If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content

Ionic bonds

AP.Chem:
SAP‑3 (EU)
,
SAP‑3.A (LO)
Ionic bonds result from the electrostatic attraction between oppositely charged ions, which form when valence electrons are transferred from one atom to another. Created by Sal Khan.

Want to join the conversation?

  • primosaur ultimate style avatar for user Evan
    Can metals only form ionic bonds with nonmetals or is it possible to have two metals in an ionic bond?
    (12 votes)
    Default Khan Academy avatar avatar for user
    • male robot donald style avatar for user Venkata
      Two metals can't form an ionic bond. The requirements for this bond are the losing of electrons by one element and gaining by another. There is no metal in existence that accepts electrons. So, ionic bond between only metals is not possible.
      (35 votes)
  • leaf green style avatar for user IIIIIIIIII1
    As elements gain electrons does their electronegativity increase? For example, if oxygen gains an electron is it now as electronegative as fluorine?
    (16 votes)
    Default Khan Academy avatar avatar for user
  • aqualine sapling style avatar for user applesauce
    So how can you look at something like NH3 or BeO, etc. and tell what type of bond it is?
    (4 votes)
    Default Khan Academy avatar avatar for user
  • leaf green style avatar for user Laksheeta Iyer
    Is it possible for Sodium to gain seven electrons instead of lose one electron to become complete ?
    (5 votes)
    Default Khan Academy avatar avatar for user
    • duskpin ultimate style avatar for user W
      One will never see that happening in nature because of Electronegativity (the amount that an atom attracts electrons). Atoms on the left of the periodic table (such as Sodium) have very low electronegativity, so they will not fight hard to keep their electrons, making it very easy to have their last electron stolen and very hard for them to nick 7 more electrons.

      Another approach is from the Coulomb Law perspective. Think about the fixed amount of positive charge in the nucleus and the growing negative charge in the valence shell. The atom in question, Sodium, will grow increasingly unstable as the electrons repel each other and the protons fail to attract hard enough.
      (12 votes)
  • blobby green style avatar for user Inha
    How do you know sodium has 1 valence electron and chlorine has 7 valence electron?
    (5 votes)
    Default Khan Academy avatar avatar for user
  • starky seedling style avatar for user lsyali
    is it possible for elements that usually lose electrons, eg sodium, to gain electrons, and vice versa?
    (6 votes)
    Default Khan Academy avatar avatar for user
  • hopper cool style avatar for user Iron Programming
    What is the most accepted definition of an ionic bond vs polar covalent vs nonpolar covalent?

    Obviously, 0 electronegativity difference would result in nonpolar covalent regardless. But besides that, I've seen numbers all over the place.

    Currently, my college professor is using the following stats:
    < 0.5 → non-polar covalent
    0.5 - 1.6 → polar covalent
    >1.6 → ionic

    I've been contact with him a lot lately, but I figured I would ask this here to give him a break. lol

    Anyway, does IUPAC or other "higher authorities" have official standards that they go by that I can cite?

    The last several years I have basically used whatever arbitrary numbers I happen to have found in the search results...

    Thanks!
    (2 votes)
    Default Khan Academy avatar avatar for user
    • leaf red style avatar for user Richard
      Using electronegativity differences between atoms in a bond is a fair way to gauge a bond's polarity. There's a couple issues with this method though. First is agreeing on what ranges to use. There isn't a single set of ranges that are unanimously agreed on. The ranges you've listed look acceptable.

      The more conceptual second reason is that it views bonds in an absolute sense. In that a certain electronegativity difference like 1.6 would be polar covalent, but slightly higher and it would be entirely ionic. With this view bonds are either one or the other, but never both or a combination of the two.

      However in reality bonds are certain percentages covalent and ionic. In this sense covalent character can be seen as to what degree bonding electrons are shared and electron density exists between the atoms. And ionic character can be seen as to what degree the electrons are transferred to one atom. We can quantify these behaviors by something called percent ionic character. This lists bonds between 0% thru 100% with 0% being completely covalent and 100% being completely ionic. Using percent ionic character, we can still classify bonds as being predominantly covalent or ionic but it reminds us that a bond is usually never completely one or the other. With the exception of completely nonpolar covalent bonds with a percent ionic character of 0%. Pretty much no ionic bond reaches 100% ionic character though since there is at least some small degree of electron sharing. Linus Pauling, the chemist who developed the Pauling scale for electronegativity, used >50% ionic character as the mark for them a bond which was predominantly ionic. Predominantly covalent bonds would have an ionic character of <50%, and this could be further broken down into polar and nonpolar covalent. These ionic character percentages correspond to electronegativity differences (50% ionic character for example would means an electronegativity difference of 1.7) so they're alternative ways of gauging bond polarity, but percent ionic character reminds us though that bond type isn't black and white.

      Another way to quantify a bond's polarity is using its dipole moment. A dipole moment is essentially a vector pointing towards the more electronegative atom showing where charge is accumulating in a bond. Bond dipole moments also correspond to electronegativity differences so they will agree with each other.

      Personally I prefer using something called the Van Arkel–Ketelaar triangle for determining bond type. It's essentially a triangle which inputs electronegativity differences and averages from two bonding atoms and plots them in a 2D plane. The x-axis being the average electronegativity and the y-axis being the electronegativity difference. The regions where bonds could possibly be form a triangle and this triangle is partitioned into ionic, polar covalent, nonpolar covalent, and metallic. It also always us to determine the percent ionic character of a bond too. So it's a wider view of bonding which includes the possibility of metallic bonding which electronegativity differences alone do not account for.

      So there are several valid ways to view bond polarity which can get increasingly complex depending on how detailed of an answer you'd like. Using simply electronegativity differences is most likely more than adequate for most general chemistry classes. So using your professors numbers will get you by. It's just good to keep in mind the variability of classifying a bond's polarity.

      Hope that helps.
      (6 votes)
  • blobby green style avatar for user Mohamed Ahmed
    How HF "Hydrogen Flouride" is a covalent compound while it's electronegativity difference is 1.9 which more than 1.7
    (4 votes)
    Default Khan Academy avatar avatar for user
    • leafers ultimate style avatar for user William Adkison
      In this case, HF is an exception to the 1.7 rule. Hydrogen is a non-metal, as is Fluorine. We know that nonmetals cannot form ionic bonds, due to the nature of the ionic bond--the transferring of electrons. Non-metals all need electrons to be added to them, removing any possibility of an electron transfer between non-metals. The only alternative, however improbable, is that HF is simple an extremely polar compound. Hope this helps!
      (1 vote)
  • duskpin sapling style avatar for user Sophie
    How do you determine the attraction between two sets of ions?
    (2 votes)
    Default Khan Academy avatar avatar for user
    • leaf red style avatar for user Richard
      Coulomb's Law quantizes the force of attraction (or repulsion) between charged particles. It has the form: F = (Kq1q2)/(r^2), where F is the force, K is Coulomb's constant, q1 and q2 are the charges of the ions, and r is the distance between the ions which is basically the atomic radii of the ions. Hope that helps.
      (4 votes)
  • blobby green style avatar for user Chris Human
    Guys, I need some help, I really don't understand, what that's means, the number above , H , Be , C , N, O , ... etc
    (0 votes)
    Default Khan Academy avatar avatar for user

Video transcript

- [Instructor] Most of what we've talked about so far has been atoms in isolation. We have thought about the number of electrons and protons and neutrons and the electron configuration of atoms. But atoms don't just operate in isolation. If that were the case, the whole universe including us would just be a bunch of atoms drifting around. What begins to be interesting is how the atoms actually interact with each other. And one of the most interesting forms of interaction is when they stick to each other in some way shape or form. And this sticking together of atoms is what we are going to study in this video. Another way to talk about it is, how do atoms bond? Now as we will see, there are several types of bonds and it's really a spectrum. But let's just start with what I would consider one of the more extreme type of bonds. And to understand it, let's get a periodic table of elements out right over here. So let's say that we are dealing with a group one element. Let's say sodium right over here. What's interesting about group one elements is that they have one valence electron. If we want to visualize the valence electrons for, say, sodium we could do it with what's known as a Lewis dot structure or a Lewis electron dot structure, sometimes just called a dot structure for short. But because a neutral sodium has one valence electron, we would just draw that one valence electron like that. Now let's go to the other end of the periodic table and say, look at chlorine. Chlorine is a halogen. Halogens have seven valence electrons so chlorine's valence electrons would look like this. It has one two three four five six seven valence electrons. And so you could imagine chlorine would love to get another electron in order to complete its outer shell. And we've also studied in other videos these atoms, these elements at the top right of the periodic table which are not the noble gases, but especially the top of these halogens, things like oxygen, nitrogen. These are very electronegative. They like to pull electrons, hog electrons. And so what do you think is going to happen when you put these characters together? This guy wants to lose the electrons and chlorine wants to gain an electron. Well, maybe the chlorine will take an electron from the sodium. On a real chemical reaction, you would have trillions of these and they're bouncing around and different things are happening but just for simplicity, let's just imagine that these are the only two. And let's imagine that this chlorine is able to nab an electron from this sodium. So what is going to happen? This sodium is then going to become positively charged, 'cause it's going to lose an electron. And then the chlorine, the chlorine is now going to gain an electron. So it's going to become a chloride anion. Anion is a negative ion. It's a sodium cation, a positive ion. Ion means it's charged. And now it's a chloride anion. So it has the valence electrons that it had before and then you could imagine that it gains one from the sodium. And now it has a negative charge. Now what do we know about positively charged ions and negatively charged ions? Opposites attract. Coulomb forces. So these two characters are going to be attracted to each other, or another way to think of it, they're gonna stick together, or another way you could think about it, they are going to be bonded. And they will form a compound of sodium chloride. And notice the whole compound here is neutral. It has a plus one charge for the sodium, a negative one charge for the chloride, but taken together it is neutral because these are hanging out together. And this type of bond between ions, you might guess what it's called. It is called an ionic bond. Ionic bond.