Describe the trend in EN moving down a group of the periodic table.

When we talk about the term 'chemical property', we're referring to characteristics of a substance that become evident during a chemical reaction. In the case of electronegativity, it is a chemical property that indicates how strongly an atom can attract and hold onto electrons that are involved in a bond. Electrons, as you may know, are negatively charged particles that orbit the nucleus of an atom and are essential to creating chemical bonds. The way an atom behaves in a reaction — whether it's eager to gain electrons or likely to lose them — is fundamental to understanding the nature of the substances all around us.

Developed by chemist Linus Pauling, the Pauling scale is a numerical way of expressing the electronegativity of an element. Represented with values typically ranging from around 0.7 to 4.0, this scale helps scientists predict how atoms might interact when they come in contact with one another. A higher number on the Pauling scale, such as Fluorine's 4.0, means an element has a stronger tendency to attract electrons toward itself in a covalent bond, akin to being more 'electron-hungry'. Understanding these numbers can be extremely useful when expecting the nature of compounds and the bonds that will form during chemical reactions.

Looking at the periodic table, the vertical columns are called 'groups'. Each group is numerically designated and consists of elements that share similar valence electron configurations. This commonality gives them comparable chemical properties. For example, Group 1 elements, also known as the alkali metals, all have one electron in their outermost energy level, making them highly reactive. Group configurations are vital for predicting how an element might behave in a given scenario, especially when forming compounds with other elements.

Valence electrons are the electrons in the outermost energy level (or shell) of an atom and are vitally important because they are the ones that engage directly in forming chemical bonds. These electrons can be 'shared' with others to create covalent bonds or 'transferred' in ionic bonds. Elements in the same group of the periodic table will have the same number of valence electrons, which is a large part of why they often exhibit similar chemical behaviors. Therefore, knowing the number of valence electrons aids in predicting how an element will react chemically.

The atomic structure is the intricate arrangement of the smallest recognized division of a chemical element. At its center, the nucleus contains protons (positively charged) and neutrons (neutral), surrounded by rapidly moving electrons (negatively charged) existing in different energy levels, or shells. The interesting part is that as we add more shells, the distance between the nucleus and the valence electrons increases. This distance plays a critical role in determining how strong the electronegative pull is, as the further the valence electrons are from the nucleus, typically, the weaker the attractive force of the nucleus upon them. This ultimately influences the atom's electronegativity and also its chemical properties.