Question

Element 87 is in Group \(1 \mathrm{~A}(1)\), Period 7. In how many principal energy levels are electrons located? Describe its outermost energy level.

Short answer

Electrons in element 87 are located in 7 principal energy levels. The outermost energy level has one valence electron in the 7s sublevel.

Step-by-step solution

Identifying the Group and Period

Element 87 is identified to be in Group 1A (1) and Period 7 of the Periodic Table. The Group number corresponds to the number of valence electrons, and the Period number indicates the highest principal energy level that contains electrons.

Determining Total Principal Energy Levels

Since the element is in Period 7, the electrons will be located in 7 principal energy levels. This is because the period number corresponds to the highest principal energy level for the valence electrons.

Describing the Outermost Energy Level

Being in Group 1A (1), the element has 1 valence electron. Since it is also in Period 7, the valence electron will be in the 7th energy level (7s sublevel). Thus, the outermost energy level of element 87 is the 7th level, specifically the 7s sublevel, which contains one electron.

Key concepts

Valence Electrons

Valence electrons are the electrons in the outermost shell of an atom and are crucial in determining an element's chemical properties. These electrons can be involved in forming bonds with other atoms. The number of valence electrons an element has is reflected by its group number in the Periodic Table for Groups 1A through 8A.
For example, elements in Group 1A (1), like element 87 from our exercise, have one valence electron, which is key in its reactivity as an alkali metal. Elements with the same number of valence electrons typically exhibit similar chemical behaviors, making it easier to predict how an element might interact chemically.

Periodic Table

The Periodic Table is a comprehensive chart that organizes elements according to increasing atomic number and recurring chemical properties. Elements are arranged into rows (periods) and columns (groups or families). The period number an element resides in corresponds to the highest principal energy level of its electrons. Knowing the period and group of an element, as seen with element 87 which is in period 7, tells us that it has electrons across seven principal energy levels.
The table is structured in such a way that elements with similar properties fall into the same column, allowing students and scientists to infer a wide range of chemical and physical characteristics simply by an element's position.

Electron Configuration

Electron configuration refers to the distribution of electrons among the different orbitals of an atom. This configuration follows a set of principles: the aufbau principle, the Pauli exclusion principle, and Hund's rule, to fill the available orbital spaces. The configuration notation lists the energy levels, sublevels, and the number of electrons in each sublevel.
Consider the example of element 87, which has an electron in the 7s sublevel as it is situated in Period 7 - this position denotes the presence of electrons in the principal energy levels up to the seventh level, with the highest energy electron in the 's' orbital of the seventh level. This information is crucial for predicting the chemical and physical behavior of an element.