Transcript I. Chemistry

I. Basic Chemistry
A. Elements and Atoms
1. Elements- Substance which cannot be
broken down into a simpler substance
a)
b)
96% of all life is Carbon, Hydrogen,
oxygen and nitrogen
3.2% Calcium, Phosphorous, Potassium
and Sulfur
2. Atom- The smallest particle of an element
a) Atomic structure
1.
2.
3.
Proton- positively
charged. In nucleus.
1 Dalton mass
Neutron- neutral
charge. In nucleus.
1 Dalton mass
Electron- negative
charge. Orbits
nucleus. 1/2000
Dalton mass
b) Electron Energy Levels
1)
Energy Level
Maximum Number
of Electrons
1st (K)
2 electrons
2nd (L)
8 electrons
3rd (M)
18 electrons
4th (N)
32 electrons
2) However, the outer energy level: valence shell
will never hold more than 8 electrons
3. Periodic Table- Chart of Elements arranged
by proton number and valence electrons
8
O
Oxygen
15.9
a) Atomic Number- indicates the
number of proton which
determines the the element
b) Symbol- Identifies the
element
c) Atomic Mass- the mass of
the atom in Daltons.
d) Atoms are Neutral- Therefore the number of proton
and electrons are equal
e) Neutron Number = Atomic mass – Atomic number
4. Bohr Diagrams- illustrations of an
atom. Example: Oxygen
6e
2e
8p
Number of electrons in 2nd energy
level
Electrons in the first energy level
8n
Nucleus with the number of
protons in & neutrons
5. Isotopes- Atoms with extra neutrons. Some are
unstable and give off radiation as they decay
Electrons are really in Orbitals- the actual
path the electron follows 90% of the time
•
•
•
No more than two electrons can occupy the
same orbital
The 1st energy level contains 1 orbital and
therefore holds a maximum of 2 electrons.
It is called the 1s orbital and it is spherical
The second energy level contains a
maximum of 4 orbitals. A spherical 2s and
3 dumbbell shaped orbitals in the X, Y, and
Z axis called the P1, P2 and P3 orbitals
Electrons fill lower energy levels before moving
to higher energy levels
B. Chemical Bonding
1. Compound- two or more elements chemically combined
2. Molecule- smallest particle of a compound
Atoms
Elements
2H2O
CO2
C2H5OH
6
3
9
24
2
2
3
3
2
1
Molecules
1
C6H12O6
1
What Determines Whether Atoms Bond?
3. Atoms with their outer energy level filled are
stable. He, Ne, Ar, Kr, Xe, Rn (Noble Gasses).
Keep in mind that helium’s first energy level is
its outer energy level and therefore requires
only two electrons in its valence shell for
stability
4. Unstable atoms will share or transfer
electrons to become stable
C. Covalent Bonding- Sharing a pair of
electrons to fill the outer energy level
Oxygen
Hydrogen
p
p
e-
ee-
2eP8
n8
e-
e-
Hydrogen
e-
e-
e-
D. Ionic Bonding-
The transfer of electrons
from one element to another to fill the outer energy
level
1.
2.
Electronegativity- a measure of the
attraction of electrons to an atom.
When atoms with high electronegativities
are placed with atoms with low
electronegativities (the difference is greater
than 1.67), Ionic bonding occurs
a)
b)
The transfer of the electron from one atom to
another causes the formation of particles called
ions
Ions with opposite charges attract
Example of Ionic Bonding
Electron Transfer
Attraction
Sodium Ion
Atom
Sodium’s valence = 1
Sodium’s
Electronegativity = 0.93
Chlorine Atom
Ion
Chlorine’s valence = 1
Chlorine’s
Electronegativity = 3.16
Electronegativity Difference = 2.23 > 1.67
E. Hydrogen Bonds- weak bonds
between polar molecules
1.
2.
When atoms with different
electronegativites covalently bond,
electrons are shared unequally
resulting in polar covalent bonds.
Hydrogen bonds can then for between
the molecules or even parts of large
molecules like DNA and proteins
F. Chemical Reactions-
breaking of
existing bonds and the formation of new ones
1.
2.
Activation Energy- energy needed
to start a reaction. (heat, stirring,
electric.)
Atoms cannot be created or destroyed
in a chemical reaction, they are only
rearranged into different molecules
3. Example: H2 + O2  H2O
4. Endergonic Vs Exergonic Reactions