Drawing Dot Structures

Dot Structures Drawing Dot Structures: Group number corresponds to how many valence electrons that particular element has The central atom is typically the one with the lowest electronegativity The 3rd period and on, elements can begin violating the octet rule (atoms CAN have less than octet if its formal charge if dealt with, such as B) You also need to put any extra electrons onto the central atom (even if it violates the octet rule, such as in the instance on the right for XeF5+) Formal Charge & Dot Structures: Formal charge is the charge assigned to an atom in a molecule, assuming that electrons in all chemical bonds are shared equally between atoms, regardless of differences in electronegativity (NH4+ has an N with a formal charge of +1 while H has a formal charge of 0) Molecules tends to like to minimize the formal charge as much as possible Resonance & Dot Structures: Resonance structures are different ways that the molecule appears (although not an accurate representation of what is occurring, in real life it's actually a hybrid of the different resonance structures with delocalized electrons throughout known as a resonance hybrid: we know this occurs because when you measure bond lengths, they are all the same length) VSEPR for 2 Electron Clouds: Valence shell electron pair repulsion (VSEPR) theory is the idea that electrons repel one another, forcing the molecule to take a particular shape When there are two electron domains then the bond shape is linear (180°) VSEPR for 3 Electron Clouds: When there are three electron domains, then the bond shape is trigonal planar (120°) Bent/angular (~120°) refers to the molecular shape when there is a nonbonded pair of electrons VSEPR for 4 Electron Clouds: When there are four electron domains, then the bond shape is a tetrahedral (109.5°) Trigonal pyramidal (~107°) refers to the molecular shape when there is a nonbonded pair of electrons (nonbonding electrons occupy a little more space and therefore repel the other electrons a little more, making the bonding angle a little smaller) Bent/angular (104.5°) refers to the molecular shape when there is two nonbonded pairs of electrons (there are two non bonding pairs of electrons and therefore make the bonding angle even smaller) VSEPR for 5 Electron Clouds: When there are five electron domains, then the bond shape is trigonal bipyramidal (180°, 120°, and 90° bond angles) Since nonbonded pairs of electrons repel each other more, nonbonded pairs of electrons in trigonal bipyramidal will be located in the equatorial position since it is only 90° to 2 other atoms as opposed to 3 if it were in the axial position (axial is the red dots and equatorial are the green dots) - See saw refers to the molecular shape when there is one nonbonded pair of electrons T shaped refers to the molecular shape when there are two nonbonded pairs of electrons Linear refers to the molecular shape when there are three nonbonded pairs of electrons VSEPR for 6 Electron Clouds: When there are six electron domains, then the bond shape is an octahedral (180° and 90°) Square pyramidal refers to the molecular shape when there is one nonbonded pair of electrons Square planar refers to the molecular shape when there are two nonbonded pairs of electrons (lone pairs will typically get as far away as possible and therefore go 180° from one another) Extra C, N, O, truly When we treat the bonds as if they were ionic Notes: and F are the only molecules that adhere to the octet rule assigning oxidation numbers/states, bonds where the more electronegative atoms is awarded the electrons (ranges from -4 → +7) while with formal charge we assume the atoms share the electrons evenly # of e- normally minus the # of e- given due to differences in electronegativities Bond order is the total number of bonds divided by the number of attaching atoms Fractional charge is the total charge on the attaching atoms divided by the number of attaching ions Oxygen is more electronegative than Fluorine