- Messages
- 198
- Reaction score
- 47
- Points
- 28
hey anglegirl.... ive not even done anything for p2..... im so damn scarrrrrrrrred
We are currently struggling to cover the operational costs of Xtremepapers, as a result we might have to shut this website down. Please donate if we have helped you and help make a difference in other students' lives!
Click here to Donate Now (View Announcement)
WA.As-Salaamu 'Alaykum.
Someone please explain to me the Electron-Pair Repulsion Theory; I don't get it at all. How do we determine what the bond angles and shapes of molecules are? Jazak Allah.
WA.
Please give this a read, it helped me quite a bit. Also, let me try to explain with an example, CH4.
The central atom is C and it is surrounded by 4 hydrogens. First find the number of electrons being shared. In this case, it is 4 from carbon and 1 from each hydrogen, totaling up to 8 electrons. Now, each bond uses 2 electrons. There are 4 bonds, and therefore no lone pairs. So CH4 has 4 bonds and no lone pairs.
Another one: NH3. The central atom is N and it makes 2 bonds with hydrogen. The total number of electrons being shared are 5 from Nitrogen and 3 from the hydrogens. So total electrons = 8. Nitrogen makes 3 bonds (which use 6 electrons), so 2 electrons are left making 1 lone pair. So NH3 has 3 bonds and 1 lone pair.
When you have the bonds and lone pairs decided, learn this:
2 bonds, 0 lone pair = linear and 180 degrees (e.g. CO2)
2 bonds, 1 lone pair = angular and 117 degrees. (e.g. BF3)
2 bonds, 2 lone pair = angular and 104.5 degrees. (e.g. H2O)
3 bonds, 0 lone pair = trigonal planar and 120 degrees. (e.g. AlCl3)
3 bonds, 1 lone pair = trigonal pyramidal = 107 degrees. (e.g. NH3 as I did above)
4 bonds, 0 lone pair = tetrahedral = 109.5 degrees. (CH4 as I did above)
5 bonds, 0 lone pair = trigonal bipyramidal = 90 and 120 degrees. (PCl5)
6 bonds, 0 lone pair = octahedral and 90 degrees. (SF6)
The theory is basically that the electron pairs arrange themselves around the central atom to minimize the amount of repulson, so they try to be as far apart as possible. Also, you need to know that lone pair - lone pair repulsion > lone pair - bond repulsion > bond-bond repulsion. Lone pair repulsions are stronger because they are closer to the atom and therefore exert more pressure.
They arise due to the lack of rotation around the C=C bond.PLease answer this question why does cis-trans isomerism arise in a molecule?
WA.
Please give this a read, it helped me quite a bit. Also, let me try to explain with an example, CH4.
The central atom is C and it is surrounded by 4 hydrogens. First find the number of electrons being shared. In this case, it is 4 from carbon and 1 from each hydrogen, totaling up to 8 electrons. Now, each bond uses 2 electrons. There are 4 bonds, and therefore no lone pairs. So CH4 has 4 bonds and no lone pairs.
Another one: NH3. The central atom is N and it makes 2 bonds with hydrogen. The total number of electrons being shared are 5 from Nitrogen and 3 from the hydrogens. So total electrons = 8. Nitrogen makes 3 bonds (which use 6 electrons), so 2 electrons are left making 1 lone pair. So NH3 has 3 bonds and 1 lone pair.
When you have the bonds and lone pairs decided, learn this:
2 bonds, 0 lone pair = linear and 180 degrees (e.g. CO2)
2 bonds, 1 lone pair = angular and 117 degrees. (e.g. BF3)
2 bonds, 2 lone pair = angular and 104.5 degrees. (e.g. H2O)
3 bonds, 0 lone pair = trigonal planar and 120 degrees. (e.g. AlCl3)
3 bonds, 1 lone pair = trigonal pyramidal = 107 degrees. (e.g. NH3 as I did above)
4 bonds, 0 lone pair = tetrahedral = 109.5 degrees. (CH4 as I did above)
5 bonds, 0 lone pair = trigonal bipyramidal = 90 and 120 degrees. (PCl5)
6 bonds, 0 lone pair = octahedral and 90 degrees. (SF6)
The theory is basically that the electron pairs arrange themselves around the central atom to minimize the amount of repulson, so they try to be as far apart as possible. Also, you need to know that lone pair - lone pair repulsion > lone pair - bond repulsion > bond-bond repulsion. Lone pair repulsions are stronger because they are closer to the atom and therefore exert more pressure.
2 bonds, 1 lone pair = angular and 117 degrees. (e.g. BF3)
You are right.. I made a mistake there. I changed it to SO2.O_O I understand now... almost.
Jazak Allah; thanks a lot that really made things simpler. Just one thing;
Isn't BF3 trigonal planar with 3 bonds and no lone pair? ;
You are right.. I made a mistake there. I changed it to SO2.
Nope, it only has 1. The oxygen's have 2 lone pairs, but sulfur has only 1.... Doesn't SO2 have two lone pairs?
All electrons have negative charges so there are repulsive forces among them.As-Salaamu 'Alaykum.
Someone please explain to me the Electron-Pair Repulsion Theory; I don't get it at all. How do we determine what the bond angles and shapes of molecules are?
And whats the shape of/bond angles in an ammonium ion, NH4+?
Jazak Allah.
syllabus states: b) explain qualitatively in terms of intermolecular forces and molecular size:
(i) the conditions necessary for a gas to approach ideal behaviour
(ii) the limitations of ideality at very high pressures and very low temperatures
ans to i is high temp and low pressure...what abt ii??
High pressure and low temperature shall lead to relatively strong intermolecular forces. This means there is potential energy among the molecules. Ideal gases don't have any molecular potential energy.syllabus states: b) explain qualitatively in terms of intermolecular forces and molecular size:
(i) the conditions necessary for a gas to approach ideal behaviour
(ii) the limitations of ideality at very high pressures and very low temperatures
ans to i is high temp and low pressure...what abt ii??
Nope, it only has 1. The oxygen's have 2 lone pairs, but sulfur has only 1.
http://www.xtremepapers.com/papers/... AS Level/Chemistry (9701)/9701_w11_qp_21.pdf
Q3d...isnt the formula of calculating enthalpy change..Enthalpy change of products - enthalpy change of reactants...?? ms is doing the opposite..
EXACTLY. i"ve posted this question so many times in different threads here but no one has answered it yet..i hope someone does soon because im really confused!This I need an answer to as well... I get this wrong almost every single time. When I memorize Enthalpy change of products - reactants, and solve a paper, the MS says reactants - products. When I do that in the next paper, THEN the MS goes back to Product - Reactants.
X_x
Actually, sulfur forms a double bond. In double bond, you add 2 electrons (as opposed to adding 1 in a single bond, I forgot to mention that sorry). So sulfur has 6, each oxygen has 2 making a total of 10 electrons. Now, in each double bond, 4 electrons will be used leaving 2 behind. These 2 form a lone pair of sulfur.Sulfur has 6 electrons, forms two bonds with two Os which makes 8 shared electrons. Which makes, as you taught, 4 shared electron pairs. 2 of these are bond pairs because there are 2 oxygens; doesn't that leave behind 2 lone pairs on the sulfur?
is there a formula for calculatiing enthalpy change of rxn using bond energies?
For almost 10 years, the site XtremePapers has been trying very hard to serve its users.
However, we are now struggling to cover its operational costs due to unforeseen circumstances. If we helped you in any way, kindly contribute and be the part of this effort. No act of kindness, no matter how small, is ever wasted.
Click here to Donate Now