Post on 13-Dec-2015
I. Basic Chemistry
A. Elements and Atoms
1. Elements- Substance which cannot be broken down into a simpler substance
a) 96% of all life is Carbon, Hydrogen, oxygen and nitrogen
b) 3.2% Calcium, Phosphorous, Potassium and Sulfur
2. Atom- The smallest particle of an elementa) Atomic structure
1. Proton- positively charged. In nucleus. 1 Dalton mass
2. Neutron- neutral charge. In nucleus. 1 Dalton mass
3. Electron- negative charge. Orbits nucleus. 1/2000 Dalton mass
b) Electron Energy Levels
Energy Level Maximum Number of Electrons
1st (K)
2nd (L)
3rd (M)
4th (N)
2) However, the outer energy level: valence shell will never hold more than 8 electrons
1)
2 electrons
8 electrons
18 electrons
32 electrons
3. Periodic Table- Chart of Elements arranged by proton number and valence electrons
8
OOxygen
15.9
e) Neutron Number = Atomic mass – Atomic number
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
4. Bohr Diagrams- illustrations of an atom. Example: Oxygen
8p
8n
6e2e
5. Isotopes- Atoms with extra neutrons. Some are unstable and give off radiation as they decay
Number of electrons in 2nd energy level
Electrons in the first energy level
Nucleus with the number of protons in & neutrons
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
2H2
OCO2 C2H5OH C6H12O6
Atoms
Elements
Molecules
6
2 2 3
9
2
3
1 1 1
24
3
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
p
p
P8
n8
2e-
e-
e-
e-
e-
e-
e-
OxygenHydrogen
Hydrogen
e-
e-
D. Ionic Bonding- The transfer of electrons from one element to another to fill the outer energy level
1. Electronegativity- a measure of the attraction of electrons to an atom.
2. When atoms with high electronegativities are placed with atoms with low electronegativities (the difference is greater than 1.67), Ionic bonding occurs
a) The transfer of the electron from one atom to another causes the formation of particles called ions
b) Ions with opposite charges attract
Example of Ionic Bonding
Sodium’s valence =Sodium’s Electronegativity =
Chlorine’s valence =Chlorine’s Electronegativity =
Electron Transfer
1 1
0.93 3.16
Electronegativity Difference = 2.23 > 1.67
Attraction
Sodium
Atom AtomChlorine
Ion Ion
E. Hydrogen Bonds- weak bonds between polar molecules
1. When atoms with different electronegativites covalently bond, electrons are shared unequally resulting in polar covalent bonds.
2. 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. Activation Energy- energy needed to start a reaction. (heat, stirring, electric.)
2. Atoms cannot be created or destroyed in a chemical reaction, they are only rearranged into different molecules
3. Example: H2 + O2 H2O
Reactants yields Products
2H2 + O2 2 H20
coefficient
Subscript
4. Endergonic Vs Exergonic Reactions