Download Chapter 5 Atomic Structure and the Periodic Table Early

Chapter 5
Atomic Structure and the Periodic Table
Early Models of the Atom
Democritus who lived in Greece in the fourth century B.C. was the first to suggest that matter is composed
of tiny fundamental particles called __________________. He believed that atoms were ...
There was no scientific testing at this time.
John Dalton(1766-1844) An English schoolteacher who experimented and developed his atomic theory.
Dalton studied...
Dalton formulated hypotheses and theories to explain his observations.
Dalton’s atomic theory.
1.
2.
3.
4.
“All atoms are identical.” True or false?
“Chemical reactions occur when atoms of one element change into atoms of
another element.” True or false?
Just How Small is an Atom?
Figure 5.2
1.0 x 107 atoms of copper(Cu) laid side by side would stretch one centimeter.
An atom is the ...
Concept Practice page 129 # 33
Structure of the nuclear atom
Section 5.2
Electrons
Much of Dalton’s atomic theory is widely accepted today. However, one important change emerged in
regards to indivisibility.
Electrons:
Thomson built a cathode ray tube. He observed that the electrified gas in the tube was attracted to a metal plate that
had a positive charge and was repelled from the plate that had a negative charge. Figure 5.4
Robert A Millikan(1868-1953) was able to find the quantity of charge carried by an electron. He also calculated
the ratio of the charge to the mass of an electron.(1916) An electron carries one unit of negative charge and its
mass is 1/1840 the mass of a hydrogen atom.
Protons and Neutrons
Cathode rays are streams of electrons. What remains of an atom after the electrons have been removed?
E. Goldstein(1886) observed rays traveling in an opposite direction to the cathode rays. He called these rays
“canal rays” and concluded that they were composed of positive particles.
These positive particles are called --------------.
James Chadwick(1891-1974) confirmed the existence of the neutron. A subatomic particle with no charge but the
mass nearly equal to the proton. Table 5.1 page 111
The Atomic Nucleus
With the discovery of subatomic particles came the question of how they were assembled into atoms. In
1911 Ernest Rutherford and his colleagues used alpha particles(helium atoms with no electrons) shot at a gold foil.
Most of the particles passed through the foil undeflected. Several others however, were deflected. Rutherford
concluded that most of the space taken up by atoms is empty. The mass and positive charge is housed in the atoms
nucleus. Figure 5.6
Section Review page 112 # 4, 5, 6. Chapter review page 129 34, 35, 36,37,
Section 5.3
Distinguishing Between Atoms
Atomic Number
Table 5.2 page 113
• Elements are different because they contain different numbers of protons.
• The atomic number of an element represents the number of protons in the atoms nucleus.
• The atomic number identifies the element.
• The number of protons is equal to the number of electrons thus atoms are electrically neutral.
• Practice problem CHEMath page 114,
7 and 8 page 115
Mass Number
The mass of an atom is concentrated in the nucleus and depends on the number of protons and neutrons.
The total number of protons and neutrons in an atom is called the mass number.
If you know the atomic number and the mass number of any atom you can determine the atom’s
composition.
mass number - atomic number = number of neutrons
Figure 5.8 shows how the element gold(Au) is represented.
How many electrons does gold have?
Practice problems 9-11 page 116
Isotopes
Iso means......
Atoms that have the same number of protons and electrons but different numbers of neutrons are called
isotopes.
Despite this difference in the number of neutrons, the isotopes are chemically alike because it is the protons
and electrons which are responsible for chemical behavior.
Hydrogen-1 has one proton and no neutrons.
Hydrogen-2 has one proton and one neutron and is called deuterium
Hydrogen-3 has one protons and two neutrons and is called tritium.
Practice problems 12 , 13 page 117
Atomic Mass
Atomic masses are very small (arsenic : 1.244 x 10-22g) Not wanting to work with large negative
exponents, a comparative rate was developed. The standard comparison was the isotope carbon-12. It represents
12 atomic mass units or amu .
Carbon-12 has 12 protons and 12 neutrons and its atomic mass is 12 amu.
The atomic mass of an element is a weighted average mass of the atoms in a naturally occurring sample of
the element.
Practice problems 14 and 15 page 120 and 16 and 17 page 121
Section review page 121 #’s 18, 19, 20, 21, 22, 23, 24,
Chapter review page 129 #’s 38, 39, 40, 41, 42, 43, 44, 45, 46,
Small Scale Lab page 122