The heaviest known alkaline earth metal is radium, atomic number \(88 .\) Find the atomic numbers of the as yet undiscovered next two members of the series.

In learning about the periodic table of the elements, one of the most critical concepts is the recognition of trends across this chart of substances that are the building blocks of the universe. The periodic table orders elements based on increasing atomic number and arranges them in a way that groups with similar chemical properties are placed together. For instance, one significant trend is that the atomic size tends to decrease from left to right within a period and increase from top to bottom within a group.

The alkaline earth metals, which include elements like magnesium, calcium, and radium, constitute Group 2 of the periodic table. A noteworthy trend within this group is that as you move down the group, each element has an atomic number which is higher than the one above it. This is due to the addition of an electron shell, which happens after the completion of the filling of the previous shell. Understanding the systematic way in which these elements are arranged is key to predicting the properties of undiscovered elements and ions within this group.

The atomic number of an element is quintessential to its identity. Simply put, it refers to the number of protons found in the nucleus of an atom of that element. The periodic table is arranged in order of increasing atomic numbers, starting with Hydrogen, which has an atomic number of 1. The atomic number not only determines an element's position on the periodic table but also gives insights into the element's chemical behavior.

As we consider alkaline earth metals, their atomic numbers determine their unique properties and are crucial when considering the periodic table trends. For example, when we explore undiscovered elements in the exercise, we use the atomic number to predict their placement in the periodic table and, by extension, their potential properties. In essence, the atomic number is a fundamental identifier for elements and a key to understanding the entire periodic system.

Electron shells, or energy levels, are regions around the nucleus of an atom where electrons are likely to be found. The number of these shells and the number of electrons in the outermost shell play an important role in determining an element's chemical properties. As we move down a group on the periodic table, each element has one more electron shell than its predecessor, which contributes to the size increase of atoms down the group.

The alkaline earth metals are characterized by having two electrons in their outermost shell. With increasing atomic number, a new electron shell is added, which is further from the nucleus and can contain more electrons. This phenomenon is reflected when predicting unknown alkaline earth metals in the exercise. By understanding the pattern of electron shells in relation to atomic number, we recognize the regular addition of electron shells and the periodic introduction of an element with similar chemical properties, continuing the trend established by known elements.