As we move across a period or down a group on the periodic table, certain patterns, known as periodic trends, become apparent. One such trend is the atomic radius trend. When moving down a group, the number of electron shells increases, leading to a corresponding increase in the atomic radius of the atom. On the other hand, as we move across a period, the atomic radius decreases due to an increase in protons and nuclear charge, pulling the electrons tightly and reducing the size of the atom.
The atomic radius trend can be graphically explained with the most active metals having the largest atomic radii. This is because their valence electrons are further away from the nucleus, enabling quicker movement. For instance, group 1 metals are considered the most reactive due to their valence electrons being further away from the nucleus, leading to increased activity.
Periodic Trends
As we go down a group, several similarities can be noticed:
- Low ionization energy
- Low electronegativity
- Low densities
On the other hand, differences become apparent between group 1 and group 2:
- Group 1 is the most reactive group with an oxidation state of +1
- Group 2 is the 2nd most reactive group with an oxidation state of +2
Moreover, the elements in group 1 and group 2 are found in nature as compounds, and to separate the elements, they can be obtained.
Moving on to groups 3-12, also known as transition metals, it is important to note that many of these elements have more than 1 oxidation state because, when they bond, they can lose electrons from their last or second to last shell. Additionally, their aqueous solutions are brightly colored (except for group 12).
Group 17, consisting of halogens, involves elements with small atomic radii that are very likely to gain electrons, resulting in high electronegativity and high ionization energy. These elements are the most active nonmetals, with Fluorine being the most reactive element in group 17 due to its similar properties with the other elements in the group.
Halogens
- The boiling point of group 17 elements increases as we move down the group, requiring more energy to boil and break the intermolecular forces, known as van Der Waals or London dispersion forces.
- Group 17 elements are obtained through the electrolysis of fused metal salts and are the only group containing each of the 3 phases of matter at STP.
- Each of the elements in group 17 (except Astatine) is diatomic and undergoes sublimation due to weak intermolecular forces.
The elements in group 18 have completely filled outer shells, making them inert. Most of them have oxidation numbers of zero, except for Krypton and Xenon. While these elements are typically monatomic and exist as monatomic molecules, under laboratory conditions, they can be forced to react with Fluorine.
It is important to note that the majority of the elements on the periodic table are metals, with F₂ and Cl₂ existing as gases, Br₂ as a liquid, and I₂ as a solid. Additionally, Mendeleev initially based the periodic table on increasing atomic mass.
Understanding these periodic trends and group properties is crucial when studying the periodic table. It allows us to comprehend the behavior and characteristics of each element, as well as predict their properties and behavior in different chemical reactions and scenarios.
