As a result, elements in the same group often display similar properties and reactivity.
![periodic table trends valence electrons periodic table trends valence electrons](http://perso.numericable.fr/vincent.hedberg/bonding/valence.jpg)
The elements in each group have the same number of valence electrons. It is important to recognize which numbering system is being used and to be able to find the number of valence electrons in the main block elements regardless of which numbering system is being used. The s-, p-, and d-block elements of the periodic table are arranged into 18 numbered columns, or groups. You will come across periodic tables with both numbering systems. In this numbering system, group 1A is group 1 group 2A is group 2 the halogens (7A) are group 17 and the noble gases (8A) are group 18. The elements in this group are also gases at room temperature.Īn alternate numbering system numbers all of the \(s\), \(p\), and \(d\) block elements from 1-18. We will learn the reason for this later, when we discuss how compounds form. These elements also have similar properties to each other, the most significant property being that they are extremely unreactive, rarely forming compounds. This group contains very reactive nonmetal elements. Group 7A (or 17) elements are also called halogens. An ion with more protons than electrons is positively charged and called a cation (comes from the metal). It is important to recognize a couple of other important groups on the periodic table by their group name. When an atom gains or loses a valence electron, it forms an ion.
![periodic table trends valence electrons periodic table trends valence electrons](https://i.ytimg.com/vi/g5PRdfrVwoc/hqdefault.jpg)
Remember, Mendeleev arranged the table so that elements with the most similar properties were in the same group on the periodic table. The same pattern is true of other groups on the periodic table. Once again, because of their similarities in electron configurations, these elements have similar properties to each other. Group 2A is also called the alkaline earth metals. Although most metals tend to be very hard, these metals are actually soft and can be easily cut. Group 1A is also known as the alkali metals. Because of their similarities in their chemical properties, Mendeleev put these elements into the same group. The elements in 1A are all very reactive and form compounds in the same ratios with similar properties with other elements. Consequently, all transition-metal cations possess d n valence electron configurations, as shown in Table 23.2 for the 2+ ions of the first-row transition metals. This is what causes these elements to react in the same ways as the other members of the family. The loss of one or more electrons reverses the relative energies of the ns and (n 1)d subshells, making the latter lower in energy. All of the 1A elements have one valence electron. A group is a vertical column of the periodic table. Remember that Mendeleev arranged the periodic table so that elements with the most similar properties were placed in the same group.