Ionic bonding involves electrostatic attraction between oppositely charged ions. Metals lose electrons to form cations, nonmetals gain electrons to form anions. All ionic compounds have some degree of covalent bonding. Bonding occurs when ionic character exceeds covalent character
Electronegativity is not uniquely defined and may vary by definition. Values are taken from WebElements as consistent set. Some highly radioactive elements have predictions not marked. Francium's value (0.7) predates relativistic calculations
Polar molecules contain regions of positive and negative charge. Nonpolar molecules have no regions of charge. Polarity arises from unequal sharing of valence electrons
Berzelius classified substances as electropositive and electronegative based on electricity. Pauling defined electronegativity as an atom's ability to attract electrons
Periodic trends show changes in properties of elements across periods and down groups. Properties include ionization energy, metallic character, nonmetallic character, electronegativity, electron affinity, and atomic size
Electronegativity measures an atom's ability to attract electrons in bonds. Higher electronegativity means stronger electron attraction. Electronegativity increases from top right to bottom left in periodic table