Afinitas Elektron | Sifat Keperiodikan Unsur | KIMIA KELAS 10

Summary

This video explains electron affinity, focusing on how energy is involved when a neutral atom in a gaseous state gains an electron to form a negative ion. The energy change can be either positive or negative, depending on whether energy is absorbed or released. The video explores examples such as chlorine and beryllium, comparing how different elements behave during electron capture. It also discusses trends in electron affinity across the periodic table, with halogens having the highest electron affinity, making them more likely to accept electrons.

Takeaways

• ⚛️ Electron affinity is the energy change when an electron is added to a neutral atom in the gas phase, forming a negative ion.
• 💡 Electron affinity can be either negative (energy released) or positive (energy absorbed) depending on the atom.
• 🔋 Chlorine has a negative electron affinity of -349 kJ/mol, meaning it releases energy when it gains an electron to form Cl⁻.
• 🔗 Beryllium, with a positive electron affinity of 240 kJ/mol, requires energy to add an electron and form a negative ion.
• ⚖️ A negative electron affinity implies that the negative ion is more stable than the neutral atom.
• ⚠️ A positive electron affinity means the negative ion is less stable than the neutral atom.
• 🌀 The larger the amount of energy released, the easier it is for an atom to capture an electron and form a negative ion.
• 🔬 Elements with a negative electron affinity have a stronger tendency to attract electrons than those with a positive affinity.
• 🧲 Halogens (Group 7A), such as fluorine and chlorine, have the highest negative electron affinities, making them highly reactive.
• 📉 Electron affinity decreases down a group and increases across a period in the periodic table, with exceptions like silicon and phosphorus.

Q & A

What is electron affinity?

Electron affinity is the energy associated with the addition of one electron to a neutral atom in its gaseous state, forming a negatively charged ion. It can either be positive or negative, depending on whether energy is absorbed or released during the process.

How is electron affinity expressed?

Electron affinity is expressed in kilojoules per mole (KJ/mol). For example, if energy is released, electron affinity has a negative value, while if energy is absorbed, it has a positive value.

What happens when chlorine (Cl) gains an electron?

When chlorine (Cl) gains an electron to form a Cl⁻ ion, energy is released. The electron affinity of chlorine is -349 KJ/mol, indicating that the process is exothermic, and chlorine easily forms a negative ion.

What is the significance of a negative electron affinity value?

A negative electron affinity value means that energy is released when an atom gains an electron. This indicates that the resulting negative ion is more stable than the neutral atom.

Why does beryllium (Be) have a positive electron affinity?

Beryllium (Be) has a positive electron affinity of +240 KJ/mol, meaning that energy must be supplied for it to gain an electron. This indicates that the resulting Be⁻ ion is less stable than the neutral Be atom.

How does the size of an atom affect its electron affinity?

As the atomic radius increases (such as when moving down a group in the periodic table), the electron affinity tends to decrease. This is because the added electron is farther from the nucleus, making the attraction between the nucleus and the electron weaker.

Why do halogens have the largest (most negative) electron affinity?

Halogens (Group 7A elements) have the largest negative electron affinities because they are one electron short of having a full outer shell, which makes them highly inclined to gain an electron to form stable negative ions.

What is the relationship between electron affinity and ionization energy trends?

The trend for electron affinity generally follows a similar pattern to ionization energy in the periodic table. Electron affinity tends to increase across a period from left to right, due to increasing nuclear charge, and decreases down a group as atomic size increases.

Why does electron affinity decrease down a group in the periodic table?

Electron affinity decreases down a group because atoms become larger, and the added electron is farther from the nucleus, which reduces the attractive force between the electron and the nucleus.

Why do Group 5A elements have lower electron affinities compared to Group 4A elements?

Group 5A elements have lower electron affinities compared to Group 4A because adding an electron to a half-filled p-orbital in Group 5A creates greater electron-electron repulsion, making it harder to add an electron.