Question

Fill in the blanks. In the periodic table, vertical columns of elements are called ___ and horizontal rows of elements are called ___.

Short answer

Answer: In the periodic table, vertical columns of elements are called **groups** and horizontal rows of elements are called **periods**.

Step-by-step solution

Vertical Columns

In the periodic table, vertical columns of elements are called **groups**.

Horizontal Rows

Horizontal rows of elements in the periodic table are called **periods**. So, the completed sentence would be: In the periodic table, vertical columns of elements are called **groups** and horizontal rows of elements are called **periods**.

Key concepts

Groups

In the periodic table, vertical columns are known as "groups." Each group contains elements that share similar chemical properties. Why, you ask? It's due to their similar number of valence electrons.
These valence electrons are the electrons present in the outermost shell of an atom. They're crucial in determining how an element reacts chemically with other substances.

• For example, all elements in Group 1, which includes hydrogen and alkali metals like lithium and sodium, have just one valence electron. This makes them quite reactive.
• Group 18 elements, known as noble gases, have complete outer shells, making them very stable and inert.

Understanding the grouping in the periodic table helps predict how elements behave and interact in chemical reactions.

Periods

Horizontal rows in the periodic table are termed "periods." Each period signifies that the elements within the same row are filling up the same principal energy level of their atoms.
When you move across a period from left to right, each subsequent element has an additional proton and electron compared to the previous one. This impacts the atomic structure as well as the properties of the elements.

• For instance, as you move across Period 2, from lithium to neon, atoms gain successively more electrons forcing them to occupy a higher energy level.
• The increase in electrons causes changes in properties such as electronegativity, ionization energy, and atomic size.

In essence, periods help in understanding the progressive filling of electron shells among elements and their periodic trends.

Elements

Elements form the fundamental building blocks of matter. They are pure substances that consist of only one type of atom. Each element is symbolized in the periodic table with a unique one or two-letter abbreviation.
With 118 known elements, the periodic table organizes them based on increasing atomic number, which equals the number of protons in an atom's nucleus. This organization helps scientists easily understand and predict an element's characteristics.

• Some elements, like oxygen and hydrogen, are essential for life and found abundantly in nature.
• Others, like gold and uranium, are more rare and have specialized uses.

Studying elements and their arrangement in the periodic table reveals much about the physical and chemical properties vital to understanding the material world.