Practice: Describe each of the following as either a(n): atomic element, molecular element, molecular compound or ionic compound.
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A chemical bond is the connection of different elements through the sharing, transferring or pooling of electrons.
Concept #1: Explanation for Bond Formation
We're going to say before we learn the different types of chemical bonds, we have to first ask ourselves, why do elements want to form bonds in the first place? Well, we know that the two major types of bondings that exist we've talked about, we have covalent compounds and ionic compounds. Covalent compounds have covalent bonds, ionic compounds have ionic bonds.
Now we're going to say that generally, the reason that ionic bonding forms is because it lowers the potential energy between positive and negative ions. Remember when two things are forming a bond they're releasing energy. Them releasing energy makes them move slower. Because they're moving slower, they're able to combine more together.
And remember if we're forming a bond it's an exothermic reaction or an exergonic reaction if we're talking about energy. If you're losing energy, you're going to become more stable. In chemistry, you're more stable when you have less energy. It's all about minimizing the amount of energy you possess. And ionic bonding does that.
Now we're going to say generally the reason that covalent bonds form is to follow what we call the octet rule. We'll learn more about the octet rule later but just realize for now, the octet rule just means elements are then surrounded by eight valence electrons. We'll learn that some elements usually follow the octet rule but there are others that break them. Some may have less than eight valence electrons, some may have more than eight valence electrons. When we come to those topics, we'll see them more in depth.
Concept #2: Understanding an Ionic Bond
We already know there are two types. We're going to say the first type is ionic bonding. We're going to say that's usually between a metal and non-metals. Now remember, this isn't always true because we could have ammonium nitrate as an example. Ammonium nitrate is also ionic, it's ionic because it comes from combining the ammonium ion which is positive plus nitrate ion which is negative.
Usually, ionic compounds are between metals because they're usually positive, they're positively charged ions, and non-metal which are negative ions, but that's not always the case for ionic bonding. Ionic bonding fundamentally is just the bonding between a positive ion and a negative ion.
Now we're going to say that the metal transfers an electron to the non-metal. Now if the metal is transferring an electron, it's losing that electron, so the metal will become positive. And we've said before that a positive ion is called a cation. The non-metal would be gaining that electron that was transferred over to it. When you gain an electron, you become more negative. A negative ion remember is called an anion. Their opposite charge is what attracts them to one another. Remember in chemistry opposites attract.
Now if we take a look at this, how does it work? Well here we're going to say that lithium wants to combine with fluorine. Lithium is a metal, fluorine is a non-metal. These dots around them are called their valence electrons. Remember we've said that if you're a main group element, your group number equals you valence electron number. Lithium is in Group 1A that's why it has 1 valence electron dot. Fluorine is in Group 7A that's why it has 7 electron dots.
Now we know lithium wants to be +1 because it's in Group 1A. And we know fluorine wants to be -1 because it's in Group 7A. So what's going to happen here is, lithium is then going to transfer over its electron over to the fluorine. When it transfers over its electrons, it's going to be +1 as its charge and then fluorine accepts that electron and becomes -1. Their opposite charges is what causes them and forces them to combine together to give us lithium fluoride.
So this is the image that you have to have in your head when you're dealing with ionic bonding. Ionic bonding is just the bonding between a positive ion and a negative ion.
An ionic bond involves the transferring of an electron from one element to another element.
Concept #3: Understanding a Covalent Bond
Now the second type of chemical bonding is we're going to say is covalent bonding. We're going to say in covalent bonding, nonmetals create bonds with other nonmetals. So this is different. Remember ionic is between a metal and a nonmetal, but covalent is only between nonmetals.
We're going to say here, we don't have the transferring of electrons between nonmetals, instead, we're going to have the sharing of electrons between the nonmetals. So in it, the nonmetals share electron pairs between their nuclei. They're going to wind up sharing electrons with one another.
What's going to happen here is both of these guys are basically going to share that one electron that they have there with each other. At the end, we're going to have an image that looks like this. I'm going to draw one chlorine in red and then another one in blue just to signify the difference. These are two different chlorines that combine together to share their electrons.
That's the fundamental difference between ionic bonding and covalent bonding. In ionic bonding, we have the transferring of electrons from metals to nonmetals and in covalent bonding, we have the sharing of electrons between nonmetals.
A covalent bond involves the sharing of electron(s) between elements.
Concept #4: Understanding a Metallic Bond
The final type of bonding, which we normally don't see, is metallic bonding. We're going to say metal atoms pool their valence electrons to form an electron sea that holds the metal ion together.
So here we have an image of the surface of a metal. So just realize visually the surface of a metal basically has free floating electrons all over it. When we talked back about the phot-electric effect in chapter six or seven, we talked about having a photon being able to hit the surface of the metal and launching an electron off. It wouldn’t be able to do that if it were not for the surface of a metal. The surface of a metal basically just has a bunch of electrons on it. Those electrons, they're not stuck on there really hard. If we have sufficient energy, we can knock one off.
Now metallic bonding, you're normally not going to see. So I wouldn't worry too much about this third type of chemical bonding. Know that it exists, but don't worry too much about what does it look like.
The most important ones are ionic bonding and covalent bonding. And remember, ionic bonding is between a cation and an anion. We have a transferring of an electron from one to the other, that's where their charges come into play. And from that, since they have opposite charges, they come together.
Covalent bonding is even more important it's because of covalent bonding that we're going to see things such as Lewis dot structures. Lewis dot structures are based on covalent binding structures. So it's more important for us to get down the fundamentals of covalent bonding most from this. So just remember the three types of chemical bondings that exist and remember the features of each.
A metallic "bond" isn't really a bond. Think of electrons as being loosely connected or "pooling" on the surface of many metals.
Depending on the element or elements involved we can describe bonds as forming: atomic elements, molecular elements, molecular compounds or ionic compounds.
Practice: Describe each of the following as either a(n): atomic element, molecular element, molecular compound or ionic compound.
Concept #5: Understanding the Ionic Bonding Model
We said up to this point that there are two major forms of chemical bonding that we're going to be concerned with, the first being ionic bonding and the second being covalent bonding. Now, also recall that ionic bonding just has to do with the transferring of an electron from one element to the other, and we're going to say this transferring of electrons causes them to gain different charges. And in chemistry opposites attract, the positive ion will be attracted to the negative ion and together they're going to form our compound.
Now we're going to say we have the transferring of the electron from the metal to the non-metal. We're going to say the metal then becomes a positive ion, which we call a cation, and the non-metal becomes a negative ion, which we call an anion. And we're going to say any time we form a ionic compound, it's going to form into a solid. So an ionic compound is going to form a solid compound.
Here we have an example of sodium and chlorine. Remember, sodium is in Group 1A, chlorine is in Group 7A. Group 1A elements want to be +1 and they do this by losing 1 electron. Group 7A elements want to be -1, by becoming -1, they pick up an electron and become just like the closest noble gas.
So what's going to happen here is we have this outside electron, it's in our third shell, for sodium. So what's going to happen is it's going to leave and transfer over to the chlorine. As a result, now sodium loses its third shell. So its outermost shell now becomes shell number 2. And in shell number 2 how many electrons does it have? It has 8. Recall we talked about this during the Lewis dot structure of elements when they lose or gain electrons. This the visual way of looking at it.
We're going to say chlorine picks up that electron that sodium transfers over, so now it becomes Cl-. It becomes chloride ion. So here we have sodium ion, here we have chloride ion. Because they're opposite charges, they're going to combine together to give us this compound right here.
Now think of an ionic compound on a molecular microscopic level. On a molecular level, it's not just one sodium ion and one chlorine ion combining. It's a bunch of them combining together to give us our ionic solid. This is the kind of thinking we have to have when we're making our compound.
Remember we've seen this before, how did they combine to form our compound? Since they have opposite charges and they're the same number, they just combine together to give us sodium chloride.
So I’ll let you guys try to attempt to do this practice question on the end of this sheet. Remember we've done this so many times. How do we create an ionic compound from the ions given? Remember all that happens are the numbers will crisscross together to give us our ionic compound. I just want you guys to familiarize yourselves with this basic concept we've done a million times before. How does K+ and P3- for example, combine together to give us our ionic compound?
An ionic bond forms when a cation and anion combine because of their opposite charges.
Practice: Determine the molecular formula of the compound formed from each of the following ions.
a. K+ & P3-
b. Sn4+ & O2-
c. Al3+ & CO32-
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