Molecular Polarity & Intermolecular Bonds

INTERMOLECULAR: intermolecular means the bonds are outside of the molecule

A. Polarity is the result of intermolecular bonds.
1) London Dispersion Force

• experience by all molecules
• results of electrons pushing on each other
• the weakest of all forces
• As the number of electrons increase LDF increases also

2)Dipole-Dipole

• Dipoles are partial separation of charges
• LDF is a type of temporary dipole
• Some molecules have a permanent dipole
• These are polar molecules
• Polarity is determined by electron affinity(how much an atom wants electrons)
• Electron affinity is called electron negativity
• Electron negativity is highest on the top right and lowest on the bottom left

• A bond between two atoms or molecules with different electron negativites result in a dipole-dipole bond.
• Dipole-dipole forces are weak versions of ionic bonds

EXAMPLES:
CHCl3 is polar because: its structural model is not symmetrical so that means it is polar.
C2H2Cl2 is both polar and non-polar depending on how you draw the structural model

Polar and Non Polar Solvents

Polar Substances have an unequal distribution of charges:


(if you were to draw a line down the middle of this diagram it would be symetrical)
Non-polar substances have unequal charge distribution (if symmetrical)


We did a lab that involved polarity and non-polarity. We mixed sugar, salt, and iodine with paint thinner and water and came to the conclusion that polar substances can combine with polar substances and non-polar substances can combine with non-polar substances but polar substances cannot combine with non polar substances.

Electrical conductivity in solutions requires charged ions to be transferred.
Iionic solutions dissociate or form ions so they always conduct.



Molecular substances do not usually dissociate.

follow the chart to determine conductivity:

Examples
element - yes/no - reason
Mercury - yes - metal
Carbon - no - solid non-metal
NaCl - yes - ionic
acetic acid - yes - acid
Iodine - no - not ionic/acid/base/metal

covalent bonds

- electrons shared between non-metals


to draw lewis dot diagrams:
- total all valence electrons in atoms
- identify the element that can form the most bonds. this will be the central atom
- draw bonds between atoms as a line (represents 2 electrons)
- any electrons not part of a bond are lone pairs around the atom
- check to make sure each atom has a full octet

example
ammonia water and ethane


C2H4


heres a extremely educational video!!

Atoms and Ions

• atoms are electrically neutral
• number of protons= number of electrons
• ions ahve different number of protons and electrons
• ions can be either positive of negative
• cation: positive ion
• anion: negative ion

Example: how many electrons do these electrons have? what type of ions are they?


S^2-: anion, sulphide ion I^1- : anion, iodide ion


chemical bonds

• a bond is an electrostatic attraction between particles
• bonds occur as elements try to acheieve noble gas electron configuration
• noble gases (usually) do not form compounds
• in noble gases the outermost energy level have stable octets
• metals lose electrons (oxidize)
• non metals gain electrons (reduced)

Lewis Dot Structure

• atoms can be represented by dot diagrams where dots represent electrons and only the valence level electrons are shown
• write the atomic symbol for the atom. this represents the nucleus and filled inner electron levels
• one dot is used to represent outer energy level electrons. one e- placed in each orbital before and pairing occurs. beginning with the 5th e-, pairing can occur up to a maximum of 8 e-

we practiced drawing lewis dot diagrams

Ionic Bonds

• electrons are transferred from metal to nonmetal. no dots are shown on the metal
• "charged" specie is written in brackets

so thats pretty much all we did today! lots of notes and lots of drawing :P

Atomic Weight

-On your periodic table silver has a weight of 107.9. The atomic mass of silver is 108. There is more than one isotope of silver and some are lighter than others.
a. 15.839% has a Mass Number of 107
b. 48.1161% has a Mass Number of 109
The element isn't split into half of the mass being 107 and 109 but it is intertwined together so it is difficult to separate. Uranium-238 is also difficult to separate.

To find the atomic weight for an element it is listed on your periodic table

24.305 would be the atomic mass for magnesium


54.938 would be the atomic weight for manganese

Emission Spectra, Atomic Structure and Isotopes

Emission Spectra

-Each element gives off a specific colour of light

-these are known as emission spectra(unique to each element)

-if electrons absorb energy they can be bumped to a higher level

-when they fall to a lower lever they release that energy as light

Atomic Structure

-atoms are made up of parts called subatomic particles

-protons(positive), electrons(negative), neutrons(neutral)

-atomic number = # of protons

Isotopes

-the # of protons determine the type of element

-changing the # of neutrons change teh isotope of the element

-all isotopes ahve the same chemical properties

Mass Number

-mass # is total of protons and neutrons

-symbol givven to mass is A

-different isotopes have different masses

-mass number = atomic # + # of neutrons(A=Z+N)