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Lecture 1

BIOL 1201 Lecture Notes - Lecture 1: Chemical Formula, Hydroxy Group, Vaporization


Department
Biological Sciences
Course Code
BIOL 1201
Professor
E.Wischusen
Lecture
1

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Cont Biol 1201 Notes
Valence: The number of elections that need to be gained or lost to fill the outer shell
of electrons
- Describe whether or not the bond with behave
- Predicts number of bonds that an atom will form
- Determines shape and structure and size
- Valence electrons, the electron in the outermost shell
Electron Shell
- K shell: 2 electrons
- L shell: 8 electrons
- M shell: 8 electrons
- Almost all the important elements exist in the first three rows of the periodic
table
Lithium has the atomic number 3. What is the valence of Li? 1 lose
- Not 7, because atoms lose/gain the smaller number for electrons
Carbon has the atomic number 6. What is the valence of C? 4 lose or gain
Oxygen has the atomic number 8. What is the valence of O? 2 gain
Sodium has the atomic number of 11. What is the valence of Na? 1 lose
Phosphorous has the atomic number 15. What is the valence of P? 3 gain or lose 5
Polarity of a molecule
- The type of bond/s within a molecule
Chemical bonds
- Form when atoms gain and lose or share electrons
- They are the result of electrical attractions between
- The Noble gases all have full outer shells, so they do not react
Ionic bonds
- The complete gain or lost of electrons
- When one atom steals all the electron of another atom
- Strongest bond when dry
Covalent bonds
- Form when atoms share elctrons
- One moment, one nucleus will have a full outer shell, and the other doesn’t,
and at the other moment, vice versa (partial negative, partial positive, partial
neutral)
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- If shares equally= covalent
- If shared unequally= polar covalent
- Strongest bond in water
Are covalent, polar covalent, and ionic bonds really different bonds?
- Nothing really different, just a degree of sharing (spectrum)
What determines the number and type of chemical bonds?
- Number= Valence
- Type= Electronegativity
o High= Really want electrons
o Low= don’t want
o The bigger difference in electronegativity, don’t share much
Electronegativity
- A measure of the tendency of an atom to attract a bonding pair of electrons
- Measure of the attractive an atom has for electrons
- Electronegativity periodic table
o Patterns
o Left to right= Get greater
o Group 1= 1 electron in outershell (low attraction)
o Group 7= 7 elections in outershell (high attraction)
o As we going up the table, the electronegativity increases
Electronegativity and Bonds
- Ionic: when the differences in electronegativity is 1.7 or greater, the bond is
usually ionic
o One has the electron so often, that its almost always there and not
shared with the other one
- Covalent: when differences of less than 0.5
o Small differences
- Polar covalent: Less than 1.7 but greater than 0.5
How do bonds influence the polarity of a molecule?
- Molecules which contain ionic bonds will be polar
- Molecules which contain many polar covalent bonds will be polar, (with just
a few exceptions)
- Molecules which contain many covalent bonds will be non-polar
Weak bonds
- Strong bonds are bonds that pull atoms together in a molecule
- Weak bonds which are not involved in making a compound
- Bonds that involve molecules interacting with eachother
Hydrogen Bonds
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