To understand what chemistry is all about, you must first ask yourself; what is it that we’re studying? In truth you should be asking yourself this of any class that you take. The question might sound stupid, “we’re studying chemistry, you know, chemicals and reactions and stuff”; but as you’ll see, for every subject there’s an underlying theme that you’re trying to understand. For chemistry this is matter.
Without getting too technical, Matter is “stuff” that is physically present in the universe. It is everything around you, from the chair you’re sitting on, to the air particles around you. Yes even the air around you (the atmosphere) is composed (made up) of matter. Think about it, most of us know that we need oxygen to survive, but if it’s so crucial then where is it? O2, elemental oxygen (the stuff you are actually breathing) is a molecule made up of two oxygen atoms. People that are way smarter than me have measured the atomic radius of oxygen at 60 picometers. Let’s think about that for a second, a picometer is 1×10−12 meters. That means that in 1 meter there are 1 TRILLION picometers. Atoms are crazy small to say the least.
Oh and don’t get too hung up on the size of things, it’s going to be impossible to conceptualize just how infinitesimally small the subjects of chemistry are. Your focus should be on what it means. A single atom of oxygen is small, yes, but it is also there. It exists and occupies an area in space, which means that it’s matter.
Oh and one more thing before we get started. There’s a definition that you need to know: a substance is matter which is uniform in composition and reacts in the same way given certain parameters. Substances have specific properties that are the same no matter how big or which part of a sample of the substance you have. However as you’ll see, matter doesn’t have to be uniform all of the time.
The 3 types of Matter.
There’s no easy way to say this, but defining things is what scientists’ do. It’s how we understand the big picture. This means that the umbrella topic of “matter” is divided into 3 different components to better understand and define it.
Look at your laminated periodic table that you carry around every where. Wait. So you’re telling me that not everybody has one of those? I see, well in any case, the periodic table is a table that shows every element known to exist at this time. Starting with the number 1 (hydrogen) in the upper left corner and ending with number 118 (Oganesson) in the lower right corner.
All of these elements show what one atom of an element is composed of. You know, how many protons, electrons, and with a little arithmetic you can figure out, on average, how many neutrons an element contains, and it’s all based off of the information on the periodic table! I won’t get in to everything that the table can tell you, but when you put all of this information together and you have an element, which is the simplest and most fundamental unit of matter.
There is something important about elements that you need to know. They are all unique. Hydrogen, iron, oxygen, sodium etc. Each of the elements on the periodic table have fixed compositions, which means that an element will always look the same, feel the same, taste the same and react the same, within a given set of parameters. But there’s a catch, no two elements have any of those things in common. Sure elements can behave in similar ways but the properties that give an element it’s identity, also make it so that no two elements are exactly the same.
Note: something we haven’t discussed is molecules. Simply put these are fundamental units in chemistry that are composed of two or more atoms that are held together by covalent bonds. A molecule can can consist of a single type of element with two or more atoms, or different types of elements. Though when you put more than one element in to a molecule you get…
When you take two or more different elements and smash them together, you’ve made a compound. Think of water, H2O, two hydrogen atoms meet up with an oxygen atom and bond to make a compound. Note that a molecule of water is always the same. Its composition is fixed, every single time no matter what, this makes it a substance. Now, I won’t go in to it in detail, but something that you need to start thinking about is the different types of compounds. There are covalent compounds (held together by shared electrons), then there are ionic compounds (bonds held in more loose association by donated electrons), and did I mention there are metallic and intermetallic bonds? Don’t worry about knowing those last two at this level.
Because scientists want to make your life miserable, somewhere along the line it was decided that a molecule would consist of covalently bonded atoms. An ionic compound is actually called a Formula Unit.
The concept of fixed composition is important so we should spend a little time talking about it. Look at your periodic table at the number just below the big “O“, you got it?
That number describes the average mass for an atom of an element across all of the different isotopes (isotopes are elements that have the normal number of electrons and protons but they have different numbers of neutrons in their nucleus) for that element. This number is called molar mass and the unit on that is an atomic mass unit (AMU). What it means is that in 1 mole (yes you will need to know what a mole is) of oxygen there are 15.999 grams (or 16 to make it easier). If you were to Measure 16 grams of pure oxygen, you would have one mole of oxygen. Now look at that same area but for Hydrogen. You should now have a 1 or pretty damn close to it.
Don’t worry if you have a little bit of trouble with moles. I mean definitely work hard to understand it, but it’s not something you encounter every day so it may take you a bit. The number below the symbol of an element always describes what one mole of that substance is. One mole of silicon is 28.086 grams, one mole of carbon is about 12 grams etc. It’s a standardized way in which we can measure out the amount of a substance so that we can perform experiments and keep track of them accurately.
Okay, now that you have that, lets think about water again, H2O. I want you to try and come up with one mole of water. That is, if 1 gram of hydrogen is equal to 1 mole of hydrogen, and there are two hydrogen’s in water you now have two grams of hydrogen. Then take your molar mass of oxygen, remember it’s 16 grams. What you now have is 2 grams of hydrogen and 16 grams of oxygen for a total of 18 grams in one mole of water. Every water molecule that has existed in the past, present, or future is composed of 2 parts hydrogen and 16 parts oxygen by mass.
However there’s a but, because an oxygen atom is 16 times heavier than an atom of hydrogen, this means that there will always be 1 oxygen for every two hydrogen atoms.
If you’re tired of reading, don’t worry this last section is short.
The concept of a mixture can be difficult because it fall’s outside of the rules which we have set up so far. For one thing a mixture is a combination of different molecules and compounds. The means that it isn’t a substance. One of the easiest examples of this, is table salt in water. It’s a mixture of Sodium Chloride and water, but you can add more salt or water and it changes the proportions of the mixture.
The previous example is obvious, but there are also other, for example a rock is usually a mixture of different compounds, that’s why if you pick two of the same type of rock up, there are differences in how they look. If you own a Gold ring, chances are that it’s not pure gold, otherwise it would bend and become scratched way too easily, that is why there are other compounds and elements added in such as nickel to harden the material and make it more “user friendly”. Different substances can be added in different ratio’s to make the desired effect.
Not that kind of rock.
There it is, your crash course on matter. Remember that matter is just stuff, and that it’s all around you and you’re made up of matter. Don’t stress about the fact that much of the concepts are on a scale so small that it’s difficult to conceptualize. Start to think about uniformity, and ratio’s as they’ll be important later on. Most of all start to think about these topics in your every day life, from the drink in front of you, to the device you’re reading this on. Till next time.
[chemistry 211 section 2.1]