I have read that hydrogen bonds form between polar R-groups and ionic bonds form between charged R-groups on an amino acids, forming the tertiary structure of the protein.
But what is the difference between a polar/charged R-group? When will a hydrogen bond form & when will an ionic bond form?
Hydrogen bonds are generally between a hydrogen atom and an atom of nitrogen, oxygen, fluorine or chlorine. An example of a hydrogen bond would be between the hydrogen of one water molecule and the oxygen of another molecule. Hydrogen bonds arise because of the difference in electronegativity between the hydrogen (not very electronegative) and the other atom (which is very electronegative). The more electronegative atom, e.g. the oxygen in water, attracts electrons more strongly, so is described as being slightly negative (you will see this represented as δ-) and the hydrogen is slightly positive (δ+). Hydrogen bonds would lead to a polar bond, because of the partial charges.
Ionic bonds only form between ions, e.g. Cl- and Na+. As opposed to the slightly negative charges (polarity) seen in hydrogen bonds, the ions in ionic bonds have an actual charge because they have lost or gained electrons. Ionic bonds result in a charged R-group because there are charged particles (ions) involved.
Remember: charged means there is a full charge, e.g. Na+, and polar means the is only a partial charge, e.g. H δ+.
Hope this helps!