Atoms are arranged in the periodic table for specific purposes. Like for groups, atoms placed in a group means that they have relatively similar qualities with each other. First, located in a certain group has similar numbers of valence electrons (except for the f-block elements). These valence electrons make the atoms in a group have similar characteristic with each other.
Group 1 elements or the alkali metals tend to lose only one electron upon ionization and are commonly found in salts. Metals in this group have relative similar physical properties: shiny, soft and very reactive at standard temperature and pressure.
Group 18 or the noble gasses have complete valence shell electrons thus making the atoms in that group the most stable. Since they have high stability noble gasses tend to be unreactive at normal conditions. They are also called the "inert gases."
Group 4 elements or the titanium group are located in the d-block group. The first three members share similar characteristics as a metal. They can be used as refractory metals under standard conditions. The fourth member however is an unstable compound due to its radioactivity.