Chemistry: Introduction to Organic Chemistry (From Anki)

• ball and stick models

  atomic radii are drawn to scale but the bond lengths are typically twice as long so that the atoms are clearly visible; give information about the relative size of atoms
• bond-line formula


  most common molecular representation on the MCAT; line intersections, corners, and endings represent a carbon atom unless a different atom is drawn in; the correct number of hydrogens to give each carbon four bonds is assumed
• condensed formula


  shows neither bonds nor three-dimensional structure; central atoms are usually followed by the atoms that bond to them even when this is not the bonding order, e.g., CH3NH2
• cyanide ion

  the carbon has three bonds and two nonbonding electrons, giving the molecule a formal charge of -1; electronegativity differences determine the charge distribution of the molecule.
• dash formula

  shows bonds between each atom of a molecule, but does not usually display lone pairs
• dash-line-wedge formula

  solid black wedges come out of the page, dashed wedges go into the page, and lines represent bonds that are in the same plane as the page
• Fischer projection


  common on the MCAT; vertical lines are assumed to be oriented into the page, and horiztonal lines are assumed to be oriented our of the page; typically portray carbohydrates
• formal charge

  = (# of valence electrons) - (# of bonds) - (# of nonbonding electrons)
• Lewis structure


  or Lewis electron dot formula, gives information about each atom's valence electrons: 1- find the total number of valence electrons for all atoms in the molecules 2- use one pair of electrons to form a single bond between each pair of atoms 3- arrange the remaining electrons in lone pairs and double or triple bonds, satisfying the duet rule for hydrogen and the octet rule for other atoms
• Newman projection

  is a view straight down the axis of one of the sigma-bonds; both the intersecting lines and the large circle represent carbon atoms; give information about steric hindrance with respect to a particular sigma-bond
• space-filling model

  3D representation of a molecule; spheres of various colors represent different elemtns with respect to their relative sizes
• valence


  the number of bonds an atom usually forms, e.g., carbon is tetravalent, nitrogen is trivalent, oxygen is divalent, and hydrogen and halogens are monovalent; using empty d-orbitals, sulfur forms 1-6 bonds and phosphorous forms 1-5 bonds