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You can try to logically reason it out looking at the electronegativity difference between the atoms in the bond. The larger the difference, the more ionic character the bond will likely express. However, without calculating electronegativity (X) using the equation X= .5(I+Ea) where I is ionization energy and Ea is electron affinity, you can't put it in one of the categories for certain. Typically, covalent bonds have X=1.5 or lower, and ionic have X=2 or higher. Lavelle stated he won't give us ions/molecules between these values.
Leila_4E wrote:This is really helpful, thank you. I'm also having trouble remembering if the ionic radius trend is different than atomic radius trend?
The ionic radius trend is the same as the atomic radius trend. Decreasing down and to the left.
Both the ionic and atomic radius trends decrease across a period and increase down a group due to the additions of energy levels. Across a period, the energy level stays the same and protons are being added, increasing the nuclear charge.
If you're given an electronegativity table, you can take the absolute value of the difference between the electronegativity values of each atom in the bond. A difference of >1.7 means the bond is ionic, 0.4-1.7 means the bond is polar covalent, and <0.4 means the bond is nonpolar covalent.
There are many ways to determine whether a molecule is polar covalent or ionic. One method that is very practical is to see if the bond is between a non metal-non metal(covalent, possibly polar) or metal-non metal which is ionic. The difference in electronegative is a good way to determine this because if the difference is great enough then it will be ionic( greater difference than 2). To determine whether a covalent bond is polar or not, is to see the difference in electronegativity great enough. For example a Cl-Cl bond has an electronegative difference of 0 so you know for sure that its non-polar but if there is a distinguishable difference it will usually be same to assume that its polar covalent. You can always draw the Lewis structure to make see if the distribution of electrons is even or not.
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