Understanding Chemical Formulas: Types, Ratios, and Structures Explained

Let's focus a little bit about chemical formulas and you have a good idea you know about this already. This is a

figure of water molecule. What it is showing is it has one oxygen atom in this case red and two hydrogen atoms and

that's why we show it like H2O two hydrogen atoms and one oxygen atom. And also now we know this is a compound and

all compounds have constant mass composition. We saw that for water it is 8 to one for oxygen and hydrogen. The

reason we always get constant composition is because in water these atoms are fixed. They are in fixed

ratios. Since they are in fixed ratios and also since an atom has a unique mass mass of an atom is in unique. So if I

take hydrogen atom from hydrogen gas or if I take hydrogen atom from water the mass of hydrogen atom is going to be

same. For therefore there are two reasons. First reason for constant composition is these atoms are in

constant or fixed ratios. Other one is all atoms have unique mass. For that reason we got that law of constant

composition. We know that this is the chemical formula of water. Basically chemical formula is showing us what are

the atoms present in this case oxygen and hydrogen and also chemical formula shows the ratios in this case two

hydrogen atoms and one oxygen atom. If you take carbon dioxide this is a chemical formula sometimes we call it as

molecular formula as well. This shows the type of atoms carbon and oxygen and also ratios of those atoms. We can see

carbon to oxygen is one carbon atom and two oxygen atom. Basically chemical formula shows the relative number of

atoms and types of atoms. I just want to emphasize this. This is a substrate that basically shows there are two hydrogen

atoms in one water molecule. And let's look at some other chemicals as well. This is sodium chloride or NCL for table

salt. When you look at this chemical formula, you can see that sodium and chlorine atoms are in 1:1 ratios. carbon

dioxide it has carbon and oxygen atoms and they are in 1 to2 ratios this is sucrossse or table sugar it has carbon

hydrogen and oxygen in this ratio I told you a minute ago about the subscript of water like H2O and probably you might

not understand what I'm trying to say here but just try to keep it in your back of your head we will address that

in a later chapter which is this of a compound can never be changed the reason you will need that information is when

we are doing chemical reactions and balancing of chemical reactions, we need that information. If you change the

subscript of a compound or molecular formula basically what you're doing is you are changing the compound. Here we

have one carbon and one oxygen we show it as CO that is carbon monoxide. This is carbon dioxide. If you change this

subscript, you will get a different compound. So carbon dioxide and carbon monoxide are totally different compound.

Carbon dioxide around us in atmosphere and it is soluble in water and you drink it in soda and carbonated water is not

non-toxic but carbon monoxide is a toxic gas. If you inhale it for a few minutes you will die. So this substrate is very

important. Now let's see how we write these chemical formulas. If I say table salt probably you remember that the

formula is NAC. Why do we write as NAC? Why can't we write Cla? It looks weird because we are so used to this NaCCl.

But it's the same thing, right? It's showing the ratios of atom. It's showing the type of elements are there. So why

we write like this? That is because we have accepted that the most metallic element goes first. When you see sodium

and chloride, chlorine or chloride ion, we will see later the difference. Sodium is a metal and chlorine is a non-metal.

Therefore, it's very easy for us to say we must write sodium first because we are going to write the most metallic

element of a compound first and then write other elements. That's easy for sodium and chlorine and also let's say

Ca and O still we write Ca because calcium is more metallic and oxygen is nonmetal. We don't write O Ca. Now it's

easy to say when you see metals and nonmetals. What if you have let's say let's say the same example C and O these

both are nonmetals carbon is a nonmetal oxygen is a nonmetal then why do we write CO why not the other way that is

because even though these are nonmetals we are looking at the relative metallic characters of these elements we will

discuss relative metallic characters of elements in a different chapter but for now please remember when you go from

right to left the metallic character increases right to left. That means these are less

metallic. These are more metallic. That is something we can understand because we know this side is nonmetals and this

side is metals. And also when you go down the periodic table metallic character increases that that means if

you compare lithium and rubidium rubidium is more metallic than lithium even though they both are metals. If you

remember when we discussed about properties of metals, the last one in red was metals tend to lose electrons.

That's what we here trying to see. When you compare lithium and rubidedium, which metal is most likely to lose

electrons easily that's a very good property of metallic character. Similarly, we know these florine and

bromine are nonmetals. But florine is less metallic than bromine. In other way, bromine is more metallic than

florine if you have to compare those two because florine is down the periodic table. Now we know something about

metallic characters. Let's see compound of carbon and oxygen. In that case, carbon is more metallic because it's

left to the oxygen. Therefore, we write CO2. Similarly, we can write for nitrogen and oxygen. Nitrogen is more

metallic than oxygen. Therefore, we can write N O2 like that. Nitrogen dioxide also oxygen and sulfur. Which one is

more metal? Sulfur, right? Because sulfur is down the periodic table than oxygen. Therefore, we write sulfur first

and oxygen second for sulfur dioxide. Always more metallic compound first. Now, types of chemical formula. This is

also pretty simple one. We already know this is the molecular formula or chemical formula of water. It shows type

of elements and the ratios of element. Also, I can write water like this. In this case in these two lines I'm showing

the bonds between oxygen and hydrogen and this type of formula is called structural formula. In structural

formula specifically shows that bonding is water is not like that H and O. This is not the way. So structural formula

shows that how these atoms are bonded. There's another one called empirical formula. What is that? Let's say H2O.

H2O is water. But if there's H2O2, this one is hydrogen peroxide we use to kill germs. In this hydrogen peroxide,

this is the molecular formula. You can see there are two oxygen atoms and two hydrogen atoms. And empirical formula is

showing the lowest or smallest ratio between atoms. In this case for hydrogen peroxide, the molecular formula is H2O2.

But we can show this ratio. The smallest ratio is HO. Basically, this HO is the empirical formula for hydrogen peroxide.

It's showing the smallest atomic ratios. Another example is glucose C6, H2L and O6. And this is the molecular formula or

chemical formula for glucose. You can see we can simplify these ratios. If you simplify these ratios, you will get C

H2O. Basically, divide everything by six. This is the empirical formula of glucose. Basically, the empirical

formula gives the smallest ratios or relative ratios of atoms. Let's look at a methane or CH4. This is the gas

natural gas we use to cook in our homes. Not the propane cylinder. It is a different gas. CH4 is the chemical

formula or molecular formula. I can draw the structural formula as this. Basically it is showing that in this

methane hydrogen is attached to carbons not any other way not like hydrogen hydrogen carbon like that. This is a

structural formula. There are two other models we call ball and stick model and space filling model. Basically these two

models show the threedimensional structure or how these atoms are arranged three-dimensionally. How is it

going to be different from structural formula? structural formula. This one does not show a threedimensional

arrangement. When you look at this formula CH4, you might think the angle between these hydrogens's are 90°. You

might think like that. That's how it is showing. But actually it is not. When you have this model, this is called ball

and stick model because it is atoms are shown as balls and bones are shown as sticks. So when you measure the angle

between hydrogen two hydrogen's it would not be 90° it would be 109.4° and 4°. Don't worry about remembering that. Just

understand structural formula does not represent the three-dimensional structure. It just show how they are

bonded. Space filling is another threedimensional but don't worry much about that. is just showing the

electrons as