Final answer:
The periodic table arranges elements into groups and periods, grouping elements with similar properties and indicating the number of electron shells. Group 1 contains alkali metals, Group 2 has alkaline earth metals, Group 17 includes halogens, and Group 18 features noble gases.
Step-by-step explanation:
The periodic table is a systematic arrangement of elements, organized in a way that groups elements with similar properties together. These groups are known as chemical groups, and are numbered 1-18. Elements in the same group have similar chemical properties because they have the same number of valence electrons. For instance, Group 1 elements are known as the alkali metals, which are highly reactive and have one valence electron.
Group 2 elements are referred to as alkaline earth metals and they have two valence electrons, making them also reactive, albeit less so than alkali metals. Moving further right, Group 17 consists of the halogens, which are very reactive nonmetals, and Group 18 contains the noble gases, known for their lack of reactivity due to a full valence shell.
The periodic table also has horizontal rows called periods, which are numbered from 1 to 7. These periods indicate the number of electron shells an element has. The periodic table helps predict the general properties of elements based on their location and allows for the classification of elements as metals, nonmetals, or metalloids.