mass = 9.11 x 10-28 grams– Most elements occur as a mixture of 2 or
more isotopes– Atomic mass is a weighted average atomic
mass that reflects both the mass and ___________________ of each isotope
– Table 4.3
– Calculate average atomic mass:• Mass of each isotope x % abundance• Add products
• Page 115, Sample Problem
• Periodic Table– Arrangement of elements based on
_________________________– Arranged in order of increasing atomic
______________– Period – horizontal row – properties vary as
you move across the period, and repeat in each row
– Group – vertical column – elements in groups have similar chemical and physical properties
• Page 119, Section Assessment, # 25 – 33
• Chapter 4 Assessment– Page 122-123, #34-73, skip 38,62,67,68– Page 124, #74, 79, 80
• Standardized Test Prep page 125, # 1 - 9
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