Question

In which period and which group is the element that has the ground-state electron configuration \([\mathrm{Ar}] 4 s^{2} 3 d^{10} 4 p^{5} ?\) Which element is this? Answer: Rewriting the electron configuration as \([A r] 3 d^{10} 4 s^{2} 4 p^{5}\) to emphasize the valence electrons, we see that the highest value of \(n\) is 4, so this atom is in the fourth period. There are a total of seven valence electrons, and the \(p\) subshell is partially filled, meaning this is a group VIIA element. It is bromine (Br).

Short answer

Answer: The element with the ground-state electron configuration $[\mathrm{Ar}] 4 s^{2} 3 d^{10} 4 p^{5}$ is in the 4th period and Group 17 (VIIA). It is Bromine (Br).

Step-by-step solution

Determine the Period

To find the period of the element, look for the highest principal quantum number (n) in the electron configuration. In this case, the highest value of n is 4 (from the 4s and 4p orbitals). Therefore, the element is in the 4th period.

Determine the Group

To find the group, count the number of valence electrons (electrons in the outermost shell). Here, we have 4s² and 4p⁵, which gives us a total of 2 + 5 = 7 valence electrons. Since the p subshell is partially filled, this indicates that the element belongs to group 17 (also known as Group VIIA).

Find the Specific Element

Now that we know the period and group, we can determine the specific element. The element in the fourth period and group 17 (VIIA) is Bromine (Br).

Key concepts

Periodic Table Period

The periodic table is a fascinating grid that categorizes elements based on their chemical properties and atomic structure. A 'period' in the periodic table refers to the horizontal rows. Each period represents a new principal energy level being filled with electrons. As we move from left to right within a period, the principal quantum number, denoted as 'n', increases. This number signifies the energy level of an electron orbiting the nucleus and is crucial for determining the period.

For example, in the exercise, we've been given the electron configuration \[\mathrm{Ar}\] 4s^{2} 3d^{10} 4p^{5}. By identifying the highest principal quantum number, in this case, 4 (from the 4s and 4p subshells), we determined that the element is in the fourth period. This tells us that the valence electrons of this element are in the fourth energy level, an essential piece of information for understanding an element's reactivity and properties.

Chemical Group

Along with periods, the periodic table is organized into vertical columns known as 'groups' or 'families'. These groupings are determined by the number of valence electrons in an element's atoms—electrons in the outermost shell. Elements within the same group often share similar chemical and physical properties because they have the same number of valence electrons, contributing to their behavior during chemical reactions.

Take the ground-state electron configuration given in the original exercise: \[\mathrm{Ar}\] 4s^{2} 3d^{10} 4p^{5}. The valence electron count is derived from the s and p sublevels of the highest energy level (4s and 4p here), which gives us 2 + 5 = 7 valence electrons. Having seven valence electrons places this element in group 17 of the periodic table, also known as Group VIIA or the halogens. This group is characterized by having seven valence electrons, which greatly influences their high reactivity and desire to gain an additional electron to achieve a stable octet.

Valence Electrons

Valence electrons are the outermost electrons of an atom and are critical in determining how the atom interacts with others. These electrons participate in chemical bonding, reactions, and ultimately determine the chemical behavior of the element. Valence electrons are often the only electrons used when drawing Lewis dot structures, which depict the bonds and lone pairs around an element.

In practice, identifying the number of valence electrons helps predict an element's place in the periodic table, as well as its reactivity. By sorting the original electron configuration \(\([\mathrm{Ar}] 4s^2 3d^{10} 4p^5\)\) to highlight the valence electrons \(4s^2 4p^5\), we counted a total of seven valence electrons. Knowing the quantity of these reactive electrons allowed us to find that this element belongs to group 17 — a highly reactive chemical group known for forming compounds by gaining an electron to complete its outer shell.