We're going to quickly cover chemical bonds. So you guys already know that chemical bonds are how individual atoms interact with one another and how they link and connect to other atoms. And really, chemical bonds fall under one of two categories, either intramolecular bonds or intermolecular bonds. Now, intramolecular bonds are bonds that exist within a molecule, whereas intermolecular bonds exist between different molecules. And so these two words sound similar, and what helps me distinguish between them is that intramolecular bonds are trapped within a molecule, whereas intermolecular bonds are not trapped, and instead, they exist between different molecules. So, in our example below, we're going to label the chemical bonds appropriately. And notice we have two different HCl molecules down below, and this bond here between the H and the Cl, the chlorine atoms, this is trapped within the molecule. So this must be our intramolecular bond. Now, the other bond shown here with the dotted line that exists between two different HCl molecules is not trapped, so this is an intermolecular bond. In our next video, we're going to talk about specific intramolecular bonds, and that includes ionic and covalent bonds. So I'll see you guys in that video.
Chemical Bonds - Online Tutor, Practice Problems & Exam Prep
Chemical Bonds Introduction
Video transcript
Ionic & Covalent Bonds
Video transcript
So you guys already know that ionic and covalent bonds are types of intramolecular bonds that occur within a molecule. And recall that ionic bonds are interactions between atoms that have opposite charges due to losing and gaining electrons, but not sharing electrons. And recall that covalent bonds occur when 2 atoms share a pair of electrons, and those electrons can either be shared equally or unequally. If the electrons are shared equally between 2 atoms, then this forms a nonpolar covalent bond, a nonpolar covalent bond. Whereas, if the electrons are shared unequally, then this forms a polar covalent bond. And what determines the polarity of a bond is actually the difference in electronegativity, electronegativity between 2 atoms.
And so, in our example below, we're going to consider the 3 types of bonds. In the left column, we have ionic bonds. So, we know that ionic bonds do not share electrons, so we can put no in here. And in fact, what they do is they transfer electrons. So there's a transfer of electrons, but no sharing. Now, covalent bonds, regardless of the type, we know that there is sharing of electrons, so we can put yes in here. Now, for polar covalent bonds, we know that there is unequal sharing of electrons, whereas for nonpolar covalent bonds, we know that there is equal sharing of electrons. Now, for the electronegativity of the atoms, in ionic bonds, the atoms differ greatly in electronegativity, and there's actually a transfer of electrons. Now, for polar covalent bonds, there's also a significant difference, and in nonpolar covalent bonds, the atoms have either the same electronegativity or a very, very similar electronegativity.
And so, for examples, recall that the classic example of an ionic bond is table salt or sodium chloride, where the sodium has one less electron and the chlorine has one additional electron than proton, and so that gives them their charges. And the opposite charges are what keep this molecule intact or allow them to create an ionic bond. Now over here for polar, we know that water molecules are polar molecules because they have an oxygen and hydrogen. Oxygens are super electronegative, whereas hydrogens are not very electronegative, and so oxygens are going to have a partial negative charge and the hydrogens are going to have a partial positive charge, and that will occur on both hydrogens. And, over here with this molecule, the carbon dioxide, there are also polar bonds. So, you can see the carbon here is going to have a partial positive charge, whereas the 2 oxygens are going to have partial negative charges. But because the polarity is going in opposite directions, so you have electron density being pulled in opposite directions, the overall molecule, even though it contains polar covalent bonds, the overall molecule is nonpolar. So for a molecule to be considered polar, you also have to consider its shape. And so this is a nonpolar molecule that contains polar bonds. And then for nonpolar covalent bonds, we have this hydrogen gas molecule where we have 2 hydrogen atoms that have the same electronegativity, and so that creates a nonpolar bond where they share electrons equally.
So in our next video, we're going to recap intermolecular bonds. So, I'll see you guys in that video.
Intermolecular Forces
Video transcript
Recall that non-covalent intermolecular forces include hydrogen bonds, dipole-dipole interactions, and van der Waals forces. Recall that hydrogen bonds are interactions that involve a hydrogen atom, as well as electronegative atoms such as nitrogen, oxygen, or fluorine. Now a dipole itself simply explains a shift in the electron density that results due to electronegativity differences between two atoms. So, if you have a dipole on one molecule where there's an electron density shift, and then you have another dipole on a different molecule, that can create a dipole-dipole interaction between the two molecules, and so, that's what we see here. Now, van der Waals forces are forces that exist between all molecules because they result from instantaneous dipoles that can exist at any moment in any molecule.
So, down below in our example, we're going to label each of these diagrams with the appropriate intermolecular force. And so here, with these carbonyl groups on these different molecules, notice that there is a dipole moment going in this direction towards the oxygen in both molecules to create a partial negative charge on the oxygens and a partial positive charge on the carbons. And so, there's an attraction or an interaction between the partial positive carbon here and the partial negative oxygen on separate molecules, and so that is our dipole-dipole interaction. Now, over here on the right, we have water molecules, which are also polar molecules and have their dipoles. And so, each of these applies to all of these water molecules. And so, there's going to be a specific type of dipole-dipole interaction called a hydrogen bond between the hydrogen atoms on one molecule and the oxygen atoms on a different molecule, and so that is what a hydrogen bond is. And so notice that a single water molecule here can form up to four hydrogen bonds. So here, we will put hydrogen bonds.
Now, for our last example, we have these two nonpolar molecules, these two nonpolar hydrogen gas molecules, and so, overall, they don't have any partial charges because they have a similar electronegativity and there's no shift in electron density. There are no dipoles. However, at any single instant, there could actually be an instantaneous dipole where one of these hydrogens could have a partial negative, and the other could have a partial positive charge. And so, this is where our van der Waals forces come into play, existing between all molecules. This is a good summary of our intermolecular forces, and I'll see you guys in our practice videos.
Which of the following is classified as a nonpolar molecule?
Identify the types of chemical bonds present in scenarios #1 & 2 below: