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Atomic structure ch 4.notebook
October 16, 2012
Subatomic particles Protons= positive p+
Chapter 4 Atomic Structure
electrons= negative e­
Atom­­smallest particle of an element that retains the properties of the element
neutrons=neutral n0
Early atomic models
Relative masses­­see p 106
Democritus­­­­Greek Philosopher (460 BC­370 BC)
First suggested existence of atoms. Atomos = indivisible
Nucleus­­contains protons and neutrons
electrons­­ outside nucleus in electron cloud
Dalton's Atomic theory­­used experimental methods
1. All elements made of atoms
2. Atoms of same element are identical
3. Atoms of different elements can combine in whole number ratios to form compounds
4. Elements never change into different elements during a chemical reaction
Atomic number­­­number of protons in nucleus
each element has different atomic number
See periodic table
Hydrogen 1
Helium 2
Lithium 3
Oct 9­10:29 AM
Oct 9­10:36 AM
Protons= electrons in an atom
mass number = protons + neutrons
neutrons= mass number ­ atomic number
Written in shorthand: mass number as superscript
atomic number as subscript
197
How many protons, neutrons and electrons:
Be mass number =9
Neon mass number= 20
Au 1H H H
Isotope = same element with different number of neutrons
Sodium mass number = 23
Oct 9­10:42 AM
Oct 9­10:46 AM
p 113 19­20
p 112 #17­18
17. d. Br
a. O e. Pb
b. S
c. Ag
19. oxygen­16
oxygen­17
oxygen­18
20. chromium­50 atomic number=24
chromium­52
chromium­53
a. carbon­12
b. Fluorine­19
c. beryllium­9
Oct 9­10:48 AM
Oct 12­2:57 PM
1
Atomic structure ch 4.notebook
Atomic mass­­decimal number on periodic table
Calculated using the weighted average of all the isotopes of an element
see p 114 table
October 16, 2012
p 117
Example: Copper
2 isotopes: mass #1 = 62.93 amu abundance =69.2%
mass #2= 64.93 amu abundance= 39.8%
Atomic mass unit (amu) defined as 1/12 the mass of a carbon­12 atom.
Protons= 1 amu
neutrons = 1 amu
electrons = negligible (almost mass­less)
Oct 9­10:49 AM
Example Bromine:
2 isotopes mass#1= 78.92 amu, abundance=50.69%
mass #2 =80.92amu abundance= 49.31%
Oct 12­3:02 PM
Periodic Table
Groups­­vertical columns
Periods­­ horizontal rows
Valence electrons­­ outermost electrons used in bonding
Can tell how many by group on periodic table
H 1 valence electron
Be 2 B 3
C 4
N 5
O 6
F 7
Ne 8
****He only 2
Oct 9­10:52 AM
2
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