Download Atoms

Bell Work
Compare and contrast the Bohr
model and the Quantum
Mechanical Model.
http://www.youtube.com/watch?v=vUzTQWn-wfE&list=PL701F0464C7551022
Sticky Note Matching Game
• Each one of you has been given an index card with a name, facts,
or diagram. Now you have to find the name, facts and diagrams
that match (not every name has a diagram).
• The Catch: you can only use ‘yes’ or ‘no’ questions to try to find
the matches.
• When you find all the matches, read over the cards and prepare a
1-3 minute explanation.
The Subatomic Particles and
the Structure of the Atom
Distinguishing Among Atoms
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Structure
Atomic/ Mass Number
Isotopes
Atomic mass
•The atomic number is the number of protons in an
atom.
•This number is unique for all elements and is used to
identify each element.
•Atoms are electrically neutral therefore:
# PROTONS = # ELECTRONS.
Mass Number is the total number of protons
and neutrons in an atom
Average
Mass number = # protons + # neutrons
Atomic number = # protons = # electrons
Mass number – Atomic number = # neutrons
10 protons
10 neutrons
10 electrons
10 protons
11 neutrons
10 electrons
10 protons
12 neutrons
10 electrons
•Isotopes are atoms of the same element
that differ in the number of neutrons.
Isotopes of the same element have the
same chemical properties, because they
have the same number of protons and
electrons.
Isotopes are identified by mass number.
Neutrons affect mass, so, isotopes with
more neutrons are heavier
Sample Problem
Three isotopes of oxygen are
oxygen-16, oxygen-17, and oxygen18. Write the symbol for each,
including the atomic number and
mass number.
http://www.youtube.com/watch?v=EboWeWmh5Pg
Atomic Mass
• The actual masses of individual atoms are very very very very
small (arsenic = 1.244 x 10 -23 )…so to measure the relative mass of
atoms, a reference isotope is used.
• The reference isotope is carbon-12. It has a mass of exactly 12
atomic mass units.
• Atomic mass units (amu) is the unit used.
Atomic Masses
Atomic mass is the weighted average of all the naturally occurring
isotopes of that element.
Symbol
Composition of the
nucleus
% in nature
Carbon-12
12C
6 protons
6 neutrons
98.89%
Carbon-13
13C
6 protons
7 neutrons
1.11%
Carbon-14
14C
6 protons
8 neutrons
<0.01%
Isotope
Carbon = 12.011amu
To calculate relative atomic mass, multiply the mass
number of each isotope by its percent abundance
changed to a decimal and total.
(Mass #)(isotope’s relative abundance) +
(Mass #)(another isotopes Rel. abundance) =
Relative atomic mass of the element
Example 1: Neon has 2 isotopes, Ne-20 with an
abundance of 90% and Ne-22 with an abundance of
10%. Calculate the average atomic mass of neon.
20 x 0.9= 18
22 x 0.1= 2.2
18 + 2.2 =20.2 amu
Why is it closer to 20 than 22?
20 is more abundant
Example 2: Carbon occurs in nature as a mixture of
atoms of which 98.89% have a mass of 12.00 u and
1.11% have a mass of 13.00335 u. Calculate the atomic
mass of carbon.
12.00 x 0.9889= 11.87
13.00335 x 0.0111= 0.144
11.87+ 0.144 = 12.014
Why is it closer to 12?
12.00 is more abundant
Sample Problem
Carbon has two stable isotopes: carbon-12
which has a natural abundance of 98.89 %
and carbon-13 which has a natural
abundance of 1.11 %. The mass of carbon12 is 12.000 amu and the mass of carbon-13
is 13.003 amu. What is the atomic mass?
Sample Problem
The element antimony (Sb) has naturally
occurring isotopes with mass numbers of 121
and 123. The relative abundance and atomic
masses are 57.12 % for mass = 120.90 amu, and
47.29% for mass = 122.90 amu. Calculate the
atomic mass of antimony.
Sample Problems
In book, page 119 numbers 24 and 25
Meet 115, the newest element on the Periodic
Table, Ununpentium
• Man-made element first by Russian scientist 10 years ago. It was replicated
by chemists in Sweden at the Lund University. Therefore making it officially
a new element.
• No official name has been given yet, so scientists are calling it Ununpentium,
based on the Latin and Greek words for its atomic number 115.
• http://www.rsc.org/periodic-table/element/115/ununpentium