Chem 112 Exam AID Course Pack

Therefore oh2 has a much smaller bond length than ch4

Info icon This preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: COHCO2H, CH2N(CH3)2, SF6, CO2, H2SO4 If structures are charged, put brackets around them and then write the charge (ex +, 2+) in the top right. - to find out which atoms the charges are on, count and see if any of the atoms have greater or fewer bonds than they normally make - for example, oxygen (normally makes two bonds) is negative if it has only one, and positive if it has three - also, the total charges of the atoms in a molecule must add to the total charge on the molecule - other than ionic compounds, no individual atom is ever likely to have a charge greater than +1 or - 1 - it is also unlikely for a molecule to have both positive and negative charges (though this is permissible under certain circumstances, if no other options are available) More precisely, we calculate formal charge: count the number of electrons around an atom (counting only one of any pairs of electrons within covalent bonds) and see if this is more or less than the atom’s group number. - for example, oxygen (group VI) is positive if it has five electrons and negative if it has seven - note that an atom which is not a noble gas may still have a valence shell of eight while still having zero formal charge, because some of those might be shared: formal charge counts only one of the electrons in a covalent bond, while a valence shell counts both - for example, oxygen with two bonds has a formal charge of zero (six electrons) but a valence of eight – while oxygen on its own with a valency of eight (unlikely to exist) would have all eight electrons entirely to itself and would have a formal charge of –2. Atoms which have the same numbers of bonds and lone pairs as each other are termed isoelectronic. - ex any carbon atom is isoelectronic with the N in NH4+ (both have four bonds, no lone pairs) Molecules may also exhibit resonance - occurs when there are multiple valid Lewis structures - the actual molecule is a mix of the individual structures - if the resonance structures are not equally stable, the most stable one (ex one with fewer charges) will dominate Ethan Newton & Barry Zhang for SOS Winter 2012 10 - only electrons may move; atoms may not - especially common when a molecule is charged also more common around electronegative atoms, like oxygen and nitrogen 3.0 Atomic Structure Molecular Geometries - electron pairs assume orientations to minimize electron repulsions Electron Repulsion...
View Full Document

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern