5.3 Electron Configuration and Periodic Properites (2/2)

Summary

This video explains key concepts in atomic physics, including electron affinity, ionization energy, and atomic/ionic radii. It discusses how atoms gain or lose electrons, with examples of halogens having the highest negative electron affinity due to their desire to form stable octets. The video also covers trends in the periodic table, explaining why electronegativity increases across a period and decreases down a group. Additionally, it introduces the concept of valence electrons and how chemical reactions are driven by electron interactions in the outermost energy levels of atoms.

Takeaways

• 🔋 Ionization energy is the energy required to remove an electron from an atom, while electron affinity is the energy released when an atom gains an electron.
• ⚛️ Adding an electron to an atom forms a negative ion and releases energy, which is expressed as negative because energy is released, not added.
• 🌀 Halogens, located next to noble gases on the periodic table, have the most negative electron affinity because they reach a stable octet by gaining electrons.
• 📉 Electron affinity becomes more negative across a period, with halogens having the most negative affinity, but group 6 has a larger electron affinity than group 7 due to orbital filling differences.
• 🧲 As you move down a group, it becomes harder to add electrons because they are farther from the nucleus, reducing the effective nuclear charge.
• 🔄 Second and third electron affinities require energy input, unlike the first affinity, because adding electrons to a negative ion creates repulsion.
• 📏 Cations (positive ions) are smaller than their neutral atoms due to fewer electrons and increased effective nuclear charge, while anions (negative ions) are larger because of additional electrons.
• 🧪 Metals tend to form cations, while non-metals form anions because metals lose electrons easily, and non-metals are close to achieving a stable noble gas configuration.
• 🔗 Valence electrons, located in the outermost energy levels, are responsible for chemical reactions, as they are most affected by external forces.
• 📊 Electronegativity measures an atom’s ability to attract electrons, with fluorine being the most electronegative element, and electronegativity increases across periods and decreases down groups.

Q & A

What is electron affinity, and how is it generally expressed?

Electron affinity is the energy released when an atom acquires an electron, forming a negative ion. It is typically expressed as negative energy because it involves energy being released rather than put into the system.

Why do halogens have the most negative electron affinity?

Halogens have the most negative electron affinity because they are one electron away from achieving a stable octet configuration. Adding an electron allows them to reach a lower energy state, releasing a significant amount of energy.

How does electron affinity change as you move across a period on the periodic table?

As you move across a period, electron affinity generally becomes more negative, with halogens having the most negative electron affinity. This is because atoms get closer to filling their outer electron shells, releasing more energy when they acquire electrons.

Why does group 6 have a larger electron affinity than group 7?

Group 6 elements have a larger electron affinity than group 7 because when you add an electron to a group 7 atom, it has to enter a sublevel that is already occupied, requiring more energy input, which reduces the overall energy released.

How does electron affinity change as you go down a group in the periodic table?

As you go down a group, electron affinity becomes less negative. This is because the added electrons are farther from the nucleus, experiencing less nuclear attraction, and are shielded by inner electron levels.

Why does adding a second electron to an already negative ion require energy?

Adding a second electron to a negative ion requires energy because the negative charge of the ion repels the incoming electron. This makes it energetically unfavorable, so energy must be supplied to overcome the repulsion.

How do the ionic radii of cations and anions compare to their neutral atoms?

Cations have smaller ionic radii than their neutral atoms because they lose electrons, resulting in fewer electron-electron repulsions and a greater effective nuclear charge. Anions, on the other hand, have larger ionic radii due to the additional electrons increasing electron-electron repulsions, spreading them farther from the nucleus.

Why do metals tend to form cations and non-metals tend to form anions?

Metals tend to form cations because they have low electron affinities, meaning they lose electrons easily. Non-metals tend to form anions because they are closer to achieving a stable noble gas configuration, so they gain electrons to complete their outer shell.

What are valence electrons, and why are they important in chemical reactions?

Valence electrons are the outermost electrons of an atom and are involved in chemical reactions. They are the most susceptible to outside influence and interact with other atoms during reactions, as they are farthest from the nucleus and experience the least shielding from inner electrons.

How does electronegativity relate to electron affinity, and how is it measured?

Electronegativity is a measure of how effectively an atom attracts electrons from another atom. It is related to electron affinity in that elements with high electronegativity also tend to have more negative electron affinities. Electronegativity is measured on a relative scale from 0 to 4, with fluorine assigned a value of 4 as the most electronegative element.