Download The periodic table

The periodic table:
Reading the periodic table:
Atomic Mass
Atomic Number
Symbol
Name
Reading the periodic table:
Number of Protons + Neutrons
Number of protons (or electrons if neutral)
How do you know the number
of protons?
• The number of protons always = the
atomic number.
• In a neutral atom, number of protons =
the number of electrons.
How do you know the number
of neutrons?
• The atomic mass = # protons + # neutronsso, if you know the protons and the mass, you
can determine the # of neutrons.
• Practice. Hydrogen has atomic #1, and
atomic mass 1amu. How many neutrons.
• Carbon has atomic #6, and atomic mass
14amu. How many neutrons.
How do you know the # of e-?
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We will consider neutral atoms.
So the charges will amount to 0.
Every proton will be balanced by an e-.
So, # of protons = # of e-.
Practice
What is the atomic #? What is the atomic mass?
How many protons, neutrons, and electrons?
How do we draw atoms
again?
Indicate the # of protons and neutrons in the nucleus
Indicate the location of electrons in the orbitals: 2 in
the first, and up to 8 in every other.
Practice Drawing atoms:
Chemical Bonding
• The rearrangement of atoms, driven by
e-s .
• There are 2 major classes of bonds,
covalent and ionic
Why bond?
• 1. All atoms want to get to the lowest
energy state possible
• 2. All atoms want to fill their valence
shell.
Valence shell
• Valence shell = The outermost shell of
e- .
• The first e- orbital only holds 2.
• All of the others we will consider hold
UP TO 8.
• (There are energy levels that hold more
than 8 e- , but you’ll get to that in
chemistry).
Octet Rule
• Octet = 8. In general, atoms bond in
order to fill their valence shell with 8 e• Noble Gasses are the elements on the
far right of the periodic table.
These have a full valence shell.
Will they bond?
How many total electrons
does each have?
How many valence electrons?
How many bonds will each
make?
Representing the Valence
Shell in Electron-Dot format
• 1. Use the atomic symbol
• 2. Determine the # of valence electrons
• 3. Begin above the symbol, and place a
dot moving clockwise for each electron.
Representing Bonds with
Electron dot Structures
1. Count the number of dots around each atom
(needs to add up to 8 or 2)
2. If atoms are sharing 1 pair of electrons, draw 3. If atoms are sharing 2 pairs of electrons, draw =
4. If atoms are sharing 3 pairs of electrons (Carbon
and Silicon), draw a triple bond.
Draw each element bonded
with enough Hydrogen atoms
to fill the valence shell.
• What do you do with Li, Be, or B?
Covalent Bonding
• “Co” means together. Atoms that share
e-s together are covalently bonded.
• There are 2 types of covalent bonds
1. Non-polar bonds share e- equally
2. Polar bonds don’t share e- equally
Non-polar bonds
• When two atoms have very similar
electronegativies they will have similar pulls
or affinities for the e-s they share.
• As a result of equal sharing, the charges of
the electrons will be equally distributed.
• This happens whenever Carbon and
Hydrogen bond together.
• This also happens when two identical atoms
bond together as in O2 or Cl2, etc.
Nonpolar bonds exist in things
like oils and waxes.
• Oils are made of H and C, they are
called Hydrocarbons
• Waxes too are Hydrocarbons
Polar Bonds
• In Polar bonds the atoms have different
electronegativities. On atom will have a
stronger affinity or pull on the e-s than the
other(s).
• This results in one “pole” where the e-s spend
more time (negative), and another “pole”
where the e-s spend less time (positive).
Example of Polar Bonds
• Water is the classic example of a polar
molecule. The Oxygen atom has a much
greater electronegativity than either Hydrogen
atom.
• The Oxygen takes on a slight negative
charge
• The Hydrogen atoms take on a slight positive
charge.
• This creates two poles - a dipole.
Ionic Bonds
• Sometimes different atoms have such
different electronegativities that one
atom will end up “stripping” e-s from the
other(s).
• The atoms are now called ions (either
positive or negative).
• The resulting ionic compounds are
called salts.
Practice Drawing Bonds
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C2H6
C2H4
C2H2
O2
H2
H2O
CH3OH
LiOH
H2O2
Ions
• After stipping (or being stripped of) an
e-, an atom takes on a permanent
charge.
• NaCl  Na+ and Cl- (Chlorine has one
more e- than +, and Na has one more +
than e-).
• Predict, HF or H2O or
MgCl
Ions
• How many +s and e-s does each atom
have?
• Li+
Be-2
Al +3
• BrK+
Ca+2
Isotopes
• Atoms with the same number of
protons, but different numbers of
neutrons (different atomic masses)
• i.e. C12 & C14
• The atoms have the same properties,
but different masses.
Practice:
(Ions, Isotopes, Different Elements, or Neutral Atoms)
Atom 1
Protons
Neutrons
Electrons
Atom 2
Protons
Neutrons
Electrons
He
2
2
2
He
2
4
2
O
8
8
8
O
8
8
8
Cl
17
18
18
Cl
17
18
18
N
7
7
7
N
8
7
8
F
9
9
9
F
9
7
9
Na
23
22
22
Na
23
22
22
Li
3
2
2
Li
2
2
2
Answers
Atom 1
Protons
Isotopes
Neutrons
Electrons
Atom 2
Protons
2
O
Neutral
Ions
17
Different
7
Isotopes
Atoms
Neutral
O
Different
Atoms
23
Different
3
Elements
8
Atoms
18
Different
Elements
7
22
Elements
Neutral
17
9
Ions
Electrons
4
18
Elements
Neutrons
Different
23
Elements
2
22
Different
Elements
Practice Bonding
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H2
H 2O
O2
H 2O 2
C 2H 6
C 2H 4
C2H2
PH3
SO
NaOH
S2
Cl2
NH3
Si2H2
Lab: Build & Draw
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Represent the elements by this color scheme:
C=Black
N=Red
O=Blue
H=White
Cl=Purple S=Yellow
Si=Brown
H2
H2O
SO
C2H2
O2
Si2H2
H2O2
S2
C2H6
Cl2
C2H4
NH3