Question

Draw Lewis structures for (a) carbon disulfide, (b) the cyanide ion, (c) germanium tetrachloride, and (d) the phosphate ion.

Short answer

CS2: central C atom double bonded to two S atoms. CN⁻: C and N atoms connected with a triple bond and lone pair on N with a negative charge. GeCl4: central Ge atom single bonded to four Cl atoms. PO4^3⁻: central P atom single bonded to four O atoms, with one double bond to an O atom and three negative charges on the oxygens.

Step-by-step solution

Count Total Valence Electrons for Carbon Disulfide (CS2)

Carbon has 4 valence electrons and sulfur has 6. There are two sulfur atoms, so the total valence electrons for CS2 is: 4 + (6 × 2) = 16.

Draw Lewis Structure for Carbon Disulfide (CS2)

Place carbon in the center and surround it with two sulfur atoms. Add double bonds between carbon and each sulfur to complete the octet for all atoms.

Count Total Valence Electrons for the Cyanide Ion (CN⁻)

Carbon has 4 valence electrons, nitrogen has 5, and there is an extra electron due to the negative charge: 4 + 5 + 1 = 10.

Draw Lewis Structure for the Cyanide Ion (CN⁻)

Connect the carbon and nitrogen atoms with a triple bond to give both atoms a complete octet and add a lone pair on nitrogen. Assign the negative charge to nitrogen.

Count Total Valence Electrons for Germanium Tetrachloride (GeCl4)

Germanium has 4 valence electrons and chlorine has 7. With four chlorine atoms, the total is: 4 + (7 × 4) = 32.

Draw Lewis Structure for Germanium Tetrachloride (GeCl4)

Place germanium in the center and add four chlorine atoms around it. Connect each chlorine to germanium with a single bond.

Count Total Valence Electrons for the Phosphate Ion (PO4^3⁻)

Phosphorus has 5 valence electrons, oxygen has 6, and there are three extra electrons due to the charge: 5 + (6 × 4) + 3 = 32.

Draw Lewis Structure for the Phosphate Ion (PO4^3⁻)

Draw phosphorus in the center with four oxygens around it. Use single bonds to connect each oxygen. Place three double bonds to satisfy the octets and allocate three extra electrons as lone pairs on the oxygen atoms not doubly bonded to phosphorus, and assign the 3- charge to the ion.

Key concepts

Valence Electrons

Understanding valence electrons is crucial for drawing Lewis structures, as these electrons play a central role in chemical bonding. Valence electrons are the electrons in an atom's outermost shell and determine how atoms connect with each other to form molecules.

For instance, carbon, the central atom in carbon disulfide (CS₂), has 4 valence electrons. Sulfur, being part of the same group as oxygen on the periodic table, has 6 valence electrons. When we calculate the total number of valence electrons for CS₂, we sum up the valence electrons of each atom: 4 (from carbon) plus 12 (6 from each of the two sulfur atoms), getting us a total of 16 valence electrons to work with for constructing the Lewis structure.

Chemical Bonding

Chemical bonding represents the force holding atoms together within molecules or compounds. Bonds form from the interactions between valence electrons. There are several types of bonds, but the Lewis structures primarily feature ionic and covalent bonds.

In carbon disulfide, the bonding between carbon and sulfur is covalent, where they share pairs of electrons to achieve stable electron configurations. Each double bond represents a sharing of two pairs of electrons. In the cyanide ion (CN⁻), the carbon and nitrogen atoms share three pairs of electrons, forming a triple bond, which is one of the strongest types of covalent bonds.

• Single covalent bond - one pair of shared electrons
• Double covalent bond - two pairs of shared electrons
• Triple covalent bond - three pairs of shared electrons

Recognizing how many bonds atoms typically form is crucial when predicting how they bond in a molecule based on the available valence electrons.

Molecular Geometry

Molecular geometry revolves around the three-dimensional arrangement of atoms within a molecule. The geometry is pivotal for determining the molecule's physical and chemical properties.

In drawing Lewis structures, we start to see hints of the molecular geometry. For instance, germanium tetrachloride (GeCl₄) forms a tetrahedral shape due to the repulsion between the four pairs of valence electrons surrounding the germanium atom. In the phosphate ion (PO₄^3-), phosphorus is also at the center of a tetrahedral arrangement, with oxygen atoms at the corners. Understanding molecular geometry is important to grasp because it affects how molecules behave, their reactivity, and how they interact with other molecules.