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Atoms and Elements
An atom is always neutral in charge. All the different types of atoms that we know of are found on the periodic table. The periodic table provides information about each of the atoms that we know to exist on Earth. For example, the periodic table is arranged based on increasing atomic number. The atomic number of each element (which is the number in the top of each box) tells you the number of protons that are located in the nucleus of that atom. Each atom has a unique atomic number, and therefore one atom cannot have the same number of protons as another atom. If we know the number of protons in the nucleus of an atom, we can identify the atom. The number of Protons = Atomic Number
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Neutrons
A single neutron is approximately the same in weight to a proton. Just like protons, neutrons are found in the nucleus of the atom. Different atoms can have the same number of neutrons, but different atoms cannot have the same number of protons. For example, Aluminum has 13 protons and 14 neutrons whereas Silicon has 14 protons and 14 neutrons.
These two atoms would be written as Aluminum-27
and Silicon-28 to show their masses!!
The mass of an atom = # of protons + # neutrons
(Rounded to the nearest whole number)
+
What do neutrons do??
Build the following atoms. N
Assume this is the nucleus of an atom. Let's specifically look at an atom of ___________. Discuss the possible purpose of the neutrons in the nucleus. HINT: what would you expect to happen with the protons in the nucleus if the neutrons were not there?
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ATOMS vs. IONS
Atoms are always neutral in charge. This means that the number of protons (positive charges in the nucleus) must be equal to the number of electrons (negative charges around the nucleus). Define, compare
and contrast
atoms, cations
and anions....
Ions are always charged (either positively or negatively charged). This happens when an atom gains or loses an electron. Anion = negative ion A negatively charged ion results when a neutral atom gains an electron.
Cation = positive ion A positively charged ion results when a neutral atom loses an electron. Memory Trick: "Cat"s have "paws" so cations are positively charged!!!
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http://listromgreenall.wikispaces.com/
Use the following program to help discover how electrons are distributed and how ions are formed. Below are a list of atoms and the common ion that the atom tends to make in nature. Draw the neutral atom and the ion for each case in your notes. 1. Hydrogen can form an H+1 or H­1 ion. Draw the neutral atom and each ion. 2. Helium, Neon and Argon are both Nobel gases, they does not like to form ions in nature. Draw the neutral atom for each. How are these structures similar? Different?
3. Lithium and Sodium can form +1 ions. Draw the neutral atom and ion for each. How are these similar to Hydrogen? Different from Hydrogen?
4. Beryllium and Magnesium can form +2 ions. Draw the neutral atom and ion for each. 5. Boron and Aluminum can form +3 ions. Draw the neutral atom and ion for each. 6. Carbon and Silicon can form +4 or ­4 ions. Draw the neutral atom and ion for each. How are these similar to Hydrogen?
7. Nitrogen and Phosphorus can form ­3 ions. Draw the neutral atom and ion for each. Why do these tend
to form negative charged ions (anions) instead of positively charged ions (cations)?
8. What do you think the most common charge for the following pairs of elements would be based on the patterns observed in questions #1­7?
(a) Oxygen and Sulfur (b) Fluorine and Chlorine
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KEY
1. Hydrogen can form an H+1 or H­1 ion. Draw the neutral atom and each ion. e-1
e-1
e-1
1P+
1P+
1P+
0N
0N
0N
Hydrogen Atom
Hydrogen Cation
H
Hydrogen Anion
+1
H-1
2. Helium, Neon and Argon are both Nobel gases, they does not like to form ions in nature. Draw the neutral atom for each. How are these structures similar? Different?
e-1 e
e-1
e-1
+
2P
2N
Helium Atom
e-1 e-1
-1
e-1 e-1
e-1
e-1 e-1 e-1e-1 -1
e
e-1 e-1
e-1e-1
e-1
e-1 e-1
10P+
10N
Neon Atom
e-1 e-1
e-1 e-1 e-1
e-1 e-1
e-1 e-1
18P+
22N
Argon Atom
As you go down a column on the periodic table,
the # of electron rings increases by one.
Each Nobel gas has a full ring of electrons - meaning
Nobel gases are STABLE (do not like to gain or lose
electrons OR do not typically take part in bonding).
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3. Lithium and Sodium can form +1 ions. Draw the neutral atom and ion for each. How are these similar to Hydrogen? Different from Hydrogen?
e-1
e-1
e-1
e-1
e-1
3P+
4N
3P+
4N
Li+1 ion
Lithium Atom
e-1
e-1 e-1
e-1 -1
e
e-1
e-1 e-1
e-1
e-1 e-1
e-1 e-1
11P+
12N
Sodium Atom
e-1
e-1 e-1
e-1 -1
e
e-1
e-1 e-1
11P+
12N
Na+1 ion
Similar to Hydrogen - the atoms of sodium
and lithium have one electron in their
outer-most electron ring (called the
valence ring). In order to create the +1
cation, the atom must loose it's lonely
valence electron.
STABILITY ­ The common ion of an atom if formed by gaining/loosing electrons until the valence ring is full or empty!!
The other charge for Group 1 atoms would
be -7 since they could also gain 7
electrons to fill the valence ring.
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4. Beryllium and Magnesium can form +2 ions. Draw the neutral atom and ion for each. e-1 e-1
e-1
e-1
e-1
e-1
4P+
5N
4P+
5N
Beryllium Atom
Be+2 ion
-1
e-1 e
e-1 e-1
e-1 e-1
e-1
e-1 e-1
e-1
e e-1
-1
e-1 e-1
e-1
e-1 e-1
e-1 e-1
12P+
12N
Magnesium Atom
e-1
e-1 e-1
12P+
12N
Mg+2 ion
STABILITY ­ The common ion of an atom if formed by gaining/loosing electrons until the valence ring is full or empty!!
The other charge for Group 2 atoms would
be -6 since they could also gain 6 electrons
to fill the valence ring.
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5. Boron and Aluminum can form +3 ions. Draw the neutral atom and ion for each. e-1 e-1
e-1 e-1
e-1
e-1
e-1
5P+
6N
5P+
6N
B+3 ion
Boron Atom
e-1 e-1
e-1 e-1
e-1e-1
e-1
e-1 e-1
e-1 e-1
e e-1
-1
e-1 e-1
e-1 e-1
13P+
14N
Aluminum Atom
e-1
e-1 e-1
e-1 e-1
e-1
13P+
14N
Al+3 ion
STABILITY ­ The common ion of an atom if formed by gaining/loosing electrons until the valence ring is full or empty!!
The other charge for Group 2 atoms would
be -6 since they could also gain 6 electrons
to fill the valence ring.
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6. Carbon and Silicon can form +4 or ­4 ions. Draw the neutral atom and ion for each. How are these similar to Hydrogen?
e-1 e-1
e-1
e-1 e-1
e-1
e-1 e-1
e-1
e-1
-1
e-1 e
e-1
e-1
e-1 e-1
e-1 e-1
6P+
6N
6P+
6N
6P+
6N
C+4 ion
Carbon Atom
C­4 ion
e-1 e-1
e-1 e-1
e-1
e-1 e-1 e-1
e-1e-1
e-1
e-1 e-1
e-1
+
14P
14N
Silicon Atom
e-1 e-1
e-1 e-1
e-1 e-1
e-1
e-1 e-1
e-1e-1
e-1
-1
e-1 e
e-1 e-1 e-1
-1
e-1 e e-1
-1
-1
e e
e-1 e-1
14P+
14N
Si+4 ion
e-1 e-1
-1
14P+
14N
e-1 e
Si­4 ion
STABILITY ­ The common ion of an atom if formed by gaining/loosing electrons until the valence ring is full or empty!!
Group 14 or 4A elements are similar to
hydrogen in that they are also half full.
Therefore, they can just as easily gain 4
electrons to have a full valence of
electrons (stable) or lose four electrons to
have an empty valence of electrons (also
stable).
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7. Nitrogen and Phosphorus can form ­3 ions. Draw the neutral atom and ion for each. Why do these tend
to form negative charged ions (anions) instead of positively charged ions (cations)?
e-1 e-1
e-1 e-1
-1
e
e-1
-1
e-1 e
-1
-1
e
-1
e
e
-1
e
e-1
e-1
e-1e-1
e-1
7P+
7N
7P+
7N
N­3 ion
Nitrogen Atom
It is easier for Nitrogen to gain 3
electrons then to loose 5 electrons.
e-1 e-1
e-1 -1
e
-1
e
e-1 e-1
-1
e
-1
e e
e-1 e-1
-1
-1
e-1 e e-1
e-1
-1
e e
e
+
15P
16N
Phosphorus Atom
-1
e-1 e-1
-1
-1
-1
e-1 e
e e-1 e-1
e-1 e-1 -1
e
e-1e-1
e-1 e-1
15P+
16N
P­3 ion
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8. What do you think the most common charge for the following pairs of elements would be based on the patterns observed in questions #1­7?
(a) Oxygen and Sulfur MOST COMMON CHARGE = -2
LESS COMMON CHARGE = +6
(b) Fluorine and Chlorine
MOST COMMON CHARGE = -1
LESS COMMON CHARGE = +7
GROUP 1A 2A 3A/13 4A/14 5A/15 6A/16 7A/17 COMMON CHARGE LESS COMMON CHARGE Why did I not include Group 18 in the table above?
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Fill in the table below:
Atom/Ion # protons # neutrons # of electrons Atomic Mass Fe
Iron Se­2
Al+3
Carbon ­14
Chlorine ­37
Br­1
Isotopes
Carbon -14 means that carbon has a mass
of 14u. You might ask yourself "how and
why..."? Since the periodic table shows it
should have a mass of 12u!!!
Similarly, Chlorine-37 means that
chlorine has a mass of 37u (yet the
periodic table shows that the mass
should be 35u...?)
COMPLETE PROBLEM SET #1
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ISOTOPES
Isotopes are atoms of the same element (the same number of protons in the nucleus) that have different numbers of neutrons. Most elements have naturally occurring isotopes. For example, Hydrogen has three naturally occuring isotopes: Hydrogen­1, Hydrogen­2, and Hydrogen­3. Hydrogen­1
atomic mass
atomic number
1
1H
Hydrogen­2
2
1H
Hydrogen­3
3
1H
Example: Almost all of the Hydrogen found in nature (99.0%) is Hydrogen­1. Approximately 0.95% of all naturally occurring Hydrogen is Hydrogen­2 and the rest is Hydrogen­3. Calculate the average atomic mass of Hydrogen. 14
Mass = # protons + # neutrons
For Fluorine:
For Titanium:
For Lithium:
Whole number? Decimal number?
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Weighted Averages: A normal average would be calculated by adding up a bunch of numbers and dividing. In this method, no one number is more important than any other. For example, the average of 12, 13 and 14 can be calculated in the following way... A weighted average is used for calculations such as your final grade where some numbers carry more "weight" than others. Consider the following situation…
You have the following students in a grade ten class: 96 girls, each about 35kg in mass. •
17 boys, each about 51kg in mass. •
Calculate the average mass of a student in grade ten based on the data given above. Why is this different than just taking a normal average of 35kg and 51kg? 16
Consider the following situation…
You mark in this class is composed of 35% daily work, 15% for quizzes, 10% for labs, and 40% for the final exam. If you get 12/15 on daily work, 11/15 on quizzes, 8/10 on labs, and 85% on your final exam… what would your final average be?
ANSWER: 81%
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EXPLAIN:
What do we mean when we say that the average number of children per family is 1.2?
Where does the decimal come from??
(since you cannot have 0.2 of a child....)
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Problems:
1. If out of 112 carbon atoms, 92 of them are carbon­12 and the rest of them are carbon­13:
(a) calculate the abundance of each atom in nature in decimal form and in percent form. (b) calculate the average atomic mass of carbon based on the data provided. (c) I just made up these numbers, how close am
I to the actual average atomic mass of carbon? Absolute Error = Measured ­ Actual (the difference) Percent Error = (Absolute Error/Actual Value) x100%
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2. For each problem below:
(a) calculate the abundance of each atom in nature in decimal form and in percent form. (b) calculate the average atomic mass of carbon based on the data provided. (c) calculate the percent error and absolute error.
If out of 1500 Boron atoms, 927 of them are boron­11 and the rest of them are boron­10. If out of 789 Phosphorus atoms, 427 of them are phosphorus­31, 198 of them are phosphorus­30 and the rest of them are phosphorus­29. 20
Weighted Averages
Practice Problems
Saskatchewan has a population of 1.3 million and Manitoba has a population of 0.9 million. If Saskatchewan has an unemployment rate of 1.2% and Manitoba of 3.4%, calculate the average unemployment rate for the two provinces combined.
Saskatchewan has two kinds of wild roses, pink and yellow. The pink roses are more fertile, and as such 9 of 10 wild roses found in nature are pink. If the pink roses have 9 leaves and the yellow roses have 13 leaves, calculate the average # of leaves per rose. The following is the # of children per family in Balgonie, Sk: 100 families have 1 child 55 families have 2 children
87 families have 3 children
33 famlies have 4 children
10 families have 5 children 2 families have 6 children
3 families have 7 children
7 families have 9 children
Calculate the average number of children per family. 21
PROBLEMS from NOTES:
1. Calculate the ave. atomic mass of natural carbon, given:
Isotope Atomic Mass (g/mol) Abundance
(%) 12
6C 12.0 98.89% 13
6C 13.004 1.11% ANSWER: 12.01g/mol
2. Boron has two naturally occurring isotopes. One of mass 10.0g/mol and abundance of 19.6%. The other of mass 11.0g/mol with an abundance of 80.4%. What is the average atomic mass of Boron? Write the symbolic representation for all isotopes of Boron. ANSWER: 10.804g/mol
ANSWER: 105B 115B 3. Iron has 4 isotopes of masses 53.940g/mol, 55.935g/mol, 56.935g/mol, and 57.933g/mol with abundances of 5.84%, 91.68%, 2.17%, and 0.31% respectively. Calculate the average atomic mass of Iron. Write the symbolic representation for all isotopes of Iron. ANSWER: 55.85g/mol
ANSWER: 5426Fe 5626Fe 5726Fe 5826Fe
COMPLETE 1. Assignment
2. Read Article "Isotopes"
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