 We know that acids give up H plus ions, right? Things like HCl or H2SO4, we know that they give out H plus ions in aqueous solutions. So things like HCl and H2SO4, these are our acids, right? Now bases on the other hand, bases are actually exactly the opposite of acids. Bases in fact pick up H plus. Bases do the opposite, they pick up H plus. So let's say that we take a container and let's say we fill it with a particular solvent. Let's say we fill it with water. And now if I add an acid to it, this is going to increase the concentration of H plus ions in the solution, right? Now if I add a base to this particular solution, if I add a base, this base is actually going to react with this H plus. It's going to pick up this H plus and remove it from the solution. So while acids give out H plus ions, bases in fact do the opposite, they pick up H plus ions from an acidic solution. Now that we have understood what a base is, let us try and figure out the kind of compounds that can act as a base. Let's see. Let's start by asking ourselves what exactly is this H plus ion? Well an H plus is simply a hydrogen atom and we know that hydrogen atom has one proton and one electron in it. And now if I remove this electron from the hydrogen atom, if I do that, I will left with my H plus ion, right? So an H plus is simply a hydrogen atom without an electron. Now do you think that this H plus ion is stable? Well of course not. In fact even a hydrogen atom that has one proton and one electron in it, we know that even a hydrogen atom is not stable and hydrogen in fact requires two electrons in its automo shell. It requires two electrons in its automo shell to achieve what we call a stable electronic configuration to achieve stability. So this H plus ion which doesn't even have a single electron is definitely not stable, right? In fact this H plus ion is actually very reactive and it is going to react with anything that is going to give it these two electrons. So anything that has extra electrons that it can donate, so anything that has extra electrons in its automo shell that are not taking part in any bonding, we call them the lone pair of electrons. So anything that has lone pair of electrons can actually donate a lone pair to this H plus ion and in this way it can form a bond with it. So it can form a bond with this H plus ion and after the bond formation, after the bond formation you can see that this hydrogen atom now has two electrons in its automo shell, right? So after the bond formation hydrogen gets two electrons in its automo shell, two shared electrons to be precise and therefore it achieves the desired stability. So anything that has a lone pair of electron, anything that has at least one lone pair of electron can actually react with H plus ions. It can pick up H plus from an acidic solution and therefore it can act as a base. So we can say that a base that a base is simply anything that has at least one lone pair of electron, anything that has at least one lone pair of electron can act as a base. Let us now take a look at a few bases. Now if I ask you to give me an example of a base, most probably I think you'd come up with NaOH. NaOH is a pretty famous base, right? In fact, NaOH is one of the most common bases that you'll find in your lab. Now NaOH actually in itself is not a base. In fact NaOH is an ionic compound. It's a solid but when we dissolve it in water, it breaks down into Na plus and OH minus ions. And now if you look at this OH minus ions, you will see that it has a lone pair of electrons. So it's actually these OH minus ions, these hydroxide ions that can pick up the H plus and act as a base. So it's actually these hydroxide ions that are acting as a base. Now OH minus definitely is not the only base. Even things like the cyanide ion CN minus. So even things like CN minus or say SH minus. So things like CN minus or SH minus or even something like F minus. So all of these have a lone pair of electrons. So all of these can act as a base. Now bases also need not be negatively charged. Even things like ammonia, which is a perfectly neutral molecule or water. Even things like say H3O plus, which is actually positively charged. All of these have lone pair of electrons. So all of these can actually act as a potential base, right? However having said that the ability of each of these ions or molecules to pick up H plus from an acidic solution is actually very different. For example, generally things that are negatively charged like OH minus, CN minus and so on. These things are actually very good at picking up H plus from an acidic solution. So these actually act as very good bases. They are very good at picking up H plus. Now on the other hand things that are positively charged like H3O plus. These are actually very very poor bases. They are very bad at picking up H plus. So H3O plus is in fact a very very poor base. So the strength of a base, which is a measure of how likely a particular base is to pick up an H plus from an acidic solution. The basic strength of each of these bases is actually very different and we'll talk a lot more about this in a later video. But for now the key takeaway is that anything that has a lone pair of electron can actually act as a potential base. Now a quick note that I'd like to add out here is that because strong bases generally have a negative charge. So you will find that a base is generally represented as B minus. But that doesn't necessarily mean that everything that has a negative charge will act as a base. Let's see. Let us take an example of BH4 minus. BH4 minus has a negative charge. So do you think that this is a base? Well we know that boron has an atomic number of five. So if you write the electronic configuration of boron it's 2.3. So boron has three electrons in its outermost shell. Now boron minus will have one extra electron. So boron minus will have four electrons in its outermost shell. Now if you look at the structure of BH4 minus you will see that these four electrons of B minus, the boron minus is actually taking part in bonding, right? So BH4 minus doesn't have an extra lone pair of electron that it can donate. So therefore BH4 minus definitely cannot act as a base. So be careful a base may or may not have a negative charge but not everything that has a negative charge will act as a base.