There are multiple trends on the periodic table, but we are going to discuss four of the trends which are the following: atomic radius, electron affinity, electronegativity and ionization energy.
- Electron affinity is the change in energy of a neutral atom when an electron is added to the atom. The electron affinity of elements decreases from top to bottom in a group, and increases from left to right in a period.
- The atomic radius is essentially how large an atom is. The atomic radius of atoms increases from top to bottom in a group, and decreases from left to right in a period. Also, we can look at the atomic radius for ions as well. Cations are smaller than the neutral atom and anions are larger than the neutral atom.
- The electronegativity is how strongly an atom pulls electrons to itself. Think of electronegativity as "greediness." How "greedy" an atom is for electrons. For example, Fluorine is the most greedy element and Cesium is the least greedy element. The electronegativity of elements decreases from top to bottom in a group, and increases from left to right in a period.
- The ionization energy is the energy required to pull an electron away from an atom. The higher the ionization energy the more energy to pull an electron away from the atom. The ionization energy of elements decreases from top to bottom in a group, and increases from left to right in a period.
Mirek2, CC0, via Wikimedia Commons
There is one more trend that needs to be discussed. The trend is called "reactivity." Groups 1A and 7A are the most reactive groups, they are only 1 electron away from having a full outer shell. Groups 2A and 6A are also very reactive. They are 2 electrons away from a full outer shell, but they are not as reactive as 1A and 7A. Group 8A elements are very unreactive because they already have a full outer shell. Watch the following two videos to learn about reactivity.