Download Atoms, Ions and Molecules The Building Blocks of Matter

1/10/2014
Atoms, Ions and Molecules
The Building Blocks of Matter
Chapter 2
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Chapter Outline
2.1
2.2
2.3
2.4
2.5
2.6
2.7
The Rutherford Model of Atomic Structure
Nuclides and Their Symbols
Navigating the Periodic Table
The Masses of Atoms, Ions, and Molecules
Moles and Molar Mass
Making Elements
Artificial Nuclides
Experiments in Atomic Structure
• J. J. Thompson (1906 Nobel Prize in Physics)
- cathode ray tube experiments; discovery of the
electron; measurement of the charge-to-mass
ratio.
• Robert Millikan (1923 Nobel Prize in Physics)
- oil-drop experiments; measured the mass of the
electron, therefore calculate the charge
• Ernest Rutherford (1908 Nobel Prize in Physics)
- gold-foil experiments; the nuclear atom
• James Chadwick (1935 Nobel Prize in Physics)
- discovery of the neutron
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J.J. Thomson Cathode Ray Tube
Experiments - Electrons
Results of “Cathode Ray” Experiments
•
•
•
•
Travel in straight lines
invisible
independent of cathode composition
bend in a magnetic field like a
negatively-charged particle would
• charge/mass = -1.76 x 108 C/g
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Thompson’s “Plum Pudding” Model of the Atom
electrons distributed throughout a diffuse, positively charged sphere.
Robert Millikan’s oil drop Experiment measured the mass of the electron
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Millikan’s Results
• The air molecules in the chamber were ionized by a beam of X-rays,
producing electrons and positively-charged fragments
• Fine mist of oil introduced into chamber; electrons adhere to the
droplets
• Negatively-charged droplets settle to bottom of chamber under
influence of gravity
• Charged repeller plates adjusted until droplets were suspended in
mid-air
• From the physics and knowledge of the size of the gravitational and
electrostatic forces, the charge on each droplet could be calculated
• Discovered that each droplet was a whole-number multiple of 1.60 X
10-19 C, so the mass = 9.11 X 10-28 g
Radioactivity and the Nuclear Atom
Spontaneous emission of particles and/or radiation from a
decaying, unstable nucleus
-particles =
-particles =
-rays =
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Ernest Rutherford - the nuclear atom
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Rutherford's Observations
b) Expected results from “plum
pudding” model.
c) Actual results.
1. the majority of particles penetrated undeflected
2. some particles were deflected at small angles
3. occasionally -particles scattered back at large angles
Rutherford’s Conclusions
• The atom is mainly empty space
because most of the -particles passed
through undeflected
• The nucleus is very dense and
positively charged because some of the
-particles were repulsed and deflected
• Electrons occupy the space around the
nucleus
• The atom is electrically neutral
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Rutherford’s Model of the Atom
atomic radius ~ 100 pm = 1 x 10-10 m
nuclear radius ~ 5 x 10-3 pm = 5 x 10-15 m
If the nucleus was the size of an orange, then the radius of the atom would
be 2.5 miles
mass p  mass n = 1840 x mass e-
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Chapter Outline
2.1
2.2
2.3
2.4
2.5
2.6
2.7
The Rutherford Model of Atomic Structure
Nuclides and Their Symbols
Navigating the Periodic Table
The Masses of Atoms, Ions, and Molecules
Moles and Molar Mass
Making Elements
Artificial Nuclides
Atomic Mass Units
• Atomic Mass Units (amu)
• Comprise a relative scale to express the
masses of atoms and subatomic particles.
• Scale is based on the mass of 1 atom
of carbon:
» 6 protons + 6 neutrons = 12 amu.
• 1 amu = 1 Dalton (Da)
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Isotopes: Experimental Evidence
Atomic number (Z) = number of protons in nucleus
Mass number (A) = number of protons + number of neutrons
= atomic number (Z) + number of neutrons
Isotopes (nuclides) are atoms of the same element (X) with
different numbers of neutrons in the nucleus
Mass Number
Atomic Number
A
ZX
Element Symbol
1
1H
2
1H
235
92
U
(D)
3
1H
238
92
(T)
U
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Practice: Isotopic Symbols
• Use the format AX to write the symbol for the nuclides having 28 protons and 31 neutrons.
• Collect and Organize:
• Analyze:
• Solve:
• Think about It:
Practice: Identifying Atoms and Ions
• Complete the missing information in the table.
• Collect and Organize:
• Analyze:
• Solve:
• Think about It:
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Chapter Outline
2.1
2.2
2.3
2.4
2.5
2.6
2.7
The Rutherford Model of Atomic Structure
Nuclides and Their Symbols
Navigating the Periodic Table
The Masses of Atoms, Ions, and Molecules
Moles and Molar Mass
Making Elements
Artificial Nuclides
The Periodic Table of the Elements
Mendeleev’s Periodic Table
Dmitrii Mendeleev (1872):
• Ordered elements
by atomic mass.
• Arranged elements in
columns based on similar
chemical and physical
properties.
• Left open spaces in the
table for elements not yet
discovered.
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The Modern Periodic Table
• Also based on a classification of elements in
terms of their physical and chemical
properties.
• Horizontal rows: called periods (1 → 7).
• Columns: contain elements of the same
family or group (1 →18).
• Several groups have names as well as
numbers.
Navigating the Modern Periodic Table –
Groups and Families
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Groups of Elements (cont.)
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These 7 elements occur naturally as diatomics (memorize) -
H2
N2
F2
O2
I2
Cl2
Br2
Metals
• found to the left of the “diagonal
line”
• lose electrons in chemical
reactions
• solids (except for Hg, Cs, and Fr)
• conduct electricity
• ductile (draw into a wire)
• malleable (roll into sheets)
• form alloys ("solid-solution" of
one metal in another)
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Nonmetals
• found to the right of the “diagonal line”
• like to gain electrons from metals, or
share electrons among themselves
• found as solids, liquids (Br), and gases
(Inert gases, H, N, O, F, Cl)
• “diatomics” - H2, N2, F2, O2 ,I2, Cl2, Br2
• oxygen also exist as ozone, O3
• insulators (except for graphite or C)
Helium-Neon lasers
Metalloids
• elements next to the
“diagonal line”
• B, Si, Ge, As, Sb, and Te
• physical properties of a
metal (can be “convinced”
to conduct electricity) and
chemical properties of a
nonmetal
Elemental Si is used in
the semiconductor
industry
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