How are elements arranged in the modern periodic table?

Elements in the modern periodic table are arranged in order of increasing atomic number, grouped by similar chemical properties.

The modern periodic table, also known as the long form of the periodic table, is a tabular arrangement of chemical elements. It is based on the atomic number, electron configuration, and recurring chemical properties. The atomic number is the number of protons in an atom's nucleus, which increases as you move from left to right across the table. This arrangement allows elements with similar properties to appear in vertical columns, known as groups or families.

The table is divided into several blocks. The s-block includes groups 1 and 2, including hydrogen and helium. The p-block comprises groups 13 to 18. The d-block encompasses transition metals, which are groups 3 to 12. Lastly, the f-block, located at the bottom of the table, includes the lanthanides and actinides.

Each horizontal row in the table is called a period. As you move from left to right across a period, the atomic number increases. The elements in a period show a trend of properties, known as periodic trends. For example, atomic radius decreases across a period from left to right, and ionisation energy generally increases.

The groups or families in the periodic table are columns of elements that share similar chemical properties. This is because they have the same number of valence electrons, which are the electrons in the outermost shell of an atom that are involved in chemical reactions. For instance, all elements in group 1, known as alkali metals, have one valence electron and exhibit similar reactivity.

The modern periodic table is a powerful tool in chemistry. It not only allows scientists to understand the relationship between various elements but also predicts the properties of new elements. It's a fundamental concept that you'll encounter frequently in your IB Chemistry studies.