Download Atoms - McEachern High School

Unit 3
Atomic Theory
Important terms to know
• Atoms – The fundamental unit of which
elements are composed.
• Element – A substance that cannot be
decomposed into simpler substances by
chemical or physical means. It consists of
the same type of atoms.
Abundances of Elements
• Nine elements
account for about
98% of the earth’s
crust, oceans and
atmosphere.
Abundances of Elements
• The elements in living
matter are very
different from those in
the earth’s crust.
• In the human body,
oxygen, carbon,
hydrogen and
nitrogen are the most
abundant elements.
Dalton’s Atomic Theory
1.
2.
3.
4.
All elements are composed of atoms.
All atoms of a given element are identical.
Atoms of different elements are different.
Compounds consist of the atoms of
different elements.
5. Atoms are not created or destroyed in a
chemical reaction.
Parts of an Atom
• Nucleus – The
Nucleus
center of the atom,
contains protons
and neutrons.
Energy
level
• Electron cloudthe outer part of the
atom where
electrons are found.
Part of the Atom
• Protons – located in the
nucleus. Has a positive
charge. Elements are
unique to the number of
protons it contains.
• Neutrons – located in
the nucleus. Has a
neutral charge.
• Electrons – located in
the electron cloud. Has a
negative charge.
Comparing parts of an atom
Anatomy of the Atom
• The Bohr’s Model of
the atom suggests
that the nucleus is in
the center of the atom
and the electrons are
located outside the
nucleus circling
around in orbitals
called energy levels.
• The periodic table gives us clues to how
many protons, neutrons, and electrons
that a neutral atom contain.
With this given information, you can easily
build the structure of the particular atom
• All you have to know the rules that atoms
follows.
• Rules
– The first energy level (or ring around the nucleus)
only can hold 2 electrons
– Once the first ring is “full”, the next set of electrons
will begin to fill in to a new energy level.
– With the exception of the first energy level, All
outer energy levels only wants to have 8
electrons.
• This is called the Octet rule
– Once the octet has been reached, a new energy
levelwill be made.
How to draw an Atom
• As stated the Periodic table gives us clues
on the structure of the atom.
How to draw an Atom
• Structure of Hydrogen
– It has 1 electron
– It has 1 proton
– We will assume it has
no neutrons
How will the Hydrogen look
like?
There is only one
energy level with
1 electron
As you can see that
there is 1 proton in the
middle of the atom.
Another example
• Structure of
Lithium
– Atomic Number
• 3 protons
• 3 electrons
• Lets assume that
there is 4
neutrons.
• Lets draw it.
How does Lithium look like?
Try some examples
• Oxygen
– Lets assume
that
It has 8 neutrons
• Argon
– Lets assume it
Has 22 neutrons
Names and Symbols for the
Elements
• Each element has a name and a symbol.
– The symbol usually consists of the first one or two letters of
the element’s name.
– The first letter of the symbol is always in capital letters
– Examples:
Oxygen O
Krypton Kr
– Sometimes the symbol is taken from the element’s original
Latin or Greek name.
• Examples:
gold Au
lead Pb
aurum
plumbum
• Compound – a substance made of two
or more different elements joined together
in a specific way.
• Law of Constant Composition
– A given compound always contains the same
proportions by mass of the elements of which
it is composed.
Formulas of Compounds
• A compound is represented by a chemical
formula in which the number and kind of atoms
present is shown by using the element symbols
and subscripts.
– Example: the simple sugar, glucose
Tools to Writing Formulas
1.Each atom present is represented by its
element symbol.
2.The number of each type of atom is
indicated by a subscript written to the right of
the element symbol.
3.When only one atom of a given type is
present, the subscript 1 is not written.
How to count Atoms
• If there is no numbers by the symbol of the
element, assume only one
– Na
– MgO
• A subscript is a number written at the
lower right corner of the chemical symbol.
If there is more than one, then a number is
used.
– H2
– Li2O
How to count Atoms
• A subscript outside a bracket multiples
all the elements inside the bracket.
– Mg3(PO4)2
• A coefficient is a number written in front
of a chemical symbol or in front of a
chemical formula which indicates the
number of atoms or molecules of the
substance.
–3 C
– 2 H 2O
Lets Practice counting Atoms…
1.
2.
3.
4.
5.
6.
7.
NaCO3
Ca3(PO4)2
K2CrO4
3 BaCl2
NH4C2H3O2
4 Al2(CO3)3
Pb(NO3)2
8. 2 (NH4)2Cr2O7
Chemical Symbols
Lets Practice…..
More Practice…
Element
Mass #
Be
9
Atomic #
23
# of
Electrons
# of
Neutrons
4
20
Na
# of
Protons
10
11
15
16
More Practice….
Element
Mass #
Atomic #
# of
Protons
# of
Electrons
# of
Neutrons
Be
9
4
4
4
5
Ne
20
10
10
10
10
Na
23
11
11
11
12
P
31
15
15
15
16
What are Ions?
Atoms can be either neutral or charged….
When they are neutral…
# of protons = # of electrons
When they are charged…..
# of protons ≠ # of electrons
These charged atoms are called Ions.
What are Ions?
Atomic Symbols for Ions
Mass Number
(# of protons + #neutrons)
23
+1
𝑁𝑎
11
Charge
Atomic number
(# of protons)
What are Ions?
• If charge is POSITIVE (+), that is how
many more protons there are to electrons.
• If charge is NEGATIVE (-), that is how
many more electrons there are to protons.
What are Ions?
7 +1
3𝐿𝑖
How many protons?
3
How many neutrons?
4
How many electrons?
2
16 −2
8𝑂
How many protons?
8
How many neutrons?
8
How many electrons?
10
More Practice…
Element
F-
Mass #
Atomic #
# of
Protons
# of
Electrons
# of
Neutrons
19
20
10
8
Se-2
46
15
18
16
More Practice…
Element
Mass #
Atomic #
# of
Protons
# of
Electrons
# of
Neutrons
F-
19
9
9
10
10
Ne+2
20
10
10
8
10
Se-2
80
34
34
36
46
P-3
31
15
15
18
16
Isotopes
• Isotopes are atoms with the same number of
protons but different numbers of neutrons.
Diatomic Molecules
Average Atomic Mass
Atomic Number
Chemical Symbol
Chemical Name
Average
Atomic Mass
Average Atomic Mass
• Average Atomic Mass – the weighted
average of the masses of all of the
isotopes of an element.
• Oxygen has 3 stable
isotopes
– O16
– O17
– O18
• It turns out in nature
we see that of all
oxygen…..
99.757% is O16
0.038% is O17
0.205% is O18
How is the average atomic mass is
calculated?
Remember Average Atomic Mass is a weighted average of
all the isotopes of any particular element.
There two things you need to know about
each isotope in order to calculate the
average atomic mass….
Mass
and %Abundance
We know that there is 3 stable isotope of
Oxygen: O16, O17, O18
In order to calculate its average atomic
mass, we need to know each isotope mass and
%abundance.
Isotopes
of unitMass
(amu)– a small
%Abundance
Atomic
mass
(amu)
unit of
Oxygen
mass. 1 amu is equal to
O
15.9949
99.757
0.000000000000000000000000166 grams.
16
O17
16.999
0.038
O18
17.999
0.205
Isotopes of Oxygen
Mass (amu)
%Abundance
O16
15.9949
99.757
O17
16.999
0.038
O18
17.999
0.205
To calculate the average atomic mass:
(15.9949x0.99757)+(16.999x0.00038)+(17.999x
0.00205) = 15.999
In the calculations be sure to
As you can see it turns
change the percentage to
out to be the same
decimal numbers. Make sure to
number on the periodic
move the decimal 2 times to the
table.
left.
Example
The element copper has naturally occurring isotopes
with mass numbers of 63 and 65.The relative
abundance and atomic masses are 69.2% for a mass
of 62.93amu for 63Cu and 30.8% for a mass of
64.93amu for 65Cu. Calculate the average atomic
mass of copper.
What do we need to know?
Mass and %Abundance of each isotope
63Cu
65Cu
62.93amu
64.93amu
69.2%
30.8%
Example
Lets calculate
63Cu
62.93amu
69.2%
65Cu
64.93amu
30.8%
Make sure to change the percentages to
decimal numbers
(62.93x0.692)+(64.93x0.308) = 63.546
Your answer should always
match up with the element
on the Periodic Table
Try this one
Calculate the average atomic mass of sulfur if
95.00% of all sulfur atoms have a mass of 31.972
amu, 0.76% has a mass of 32.971amu and 4.22%
have a mass of 33.967amu.
(31.972x0.95)+(32.971x0.0076)+(33.967x0.0
422) = 32.057
Use the Periodic Table to check your answer.