This is a great question. The brief answer isactually the the electrons aren"t exactly"fixed" in details "positions" "above" theoxygen.

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castle reside in lone pair orbitals,which means they have a probability that existingin some an ar of an are which is generallydepicted as being "above" the oxygen, and anextremely low however finite (non-zero) probability ofbeing exterior of that an ar (e.g. Closer come thebonds the oxygen develops with the hydrogen atoms.

But let"s ago up a small and first thinkabout what comprises a water molecule. A watermolecule is made up of 2 hydrogen atoms, eachof which are covalently bonded to an oxygen atom.There are a complete of 2 covalent binding in themolecule, one between the first hydrogen atom andthe oxygen atom, and also another bond in between thesecond hydrogen and the oxygen. This single,covalent bonds are referred to as "sigma" bonds.Each sigma bond has actually "room" for 2 electrons. Nowlet"s think around how this sigma bond areformed...

Each hydrogen atom has a single valenceelectron which that "shares" v the oxygen atom inits respective sigma bond. The oxygen atom, inturn, has actually six valence electrons available, 2 ofwhich go toward the sigma bonds made with thehydrogen atoms (one valence electron to every sigmabond). That means there are four remainingelectrons, i beg your pardon reside on the oxygen as lonepairs. In each lone pair, one of the electronsexists in a "spin up" configuration, if theother exists together a "spin down" electron. Why isthis? it is energetically favorable because that theelectrons to exist in this configuration.

Furthermore, if the electrons existed in thesame rotate state and also belonged come the exact same orbital,we would certainly be violating the Pauli ExclusionPrinciple, which forbids particles from havingthe precise same four quantum numbers, i m sorry youhave probably learned around in her chemistryclasses, however if you room rusty have the right to look increase in yourold chemistry publication or in ~ the UC Davis Chem Wikipage on quantum numbers.

So why did we go through every one of that? Whatwe"ve said so much is that there are two sigma bondorbitals, each v two electrons, and also two lonepairs, additionally comprised of two electrons each,associated v the oxygen atom in the watermolecule. All these orbitals (bonds and lonepairs) have electrons distributed amongst them. Theorbitals themselves are a way of explicate theprobability of whereby an electron may be found.

Look at the following figures because that a clear photo of the process.

Fig. 1 depicts a cartoon version of one O-Hsigma bond. The "probability density" that findingthe electrons is highest in between the O and H, andis very low outside of this area (thus, wehave a bond, since the electron are most likelyto it is in found in between the O and also H). The electrons inturn lure the nuclei the the O and also H atoms, thus"keeping them" "close" together.

Now, all of the electrons in the orbitals arenegatively charged, which way they have arepulsive interaction with the various other electrons inother orbitals. Thus, the sigma bonds and also the lonepairs will be oriented in together a method as tominimize the overlap in between different bag ofelectrons. Hence we view the tetrahedral shape ofthe orbitals in Fig. 2. Note that we"re usinglines come depict the bonds between the O atom andthe H atoms, yet really over there is a "cloud" ofelectron density between those atom describingthe likelihood to uncover electrons there.

At this point, you might ask, "if the electronsrepel every other, why execute two of lock share anorbital?" and that would be a great question.Hund"s Rule states that we have to fill theorbitals for this reason they have one electron each, and thenstart pairing them when we have worn down all theempty orbitals. This comes earlier to the idea ofquantum numbers. The primary quantum number(1,2,3,...) synchronizes to how much away theelectrons are from the nucleus, or how large theorbital is. The greater the quantum number, thelarger the orbital and also the greater (in general) energy of the "state" of the system. It is morefavorable/stable to be in a lower energy state, sowe view that electrons commonly fill the orbitalsfrom low to high principal quantum number. Foroxygen, there space 8 easily accessible "spots" for theelectrons to be in the n=2 shell. In the watermolecule, 6 that the electron come from the oxygenatom itself, and the various other two are "shared" withthe hydrogen atoms. Therefore why not start filling then=3 orbitals through one electron each? that wouldresult in a higher total energy of the system,which is much less stable.

OK. That was a the majority of information. Let"s recapbriefly: ultimately, the electron in the orbitals(both bonding and lone pair) approximately the oxygenatom in a water molecule room oriented in a way tominimize electron density overlap.

i hope thishelps!

Answer 2:

You have fantastic question. You want toknow why the electron holes are situated “above”the oxygen in a water molecule quite than ~ above thesides. Girlfriend may have actually seen molecules defined witha Lewis structure where electrons and also holes andrepresented as dots on the molecule. You might haveseen valence shells represented with the moleculargeometry as well. One can find examples in ~ thiswebsite click below please . The geometric design isgreat due to the fact that it is straightforward to store track of chargesand we space going to usage it for now.

Molecules, as most things, want to minimizetheir total energy. Oxygen has an orbit shapewith sp4
bonds all located around 109degrees from every other. This shape enables for theelectrons to it is in as much apart indigenous each various other whilestill pour it until it is full the oxygen’s valance shell. Theyoxygen and hydrogen space both doing not have electrons tohave a full valance covering so they share at 2 ofthe oxygen’s sp4 sites. The other 2 pairs ofelectrons desire to be as far apart as possible,otherwise the power of the molecule willincrease. Those electrons bag are situated at theunused orbital location. The extra electrons pairsfill orbitals on the various other side the the oxygen indigenous hydrogen. The Lewis structure have the right to bemisleading due to the fact that they space not both sit ontop the the oxygen but rather the two pairs space atan angle. Please look at the photos on Universityof Wisconsin’s website. ~ above the reference offered youcan view that the hydrogen space actually 104 degreesapart from each other, at this time that is a minordetail.

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ns am walking to leave you v a an ext advanced wayof thinking around electrons in molecules. Ratherthan presume the electrons are unique particleswhich are calmly staying at the lowest energyposition the the molecule, let united state think about themas clouds of an unfavorable charge with a probability offinding the fragment at different places. If onewas to probe the water molecule for the locationof the electrons, one would uncover that the locationwould be various each time. The highestprobability of recognize the electron is thelocation provided by the geometric model. Many of thetime girlfriend will uncover the electron bag ~109 degreesfrom every other. Sometimes it will be possible tofind the electrons on the “side” of the oxygenatom or at various angles. Over there are other areaswhere the probability of recognize the electron goesto zero. This cloud property is because of theelectrons quantum mechanically nature.