My own chemistry questions....

[albertlee]

strange.... this is my second year at school studying chemistry...

 

why do I never encounter "electronstatics" at school?

 

by the way, for the "potential energy", I think some of you have answered this long ago, but I wasn't able to absorb it.... if you people are kind enough... can you tell me about that again?

(I only know "potential energy" as energy obtained due to the object's position, in most cases, due to gravity. However, I cant picture any possible potential energy in particles...)

 

 

thx

[jdurg]

Okay you've got a good background on what potential energy is. Potential energy is the energy something can 'potentially' use if it needs to. When you hold a lead brick above the ground, the brick has a bunch of 'potential energy' because it can potentially release it if it falls down to the ground.

 

Electrons and atoms are the same way. The electrons in one atom have an attraction to the nucleus of that atom, or of another atom. Remember that the nucleus is full of protons which are positively charged, and electrons are negatively charged. Because of this attraction, the electrons need to have a certain amount of energy to avoid being swallowed up by the protons. They have this energy in the form of kinetic energy (I.E. energy of motion). The electrons are whipping around the nucleus at fast speeds so that they don't get sucked into the nucleus. The overall energy that the electron has is quantized; that means that it is a set amount of energy. So the electron has the kinetic energy of it moving around the nucleus, but it also has the potential energy due to its distance from the nucleus. This potential energy is the amount of energy it could give up by falling closer to the nucleus. So if you're close to the nucleus, you have a lot of kinetic energy but a little bit of potential energy. (It's like having a brick only a few inches above the ground. Not much potential energy there).

 

Electrons all move around the nucleus at about the same speed, but those that are further away have more energy because they have a higher potential energy. (Since they are further from the nucleus. It's like a brick that's two feet above the ground compared to one that's two inches above the ground). So what happens when two atoms combine into a molecule?

 

Well when they are lone atoms, their electrons have a set amount of energy between the kinetic energy and potential energy each electron has. The electrons that are involved in reactions are the outer electrons of the atoms, so they have an elevated potential energy. As an analogy, let's say that Atom A is a five story building and Atom B is a 6 story building. There's a lead brick on the top floor of each building which has a set amount of potential energy in it. When the two atoms combine, it's like they combine into one bigger building that is only 3 stories tall. As a result, those lead bricks have to drop a few stories in order to remain on the top floor. They thus lose some potential energy and it goes out as the kinetic energy of them falling. The same thing happens to electrons involved in a chemical reaction.

 

In the individual atoms, they have a certain amount of potential energy due to their distance from the nucleus. When they combine, they wind up at a different distance from the nucleus. If they are to stay at this distance, they have to give up some of their energy. (Since when you're closer to the nucleus you have less potential energy). This difference in energy is what is given off as heat and/or light in an exothermic reaction.

 

In an endothermic reaction, it's as if those two building combined and made an even taller building. Now, in order to remain on the top floor, the lead bricks have to take in some energy in order to move upwards. As a result, they will absorb energy from the surroundings. This is seen by endothermic reactions as the temperature drops. Does this kind of make more sense?

[albertlee]

thanks...

 

however, I have only met the idea of "energy" in atoms now... so I may not be all clear..

 

so, jdurg..

 

in your post, do you mean that if electrons are nearer to the nucleus, potential energy decreases and kinentic energy increases, if are furthur apart from.. vice versa??

 

secondly, your exp with building is abit obscure to me.... does that refer to the energy level, or the distance from the nucleus??

 

As a consequence, I have some trouble picturing why bonds formed release energy ...

 

 

plz help.. thx

[albertlee]

any body?????

 

btw, can any one explain the graph of post #15??? I just cant imagine how can potential energy be negative....

[jdurg]

thanks...

 

however' date=' I have only met the idea of "energy" in atoms now... so I may not be all clear..

 

so, jdurg..

 

in your post, do you mean that if electrons are nearer to the nucleus, potential energy decreases and kinentic energy increases, if are furthur apart from.. vice versa??

 

secondly, your exp with building is abit obscure to me.... does that refer to the energy level, or the distance from the nucleus??

 

As a consequence, I have some trouble picturing why bonds formed release energy ...

 

 

plz help.. thx[/quote']

 

Kind of. As the electrons move closer to the nucleus, their potential energy does drop off. The kinetic energy of all electrons is basically the same. They are all moving around at the same speed. It's just that those which are further away have more energy in them because they are further away. (It's like they are higher up off of the ground).

 

Let's try the building analogy again. Let's say that a lead brick is an electron and the ground is the nucleus. The brick is highly attracted to the ground and will do what it can to get back down to the ground. The higher up you hold the brick, the more potential energy it has because it's getting further away from the ground. Let's say that a building is an atom. Each floor of the building represents an energy level of the atom. The lower the energy level (The closer to the ground the floor is), the lower the potential energy. In chemical reactions, the electrons that participate in reactions are those in the energy levels furthest away from the nucleus. So in our analogy, we'll just look at the lead bricks on the top floor.

 

Building A is the first atom. It has five energy levels, and the active electron (brick) is on the top floor. Building B is the second atom. It has 7 energy levels and the brick is therefore on the 7th floor. Each of these bricks has a potential energy due to their distance from the ground floor (nucleus). When a chemical reaction happens, atom A and atom B combine to form the molecule AB. This AB molecule will contain the electrons from the top floor of Atom A and Atom B. Molecule AB's highest energy level, however, is only 4 stories high. So the electron from Atom A is now down to the 4th floor and the electron from Atom B is down to the 4th floor. (Remember, these are the outer electrons we're talking about here and after the reaction they remain as 'outer' electrons). So our new molecule AB is now a wider building that is only four floors high. Because of this, those two bricks have less potential energy than they did before. This potential energy had to go somewhere, so it was released in the form of heat and light.

[albertlee]

thanks jdurg....

 

now I have come a few more questions....

 

 

What keeps the eletrons from "falling" towards the necleus?

 

In addition to your post, what is happening in ionic bonding instead?

Take for example, the difference between Potassium reacting with water to form Potassium Hydroixde and Cesium to form Cesium Hydroxide....

 

 

thanx

[albertlee]

and yet, another question.

 

Say, a chemical cell with Copper and magnesium electrodes and HCl electrolyte..

 

I know Magnesium is more ready to give up its electrons, that's why it reduces in size... however, what tells Copper not to give up its electrons?? I was like expecting both give up their electrons although Magnesium has a faster rate.....

[albertlee]

and one more supplement question to the previous, why the greater difference in reactivity of two different metal electrodes cause a greater voltage?

[Alchemist]

Basically when two atoms react with one another they need to come in contact with one another. So in other words they have collide with one another, when this happens they release energy namely in the form of heat (some reactions release energy in a different form, light for example; chemical luminescence) this is for exothermic reactions.

 

For endothermic reactions there is more energy needed for the atoms to react (collide with one another) then there is released namely energy in the for of heat is needed.

For the reaction to take place thermic energy is used, meaning that the surrounding temperature drops.

 

(Exothermic reactions produce energy in the form of heat)

(Endothermic reactions use energy in the form of heat (from the surroundings) meaning that the surrounding temperature drops)

 

I hope that this information will help understand why Albert.

[budullewraagh]

well, energy is released upon bond formation because electrons involved in the bond end up at a combined lower energy level than before. the reaction. it is this truth that drives all reactions. upon bond cleavage, energy is absorbed so the electrons may reach the higher energy level once more

[albertlee]

yes, but can you explain this with the potential and kinetic energy that Jdurg has demonstrated??

 

thanx

[albertlee]

plz, where is jDurg?? plz help me!!