Problem 18 - An Introduction to Physical Science

Question

What formal term is applied to (a) the horizontal rows of the periodic table, and (b) the vertical columns?

Step-by-Step Solution

Answer

(a) Periods, (b) Groups

Step 1: Identify the Horizontal Rows

In the periodic table, the horizontal rows are known as **periods**. Each period corresponds to the successive filling of the electron shells and the elements in a period have sequential atomic numbers. Therefore, their chemical properties show a periodic recurrence.

Step 2: Identify the Vertical Columns

In the periodic table, the vertical columns are called **groups** or **families**. Elements in a group share similar chemical and physical properties because they have the same number of valence electrons.

Key Concepts

Periods

Periods in the periodic table are the horizontal rows that represent a fundamental concept in chemistry. Each period indicates the completion of one electron shell before starting to fill another. Electrons fill the shells around an atomic nucleus in a particular order, known as the Aufbau principle.
The number of elements in a period is determined by the maximum number of electrons that can fit into the orbital within that particular shell level. This is why the first period has only two elements, hydrogen and helium, as it fills the 1s orbital. Subsequent periods contain more elements because they fill d- and f- orbitals as well.
As you move across a period from left to right, properties gradually change due to the increase in the number of protons and electrons. For instance:

• The atomic number increases.
• The atomic radius decreases initially until reaching the noble gases.
• Ionization energy generally increases.
• Metallic character decreases.

Groups

Groups in the periodic table are vertical columns that classify elements with similar traits due to their valence electron configuration. Each group contains elements that react similarly chemically. This is because these elements have the same number of electrons in their outermost shell, known as valence electrons. This similarity influences how they bond with other elements.
There are 18 groups in the periodic table, ranging from 1 to 18. Some common ones include:

• Group 1: Alkali metals, very reactive especially with water.
• Group 2: Alkaline earth metals, quite reactive but less so than alkali metals.
• Group 17: Halogens, which are highly reactive non-metals.
• Group 18: Noble gases, known for their lack of reactivity.

As you go down a group, the atomic size typically increases, and the tendency to lose electrons enhances due to the increase in the number of inner electron shells. This lateral relationship makes groups a vital part of predicting chemical reactions.

Chemical Properties

Chemical properties describe how an element behaves in a chemical reaction and are heavily influenced by its position on the periodic table. Both periods and groups play a big role in defining these properties.

Period Influence:

As elements go across a period, they fill up their orbitals and increase their atomic number, which affects properties such as electronegativity, ionization energy, and atomic radius. For example, as you move from left to right, metals give way to metalloids and then non-metals, showcasing a shift in reactivity.

Group Influence:

Within a group, elements share similar valence electron configurations, which offers a predictability in their reactivity and bonding characteristics. For instance, the alkali metals in Group 1 are consistently more reactive than alkaline earth metals in Group 2, largely due to their single valence electron, which they can easily lose to form cations.
Overall, the combination of an element's group and period positions allows scientists to predict its chemical behavior, making the periodic table a powerful tool in chemistry studies.