Question

The first four ionization energy values of an element are \(190,578,872\) and \(5960 \mathrm{k}\).cal. The Number of valence electrons in the element is? (a) 1 (b) 2 (c) 3 (d) 4

Short answer

The element has 3 valence electrons. Answer: (c) 3

Step-by-step solution

Understanding Ionization Energy

Ionization energy is the energy required to remove an electron from an atom in its gaseous state. With each subsequent electron removed, more energy is typically required. A large increase in ionization energy indicates that electrons are being removed from a closer, more strongly bound shell.

Analyze Ionization Energies Given

The given ionization energies for the element are 190, 578, 872, and 5960 kcal/mol. Notice the large jump between the third and fourth ionization energies, from 872 to 5960 kcal/mol. This suggests that the first three electrons were removed with less difficulty, and the fourth requires a significantly higher energy.

Determine Number of Valence Electrons

A large increase in ionization energy typically occurs when electrons start being removed from a more stable, inner electron shell. Since the large increase occurred after the third ionization, the element had 3 valence electrons, corresponding to the complete removal before moving to a new shell.

Key concepts

Valence Electrons

Valence electrons are the electrons located in the outermost shell of an atom. These electrons play a crucial role in chemical bonding and reactivity. Atoms strive to have a full outer shell, which typically means having eight valence electrons, a state known as an "octet."

• Valence electrons are important because they determine how an atom will react with other atoms.
• The number of valence electrons is a key factor in predicting chemical behavior and bonding properties.
• To find the number of valence electrons, you often look at the group number of the element in the periodic table.

For example, elements in Group 1 have one valence electron, while elements in Group 17 have seven valence electrons. Knowing the number of valence electrons helps in understanding elements' ionization tendencies and how they form compounds.

Electron Shells

Electron shells are regions around the nucleus of an atom where electrons are likely to be found. Each shell can hold a certain number of electrons, which increases with distance from the nucleus. These shells are labeled with numbers or letters, starting with the innermost shell.

• The inner shells are filled first before electrons are added to outer shells. This is due to the principle of energy minimization.
• The first shell can hold up to 2 electrons, the second up to 8 electrons, and so on.
• A significant increase in ionization energy usually occurs when electrons start being removed from a filled inner shell.

The concept of electron shells helps explain why elements react in certain ways. For instance, elements with one or two electrons in their outer shell are eager to lose or share these electrons to achieve a full shell, leading them to be highly reactive.

Ionization Process

The ionization process involves removing electrons from an atom, turning it into a positively charged ion. Each electron removed corresponds to a specific ionization energy, and each successive ionization energy is generally higher than the last.

• It involves applying enough energy to overcome the attraction between the nucleus and the electron.
• A large jump in ionization energy indicates the removal of an electron from a more stable, closershell.
• Knowing the ionization energies can help identify the number of valence electrons, as these electrons are typically removed first.

When analyzing ionization energies, the pattern observed provides hints about the electronic configuration and nature of the element. A sharp increase between consecutive ionization energies suggests a transition between releasing outer valence electrons and beginning to remove inner electrons.