why are some semimetals considered as a metal, and some, a nonmetal when paired with some atoms. Like in BF, it is an ionic bond, but in SiCl, it is a covalent bond. Do their electronegativities matter?

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    $\begingroup$ I would never call a $\ce{B-F}$ bond ionic. $\endgroup$ – Ivan Neretin Feb 18 '16 at 14:24

Yes, in fact difference in electronegativity is the defining property. Ionic character of a bond is given by: $$ \mathrm{\% IC = 1-exp[-\frac{1}{4}(\chi_A - \chi_B)^2]}$$ Where $\chi_A$ and $\chi_B$ are the electronegativities of the anion and cation species. When $|\chi_A - \chi_B|$ exceeds 1.665 the ionic character transitions from less than $50\%$ ionic to more than $50\%$ ionic, making the compound ionic.

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  • $\begingroup$ oh so, if i subtract the electronegativity of a, for example, a semimetal and a nonmetal, and if it is greater than 1, will the semimetal become a metal? $\endgroup$ – user26957 Feb 18 '16 at 14:23
  • $\begingroup$ No, not at all. Electronegativity is only informative about the ionic nature of the bond. $\endgroup$ – A.K. Feb 18 '16 at 14:57
  • $\begingroup$ It's only a suggestion about nature of bonding chemistry.stackexchange.com/questions/17064/… $\endgroup$ – Mithoron Feb 18 '16 at 16:50

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