Question Video: Determining the Period Number for Atoms When Given the Valence Shell Number | Nagwa Question Video: Determining the Period Number for Atoms When Given the Valence Shell Number | Nagwa

# Question Video: Determining the Period Number for Atoms When Given the Valence Shell Number Chemistry • Second Year of Secondary School

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In which period of the periodic table is the fourth electron shell of an atom the valence shell?

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### Video Transcript

In which period of the periodic table is the fourth electron shell of an atom the valence shell?

Let’s begin by looking at the periodic table of elements. The horizontal rows on the periodic table are known as periods. Periods are collections of elements with the same highest occupied electron shell, or valence shell. Every atom consists of a nucleus surrounded by a cloud of electrons. In a simple model, we can describe electrons as occupying electron shells at various distances from the nucleus. These distances represent different energy levels.

Now let’s look at a few examples to help us answer the question. An atom of hydrogen has only one electron, and we usually find that electron in the first electron shell. So, hydrogen is found in the first period of the periodic table. Helium is also in period one because atoms of helium only have two electrons, which sit in the first electron shell. Lithium, however, is in period two. Atoms of lithium have three electrons, and there’s only space in the first shell for two electrons. So, the third electron goes in the second electron shell. We see something similar when we get to sodium. The highest occupied electron shell for sodium atoms is the third electron shell.

This pattern continues all the way down the periodic table. So, we can use the periodic table and electron shell diagrams to convert the period number to the shell number of the highest occupied electron shell. With this in mind, atoms in which the fourth electron shell is the valence shell will be found in period four.

In which period of the periodic table is the fourth electron shell of an atom the valence shell? The answer is period four.

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