Question

How many valence electrons does each of the following species contain? (a) \(\mathrm{N}_{2} ;\) (b) \(\mathrm{HCl} ;(\mathrm{c}) \mathrm{NH}_{4}^{+} ;(\mathrm{d}) \mathrm{CN}^{-}.\)

Short answer

Answer: (a) N2 has 10 valence electrons; (b) HCl has 8 valence electrons; (c) NH4+ has 8 valence electrons; and (d) CN- has 10 valence electrons.

Step-by-step solution

(a) Determine valence electrons for N2

N (Nitrogen) has 5 valence electrons (as it is in group 15 of the periodic table). In N2, there are two nitrogen atoms, so there are 5 * 2 = 10 valence electrons in total.

(b) Determine valence electrons for HCl

H (Hydrogen) has 1 valence electron and Cl (Chlorine) has 7 valence electrons (as it is in group 17 of the periodic table). Therefore, there are 1 + 7 = 8 valence electrons in total.

(c) Determine valence electrons for NH4+

N (Nitrogen) has 5 valence electrons, and H (Hydrogen) has 1 valence electron. There are 4 hydrogen atoms, so we have 5 (N) + 4 * 1 (H) = 9 valence electrons for the neutral molecule. However, since the species has a +1 charge, we need to subtract 1 electron; thus, there are 9 - 1 = 8 valence electrons in total.

(d) Determine valence electrons for CN-

C (Carbon) has 4 valence electrons and N (Nitrogen) has 5 valence electrons. Therefore, there are 4 + 5 = 9 valence electrons for the neutral molecule. Since the species has a -1 charge, we need to add 1 electron; so there are 9 + 1 = 10 valence electrons in total. Hence the number of valence electrons for each given species is as follows: a) N2: 10 valence electrons b) HCl: 8 valence electrons c) NH4+: 8 valence electrons d) CN-: 10 valence electrons

Key concepts

Molecular Compounds

Molecular compounds are fascinating structures that consist of atoms bonded together in definite proportions. They are made up of molecules, which are groups of atoms held together by covalent bonds. These compounds typically consist of nonmetal elements. In molecular compounds, atoms share electrons to achieve stability, commonly aiming for an octet configuration, meaning eight electrons in their outer shell.

Molecules like \( \mathrm{N_2} \) (nitrogen gas) and \( \mathrm{HCl} \) (hydrogen chloride) are perfect examples of molecular compounds. These molecules involve atoms sharing electrons mutually. For instance, in nitrogen gas, each nitrogen atom shares three of its valence electrons with another nitrogen atom, forming a strong triple bond.

• Molecular compounds often exist as gases, liquids, or solids at room temperature.
• They typically have lower melting and boiling points compared to ionic compounds.
• Their physical state and appearance vary widely but are often non-conductive of electricity.

Understanding molecular compounds can provide insights into many natural and synthetic processes important for fields like chemistry, biology, and materials science.

Chemical Bonding

Chemical bonding is the glue that holds atoms together, forming the vast array of substances in the universe. There are three primary types of chemical bonds: ionic, covalent, and metallic. In molecular compounds, covalent bonds play a key role.

Covalent bonds occur when atoms share pairs of electrons. This sharing allows each atom to fill its outer electron shell, achieving a stable electron configuration. Consider \( \mathrm{HCl} \), a common chemical where hydrogen and chlorine share a pair of electrons to attain full outer shells: hydrogen aims for two and chlorine for eight electrons.

• Covalent bonds can be polar or nonpolar depending on the electronegativity difference between atoms.
• Polar covalent bonds have unequal sharing of electrons, leading to partial charges, as seen in \( \mathrm{HCl} \).
• Nonpolar covalent bonds involve equal sharing, evident in molecules like nitrogen gas \( \mathrm{N_2} \).

Understanding chemical bonding helps explain why substances have the properties they do, affecting everything from electrical conductivity to melting and boiling points.

Electron Configuration

Electron configuration is a crucial concept for understanding how atoms interact to form molecules. It describes how electrons are distributed among the various atomic orbitals. Valence electrons, the ones involved in bonding, are found in the outermost electron shell.

In a chemical reaction, the electron configuration determines how atoms will bond with each other. For example, nitrogen has an electron configuration of \(1s^2 2s^2 2p^3\). This means it has five valence electrons, which it can share to form bonds and achieve a stable octet.

• An electron configuration that fulfills an octet is particularly stable for elements in groups 14-18 of the periodic table.
• Changes in electron configuration can indicate whether an atom is likely to form cations or anions.
• Understanding electron configuration helps predict molecular structure and bond formation.

These configurations guide the way atoms interact, form structures, and ultimately determine the substance's properties, highlighting the essence of how chemistry shapes our world.