Basic Chemical Bonding (How Compounds Form)
Chemical bonds are lovely bits of fiction. They aren't real, tangible things (much like electron orbitals are not fixed rings around the nucleus), but the idea of chemical bonds helps explain how a hundred or so elements make up millions and millions of compounds.
It's better to think of chemical bonds as the result of attractive forces. Early on I told you that understanding how magnets work (like charges repel, opposites attract) will help you understand many underlying concepts in chemistry. Still true. The forces that bond atoms together are the same basic electrostatic attractions that make opposite poles of a magnet attract or that keep electrons attracted to the protons in the nucleus.
These resources will help you understand the basics of bonding:
Things that determine/predict how atoms will bond:
The Octet Rule*
When we studied electron configuration you learned that s orbitals hold 2 electrons, p orbitals hold up to 6 electrons, d orbitals hold up to 10 electrons, and f orbitals hold up to 14 electrons. So why all the emphasis on 8 ("octet")? Because 8 valence electrons between the s (2 e-) and p (6 e-) orbitals is the configuration of the Noble Gases! Notice every Noble Gas ends in an s2p6 configuration.
Are there exceptions (is this chemistry?)? Of course there are! Boron is content to share to see only 6 valence electrons and occasionally you can coax Noble Gases into expanding their octets. Maybe we should rename it the "Octet Suggestion."
Ionic vs. Covalent Bonding
Compounds form when elements bond chemically. There are two main types of chemical bonds: covalent and ionic (electrovalent).
So what's the difference?
How Can You Tell Which Type of Bond will Form?
Use your Periodic Table to determine whether an element is a metal or a non-metal and how many valence electrons it has to help determine if it will bond by transferring (ionic/electrovalent) or sharing (covalent) valence electrons.
How much do you need to know about bonding?
Charge-Balancing Ionic Compounds
Charge-Balancing Binary Ionic Compounds
Once an atom "ionizes" (gives up or captures valence electrons) the ion has a (+) or (-) charge. When two oppositely charged ions come together they bond "electrovalently," meaning they are electrostatically attracted to each other (remember - magnets?). In order to write the correct chemical formula we need to make sure all the (+) and (-) charges cancel each other out.
The math here is very straightforward - every negative charge has to be balanced out by a positive charge so the final compound (write this down) has a net charge of zero. This is what makes compounds charge neutral!
The easiest compounds to charge are the ones with a 1:1 charge ratio.
When you don't have a 1:1 ratio you have to find the combination that balances all of the charges
How did I determine these subscripts? Easy! It's just like finding the lowest common denominator in fractions! Look for a common number both charges will divide evenly into. When one ion has a charge of 2 and the other has a charge of 3, for example, a good "target" number they will both divide into is 6.
Charge-Balancing Ionic Compounds with Polyatomic Ions
All of the examples above contained monoatomic ions (ions with ONE element). But nature is full of polyatomic ions, too. Polyatomic ions are made up of more than one element. Polyatomic ions include ions like NO3 1- (the nitrate ion) and CO3 2- (the carbonate ion). Here is a list of common polyatomic ions and their charges.
The idea of charge balancing compounds with polyatomic ions is the same. You just need to be careful about using parentheses as needed. The general rule is: If you only need 1 of the polyatomic ions then you don't need to surround them with a parentheses. If you need 2 or more of a polyatomic ion then you do need to put them in parentheses so it's clear which subscript belongs to the polyatomic ion and which subscript is there as the charge balancing "inventory" number. Here are some example:
These websites/videos will give you more information (and lots of examples!) on how to charge balance and write chemical formulas. While we haven't looked at naming compounds just yet, they are still good practice resources:
How much do you need to know about charge-balancing?
Naming Ionic Compounds
Ionic compounds form between a metal (cation) and a non-metal (anion), or between a metal (cation) and a polyatomic ion. If your compound contains a metal it's ionic.
This is definitely one of those topics where mastery comes with practice. The rules seem deceptively simple, and as you read through the rules for each group of compounds naming itself may seem initially simple. But beware - when the compound types start getting mixed together you really need to be able to identify which is type of compound is which and know the naming rules for each type.
Simple Binary Ionic Compounds
Ionic Compounds with Polyatomic Ions
Ionic Compounds with Transition Metals
There are exceptions (surprise!). Because their charges never vary silver and zinc do not require roman numerals in their names.
These resources will help you understand how to name ionic compounds:
Naming Binary Molecular (Covalently Bonded) Compounds
These compounds contain covalent bonds either between two non-metals or between a non-metal and a metalloid. We are only going to look at naming very simple binary compounds.
The most important thing to know about naming binary molecular compounds? You must use PREFIXES to indicate how many of each element are in the compound.
Binary Molecular Compounds
This is chemistry so of course there are exceptions:
Honors Extension: Naming Acids, Bases and Hydrates
We'll do a whole unit toward the end of the year just on Acids and Bases, so for now we're just going to look at how to name them and write/recognize their chemical formulas. Why? So you recognize them in the lab!
There are two basic types of acids: 1) Binary acids (made up of two elements, one of which is hydrogen) and Oxo acids (which form when hydrogen bonds with a polyatomic ion).
Binary or "Hydro" acids
Practice worksheet with supplemental notes and an answer key.
Most common bases are formed when a metal (especially Groups 1A and 2A) bonds with a hydroxide. naming bases once you've identified them is easy!
Hydrates are ionic compounds with water molecules bonded into their crystal structure. Their formulas have a • between the ionic compound and the hydrate.
How much do you need to know about naming compounds?