Problem 31 - Chemistry The Central Science

Question

(a) What is meant by the term covalent bond? (b) Give three examples of covalent bonding. (c) A substance XY, formed from two different elements, boils at \(-33{ }^{\circ} \mathrm{C}\). Is XY likely to be a covalent or an ionic substance? Explain.

Step-by-Step Solution

Answer

(a) Covalent bond refers to the sharing of electron pairs between atoms. It allows atoms to achieve stable electron configurations by forming molecules. (b) Examples of covalent bonding include H₂ (hydrogen molecule), O₂ (oxygen molecule), and CH₄ (methane molecule). (c) Substance XY, with a boiling point of -33°C, is likely a covalent substance due to its low boiling point, which suggests weak intermolecular forces.

Step 1: (a) Definition of Covalent Bond

Covalent bonding involves the sharing of electron pairs between atoms. In covalent bonds, atoms share valence electrons in order to achieve stable electron configurations (usually a full octet), resulting in the formation of molecules.

Step 2: (b) Covalent Bonding Examples

Here are three examples of covalent bonding: 1. Hydrogen molecule (H₂): Two hydrogen atoms, each with one valence electron, share a pair of electrons to achieve stable electron configurations. 2. Oxygen molecule (O₂): Two oxygen atoms, each with six valence electrons, share two pairs of electrons (double bond) to achieve stable electron configurations. 3. Methane molecule (CH₄): A carbon atom, with four valence electrons, shares one pair of electrons with four hydrogen atoms to achieve stable electron configurations.

Step 3: (c) Identifying Bond Type in Substance XY

The substance XY boils at -33°C, which indicates that it has a low boiling point. In general, covalent substances have lower boiling points compared to ionic substances, as covalent substances are composed of molecules with weaker intermolecular forces. Ionic substances, on the other hand, have strong electrostatic forces between the positively and negatively charged ions in their lattice structures, resulting in higher boiling points. Given the low boiling point of XY, it is likely that this substance has covalent bonding, as the weak intermolecular forces make it easier to separate the molecules when heated.

Key Concepts

Electron Sharing in Covalent Bonds

Understanding covalent bonding is crucial when diving into the world of chemistry. When atoms come close together, they have the opportunity to share electrons. This sharing is not just a friendly exchange; it's a strategic move to stabilize the atoms involved. In covalent bonds, atoms with similar electronegativity values avoid taking electrons from each other and instead settle on an equitable distribution. Each participating atom provides one or more electrons to the shared pool, leading to the formation of a bond.

Imagine atoms as people wanting to pair up to dance. They each bring some dancing skills (electrons) to the table. By sharing their skills, they create a dance duo (molecular bond) that looks complete and elegant (stability). This sharing allows them to achieve full outer shells, which in chemical language means reaching a noble gas configuration—the essence of chemical stability.

In simple terms, the atoms hold hands (electron pairs) to form a stable arrangement that is powerful enough to keep them together until some larger force comes and disrupts this union. These shared electron pairs create a balance that chemically satisfies the atoms, leading to the creation of molecules, the basic units of chemical compounds.

Examples of Covalent Bonding

To further clarify how covalent bonding works, let's consider a few real-life examples. Water (H₂O) is a substance that's essential to life and exhibits covalent bonding. Oxygen (O), which craves a complete outer shell, shares its electrons with two hydrogen (H) atoms. These hydrogen atoms are overjoyed to participate as they also get to complete their shells, resulting in a molecule that's as stable as it is vital for our existence.

Another common example is carbon dioxide (CO₂), where carbon shares electrons with two oxygen atoms in a double bond fashion. This structure is like a tightrope walk where carbon is the performer, balancing with an oxygen supporter on each side, making for a very stable act.

Finally, ammonia (NH₃) showcases covalent bonding with nitrogen sharing its three available electrons with three hydrogen atoms. Picture a tabletop with one leg in the center (nitrogen) and three legs around it (hydrogen atoms), creating a sturdy, level surface. These examples help us visualize the dynamic world of covalent bonds, which keeps the particles in our universe in harmonious order.

Distinction Between Covalent and Ionic Substances

When comparing covalent and ionic substances, we're looking at two distinct types of chemical friendships. Covalent bonds are all about sharing—the 'what's mine is yours' approach. Ionic bonds, on the other hand, are more transactional, with one atom giving up electrons and another one receiving them, creating a relationship based on charge imbalances.

In terms of physical properties, these differences make covalent substances typically have lower melting and boiling points, as seen in the case of substance XY with its relatively chilly boiling point at -33°C. They're like the loosely held-together social groups, where it's easier to drift apart with a little heat. Ionic substances, such as table salt (NaCl), are like intensely bonded teams with connections so strong that only significant energy can break them apart, resulting in higher melting and boiling points.

To sum up, if you're dealing with a substance that easily melts or boils, you're likely looking at a covalent compound, held together by a mutual sharing of electrons. If it's stubborn and remains solid at high temperatures, chances are it's ionic, with atoms locked in a tight embrace by the forces of opposite charges.