Question

\(\mathrm{BF}_{3}\) does not obey the octet rule.

Short answer

Explain your answer. Answer: No, the molecule BF₃ does not obey the octet rule. This is because the central boron atom has only six electrons in its valence shell instead of the expected eight electrons, according to the octet rule.

Step-by-step solution

Identify Elements and their Valence Electrons

We are given \(\mathrm{BF}_{3}\), which is a molecule composed of one boron (B) atom and three fluorine (F) atoms. The valence electrons for each atom are as follows: Boron (B) - 3, Fluorine (F) - 7.

Draw the Lewis Structure

Begin by drawing the Lewis structure for the \(\mathrm{BF}_{3}\) molecule. Place boron as the central atom since it has fewer valence electrons and surround it with the three fluorine atoms. Add electrons to the atoms such that each fluorine atom completes its octet, by forming a single bond with boron: ``` F \ B - F / F ``` The single bond represents 2 shared electrons (one from B and one from F in each bond).

Count electrons around the central atom

In the resulting Lewis structure, the boron atom has three single bonds with three fluorine atoms, and each single bond represents 2 electrons. So, the total number of electrons around the boron atom is 3x2 = 6 electrons.

Compare the number of electrons with the octet rule

In the octet rule, atoms are stable if they have 8 electrons in their valence shell. In \(\mathrm{BF}_{3}\), however, the boron atom has only six electrons around it in the valence shell, not 8.

Conclusion

Therefore, \(\mathrm{BF}_{3}\) does not obey the octet rule, as it has only six electrons in the valence shell of the central boron atom instead of the expected 8 electrons.

Key concepts

Lewis Structure

Understanding the Lewis structure is key for visualizing the electrons involved in the chemical bonds of a molecule. It's a diagrammatic method that represents the valence electrons around atoms. To draw a Lewis structure, firstly, identify the total number of valence electrons available for bonding. Then, decide on a central atom; generally, the least electronegative atom that isn't hydrogen plays this role. After arranging the atoms, draw lines or dots to represent shared or unshared electron pairs, respectively.

For the molecule \( \mathrm{BF}_{3} \) the Lewis structure portrays each fluorine (F) atom with seven valence electrons, while boron (B) has three. The structure reveals that while the fluorine atoms each achieve an octet of electrons, boron does not, showcasing an exception to the octet rule. This seemingly incomplete electron configuration for boron is actually common for it and a few other elements that can have fewer than eight electrons in their valence shell.

Valence Electrons

Valence electrons are the electrons located in the outermost shell of an atom, which determine its bonding behavior. These electrons are essential in the formation of chemical bonds because they can be shared with, lost to, or gained from other atoms. The number of valence electrons determines an atom's reactivity and its ability to reach a stable electron configuration, often an octet.

In the molecule \( \mathrm{BF}_{3} \) boron has three valence electrons and fluorine has seven. The valence electrons from boron and fluorine combine to form chemical bonds, where fluorine atoms each share one electron with boron. These shared electrons contribute to the atoms' valence shells. Fluorine reaches an octet, satisfying the octet rule, while boron remains stable with six valence electrons - an acceptable state for this particular element.

Chemical Bonding

Chemical bonding involves the joining of atoms through the transfer or sharing of valence electrons to achieve a full valence shell. There are three primary types of chemical bonds: ionic, covalent, and metallic. Ionic bonds occur when electrons are transferred from one atom to another, creating ions that attract each other. Covalent bonds form when atoms share electrons to fill their outermost shells, and metallic bonds happen between metal atoms when electrons are free to move within a lattice.

In the case of \( \mathrm{BF}_{3} \) the bonding is covalent, with boron sharing each of its three electrons with three separate fluorine atoms. This distribution results in a molecule where fluorine attains an octet through single bonds, and boron has six electrons in its outer shell. The \( \mathrm{BF}_{3} \) molecule's structure illustrates that while the octet rule is a guideline for many molecules, exceptions, such as in the case of boron, do occur in chemical bonding.