Question

Which of the following elements shown as pairs with their atomic numbers belong to the same period? (a) \(Z=19\) and \(Z=38\) (b) \(Z=12\) and \(Z=17\) (c) \(Z=11\) and \(Z=21\) (d) \(Z=16\) and \(Z=35\) \(-v\)

Short answer

The elements with atomic numbers 12 (Mg) and 17 (Cl) belong to the same period, which is period 3.

Step-by-step solution

Identify the Period for Z=19 and Z=38

First, determine the periods of the elements with atomic numbers 19 and 38. Element 19 is potassium (K), and it belongs to period 4. Element 38 is strontium (Sr), and it also belongs to period 5. Thus, they do not belong to the same period.

Identify the Period for Z=12 and Z=17

Determine the periods for elements with atomic numbers 12 and 17. Element 12 is magnesium (Mg), which is in period 3. Element 17 is chlorine (Cl), also in period 3. Therefore, they belong to the same period.

Identify the Period for Z=11 and Z=21

Check the periods for atomic numbers 11 and 21. Element 11 is sodium (Na), found in period 3. Element 21 is scandium (Sc), located in period 4. Hence, they are not in the same period.

Identify the Period for Z=16 and Z=35

Look up the periods for atomic numbers 16 and 35. Element 16 is sulfur (S), in period 3. Element 35 is bromine (Br), which is in period 4. They do not share the same period.

Key concepts

Atomic Number

When exploring the fundamental concepts of chemistry, the atomic number plays a pivotal role. It is denoted by the symbol Z and refers to the number of protons found in the nucleus of an atom. This number is essential because it not only determines the identity of a chemical element but also its position on the Periodic Table. For instance, an element with the atomic number 11 is always sodium (Na), and this uniqueness helps chemists to quickly identify elements and predict their chemical behavior.

Furthermore, atomic numbers are sequential, which means no two elements can have the same number. As you increase Z from one element to the next, you are essentially moving from left to right across the Periodic Table. Each increase by one corresponds with an element that has one more proton in its nucleus than the previous element. This systematic incrementation is why elements with higher atomic numbers typically have greater mass and more complex electron configurations.

Chemical Elements

Chemical elements are the alphabet of the language of chemistry. They are the simplest substances that cannot be broken down further by ordinary chemical means and are made up of atoms with the same atomic number. Every element has its own unique set of properties, which include melting and boiling points, density, and various chemical reactivities.

The known elements are neatly organized into a chart called the Periodic Table, and they're listed in increasing order of their atomic numbers. The table is structured in such a way that elements with similar properties are grouped together, thus making it easier to anticipate an element's behavior by looking at its position on the table. To make studying chemistry more accessible, elements are often represented by one- or two-letter symbols, like H for hydrogen or Fe for iron. These symbols serve as a shorthand for the full names of the elements and are universally recognized in scientific circles.

Periodicity

The concept of periodicity is foundational to the organization of the Periodic Table. It refers to the recurring trends that are observed in the properties of elements as one moves across a period (row) or down a group (column) on the table. These trends exist because of the periodic patterns of electron configuration as the atomic number increases. Each period begins with an alkali metal and ends with a noble gas, which results in a clear shift from metals to nonmetals as you move from left to right across a period.

The periods are key to understanding why certain elements, such as those in the exercise with atomic numbers 12 (magnesium, Mg) and 17 (chlorine, Cl), belong to the same period; they both end up in the third row as you follow the sequence laid out by their atomic numbers. Recognizing these patterns helps students predict and explain the chemical properties and reactions of different elements. For enhanced clarity, remember that elements in the same period have the same number of atomic orbitals. This common characteristic is crucial to many of their shared physical and chemical properties.