Chapter U2, Problem SI3RE

Solution

(a)

Interpretation : Number of lone pairs present in the given carbon dioxide molecule has to be identified.

Concept Introduction :

When atoms combine together to form molecule they share valence electrons to complete the noble gas configuration of eight electrons. Some electrons are part of the bonds formed while some are not. Pair of electrons that are not shared between atoms in a molecule are called lone pair of electrons.

In CO₂ molecule there are two lone pairs of electrons on each oxygen atom and no lone pair on carbon atom. The two oxygen atoms are joined by double bonds to carbon atom.

In carbon dioxide molecule, one carbon atom bonds with two oxygen atoms through double bonds. So, all four valence electrons of carbon bond with a pair of electrons of oxygen. Since oxygen has 6 valence electrons, only two electrons are used in bonding. Two pairs of lone electrons are left. Hence, there are two lone pairs of electrons on each oxygen atom and no lone pair on carbon atom.

(b)

Interpretation : Number of lone pairs present in the given silicon SiF₄molecule has to be identified.

Concept Introduction :

When atoms combine together to form molecule they share valence electrons to complete the noble gas configuration of eight electrons. Some electrons are part of the bonds formed while some are not. Pair of electrons that are not shared between atoms in a molecule are called lone pair of electrons.

In SiF₄ molecule there are zero lone pairs on silicon atom and three lone pairs of electrons on each fluorine atom.

In SiF₄molecule, one silicon atom bonds with four fluorine atoms through single bonds. So, all four valence electrons of silicon bond with a one valence electron of fluorine. Since fluorine has 7 valence electrons, only one electron is used in bonding. Three pairs of lone electrons are left on each fluorine atom. Hence, there are three lone pairs of electrons on each fluorine atom and no lone pair on silicon atom.

(c)Interpretation : Number of lone pairs present in the given methane molecule has to be identified.

Concept Introduction :

When atoms combine together to form molecule they share valence electrons to complete the noble gas configuration of eight electrons. Some electrons are part of the bonds formed while some are not. Pair of electrons that are not shared between atoms in a molecule are called lone pair of electrons.

In CH₄ molecule there are zero lone pairs on carbon atom and hydrogen atom.

Carbon combines with four hydrogen atoms to form methane, CH₄. Carbon has four valence electrons and hydrogen has one electron. So each hydrogen atom shares l electron with carbon to form four single bonds. All the electrons of carbon and hydrogen form bonded pair of electrons. Hence, there are no lone pairs of electrons on methane molecule.