Covalent Bonds - Online Tutor, Practice Problems & Exam Prep

Covalent Bonds Concept 1

So with covalent bonding, we say that a key feature of covalent compounds is where molecular bonds involve sharing valence electrons between nonmetals. Remember, covalent compounds only involve nonmetals. Recall they do this in order to achieve 8 valence electrons or a filled outer shell like the noble gases. Now we're going to say with this idea we have what's called the octet rule and the duet rule. With the octet rule, that's when an element reacts in order to achieve 8 valence electrons. And with the duet rule, this is specifically for the element of hydrogen. Here, it reacts in order to achieve 2 valence electrons. Doing this helps it to establish a filled outer shell like the noble gas of helium. Remember, from hydrogen to helium, hydrogen only needs to gain one more electron to be just like the noble gas of helium. So just remember, nonmetals form bonds in order to obtain electron arrangements like the noble gases. They do this to fulfill either the octet rule or the duet rule in terms of hydrogen.

Covalent Bonds Concept 2

So with the duet rule and the octet rule, remember, hydrogen follows the duet rule. Here we have 2 hydrogens. Both of their electron configurations are s1. If they can gain 1 electron, they can become 1s2 and become just like the noble gas helium. When it comes to covalent bonds, though, there is no transferring of electrons. It's the sharing of valence electrons. So what they do here is that they each share their one valence electron. So basically, they don't have sole possession of both electrons, they're sharing amongst each other. That gives each of them an electron configuration of 1s2, just like the noble gases in terms of helium. Other non-metals, they have more shells and therefore they want to follow the octet rule. If we take a look here at fluorine, fluorine is 1s22s22p5. If it can get to 2p6, it can become just like the noble gas of neon. What each fluorine decides to do is they decide to share their one electron. So here, neither one has sole possession of both electrons within this bond. They're sharing them with each other. And in that way, they each can have the 2p6 electron configuration that they desire. Doing this allows them to have or mimic the electron configuration of neon. So in both instances, the duet rule and the octet rule allow for a noble gas to mimic the electron configuration or electron arrangement of the nearest noble gases to them.

Covalent Bonds Example 1

Which of these elements is unlikely to form covalent bonds? We have sulfur, hydrogen, potassium, argon, and silicon here. Remember, covalent bonds involve the sharing of electrons between nonmetals. So, if we take a look here, sulfur is a nonmetal, so sulfur could form covalent bonds. Hydrogen is a nonmetal. Potassium is a metal; we said that it's between nonmetals. So, it can't ever form covalent bonds. Let's look at the other options. We have argon and then we have silicon. Argon is a nonmetal. Silicon is a metalloid. Now, technically, remember metalloids share characteristics of both metals and nonmetals, and since it's a metalloid and shares some nonmetal characteristics, there is the potential to form covalent bonds. So, e has the potential. c can't ever have the potential in forming covalent bonds because it's strictly a metal. So just remember, when it comes to covalent bonding, it's the sharing of electrons between elements that have nonmetallic characteristics.

Covalent Bonds Concept 3

When it comes to the properties of covalent compounds, we can take a look at their physical states, their conductivity, as well as their temperature. Now we're going to say because of the nature of their sharing of valence electrons, they can exist in any of the three states of matter at room temperature. So they can exist as solids, liquids, or gases. In terms of conductivity, we're going to say that they represent poor electrical conductors, and that's because they're not easily dissolved when I place them in a solvent like water. And then also we're going to say here that in terms of temperature, they tend to have lower melting points and lower boiling points.

Covalent Bonds Example 2

Which of the following compounds is expected to have the lowest boiling point? So here we have LiBr, lithium bromide, we have sulfur dioxide, we have sodium metal, we have zinc chloride, and then we have lead. Alright. So low boiling points are indicative of covalent compounds. Now before we even talk about that, realize that we have sodium metal and we have lead. Metals, when you think about metals in everyday life, you see metal structures, you see that they're pretty strong and rigid. We'd expect them to have higher boiling points. So choices (c) and (e) are out. Choices (a) and (d) are compounds composed of a metal, in this case, lithium and zinc, with a nonmetal in terms of bromine and chlorine. So they would represent ionic compounds. Ionic compounds tend to have higher boiling points. (b) is the answer because we have sulfur with oxygen. We have only nonmetals bonded together. So this represents a covalent compound, which tends to have a lower boiling point.