User talk:Kroucacj

Matter
Hi Neels,

I'm probably crazy to try to answer your question, but fools rush in where angels fear to tread.

Electricity, of course, has to do with matter that carries electric charge—that quantity which can be positive or negative, or 0, or any integral multiple of the charge on an electron. Which also feels and responds to the electric force, a force which is attractive for opposite charges, and repulsive if the charges are the same sign. If the charges on two particles are q1 & q2, and the distance between then r, then the force of attraction is


 * F = - k q1 q2 / r2,

where F is the force, k is a constant, and the "-" sign makes the attraction positive if q1 & q2 have opposite signs, negative (ie, repulsive) if the signs are the same. It is really quite similar to the gravitational force law, except that is always attractive, and much much weaker: if all the electrons in a gm of H were stripped off the protons, and the electrons were placed at the North Pole, and the protons at the South Pole, the attractive force between them would be hundreds of tons, even though the distance r would be over 12,000 km.

Then there are all these elementary particles, some with charge, some not. There are just three you really must know to start: the electron, e, with charge -e, the proton, p, with charge +e, and the neutron, n, with charge 0. These are the only particles that are important for understanding all of chemistry, all of biology, and most of elementary physics. These particles all have mass, which is to say they are heavy, and have inertia. Physicists like to measure mass (and also energy) in "electron volts" (eV). In these units, the mass of an electron is about 511,000 eV, a proton about 938,000,000 eV, and a neutron about 939,000,000 eV. (We often abbreviate these, 1000 eV = 1 keV, & 1,000,000 eV is 1 MeV, so in MeV units the mass of an electron is 0.511 MeV, a proton about 938 MeV, and a neutron about 939 MeV.)

And that is almost all you need to know for basic science! Well, there is another, very strong force, that binds p's & n's together. But all you need to know about it is that it is strong, and not affected by the electric force; end of story.

That is practically all you need to know to understand about atoms, which are made of e's, p's, and n's. The simplest, basic atom is hydrogen (H), that has one p and one e.  Of course they attract each other electrically, and the electron stays close to the (much heavier!) p, so that the two together form a neutral combination, a hydrogen atom, about 0.000,000,01 cm in diameter, with a mass about the sum of the masses of the e & the p.  Then because of the strong force, 2 p's and 2 n's like to bind together to form a tiny object (about 100,000 times smaller than a H atom). (I guess I have to say that all these particles are tiny. The p & n are nearly the same size, and the e is smaller still, but moves around a lot because of its small mass.)  So this lump of 2p's+2n's is tightly bound together by the strong force, and it will then generally attract two e's, to move around it, and form the next atom, helium (He), which is about the size of an H atom, but weighs 4 times as much (because the n & p weigh almost the same, and the electrons weigh hardly anything by comparison). Notice that the He is also neutral.

Why 2p+2n makes a stable object (note the huge repulsive electric force between the p's, which the strong force overcomes) but 2p's don;t, and 2n's don't, is a deeper mystery than we can tackle tonight, but certain combinations of n's & p's, typically with the numbers of n's & p's roughly equal, are held tightly together, and others are not. This is just because the strong force is complicated, as well as strong. But it only acts over a very short distance, of the order of 1/100,000th the size of an atom, so it holds p's and n's together in the center of atoms, while the e's fly around like a swarm of bees. The lump at te center is called the nucleus. For normal neutral atoms, the number of p's and the number of e's must be equal, and the number of n's roughly the same as the number of p's.

The next atom is lithium (Li), 3p's and 3e's, and either 3 or 4 n's. Because the number of electrons has to be equal to the number of protons for the atom to be neutral (and the terrific, long range, electric force guarantees that almost all atoms are exactly neutral), and because the nucleus clumps together as a tiny tiny lump at the center (held together by the strong force...), all the outside world sees of the atom is the swarm of electrons. So the number of protons determines the number of electrons, and the number of electrons determines almost all the important properties (chemical properties anyhow) of the atom. This number is called the atomic number. (I suppose I have to confess that the detailed ways the electrons arrange themselves around the nucleus is complicated, and important in chemistry.) H is 1, He is 2, Li is 3,... clear up to uranium, U is 92, and even beyond (though not found in Nature). All the atoms in between, and how they interact with each other, makes up the entire subject of chemistry. So there are 92 kinds of atoms, or elements in nature: 1,2,3,...,92. The number of n's in a nucleus can vary a bit from atom to atom, which affects the mass some but not the chemistry. So there is 7Li3, which has 3p's and 4n's (the 7 = 3+4 is basically the mass, in units of a p's mass), and also 6Li3, which has just 3n's. The different kinds of Li are called isotopes. The next three really important atoms are carbon (C), nitrogen (N), and oxygen (O). The complete symbols of their most common isotopes are 12C6, 14N7, and 16O8, respectively.

Well, that has to be enough for tonight. It is all a high school sophomore really needs, and will get you through everything in HS except physics and chemistry, and is the foundation of those. Few people with only a HS education know any more.

Good luck! Wwheaton (talk) 08:59, 30 April 2009 (UTC)


 * I am sorry that I do not know any such person personally. There are many textbooks you might consult.  Are you interested in ionized gases (eg, plamas), or condensed matter, like metals, electrolytes, or semiconductors? These are all specialized topics, with large literatures.  Wwheaton (talk) 18:35, 12 June 2009 (UTC)

Electricity has to do with the fact that the electrons (the e's) of the atom can be extracted from the atom and controlled so as to supply electrical energy and/or do work at the locations where it is needed. They are also used in other kinds of things like communication devices, medical devices, and computers.WFPM (talk) 13:32, 26 August 2009 (UTC)When I was in a high school sophomore I didn't know any of that stuff. So get busy and start learning and read Isaac Asimov science articles.WFPM (talk) 01:47, 4 September 2009 (UTC)