Question

Arrange these elements in order of increasing metallic character: Sr, N, Si, P, Ga, Al.

Short answer

N < P < Si < Al < Ga < Sr

Step-by-step solution

- Understanding Metallic Character

Metallic character is the tendency of an atom to lose electrons easily to form positive ions (cations). Moving from right to left across a period of the Periodic Table, the metallic character generally increases because atoms have fewer valence electrons that can be easily removed. Moving down a group, the metallic character also increases because the outer electrons are farther from the nucleus and more easily removed.

- Position in the Periodic Table

Before arranging the elements, identify their position in the Periodic Table. Nitrogen (N) is in period 2, group 15; Phosphorus (P) is below Nitrogen in the same group; Silicon (Si) is in period 3, group 14; Aluminum (Al) is in period 3, group 13; Gallium (Ga) is below Aluminum in the same group; Strontium (Sr) is in period 5, group 2 and is an alkaline earth metal.

- Ordering by Groups and Periods

First, order the elements within the same group. N is above P in group 15, Si is above Al and Ga in group 13/14 boundary, and Sr is in a separate group. Then, arrange them by period, comparing with elements in other groups if necessary.

- Arrange in Order of Increasing Metallic Character

Now, arrange the elements in the order of increasing metallic character. From least to most metallic, it is: N < P < Si < Al < Ga < Sr. This is because N is a nonmetal, and as we proceed down a group to P, the metallic character increases. For elements in periods, Si has less metallic character than Al (as we move right to left across a period, metallic character decreases), Ga is below Al and thus more metallic, and Sr is a heavier alkaline earth metal and exhibits a stronger metallic character than the others.

Key concepts

Periodic Table Trends

The Periodic Table is a powerful tool for predicting the chemical behavior of elements. One crucial property that varies across this table is the metallic character.

As we move from the top right to the bottom left of the Periodic Table, metallic character increases. This trend is due to two main factors: the number of valence electrons and the distance of these electrons from the nucleus. Metals tend to have one to three valence electrons, which they can easily lose to form cations, a characteristic willingness differentiating them from nonmetals.

Within a Group

Within a group (a vertical column on the Periodic Table), metallic character increases as you move down. This increase is because the electrons are progressively further from the nucleus, due to the addition of new electron shells. This increased distance weakens the electrostatic attraction between the nucleus and the valence electrons, making the electrons easier to remove, hence, increasing metallic character.

Across a Period

Across a period (a horizontal row), the trend is the opposite; metallic character decreases as you go from left to right. This is because atoms gain more protons and draw their electrons closer, making it harder for the atoms to lose electrons and therefore exhibit metallic properties.

Metallic Character Increase

Understanding the factors that contribute to the increase of metallic character is essential when comparing elements. There are two primary reasons why this characteristic becomes more pronounced in certain directions of the Periodic Table.

Atomic Size

As we consider elements further down a group, we notice an increase in atomic size. This larger atomic size means that valence electrons are more shielded by the inner electron shells from the attractive force of the positively charged nucleus. Consequently, these electrons can be lost more readily, contributing to the higher metallic character of the element.

Electron Shielding

Additionally, the effect known as electron shielding also plays a role. With each additional electron shell, the inner shells act as a 'shield', reducing the effective nuclear charge felt by the outermost electrons. This phenomenon makes the outer electrons less tightly bound to the atom, which in turn enhances the metallic character.

Atomic Structure and Metallic Character

The atomic structure of an element profoundly affects its metallic character. Specifically, the arrangement and the number of electrons around the nucleus, also known as the electron configuration, determine how easily an atom can lose electrons.

Valence Electrons and Reactivity

The valence electrons—the electrons in the outermost shell—are the key players in determining an element's metallic nature. Metals, having few valence electrons, are more inclined to lose them and form positive ions or cations. This loss of electrons constitutes the metallic character and is associated with classic metallic properties such as conductivity and malleability.

Effective Nuclear Charge

Another aspect of atomic structure impacting metallic character is the effective nuclear charge (Z_eff), which is the net positive charge experienced by valence electrons. Lower Z_eff makes it easier for an element to lose valence electrons, enhancing its metallic character. As we move from left to right across a period, Z_eff increases due to an increase in protons, while as we move down a group, inner electron shells provide more shielding, decreasing Z_eff and thereby increasing metallic character.