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Atomic Theory
Atoms are building blocks of elements
Similar atoms in each element
Different from atoms of other elements
Two or more different atoms bond in
simple ratios to form compoundsLecturePLUS Timberlake
Subatomic Particles
Particle Symbol Charge Relative
Mass
Electron e- 1- 0
Proton p+ + 1
Neutron n 0 1LecturePLUS Timberlake
Location of Subatomic Particles
10-13 cm
electrons
protons
neutrons
10-8 cmLecturePLUS Timberlake
nucleus
Periodic Table
Represents physical and chemical behavior of elements
Arranges elements by increasing atomic number
Repeats similar properties in columns known as chemical families or groups
LecturePLUS Timberlake
All atoms of an element have the same number of
protons
11
NaLecturePLUS Timberlake
11 protons
Sodium
Learning Check AT 1
State the number of protons for atoms of each of the following:
A. Nitrogen
1) 5 protons 2) 7 protons 3) 14 protons
B. Sulfur
1) 32 protons 2) 16 protons 3) 6 protons
C. Barium
1) 137 protons 2) 81 protons 3) 56 protons
LecturePLUS Timberlake
Solution AT 1
State the number of protons for atoms of each of the following:
A. Nitrogen
2) 7 protons
B. Sulfur
2) 16 protons
C. Barium
3) 56 protons LecturePLUS Timberlake
Number of Electrons
An atom is neutral
The net charge is zero
Number of protons = Number of electrons
Atomic number = Number of electrons
LecturePLUS Timberlake
Atomic Symbols
Show the mass number and atomic
number
Give the symbol of the element
mass number
23 Na sodium-23
atomic number 11 LecturePLUS Timberlake
More Atomic Symbols
16 31 65
O P Zn
8 15 30
8 p+ 15 p+ 30 p+
8 n 16 n 35 n
8 e- 15 e- 30 e-
LecturePLUS Timberlake
Isotopes
Atoms with the same number of protons, but different numbers of neutrons.
Atoms of the same element (same atomic number) with different mass numbers
Isotopes of chlorine
35Cl 37Cl17 17
chlorine - 35 chlorine - 37LecturePLUS Timberlake
Learning Check AT 2 Naturally occurring carbon consists of
three isotopes, 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of these carbon atoms.
12C 13C 14C 6 6 6
#P _______ _______ _______
#N _______ _______ _______
#E _______ _______ _______ LecturePLUS Timberlake
Solution AT 2
12C 13C 14C 6 6 6
#P __6___ _ 6___ ___6___
#N __6___ _ _7___ ___8___
#E __6___ _ 6___ ___6___
LecturePLUS Timberlake
Learning Check AT 3An atom of zinc has a mass number of 65.
A. Number of protons in the zinc atom
1) 30 2) 35 3) 65
B. Number of neutrons in the zinc atom
1) 30 2) 35 3) 65
C. What is the mass number of a zinc isotope
with 37 neutrons?
1) 37 2) 65 3) 67LecturePLUS Timberlake
Solution AT 3
An atom of zinc has a mass number of 65.
A. Number of protons in the zinc atom
1) 30
B. Number of neutrons in the zinc atom
2) 35
C. What is the mass number of a zinc isotope
with 37 neutrons?
3) 67LecturePLUS Timberlake
Learning Check AT 4
Write the atomic symbols for atoms with the following:
A. 8 p+, 8 n, 8 e- ___________
B. 17p+, 20n, 17e- ___________
C. 47p+, 60 n, 47 e- ___________
LecturePLUS Timberlake
Solution AT 4
16OA. 8 p+, 8 n, 8 e- 8
B. 17p+, 20n, 17e- 37Cl 17
C. 47p+, 60 n, 47 e- 107Ag 47
LecturePLUS Timberlake
Learning Check AT 5An atom has 14 protons and 20 neutrons.
A. Its atomic number is
1) 14 2) 16 3) 34
B. Its mass number is
1) 14 2) 16 3) 34
C. The element is
1) Si 2) Ca 3) Se
D. Another isotope of this element is
1) 34X 2) 34X 3) 36X
16 14 14
LecturePLUS Timberlake
Solution AT 5An atom has 14 protons and 20 neutrons.
A. It has atomic number
1) 14
B. It has a mass number of
3) 34
C. The element is
1) Si
D. Another isotope of this element would be
3) 36X
14 LecturePLUS Timberlake
Do Now
Complete Do Now Worksheet and please include the question below on to your worksheet.
What is an Isotope?
LecturePLUS Timberlake
Masses of Atoms
A scale designed for atoms gives their small atomic masses in atomic mass units (amu)
An atom of 12C was assigned an exact mass of 12.00 amu
Relative masses of all other atoms was determined by comparing each to the mass of 12C
An atom twice as heavy has a mass of 24.00 amu. An atom half as heavy is 6.00 amu.
LecturePLUS Timberlake
Atomic Mass
Listed on the periodic table
Gives the mass of “average” atom of each element compared to 12C
Average atom based on all the isotopes and their abundance %
Atomic mass is not a whole number
LecturePLUS Timberlake
Na22.99
Learning Check AT6
Using the periodic table, specify the atomic mass of each element (round to the tenths place):
A. calcium __________
B. aluminum __________
C. lead __________
D. barium __________
E. iron __________
LecturePLUS Timberlake
Solution AT6
Using the periodic table, specify the atomic mass of each element (round to the tenths place):
A. calcium _40.1 amu _
B. aluminum _27.0 amu _
C. lead _207.2 amu_
D. barium _137.3 amu_
E. iron _55.8 amu__
LecturePLUS Timberlake
Calculating Atomic Mass
Percent(%) abundance of isotopes
Mass of each isotope of that element
Weighted average =
mass isotope1(%) + mass isotope2(%) +
…
100 100
LecturePLUS Timberlake
Atomic Mass of Magnesium
Isotopes Mass of Isotope Abundance 24Mg = 24.0 amu 78.70%
25Mg = 25.0 amu 10.13%
26Mg = 26.0 amu 11.17%
Atomic mass (average mass) Mg = 24.3 amu
LecturePLUS Timberlake
Mg24.3
Learning Check AT7
Gallium is a metallic element found in small lasers used in compact disc players. In a sample of gallium, there is 60.2% of gallium-69 (68.9 amu) atoms and 39.8% of gallium-71 (70.9 amu) atoms. What is the atomic mass of gallium?
LecturePLUS Timberlake
AT 7Isotope Mas
s% Convert
PercentageMultiply
Mass with %
Mass by %
Gallium - 69
68.9
60.2%
60.2/100= .602
68.9 x .602=
41.5 amu
Gallium - 71
70.9
39.8%
39.8/100= .398
70.9 x .398=
28.2 amu
LecturePLUS Timberlake
Now we add the masses of both isotopes to get the Average Atomic Mass.
41.5 amu + 28.2 amu = 69.7 amu
Average Atomic Mass of Ga = 69.7 amu
Finding An Isotopic Mass
A sample of boron consists of 10B (mass 10.0 amu) and 11B (mass 11.0 amu). If the average atomic mass of B is 10.8 amu, what is the % abundance of each boron isotope?
LecturePLUS Timberlake
Assign X and Y values:
X = 10B =10 amu Y = 11B =11 amu
Determine Y in terms of X
X + Y = 100% or 1.0
In this case we will use 1.0 to represent 100%
X + Y = 1.0
Subtract X in order to solve for Y
Y = 1.0 - XLecturePLUS Timberlake
Now we will solve for X:
X + Y = 10.8 Average atomic mass of Boron
Insert the mass for X and Y
(10)X + (11) (1.0 – X) = 10.8
10X + 11 – 11X = 10.8
10X - 11X = 10.8 – 11
-1X = - .20 Multiply by -1 to get rid of the negative
X = .20
Multiply by 100% to get percentage
X = .20 x 100% = 20%LecturePLUS Timberlake
So if X = 20%
Then Y = 80%
How:
X + Y = 100%
Y = 100% - X
Y= 100% - 20%
Y = 80%
So Boron–10 = 20% and Boron-11= 80% LecturePLUS Timberlake
Learning Check AT8
Copper has two isotopes 63Cu (62.9 amu) and 65Cu (64.9 amu). What is the % abundance of each isotope? (Hint: Check periodic table for atomic mass)
LecturePLUS Timberlake
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