Introduction
This series of posts seeks to present the material covered in the first semester of a college level general chemistry course, in an easily digestible steemit blog post format. The series is intended to be read, and experienced in sequential order starting with Post 1. The material will build upon itself, and potential exercises included (problem sets), will pertain to the post they are contained in, or any previous post. Each post will pick up immediately where the previous in the series left off. Please check out the #chemistry-lesson tag for all posts in this series. I hope you find this series to be informative and beneficial toward your understanding of chemistry and science in general.
Immediate Preceding Post
Part 2: Factor Labeling, Conversions, and Intro to Atomic Theory
Legend for This Section
As subscripts do not currently work on steemit, to symbolize when a number should be sub-scripted I will be writing it as follows: /x/.
How to Identify Atoms
All atoms are identifiable by looking at the number of protons and neutrons that they have. The number of protons that an atom has is referred to as its Atomic Number (Z). While the atomic mass (A) of an atom is equal to the sum of the number of protons and neutrons. Thus we can calculate the number of neutrons present by subtracting the atomic number from the atomic mass (A – Z). As an example of this let us look at Nitrogen (N). The atomic number of nitrogen is 7 while the atomic mass of nitrogen is 14.01. Thus the number of neutrons is equal to atomic mass – atomic number (14.01 – 7) = 7.01. So there are 7 neutrons found in the nucleus of a Nitrogen atom. Not all atoms of an element have the same mass. This is because there are often times a variety of isotopes for each element. An isotope is an atom which shares the same atomic number (so same number of protons) but has a different atomic mass number (which means the number of neutrons change!) To identify these two numbers the elemental symbol is often written like this:
Figure 1: How to Write an Atomic Symbol
If you were to look up polonium (on the periodic table at the bottom of this post) you would find that its atomic mass is written as (210) the parentheses just mean that the element is radioactive, however you might also notice that the atomic mass listed there is not what I gave in the example. This is because Polonium 208 is one of the isotopes, there are actually 32 other isotopes, all of which are radioactive. Speaking of the periodic table…
The Periodic Table
The Periodic Table is a chart where all of the elements we know of (and the list is actually expanding!) are grouped together based upon the properties that they have. The vertical columns on the periodic table are known as Groups, while the horizontal rows are known as Periods. The first thing to notice when looking at the provided periodic table is that the elements are color coded. These colors assist you in dividing the elements up into their three broad classes: Metals, Metaloids and Nonmetals. Metals are elements which are good conductors and are malleable (aka you can smash them out into thin sheets with a hammer, they aren’t brittle or crystalline). Nonmetals are not good conductors and are not malleable, they are more fragile than metals. Finally metalloids have properties that are somewhat in-between metals and nonmetals, with some properties from both types.
On the periodic table the dark orange, light orange, three lightest green shades and yellow colored elements are all metals, while the bright green colored elements (B, Si, Ge, As, Sb, Te, At and Po) are metalloids. Finally the purple, pink, and light blue elements are your non-metals. There are also special subclasses which are given to elements found in particular families on the periodic table. Those in Group 1 (the column labeled 1) are called the Alkali Metals, those in Group 2 are called the Alkali Earth Metals, those in Group 17 are called the Halogens and finally those in Group 18 are the Noble Gasses.
Compounds and Nomenclature
As we mentioned previously in Part 1, compounds are things which consist of two or more elements from the periodic table. There are two types of compounds Ionic and Molecular. In order to talk about compounds and how we name them we must first discuss Chemical Formulas. Chemical formulas show us the composition of both molecular and ionic compounds in terms of their chemical symbols (eg. Sodium is Na, and Chloride is Cl, these are what are listed on the periodic table). There are two types of chemical formulas: Molecular Formulas and Empirical Formulas. Molecular formulas tell us the exactly how many atoms are to be found in each individual unit of substance. For instance the molecular formula for Nitrogen is N/2/, while Hydrogen is H/2/. For a more complex example let us use methane gas (CH/4/) this formula indicates to us that it is composed of 1 Carbon atom (C) and 4 Hydrogen atoms (H). While empirical formulas tell us the smallest whole number ratio of elements which are present in the atoms of something. As an example let us take Acetylene (the molecular formula for acetylene is C/2/H/2/) the smallest whole number ratio for acetylene is CH (because we can divide the molecular formula by 2). Where things can be confusing for people with empirical formulas is that many compounds can end up with the exact same empirical formula. Take Benzene for instance (the molecular formula for benzene is C/6/H/6/) it also has an empirical formula of CH (because we can divide its molecular formula by 6), as CH is the lowest whole number ratio for its formula. The concept of an empirical formula may seem confusing so put it on the back burner for now (we however will make good use of these in the future!).
Naming Ionic Compounds
An Ion is an atom or group of atoms that possesses a charge (could be positive or could be negative). The number of protons in the nucleus of an ion never changes, however the number of electrons does (electrons have a negative charge)! Negatively charged ions have the same number of additional electrons as their negative charge, while positively charged ions are missing the same number of electrons as their positive charge. As an example the chloride ion (Cl-) has one extra electron (adding the electron leaves you with extra negative charge no longer balanced out by the positively charged protons in the nucleus), negatively charged ions are called anions. While the Potassium ion (K+) has lost an electron (taking away an electron leaves you with extra positive charge from the nucleus), positively charged ions are called cations (because everyone likes cats, so they are positive).
An ionic compound is one which is formed by combining together anions and cations in equivalent ratios such that the charge is neutral (they also contain one metal and one nonmetal). Sodium Chloride (NaCl, table salt) is one such compound. It is the combination of one sodium Ion Na+ with one chloride ion Cl-. When we write the names for these compounds the cation is always just called the name of the element, while the anion gets the name of the element with the prefix –ide added to it.
Examples:
The ionic form of Fluorine (F-) is Fluoride
The ionic form of Chlorine (Cl-) is Chloride
The ionic form of Sulfur (S-2) is Sulfide
The ionic form of Phosphorous (P-3) is Phosphide
Things get a bit more complicated as not all ions are monatomic (just of one atom) some of them are polyatomic (aka have 2 or more atoms). I will provide you a list of some common polyatomic ions for use in naming. It is located in the references section at the bottom of this blog, and also right HERE.
Lets Name a Few Ions!!
What is the name for K/2/S?
Well we know the name of the cation (Ionic compounds are always listed cation then anion) is just the name of the element so Potassium, and we know that Sulfur’s anionic name is Sulfide. So this ionic compound is Potassium Sulfide.
What is the name for RbI?
Again we know the name of the cation is just the name of the compound so Rb = Rubidum, and the anion is an Iodine, so that is called Iodide. This this compound’s name is Rubidum Iodide.
Finally what is the name for this ionic compound: (NH/4/)OH.
Oh damn, this one is composed of a lot of elements, these must be polyatomic ions, better check the list. Well my cation NH/4/+ is called Ammonium, and my anion OH- is called Hydroxide. So this compound is Ammonium Hydroxide.
Naming Molecular Compounds
Molecular compounds are composed of two nonmetals, you will (usually) not find any metals in molecular compounds. These compounds also have different naming rules then ionic compounds, however for binary compounds it may seem similar. For instance HI composed of one hydrogen and one iodine. We say the name of the first compound regularly, and the second gets –ide added to it just like for an ionic compound. So HI would be Hydrogen Iodide. Things get more complicated when you have more than one of an element in a compound, for this situation use a Greek prefix to indicate how many of that element is in the compound.
Table of Greek Prefixes
| Number of Units | Prefix |
|---|---|
| 1 | mono |
| 2 | di |
| 3 | tri |
| 4 | tetra |
| 5 | penta |
| 6 | hexa |
| 7 | septa |
| 8 | octa |
| 9 | nona |
| 10 | deca |
So we can use these Greek prefixes to aide us in naming some more complicated compounds!
Lets Name Molecular Compounds!!
What is the name for H/2/O?
Water, duh. Next! … Oh wait we have to use official naming conventions... Fine. First, we have 2 hydrogens, so we must use a Greek prefix, Dihydrogen. We have one oxygen, oxide, but it also gets its Greek prefix Monooxide (which looks weird so we shorten it to Monoxide, the double oo thing … yuck). So the name for H/2/O is Dihydrogen Monoxide.
What is the name for SF/6/?
Okay so one sulfur, Monosulfur, and 6 fluorines so Hexafluoride. Monosulfur Hexafluoride. As a side note, any compound with only one of the first component, like here with one sulfur. The “mono” is optional. This compound is also correctly named as Sulfur Hexafluoride.
End of Periodic Table and Nomenclature Problem Set
We’ve reached the end of this section, and as with the end for previous sections, I will provide you with a problem set so you could (if you want, you’re an adult I can’t force you to do anything!) test yourself to see if you are fully understanding the material.
Problem Set 2
Problem Set 2 Answer Key
Future Posts
Subsequent posts will cover: Chemical Reactions, Stoichiometry, Electronic Configuration of Atoms, Chemical Bonding, and Molecular Geometry, and more.
Reference Figure: Periodic Table
Other References
Constants and Conversions List
Source for Additional Constants
Some Common Ions
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