What is Vsepr: Definition and 20 Discussions

Valence shell electron pair repulsion theory, or VSEPR theory ( VESP-ər, və-SEP-ər), is a model used in chemistry to predict the geometry of individual molecules from the number of electron pairs surrounding their central atoms. It is also named the Gillespie-Nyholm theory after its two main developers, Ronald Gillespie and Ronald Nyholm.
The premise of VSEPR is that the valence electron pairs surrounding an atom tend to repel each other and will, therefore, adopt an arrangement that minimizes this repulsion. This in turn decreases the molecule's energy and increases its stability, which determines the molecular geometry. Gillespie has emphasized that the electron-electron repulsion due to the Pauli exclusion principle is more important in determining molecular geometry than the electrostatic repulsion.VSEPR theory is based on observable electron density rather than mathematical wave functions and hence unrelated to orbital hybridisation, although both address molecular shape. VSEPR has a physical basis in quantum chemical topology (QCT) methods such as the electron localization function (ELF) and the quantum theory of atoms in molecules (AIM or QTAIM).

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  1. Z

    Chemistry How do we know ##BF_3## has Lewis structure but ##Al_2S_3## does not?

    The first thing we notice is that we have a metal and a nonmetal, so we would think about an ionic model. These elements form the ions ##Al^{3+}## and ##S^{2-}##. These ions form a lattice structure and we get an ionic crystal. But apparently no bond is perfectly ionic or covalent. The...
  2. Frigus

    How can I understand valence bond theory and VSEPR theory?

    I think these theory is made to match the experimental results because I watched videos from Khan academy, jg e.t.c all of them teaching in video is that how do we calculate hybridisation, sigma bonds, π bonds e.t.c and to me these these sources are best because most of the times they gives...
  3. L

    Which molecule most likely to deviate from ideal values?

    Hi, Hoping I could get some help on this one. How would I know what causes bond angles to deviate from the ideal values? I greatly appreciate any help and advice on this. Thanks
  4. Y

    What really are resonance structures?

    This is a concept I have never really understood. I mean to say is how can we include such a thing in a theory? How can we use them if we know that they don't actually exist? Are they some sort of calculation tool?
  5. J

    Memorizing VSEPR Structures: A Simple Method for Success

    So I'm just posting this here for anyone else currently trying to memorize the VSEPR table, or just for future reference for anyone else. There's not a whole lot online about memorizing this table so I thought I'd throw my method out there. There's really not a whole lot to it other than good...
  6. N

    Geometric Interpretation of VSEPR Theory

    I am making a Geometric model for VESPR theory, which states that valence electron pairs are mutually repulsive, and therefore adopt a position which minimizes this, which is the position at which they are farthest apart, still in their orbitals. For example, the 2 electron pairs on either side...
  7. W

    Chemistry VSEPR - Bonding and Molecular Geometry

    Homework Statement What is the electron pair geometry of the following? SCN− BeCl2 O3 The Attempt at a Solution SCN− Linear BeCl2 Linear O3 Trigonal Planar Homework Statement Would the following structures be polar or nonpolar? (Not applicable if the structure is an...
  8. J

    CH3CH3 tetrahedral VSEPR structure

    Homework Statement Draw the VSEPR structures. CH3CH3 Homework Equations The Attempt at a Solution This is throwing me off because there are basically 2 tetrahedral. So, that is what I did. I drew a tetrahedral VSEPR structure and I connected another one to it upside down. Is...
  9. J

    Draw VSEPR Structures: CsF Ionic, Polar Covalent or Non-Polar?

    Homework Statement I'm supposed to draw VSEPR structures showing all valence electrons for the molecule. Draw in the partial charges δ+ and δ- if they exist. Classify the molecules as ionic, polar covalent or non-polar covalent. Some molecules may be of hypothetical existence. Homework...
  10. P

    VSEPR t-shaped geometry vs trig. planar

    Homework Statement i'm confused as to why a molecule with 3 bonding pairs and 2 lone pairs takes on a t-shape rather than a trigonal planar shape. My notes say that this is because in a t-shape, there are less 90 degree angles between the lone pairs and the bonding pairs than in a...
  11. V

    VSEPR Model: Bond Angles of TeCl4

    Homework Statement What are the bond angles of TeCl4 Homework Equations none The Attempt at a Solution The electronic geometry should be Trigonal Bipyramidal The molecular geometry should be See-Saw shaped (Steric Number 5, One lone pair) I know the angles are less than those...
  12. E

    VSEPR Theory - not homework related

    This is an excerpt from http://www.s-cool.co.uk/alevel/chemistry/atomic-structure/shapes-of-molecules.html" SCROLL DOWN. My question is quite simple : what does this mean ? What are they trying to say ?
  13. M

    Learn VSEPR Theory: Carbon & Oxygen Bonding

    okay so I am learning the Valence bond theory and the VSEPR theory in chemistry. and so far its been going well. but i don't understand how carbon and oxygen combine together forming a triple boond creating CO (carbon monoxide) because we only have 4 valence carbon electrons so how can it form...
  14. E

    Lewis structure, hybridization and VSEPR

    Homework Statement Consider the related molecules POF2- and POF3. Choose all the following statements that are correct for both molecules. Homework Equations A) P atom is sp3-hybridised B) The F-P-F bond angle will be approximately 109.5 degrees C) Geometry around he P centre is...
  15. F

    VSEPR Method: Finding Geometry of SiO4^2-

    Homework Statement Hi I've been torturing my head for hours, trying to find the geometry of [SiO4]2- using the VSEPR method. Thus, I'd be really grateful if you can help me find: 1) If [SiO4]2- really exists 2) If it exists, then what's its geometry?Homework Equations The Attempt at a Solution...
  16. K

    VSEPR Model for AsH3 and OF2: Understanding Molecular Geometry

    Homework Statement What is the geometry of AsH3 according to the VSEPR model? The Attempt at a Solution As has 5 valence electrons and H has one. The molecule therefore has four sets of electron pairs, whereof one is unshared. This gives a tetrahedral structure where the As-H angles...
  17. K

    Resonance Structures and VSEPR

    Hi, I'm having trouble figuring out which of the following molecules can be described using three charge-minimized resonance structures. Does anyone have any idea which molecules this would include? a. SF4 b. SO3 c. SO32- d. HSO4- e. SO2+
  18. V

    Where Can I Find Advanced Tutorials on VSEPR Theory and Lewis Dot Structures?

    does anyone have good tutorials on the vsepr theory...anything about the lewis dot structure...more advanced.
  19. C

    Unravelling the Mystery of VSEPR Theory

    VSEPR Theory... I am completely at ease with being able to use VSEPR theory to answer questions, etc, but I just can't get my head round why it actually happens? All I am told is "electron clouds repel each other to be as far apart as possible", but this seems to completely disagree with the...
  20. T

    VSEPR Theory: Investigating Ionic Molecules

    Vsepr Theory Hey Guys! How are u guys doing today? I was wondering how do we know dat BeF2 is polar?..i drew it out by using the VSEPR theory..but what confuses me is dat BeF2 ionic..can we still use VSEPR theory to draw it out? Tanya Thank you in advance! :smile: