Question

Suggest explanations for the following. (a) High values of ionization energies are associated with the noble gases. (b) The enthalpy changes associated with the attachment of the first and second electrons to an \(\mathrm{O}\) atom are exothermic and endothermic, respectively. (c) In an Li atom in its ground state, the outer electron occupies a \(2 s\) rather than a \(2 p\) orbital.

Short answer

(a) Noble gases have stable, full electron shells; (b) First electron attachment to O is exothermic, the second is endothermic due to repulsion; (c) 2s orbital in Li is more stable than 2p.

Step-by-step solution

Understanding Ionization Energies in Noble Gases

Ionization energy refers to the energy required to remove an electron from an atom in its gaseous state. Noble gases have high ionization energies because they have a full outer electron shell, which is a stable configuration. Removing an electron from this stable configuration requires more energy than it would in other elements.

Analyzing Electron Attachment Energies in Oxygen

The first electron attachment to an oxygen atom is exothermic because oxygen wants to complete its outer shell by gaining electrons, releasing energy in the process. However, the second electron attachment is endothermic because adding another electron results in electron-electron repulsion and requires external energy to overcome these repulsions.

Exploring Electron Configuration in Lithium

In a lithium atom in its ground state, despite both being at the second energy level, the 2s orbital is lower in energy than the 2p orbital. Therefore, an electron will occupy the 2s orbital rather than the 2p orbital to maintain a lower energy state, which is more stable.

Key concepts

Noble Gases

Noble gases, occupying the far right column of the periodic table, are known for their inertness and stable nature. These elements include helium, neon, argon, krypton, xenon, and radon. One of the primary reasons noble gases exhibit high ionization energies is due to their complete outer electron shells. This configuration offers maximal stability, making any change, such as the removal of an electron, quite energy-intensive. The stability is principally because these atoms do not have any tendency to gain or lose electrons. Therefore, a significant amount of energy must be supplied to dislodge an electron from this stable shield. To put it simply:

• Noble gases have filled outer electron shells.
• This filled shell leads to a stable, low-energy state.
• Removing an electron disrupts this stable state, requiring more energy.

Understanding this helps explain why ionization energies rise when you move towards the noble gases in the periodic table. The more complete the outer shell, the harder they hold onto their electrons.

Electron Configuration

Electron configuration plays a crucial role in determining many chemical properties of elements, including their reactivity and ionization energy. It refers to the arrangement of electrons around the nucleus of an atom in specific energy levels and orbitals. Electrons tend to fill the lowest energy orbitals first to achieve a state of lowest energy and maximum stability. For example, in a lithium atom in its ground state, the electron for the second energy level will fill the 2s orbital before the 2p orbital despite being both part of the second energy level.

• Electrons occupy the lowest energy orbitals available.
• In lithium, the 2s is lower in energy than the 2p orbital.
• Configuration impacts stability and reactivity of the atom.

Understanding electron configuration helps to predict how an element might react chemically. It also assists in understanding ionization energy trends across the periodic table, as atoms seek to maintain or achieve stable electron configurations.

Exothermic and Endothermic Reactions

In chemical reactions, energy exchange is crucial in determining whether a reaction is exothermic or endothermic. An exothermic reaction releases energy into the environment, typically in the form of heat, as the system loses energy. Conversely, an endothermic reaction absorbs energy, requiring heat from the surroundings to proceed. These terms often apply when discussing electron attachments to atoms—the energy dynamics of adding an electron can often vary drastically. For instance, when an oxygen atom gains its first electron, it forms a stable oxide ion, and energy is released in the process, making it exothermic. However, adding a second electron encounters repulsion due to like charges, necessitating an input of energy to overcome this, classifying it as endothermic.

• Exothermic reactions release energy; endothermic reactions absorb energy.
• First electron attachment to oxygen is exothermic (energy is released).
• Second electron attachment is endothermic (energy is required).

These concepts are essential in chemistry, as they explain how and why substances change and what energy transformations occur during reactions. This understanding helps to predict the energy requirements and releases in chemical processes.