What are Ions?

In this video we will learn about

ions

, we will learn how and why

ions

are formed, we will learn the difference between anions and cations and finally we will learn a quick and easy way to determine the charge of an ion, so why? I have a photo here of a salt shaker, that's because two extremely common ions can be found in table salt and table salt is called sodium chloride which is usually written like this: NaCl and we'll talk about this particular compound and these two ions specifically. In this video, let's start with the definition, so an ion is an atom or group of atoms with a net positive or negative charge, but how does an atom get this positive or negative charge?

To understand this, we have to revisit the atom and observe.

what

the atom looks like now in the nucleus of the atom we have the protons and the neutrons and they're pretty well trapped there, they're not really going to be able to move much so let's say it's impossible to remove one of those particles from the atom now this green particle here on the outside this is the electron and the electrons are different they are actually quite mobile we know that they are flying around the outside of the atom here and according to the cloud model they can basically move anywhere now the other thing that the electrons can do is that they can actually be separated from an atom or atoms can even attract electrons to themselves and so why would an atom want to gain or lose electrons?

Well it all comes down to a very simplified rule that will work most of the time and this rule is called the octet rule and here is the octet rule again it works most of the time and for our purposes we are just going to say that everything works time but this is

what

the octet rule says: it says that all atoms are trying to get eight electrons in their valence shell and the valence shell is a fancy term for the outermost energy level of an electron or the outermost shell so if you think about the Bohr diagram if you think about the last ring that you draw that's the valence shell okay so let's go ahead and take a look at sodium and chlorine on the attic table off the dock, here's the sodium and then here's the chlorine and we'll see how these particular atoms convert. ions so let's start with chlorine here's a dash diagram for chlorine and chlorine has 17 electrons and we can see the 17 electrons there in green and if I count the number of electrons in the valence shell remember that's the outermost shell here we get seven electrons and then chlorine wants to have eight because all atoms want to have eight and that's why it needs to gain an extra electron, so if we add an extra electron like that then it would have 18 electrons now it has eight electrons in the valence shell and so it's happy but it will have a charge so let's take a look at what the charge of chlorine would be to understand the charge we will have to look at the total number of protons in this ion and we will also look at the total. number of electrons now so before anything happened here and even now we have the same number of protons we have 17 that is the atomic number of chlorine now before we added that extra electron there were also 17 electrons but now there will be 18 electrons.

Remember that protons have a positive charge and electrons have a negative charge, so this is really like a positive 17 and then we have this negative 18. Now if we look at the difference between these, we can see that we have an extra electron and a positive one. the charge will completely cancel out a negative charge, those will cancel each other out, we're going to have an excess of a negative charge which will be our excess charge here, so the charge on chlorine is actually negative, now it's a negative ion. we call it anion and so chlorine is an anion because it has a negative charge and that's how we would write the symbol for the chlorine ion, it would be CL, that's the symbol on the periodic table and we just put that negative charge in there. we don't have to put the 1, we can just put a negative and assume that means now another thing to mention is that when we talk about the chlorine ion we actually give it a specific name, we call it chloride and any anion that is monatomic in other words just has an element like chlorine, there is only the element chlorine, we call them monatomic, the prefix mono means one, so we have an ion of one atom here we always change the ending of those ions to IDE and that will describe an anion, okay, let's go ahead and look at sodium now and soda, sodium here we can see on the periodic table that it has 11 electrons and here is the board diagram for sodium and we could see that it has that electron in the valence shell, this electron, TRUE? here in the valence shell, so the sodium should gain seven more electrons, well we could do that, but that's going to get quite difficult if you notice that the next shell below this shell here has eight electrons, so if the sodium just got rid of that extra electron it would have a new valence shell with eight electrons and that's what sodium does and all the atoms will take the easiest route to get to eight, so if they only need to lose one, two or three electrons, they will lose them. instead of gaining a bunch of extra electrons, then sodium, since it lost an electron and electrons have a negative charge, sodium will have a positive charge, it's missing an electron and the way we would write this symbol would be na with a more and then, that's the sodium ion and we still call it sodium, we don't change the ending of the positive ions, but the positive ions will be called cations.

Well, you may have noticed something interesting here: sodium was losing an electron and chlorine. gaining one electron and then why couldn't sodium just have given its electron here to chlorine to give it eight electrons and that's actually what happens and that's why this is called an ionic compound when one element gives its electron to another L and ionic compounds are compounds that are made up of ions and if we remember that sodium had a positive charge and chlorine had a negative charge and these charges, since they are different, they will attract each other, it is like these magnets if you bring the opposite poles of a magnet. together they will attract each other and stick together and those are ionic compounds.

Well, finally here is a quick and easy way to determine the number of valence electrons and therefore the charge of an element. All we have to do is take a look at the periodic table here and number the columns starting here with 1 and then 2 and what we actually also want to do is ignore the transition metals, they don't follow this rule so we just we're going to pretend for this particular rule here that says they don't exist, so if we just erase them and create this new periodic table here, we just put the two halves together here, the transition metal should have been in the middle if we put them together.

This way we can number the columns from 1 to 8 and that is the number of valence electrons, so if I look down the first row here, sorry, first column, everything in that first column has a valence electron. and then everything in that first column will lose an electron and have a positive charge, everything in the second column will have a positive charge two now, once we get past the number four, then in this fourth column everything will have four valence electrons and actually They're not really going to lose or gain, they're actually going to share their electrons, we'll forget about them for now, we'll talk about them later, but once we get to the number five that's when we start gaining electrons and so on. the fifth column here starting with nitrogen will have a charge of three minus and then a charge of two minus and a charge of one minus and then the last group here the noble gases are not going to do anything because they are already satisfied with that octet rule they have eight electrons and that's an introduction to ions