Question

Which of these molecules are linear? \(\mathrm{ICl}_{2}^{-}, \mathrm{IF}_{2}^{+}, \mathrm{OF}_{2}\), \(\mathrm{SnI}_{2}, \mathrm{CdBr}_{2}\).

Short answer

ICl2-, SnI2, and CdBr2 are linear.

Step-by-step solution

Step 1', 'Checking ICl2-

ICl2- : The central atom (Iodine) has two regions of bonding electrons (I-Cl) and three lone pair electrons due to its 7 valence electrons and one gained; hence forms a linear structure.

Step 2', 'Checking IF2+

IF2+ : The central atom (Iodine) has two regions of bonding electrons (I-F) and two lone pair electrons due to its 7 valence electrons and one lost; hence it does not form a linear structure.

Step 3', 'Checking OF2

OF2 : The central atom (Oxygen) has two regions of bonding electrons (O-F) and two lone pair electrons due to its 6 valence electrons; hence it does not form a linear structure.

Step 4', 'Checking SnI2

SnI2 : The central atom (Tin) has two regions of bonding electrons (Sn-I) and no lone pair, due to its 4 valence electrons, which all form bonds; hence it forms a linear structure.

Step 5', 'Checking CdBr2

CdBr2 : The central atom (Cadmium) has two regions of bonding electrons (Cd-Br) and no lone pair due to its 2 valence electrons, which all form bonds; hence it forms a linear structure.

Key concepts

linear_molecule

A linear molecule is one where all the atoms lie in a straight line. This molecular geometry is characterized by a bond angle of approximately 180 degrees. Linear molecular structures are often simple to predict, especially for diatomic molecules, due to their straightforward arrangements.

To determine whether a molecule is linear, examining the regions of electron density around the central atom is critical. If there are only two areas of bonding without any influence of lone pairs that alter the shape, the molecule is typically linear. Such configurations do not deviate because there are no lone pairs pushing bonded atoms away. Hence, molecules like \(\mathrm{ICl}_{2}^{-}\), \(\mathrm{SnI}_{2}\), and \(\mathrm{CdBr}_{2}\) have a linear geometry because they have two bonding regions and either no or a balancing set of lone pairs.

Understanding this concept helps predict and rationalize the properties of a molecule, such as polarity, reactivity, and phases.

valence_electrons

Valence electrons are the electrons located in the outermost shell of an atom. They play a crucial role in chemical bonding and molecular geometry because these are the electrons involved in forming bonds.

For an atom, the number of valence electrons determines how and with what it will bond; they also dictate the atom's reactivity. Consider iodine, which has seven valence electrons. When it forms ions, it either gains or loses electrons, affecting its ability to bond with other atoms and determining its final molecular shape.

Valence electrons are crucial in understanding molecules like \(\mathrm{ICl}_{2}^{-}\), where additional electrons influence both electronic structure and geometry. These electrons dictate not only bonding but also the presence of lone pairs, which can alter a molecule's shape.

lone_pair_electrons

Lone pair electrons are the valence electrons not involved in bonding. They remain unshared and can impact the shape of a molecule tremendously.

In molecular geometry, lone pairs are significant because they exert a repulsive force that is stronger than bonded pairs. This is due to their closer proximity to the nucleus. For example, in \(\mathrm{OF}_{2}\), the presence of two lone pairs on oxygen leads to a bent shape rather than a linear one.

The influence of lone pairs on molecular geometry is illustrated by comparing molecules with similar electron counts but different structures due to lone pairs. Therefore, understanding lone pair electrons is essential when predicting and describing the shape and properties of molecules.