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s-Block Elements - Concept

Teacher/Instructor Jacqueline Spivey
Jacqueline Spivey

Ph.D.,U.C.Santa Cruz
Teaching at a top-ranked high school in SF

She teaches general and chemistry at a top-ranked high school in San Francisco. Prior to that, she lead and published a number of research studies and lectured at SF State University.

The s-block elements share electron configurations. s-block elements are the elements found in Group 1 and Group 2 on the periodic table. Group 1 are the alkali metals which have one valence electron. They have low ionization energies which makes them very reactive. Group 2 is the alkali earth metals which have two valence electrons, filling their s sublevel. Because they have 2 valence electrons they are less reactive than group 1. Hydrogen is a nonmetal grouped with the alkali metals because it has one electron in its valence shell.

So let's talk about the periodic table kind of in more depth and let's start talking about the s-Block elements. So when I say s-Block elements, what exactly do I mean? So I'm referring to group 1a and group 2a and so when I'm saying s-Block I'm referring to the electronic configurations that the elements in these two groups or families actually have so let's kind of talk about what that means. So again the electronic configurations, so how you kind of map where the electrons are in the atom is more specifically where they what their valence show electrons are like or their outer most shell electrons.

Okay so remember that the s valence shell can have two electrons maximally and one of them is spin up and one of them is spin down right so they're spin paired. So more specifically group 1a elements are the alkali metals and so these guys include; Lithium, sodium, potassium, rubidium, cesium and francium, so they have one valence electron, so one electron in their outer most shell. So they also have low ionization energies and that makes them very reactive so when something has a low ionization energy that just means that the ability of another of a nonmetal basically to come remove the electron from the outer most shell is it doesn't take very much energy it's low ionization energy so it can kind of just come pluck it out. So basically when it loses that electron that means that its oxidized and it forms a +1 ion so for instance, sodium will form sodium +ion usually that happens with an nonmetal. Remember, the nonmetals are off to the right hand side of the periodic table, so for example sodium and chloride so sodium will form a +ion, chlorine will form a –ion. And so these guys because they're so reactive and they're so willing to lose that one electron they exist in nature only as compounds.

So let's move to the neighboring group which are the group 2a molecules and so pardon me atoms, so these guys are the alkali earth metals group 2a and they have 2 valence electrons, so 2 electrons in their outer most shell. And these guys have a higher ionization energy than their neighbors in group 1a so they're not quite as reactive but they're still pretty reactive. These guys also get oxidized to form 2+ions so for example calcium will form a 2+ion. Again because their ionization energies are fairly low, not as low as group 1, but they're willing to loose those two electrons to become ions they primarily form ionic compounds with nonmetals and other polyatomic ions so for instance calcium can form calcium carbonate where calcium has a 2+ charge and carbonate has a 2- charge to give an overall 0 charge on that polyatomic ion. So these guys are called alkali earth metals because the “earths” of this group say the calcium and the magnesium, they form, the calcium forms lime which is calcium oxide and the magnesia forms magnesium oxide and then these guys make alkaline reactions so therefore they have the name of alkali earth metals.

So last but not least in these group 1 and group 2, you'll see that hydrogen is up here at the top and it's color coded pink because it is in fact a nonmetal although it is grouped with the group 1a elements and so it is grouped with them because it has a 1s1 electron configuration so it does have the 1 electron in it's valence shell. However again it is a nonmetal and it occurs as a colorless diatomic gas H2 similar to chlorine gas and nitrogen gas. So it's grouped here because the ionization energy of hydrogen is higher than that of group 1a so it has a lesser tendency to lose that 1 electron and become a proton then say sodium does to loose its electron and becomes sodium+ but it does in fact lose an electron so it forms molecular compounds and it also reacts with metals to form what call metal hydrides and when a proton is in form, when hydrogen is in the form of a hydride that means that actually has a negative charge on it. So we can form a metal hydride say with sodium so it will be sodium and hydride together, sodium having a +charge hydride having a negative charge so the fact that hydrogen can form a hydride with a negative charge is all the more evidence that it does not have the same properties as this other group 1a counterparts. And that is s-Block elements.