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