Chapter 5

Can a molecule also be an elemental substance? If so, give some examples.

The attractive force between atoms that results from the sharing of two valence electrons between those atoms has a special name. What is it?

Why does the sharing of two electrons between two atoms bond the atoms to each other?

In terms of energy, why is an \(\mathrm{H}_{2}\) molecule more stable than two isolated \(\mathrm{H}\) atoms?

In terms of interaction between the atoms, why is an \(\mathrm{H}_{2}\) molecule more stable than two isolated H atoms?

The bond distance in an \(\mathrm{H}_{2}\) molecule is \(0.74 \AA\). Why isn't it shorter than this? Why isn't it longer than this?

Is energy released or absorbed when a covalent bond forms between two atoms?

Why are an atom's valence electrons the only electrons involved in bonding?

Suppose one of the electrons from the covalent bond in \(\mathrm{H}_{2}\) suddenly vanished. Why would the bond between the atoms weaken?

A student decides to boil water to produce hydrogen gas and oxygen gas. Will this work? Explain your answer.

What do we mean by "double-counting" when it comes to counting the electrons around an atom in a molecule?

What is the accepted shortcut for drawing a shared pair of electrons (a covalent bond) in a molecular drawing?

How many electrons does an atom gain for ea covalent bond that it forms in a molecule?

For any representative element, what is the relationship between the element's Romannumeral group number and the number of dots in the Lewis dot diagram?

Chlorine (Cl), neon (Ne), and helium (He) all exist as gases, but only one of them is diatomic. Which is it, and why is it diatomic while the others are monatomic?

Valence electrons in an isolated atom can exist in either of two ways. What are they?

Why isn't the formula for water HO?

Hydrogen (H) and sulfur (S) form the toxic compound hydrogen sulfide, a gas that smells like rotten eggs and is spewed from volcanoes. Predict the formula of hydrogen sulfide starting with dot diagrams for the atoms.

Phosphorus (P) and bromine (Br) form a compound. Predict the formula of this compound starting with dot diagrams for the atoms.

Ethers are compounds of \(\mathrm{C}, \mathrm{H}\), and \(\mathrm{O}\) that are often used as solvents. One particular ether molecule has the formula \(\mathrm{C}_{2} \mathrm{H}_{6} \mathrm{O} .\) The structure is such that both carbons are attached to the oxygen atom, and there are no \(\mathrm{O}-\mathrm{H}\) bonds. Starting with dot diagrams for the atoms, draw a dot diagram for this ether molecule. How many bonding pairs does the molecule have? How many lone pairs?

The molecule \(\mathrm{HCl}\) is known, but the molecule \(\mathrm{HeCl}\) is not. Explain why this is so.

The valence electrons in a helium atom are paired, but suppose they were not. Postulate what might form if oxygen atoms reacted with helium atoms that had their valence electrons unpaired.

Oxygen, in almost all of its compounds, forms two bonds. Explain why this is so.

How many bonds will an atom from group VA generally form? Explain why this is so.

Draw a dot diagram for ethylene, \(\mathrm{C}_{2} \mathrm{H}_{4}\).

Is the bond between the carbon atoms in the ethylene molecule of Problem \(5.84\) stronger or weaker than the bond in acetylene, \(\mathrm{C}_{2} \mathrm{H}_{2}\) (WorkPatch 5.7)? Explain fully.

Explain what is meant by resonance forms.

Draw a dot diagram for the molecule \(\mathrm{SO}_{2}\), sulfur dioxide, a gas that comes from burning coal and is responsible for acid rain. (Hint: Sulfur is in the mid?le.)

Draw a dot diagram for the molecule \(\mathrm{O}_{3}\), ozone, the molecule in our upper atmosphere that protects us from the Sun's harmful ultraviolet electromagnetic radiation. (Hint: Only the middle oxygen atom forms bonds with the two other oxygen atoms.)

A student claims that the bonds in ozone are really not double bonds or single bonds but somewhere between (roughly \(1.5\) bonds between each oxvgen). Justify this statement.

Experiments show that it takes more energy to break the bond between oxygen atoms in the \(\mathrm{O}_{2}\) molecule than in the \(\mathrm{O}_{3}\) molecule. How can you explain this?

How many covalent bonds do you think would form between the phosphorus atoms in the molecule \(\mathrm{P}_{2}\) ? Explain your answer and draw a dot diagram.

Draw a dot diagram for the nitrate \(\left(\mathrm{NO}_{3}^{-}\right)\) ion.

Draw a dot diagram for the hypothetical \(\mathrm{O}_{2}^{2+}\) ion.

The acetate ion has the formula \(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}^{-}\). Draw a dot diagram for it given the following atomic connections. (Hint: Watch for resonance forms.)

Draw a dot diagram for perchloric acid, \(\mathrm{HClO}_{4}\). The chlorine is the central atom to which all the oxygens are attached, and the hydrogen is attached to one of the oxygens.

Draw a dot diagram for the \(\mathrm{NO}_{2}^{+}\) cation.

Hydrogen isothiocyanate has formula HNCS, and its atoms are connected in the order written. Draw dot diagrams showing all the valid resonance forms.

There is one very important word missing from the following definition of electronegativity. What is it? "Electronegativity is an indication of an atom's ability to attract electrons to itself."

What is the most electronegative element in the periodic table? What is the least electronegative element? What kind of compound would form if these two elements were brought together?

How do the categories metal and nonmetal relate to electronegativity?

What are the trends for electronegativity in the periodic table: (a) Down a group? (b) Across a period from left to right? (c) Going from the bottom left corner to the upper right corner?

What are the guidelines for using electronegativity to predict which type of bond forms between two atoms?

How does a polar covalent bond differ from. a covalent bond? Give examples of diatomic molecules that contain a polar covalent bond and of diatomic molecules that contain a covalent bond.

Would you classify the \(C-H\) bonds in ethane \(\left(\mathrm{C}_{2} \mathrm{H}_{6}\right)\) as covalent, polar covalent, or ionic? Explain.

Lithium is a metallic element. Consider the hypothetical species dilithium, \(\mathrm{Li}_{2}\). Predict whether the bonding in such a species would be covalent, polar covalent, or ionic. Explain fully.

Which molecule has bonds that are the most polar covalent? (a) \(\mathrm{H}_{2}\) (b) \(\mathrm{CO}\) (c) \(\mathrm{H}_{2} \mathrm{~S}\) (d) \(\mathrm{H}_{2} \mathrm{O}\)

Chemists sometimes think of molecules with polar covalent bonds as being part covalent and part ionic. How can a bond be both covalent and ionic?

In the following molecule \(\mathrm{AB}\), one of the atoms is more electronegative than the other. Which is more electronegative, and how do you know? \(\delta-\delta+\) \(\mathrm{A}-\mathrm{B}\)

Consider the following: \(\begin{array}{llllll}\mathrm{Cl}_{2} & \mathrm{CF}_{4} & \mathrm{MgO} & \mathrm{NaCl} & \mathrm{PH}_{3} & \mathrm{SCl}_{2}\end{array}\) (a) Which of these substances is ionic? (b) Which of these substances has nonpolar bonds? (c) Which of these substances has polar covalent bonds?