3.2. Periodic Classification of Elements: Laws of Periodic Classification

The Periodic Classification of Elements, also known as the Periodic Table, is an extremely important tool in Chemistry. It was developed to organize chemical elements according to their properties and characteristics, facilitating their study and understanding. In this chapter of our e-book, we are going to explore the laws that govern this classification and how they apply in preparing for the Enem test.

The periodic table we know today is the result of many attempts by scientists throughout history to classify elements in a way that makes sense. The first version of the periodic table was proposed by Dmitri Mendeleev in 1869. He arranged the elements according to their atomic mass and noticed that there was a periodic pattern in the properties of the elements.

Mendeleev's periodic law, also known as the first law of periodic classification, states that: "The properties of elements are a periodic function of their atomic masses." This means that if you arrange the elements in order of increasing atomic mass, you will notice that the properties of the elements repeat at regular intervals, or periods.

Mendeleev's table was not perfect, however. He had to leave empty spaces for elements that hadn't yet been discovered, and some elements didn't quite fit the pattern. For example, tellurium and iodine, tellurium has a greater atomic mass than iodine, but Mendeleev had to put it before iodine for the properties to match.

This led to the development of the modern periodic table, which is based on Moseley's periodic law. Henry Moseley, an English physicist, discovered in 1913 that the charge of the nucleus of the atom (the atomic number) is what determines the properties of the elements. Moseley's periodic law, or the second law of periodic classification, states that: "The properties of elements are a periodic function of their atomic numbers".

The modern periodic table is arranged in order of increasing atomic number, not atomic mass. This solved the problems of Mendeleev's table and allowed the inclusion of new elements that have since been discovered.

The modern periodic table is divided into groups (columns) and periods (rows). Elements in the same group have similar chemical properties and the same electronic configuration in their last energy level. Elements in the same period have the same number of energy levels.

There are 18 groups in the periodic table, numbered 1 to 18, and 7 periods, numbered 1 to 7. The groups can be divided into blocks: the s block (groups 1 and 2), the p block (groups 13 to 18), the d-block (groups 3 to 12) and the f-block (the lanthanides and actinides).

Understanding the periodic table and the laws of periodic classification is essential to the study of chemistry. It allows you to predict the properties of elements and their chemical reactions, which is extremely useful in solving Enem questions.

We hope this chapter has helped you to better understand the Periodic Classification of Elements. Keep studying with our e-book to prepare for the Enem test!

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31Periodic Classification of Elements: Organization of elements in the periodic table

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