Counting valence electrons for main group elements (video) | Khan Academy
Ans: The combining capacity of an atom is called its valency. Actually it can be defined as the number of electrons that an atom may lose (or) gain during a. Nov 29, What is the Difference Between Valency and Valence Electrons? usually show one valency whereas the transition metals are famed for. But it is wrong to apply the concept to determine the valency of the state is + 7, notice the difference that there is no plus or minus sign in valency). . are transition elements, and each posses one or two valence electrons in.
And that's very convenient, because sodium is found in group one. And so we can say that for main groups, if you want to figure out how many valence electrons you have, it's just equal to the group number. So the group number is equal to the number of valence electrons.
And so that makes everything really easy. And so if I wanted to represent a neutral atom of sodium with its one valence electron, I could draw sodium here, and I could draw one valence electron next to sodium like that.
Let's go ahead and write the electron configuration for chlorine next. So here's chlorine over here. And so if I wanted to write the electron configuration for chlorine, it would be 1s2, 2s2, 2p6, and once again, that takes me all the way to neon. And so now, I'm over here in the third energy level, or the third period. I can see that I would fill 3s so 3s3. And that puts me into my P orbitals. So how many electrons are in my P orbitals? One, two, three, four, five-- so I'm in the third energy level, I'm in P orbitals, and I have five electrons.
And so that would be the electron configuration for chlorine. If I want to figure out how many valence electrons chlorine has, I have to look for the electrons in the outermost shell, or the outermost energy level. So I have, once again, the first energy level, the second energy level, and the third energy level. So I want the total number of electrons in the outermost energy level.
So how many electrons are in the third energy level? Well, there's two and five, for a total of seven. So chlorine has seven valence electrons. And once again, that's very convenient, because chlorine is in group seven. And so let's go ahead and draw chlorine with its seven valence electrons. So here is chlorine. So one, two, three, four, five, six, and seven, like that-- and so the reason I picked sodium and chlorine is, of course, because the sodium and chlorine will react together to form sodium chloride.
And let's analyze what happens using our electron configurations. And so sodium is going to lose one electron. So a neutral atom of sodium has equal numbers of protons and electrons. But if sodium loses its one valence electron-- so it's going to lose its one valence electron, and I can show its one valence electron, actually, is moving over here to the chlorine.
So now, when I draw sodium, I have to represent it as an ion, a cation. Sodium used to have equal numbers of protons and electrons, but it just lost one electron.
Therefore, it's left with an unbalanced number of protons. So it has one more proton than electrons. So it's a plus one charge. The sodium cation is stable. And the reason why has to do with the resulting electron configuration. So if I look at the resulting electron configuration-- let me go ahead and use yellow here-- it would be 1s2, 2s2, 2p6. And so the electron configuration for the sodium cation is the same as neon, which is a noble gas.
And we know that noble gases are generally unreactive, and that has to do with the fact that their electron configurations are full in their outermost energy level. So the sodium cation is stable, because it has an electron configuration like that of a noble gas. So for chlorine, if we think about how chlorine reacts, chlorine has seven valence electrons.
And let's find it on our periodic table here. Chlorine has seven valence electrons.
Valence Electrons - Chemistry | Socratic
If chlorine gets one more, then chlorine would have an electron configuration like a noble gas, like that of argon. So chlorine will gain an electron here. So let's go ahead and write the new electron configuration. If a neutral atom of chlorine picks up an electron, well, the electron would add right in here. So instead of 3p5, we would write 3P6. And so the electron configuration for the chloride anion would be 1s2, 2s2, 2p6, 3s2, 3p6.
The most reactive kind of metallic element is an alkali metal of group 1 e. An alkaline earth metal of Group 2 e. Within each group each periodic table column of metals, reactivity increases with each lower row of the table from a light element to a heavier elementbecause a heavier element has more electron shells than a lighter element; a heavier element's valence electrons exist at higher principal quantum numbers they are farther away from the nucleus of the atom, and are thus at higher potential energies, which means they are less tightly bound.
A nonmetal atom tends to attract additional valence electrons to attain a full valence shell; this can be achieved in one of two ways: An atom can either share electrons with a neighboring atom a covalent bondor it can remove electrons from another atom an ionic bond. The most reactive kind of nonmetal element is a halogen e. Such an atom has the following electron configuration: To form an ionic bond, a halogen atom can remove an electron from another atom in order to form an anion e.
To form a covalent bond, one electron from the halogen and one electron from another atom form a shared pair e. Within each group of nonmetals, reactivity decreases with each lower rows of the table from a light element to a heavy element in the periodic table, because the valence electrons are at progressively higher energies and thus progressively less tightly bound. In fact, oxygen the lightest element in group 16 is the most reactive nonmetal after fluorine, even though it is not a halogen, because the valence shell of a halogen is at a higher principal quantum number.
In these simple cases where the octet rule is obeyed, the valence of an atom equals the number of electrons gained, lost, or shared in order to form the stable octet.
However, there are also many molecules which are exceptionsand for which the valence is less clearly defined. Electrical conductivity[ edit ] Valence electrons are also responsible for the electrical conductivity of an element; as a result, an element may be classified as a metala nonmetalor a semiconductor or metalloid.
Metallic elements generally have high electrical conductivity when in the solid state. In each row of the periodic tablethe metals occur to the left of the nonmetals, and thus a metal has fewer possible valence electrons than a nonmetal.
Valence electron - Wikipedia
However, a valence electron of a metal atom has a small ionization energyand in the solid state this valence electron is relatively free to leave one atom in order to associate with another nearby.
Such a "free" electron can be moved under the influence of an electric fieldand its motion constitutes an electric current ; it is responsible for the electrical conductivity of the metal. Copperaluminiumsilverand gold are examples of good conductors. A nonmetallic element has low electrical conductivity; it acts as an insulator.
Such an element is found toward the right of the periodic table, and it has a valence shell that is at least half full the exception is boron.