What kind of bond joins B and H in BH4-?
The kind of bond that joins B and H in BH4- is a covalent bond.
The type of bond that joins the "B" (boron) and "H" (hydrogen) in the BH4- (borohydride) ion is a covalent bond. Specifically, it is an ionic-covalent bond, where the boron atom donates its electrons (forming an ionic interaction) while the hydrogen atoms share their electrons with the boron atom (forming covalent bonds).
To determine the type of bond that joins the elements B (boron) and H (hydrogen) in the BH4- ion, we can look at the electron configuration and bonding preferences of these elements.
Boron has an atomic number of 5 and its electron configuration is 1s2 2s2 2p1. It has three valence electrons available for bonding.
Hydrogen has an atomic number of 1 and its electron configuration is 1s1. It has one valence electron available for bonding.
BH4- is an anion with a charge of -1, indicating that it has gained an extra electron. This brings the total number of valence electrons in BH4- to 4 (from boron) + 1 (from each hydrogen) + 1 (from the extra electron) = 6 valence electrons.
Based on the number of valence electrons, we can determine that there are 4 covalent bonds formed between boron and hydrogen in the BH4- ion. Each hydrogen atom shares one electron with the boron atom, and boron shares one of its valence electrons with each hydrogen atom.
Therefore, the bond between boron and hydrogen in BH4- is a covalent bond.