Chem301 Ch1 USD
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as a result of the motion of electrons.
- "vital force": stipulated that it should be impossible to convert inorganic compounds into organic compounds without the introduction of an outside vital force.
- Destroyed by German chemist Friedrich Wohler in 1828 by the conversion of ammonium cyanate (a known inorganic salt) into urea, a known organic compound found in urine:
- NH4OCN --Heat-->
- have different physical properties and different names but have the same elements and the same number of each element (same moleculare formula) but attached differently.
- EX: Ammonium cyanate and Urea
- or Dimethyl ether and Ethanol
- describes the number of bonds usually formed by each elemnt.
- EX: Carbon makes four bonds and is called tetravalent.
- Makes four bonds.
- EX: Carbon "C"
- Makes three bonds.
- EX: Nitrogen "N"
- Makes two bonds.
- EX: Oxygen "O"
- Makes one bond.
- EX: Hydrogen "H"
Existence of electron
- Was first introduced in 1874 by George Johnstone Stoney.
- In 1897 J.J. Thomson demonstrated this and is credited to discovering the electon.
- Two atoms sharing a pair of electorns.
- Note: Gilbert Lewis defined covalent bond in 1916.
- Electro negativity value under (1.8??)
The electrons in the outer most shell of an atom.
nonbonding pair of electrons.
is associated with any atom that does not exhibit the appropriate number of valence electrons.
- The measure of the ability of an atom to attract electrons.
- Note: typically Florine is the strongest and the electonegitivity decresses as you move away from "F".
Nonpolar covalent bonding
- will have an electronegativity of less than 0.5.
- This means that the two atoms sharing the electons are doing so rather if not completly evenly.
Polar covalent bonds
- Will have an electronegativity value between 0.5 and 1.7.
- This meas that although the two atoms are sharing a pair of electrons, the pull (or attraction) is not even and will cause each atom to be slightly charged, one positive and the other negative.
- Will have an electronegativity value above 1.7.Is when one atom "steals" an electron from another.
Second-row elements generally obey this rule, bonding to achive noble gas electron configuration.
- 1924 french physicist Louis de Broglie suggested that electrons, heretofore considered as particles, also exhibited wavelike properties.
- 1926 Erwin Schrodinger, Warner Heisenberg, and Paul Dirac independently proposed a mathmatical description of the electron that incorperated its wavelike properties.
An equation is constructed to describe the total energy of a hydrogen atom (i.e. one proton plus one electron). This equation takes into account the wavelike behavior of an electron that is in the electric field of a proton.
is given when the wave equation is solved. The greek symbol psi (
) is used to denote each wavefunction with a subscript number(2
). Each of these wavefunctions corresponds to an allowed enegy level for the electron. This result is incredably important because it suggests that an electron, when contained in an atom, can onlyexist at discrete energy levels. In other words, the energy of the electron is quantized
The probability of finding an electron in a particular region of space.
The shape of an orbital refers to the region of space that contains 90 - 95% of the electron density. Beyond this region, the remaining 5-10% of the electron density tapers off but never ends. In fact, if we want to consider the region of space that contains 100% of the electron density, we must consider the entire universe.
- An occupied orbital must be treated as a cloud of electron density. Because it is a region of space defined with respect to the nucleus of a single atom.
- EX: s, p, d, f
Locations where a wave hits a zero value. or when
Orbitals with the same energy level.
The lowest-energy orbital is filled first.
Pauli exclusion principle
Each orbital can accomodate a maximum of 2 e-
that have opposite spin. To understand what "spin" means, we can imagine an e-
spinning in space (although this is an oversimplification explanation of the term "spin"). For reasons that are beyond the scope of this coarse, electrons only have two positive spin states (designated by
). In order for the orbital to accomodate 2 e-
, the e-
must have oppisite spin states.
When dealing with degenerate orbitals, such as p orbitals, 1 e- is placed in each degenerate orbital first, before electrons are paired up.
produces a wave with larger amplitude.
results in waves canceling each other, which produces a node.
Valence bond theory
a bond is simply the sharing of electron density between two atoms as a result of the constructive interference of their atomic orbitals.
- The overlap of of an orbital between to atoms; the electon density of this bond is primarily located on the bond axis (the line that can be drawn between the 2 atoms).
Molecular orbital (MO) theory
describes a bond in terms of the constructive interference between 2 overlapping atomic orbitals (like bond theory). However it goes further by using mathmatics as a tool to explore the consequences of atomic orbital overlap. The mathmatical methode is called the linear combination of atomic orbitals (LCAO). According to this theory, atomic orbitals are mathmatically combined to produce new orbitalls, called molecular orbitals.
the new orbitals formed from overlapping orbitals.
the lower energy molecular orbital is the result of constructive interference of the original 2 atomic orbitals.
The higher the energy molecular orbital is the result of destructive interference. Notice that the antibonding MO has 1 node, which explains why it is higher in energy.
Highest occupied molecular orbital
(HOMO); the highest energy orbital from among the occupied orbitals.
Lowest unoccupied molecule orbital
(LUMO); the lowest energy orbital from among the unoccupied orbitals.
hybridized atomic orbitals
A hybrid orbital is an orbital formed by the combination of two or more atomic orbitals.
- The p orbitals actually overlap with each other as well as in ethylene.
- note: that there is only 1 pi bond above, NOT 2.
Example of 1 sigma bond and 2 pi bonds
- or rather
What does VSEPR stand for
Valence Shell Electron Pair Repulsion
- total sigma bonds
- + total pi bonds
- = Steric #
Steric number 4 (sp3) could be what geometries?
- Trigonal pyramidal
Steric number 3 (sp2) could be what geometries?
Steric number 2 (sp) could be what geometries?
occur between two molecules that possess permanent dipole moments.
a special type of dipole-dipole interaction that occures when the lone pairs of an electonegative atom interact with an electron-poor hydrogen atom. Compounds that exhibit hydrogen bonding have higher boiling points than similare compounds that lack hygrogen bonding.
1 debye = 10-18
The attractive forces between the individual molecules.
- a special type of dipole-dipole interaction that occurs between an electronegative atom and a "H" atom that is connected to another electronegative atom.
- Note: except when attached to F,O,N.
- any compound that has a proton connected to an electnegative atom.
- EX: ethanol.
Compounds that contain carbon and hydrogen and only have single bonds.
London dispersion forces
Have a polar head and nonpolar tail (extnsive at times). compounds that will contain both hydrophylic and hydrophobic regions. The hydrophobic tails surrond nonpolar compounds, forming a water-soluble micelle.
a ball of polar heads on the outside with nonpolar tails on the inside.
Hydrogen deficiency index
- [HDI] = [(2C + 2 + N - X) - H] / 2
- Note: C = # of carbon, N = # of nitrogen, X = # of all halogens, H = # of hydrogens.
- 0 = all single bonds
- 1 = double bond or ring
- 2 = Triple and/or double and/or enclosed (ring).
- Note: there could be a double and a ring for an answer of 2 or any combination of the possabiliyies.
What happens when you cross a node with the electon density?
- The node itself means no density, after you cross it it will be the oppisite spin (charge).
What are the electronegativity values for bonds?
- Non-polar covalent: < 0.5
- polar covalent: = .5 - 1.7
- Ionic: = 1.7 and up
Electrostatic attraction between ions of oppisite charges.
Delta EN is always a prediction, so we write WE PREDICT
- the # of occupied sites around the atom.
- # of atoms attached + # of lone pairs (or partial lone pairs).
- Steric # shapes:
- 2 = Linear
- 3 = Bent, triaganol planer
- 4 = Bent, triaganal paramidail, tetrahedral
typiclly . . .1s' 2p3 . . . whenever the first half of an orbital is filled.
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