Question

Among \(\mathrm{BF}_{3}, \mathrm{NF}_{3}, \mathrm{PH}_{3}, \mathrm{IF}_{3}, \mathrm{IF}_{5}\) and \(\mathrm{SF}_{4}\), the number of species having the same number of lone pair of electrons on the central atom is

Short answer

There are 4 species with the same number of lone pairs on the central atom.

Step-by-step solution

Determine the Central Atom and Its Valence Electrons

For each molecule, identify the central atom and determine the number of valence electrons based on its group in the periodic table. - For BF\(_3\), the central atom is B with 3 valence electrons.- For NF\(_3\), the central atom is N with 5 valence electrons.- For PH\(_3\), the central atom is P with 5 valence electrons.- For IF\(_3\), the central atom is I with 7 valence electrons.- For IF\(_5\), the central atom is I with 7 valence electrons.- For SF\(_4\), the central atom is S with 6 valence electrons.

Count Electrons Used in Bonding

Determine the number of bonding electrons for each molecule. Each fluorine or hydrogen forms a single bond contributing 1 electron from the central atom:- BF\(_3\): Boron forms 3 bonds, using 3 electrons.- NF\(_3\): Nitrogen forms 3 bonds, using 3 electrons.- PH\(_3\): Phosphorus forms 3 bonds, using 3 electrons.- IF\(_3\): Iodine forms 3 bonds, using 3 electrons.- IF\(_5\): Iodine forms 5 bonds, using 5 electrons.- SF\(_4\): Sulfur forms 4 bonds, using 4 electrons.

Calculate Remaining Electrons as Lone Pairs

Subtract the number of bonding electrons from the total valence electrons for each central atom to find the number of lone pair electrons:- BF\(_3\): 3 - 3 = 0 lone pairs.- NF\(_3\): 5 - 3 = 2 lone pairs.- PH\(_3\): 5 - 3 = 2 lone pairs.- IF\(_3\): 7 - 3 = 4 lone pairs.- IF\(_5\): 7 - 5 = 2 lone pairs.- SF\(_4\): 6 - 4 = 2 lone pairs.

Identify Molecules with Same Number of Lone Pairs

Compare the number of lone pairs for each molecule. NF\(_3\), PH\(_3\), IF\(_5\), and SF\(_4\) each have 2 lone pairs. Therefore, there are 4 species with the same number of lone pairs.

Key concepts

Valence Electrons

Valence electrons are the electrons in the outermost shell of an atom and play a crucial role in determining how an atom bonds with others. The number of valence electrons can be determined by an element's group in the periodic table. For instance, in Group 13, boron has 3 valence electrons. Group 15 holds both nitrogen and phosphorus, each with 5 valence electrons. Iodine, found in Group 17, boasts 7 valence electrons, while sulfur in Group 16 holds 6.

A fundamental part of understanding valence electrons is realizing how they contribute to chemical bonding. When atoms form molecules, these valence electrons are either shared with or donated to other atoms, establishing chemical bonds.

• Shared valence electrons lead to covalent bonds, where electrons are shared between atoms.
• Transferred valence electrons create ionic bonds, forming charged ions.

In this exercise, counting the valence electrons allowed us to understand how many are available for bonding versus remaining as lone pairs on the central atom.

Molecular Geometry

Molecular geometry refers to the three-dimensional arrangement of atoms in a molecule, which influences the physical properties and reactivity of the molecule. The VSEPR (Valence Shell Electron Pair Repulsion) theory is instrumental in predicting molecular shapes based on repulsion between electron pairs (both bonding and lone pairs) surrounding a central atom.

In molecules like BF eee 3, the absence of lone pairs allows for a trigonal planar shape, achieved by spreading the three B-F bonds as far apart as possible. In contrast, NF eee 3 has two lone pairs on the nitrogen atom, forcing the molecule into a trigonal pyramidal shape with the lone pairs pushing the F atoms.

Molecular shapes are pivotal in determining how molecules interact with each other. For example:

• Linear, planar, or spherical shapes often lead to non-polar molecules.
• Bent or angular shapes typically result in polar molecules due to unequal sharing of electrons.

Understanding a molecule's geometry helps predict the behavior and reactivity of molecules in chemical reactions.

Central Atom

The central atom is the atom in a molecule to which other atoms are bonded. The central atom is typically the atom with the lowest electronegativity, allowing it to share more of its electrons and form bonds with surrounding atoms. In molecules like BF eee 3, boron is the central atom around which the three fluorine atoms are situated.

To identify the central atom effectively, consider factors like valence electrons and electronegativity. Sometimes, the atom present in the smallest quantity is the central one, especially when bonded symmetrically in simple molecules. This is true for molecules like PH 3 or SF 4, where phosphorus and sulfur serve as central atoms, respectively.

Learning about central atoms is essential for constructing Lewis structures, predicting molecular shapes, and understanding reactivity. It helps in determining how other atoms arrange around the central atom, impacting both bond angles and molecular geometry. By understanding which atom serves as the hub in a molecule, students can better visualize and predict the molecule's three-dimensional form.