Download atomic number, mass, isotopes

Outline the history of the atomic model.
Agenda for Tuesday Dec 14th
1. Atoms
2. Atomic mass, #, protons, etc
Atoms
• Nucleus in the center
– Protons and neutrons
• Electrons on outside of nucleus
– Electron cloud model
– Electrons exist in energy levels – based on # of
electrons
Atomic Number and Atomic Mass
Element name
Symbol
boron
5
Atomic number
B
10.811
Atomic mass
• Atomic number: # of protons in nucleus
• Each element has a different atomic #
• Identifies the element
• Hydrogen = smallest atomic # (1)
• # of protons = # of electrons
• Atomic mass: total mass of protons and
neutrons in an atom, measured in atomic
mass units (amu)
– Atomic weight
• Atoms of the same element can have different
numbers of neutrons - isotopes
• # on periodic table is the average atomic mass
for that element
• We will round the average atomic mass to get
a whole # called the mass number.
• Examples:
Sodium (Na)
Avg. atomic mass = 22.990 amu
Mass # = 23
Nitrogen (N)
Avg. atomic mass = 14.007 amu
Mass # = 14
• Finding # of neutrons
mass # - atomic # = # of neutrons
For Na:
23 – 11 = 12 neutrons
For N:
14 – 7 = 7 neutrons
Practice
Find the mass number, protons,
neutrons, and electrons for Bromine.
Agenda for Wednesday Dec 15th
1. History of the Atom Flash Cards
2. Practice with mass, protons, etc
3. Isotopes
Element
Name
carbon
Atomic
Number
6
Number of
Protons
6
6
Oxygen
8
8
hydrogen
1
1
Carbon
6
hydrogen
nitrogen
1
7
Number of
Neutrons
8
8
1
7
12
16
1
0
6
Mass Number
2
7
14
3
14
Isotopes
• Atoms of the same element can have different numbers of
neutrons  isotopes
• # of protons and electrons stays the same for a particular
element
– Mass changes
– Means # of neutrons changes
• Atomic mass on your P.T. is an average of all the isotopes
• For Boron:
.8 (10 amu) + .2 (11 amu) = 10.811 amu
More on Isotopes
• Because the numbers of neutrons in the isotopes
are different, the mass numbers are also different
• You use the name of the element followed by the
mass number of the isotope to identify each
isotope: boron-10 and boron-11
• Example:
– Neon. All neon atoms have 10 protons and 10
electrons. Some neon atoms have 10 neutrons
and some have 12.
– Both isotopes of neon
Mass # (protons + neutrons).
Different for each isotope
20
10
Ne
or
Ne-20
22
10
Ne
or
Ne-22
Atomic # (# of protons)
Mass # (protons + neutrons).
Different for each isotope
Atomic # (# of protons)
What is an isotope?
Agenda for Thursday Dec 16th
1. Isotopes practice
2. Valence Electrons
3. Lewis Dot Structures
What’s the point of Isotopes
• You can tell how old something is
– Radiocarbon Dating
• Use as markers in research
– Follow a certain molecule, atom
Practice Problems
You will need your periodic table!
1. For Mg-25: How many protons, electrons,
and neutrons?
2. For N-15: How many protons, electrons,
neutrons?
3. For P-31: How many protons, electrons,
neutrons?
Practice
• For each isotope, give the number of protons, electrons, and neutrons:
•
C-14
_________ p
_________e
___________n
•
Zn-65
_________ p
_________e
___________n
•
Na-21
_________ p
_________e
___________n
•
Be-8
_________ p
_________e
___________n
•
S-31
_________ p
_________e
___________n
Atoms
• Nucleus in the center
– Protons and neutrons
• Electrons on outside of nucleus
– Electron cloud model
– Electrons exist in energy levels – based on # of
electrons
Electrons and Energy Levels
• Electrons with different amounts of energy
exist in different energy levels
• Many possible energy levels an electron can
occupy
• Number of energy levels depends on the
number of electrons
Valence Electrons
• Electrons in the outermost energy level
• Valence electrons determine reactivity and
other chemical properties
• 8 valence electrons means a stable atom = do
not want to react with other atoms
Valence
electrons
•A way to draw an atom
showing where
electrons are found
Help! We’re
so
vulnerable!
13 p+
14 n0
Valence electrons
Carbon -12 has 4
electrons in the last
energy level . . .
therefore carbon-12 has
4 valence electrons
2nd shell can hold
8 e-
Bohr’s Model
1st shell can hold
2 e-
Nucleus
3rd shell can
hold 8 e-
How many electrons in each shell?
•
•
•
•
1st shell = 2 electrons
2nd shell = 8 electrons
3rd shell = 8 electrons
4th shell = 18 electrons
Drawing Carbon-12 with Bohr’s Model
Steps:
1. Find number of
neutrons and
protons.
2. Find number of
electrons.
3. Fill in electrons,
beginning with
the 1st energy
level.
6P
6N
How many valence electrons does Nitrogen
have?
NUCLEUS
How many valence electrons does Calcium
have?
Calcium
has 2
Valence
electrons
NUCLEUS
How many valence electrons does
Phosphorous have?
Phosphorous
has 5 Valence
electrons
NUCLEUS
How many valence electrons does Boron
have?
Boron has 3
Valence
electrons
NUCLEUS
Cool Trick!
1
2
3 4 5 6 7
8
About Lewis Dot Structures
• Gilbert Newton Lewis
– American chemist
• Proposed the idea of Lewis Dot Structures
– use the element’s symbol and small dots to
represent the valence electrons present in a
specific atom
Lewis dot structures
• Lewis dot structures are a way to draw atoms
showing only the valence electrons
• the symbol for the element is used to
represent the atom and its core electrons
Ca
Remember this?
It makes life easy now
1
2
3 4 5 6 7
8
Lewis dot structures
• Used to show valence electrons
N
• Start with single electrons on all four sides
first before starting to pair up
You try
Ne
C
O
Cl
Bonding potential
• Unpaired electrons are used in chemical
bonds.
• How many bonds can Nitrogen have?
N
• 3 unpaired electrons  3 potential bonds
Let’s try one together
How many valence electrons does potassium
have?
K
One more example
What element is Rn?
Radon
How many valence electrons does Rn have?
Rn