Without looking at the periodic table, identify the period and group in which each of the following elements is located. $$\begin{array}{l}{\text { a. }[\mathrm{Rn}] 7 s^{1}} \\ {\text { b. }[\mathrm{Ar}] 4 s^{2}} \\ {\text { c. }[\mathrm{Ne}] 3 s^{2} 3 p^{6}}\end{array}$$

The periodic table is an organized chart of elements that provides a wealth of information about the properties of the different elements. One of the key organizational elements of the periodic table are the groups, or families. These groups are columns on the periodic table and are usually numbered from 1 to 18. Elements within the same group have similar chemical characteristics because they have the same number of valence electrons (the electrons available for bonding in the outermost shell).

For example, all elements in Group 1, also known as the alkali metals, have one valence electron in their outermost shell; thus, they tend to lose one electron and form +1 ions. Similarly, Group 17 elements, or halogens, have seven valence electrons and typically gain one electron to form -1 ions. Understanding the group an element belongs to can greatly assist in predicting its chemical behavior.

Atomic shells are essentially the orbits or energy levels where electrons reside around the nucleus of an atom. These shells are labeled with numbers starting from 1 for the innermost shell, progressing outward. Each shell has a maximum number of electrons it can host: two electrons can fit in the first shell, while subsequent shells can hold a larger number of electrons following specific rules.

The electrons in these shells contribute to the chemical properties of the atom. For example, noble gases have full outer shells, which makes them highly stable and mostly non-reactive, while other elements with incomplete outer shells are more reactive. The electron configuration of an element, a way of representing the distribution of electrons among the atomic shells, provides essential information about its chemical properties and reactivity.

Periods in the periodic table are the horizontal rows, and they are sequential, starting from period 1 at the top to period 7 at the bottom. The period number an element belongs to corresponds to the highest number of energy levels or shells that its electrons occupy. As we move from left to right across a period, each element has one more proton and is one electron richer than the element before it.

This increase in the number of electrons and protons gradually changes the properties of the elements. The periodic table is meticulously arranged so that elements show a trend in properties such as reactivity, metallicity, and electron affinity across a period. For instance, elements on the left side of a period tend to be metals, while those on the right are nonmetals or noble gases.

Within atomic shells, there are subshells that consist of orbitals, each of which can hold a maximum of two electrons. The 's' and 'p' refer to different types of orbitals within these subshells. The s orbital is spherical in shape and can be found in all shells starting with the first shell. There's only one s orbital in each shell, which can contain 2 electrons.

On the other hand, p orbitals are dumbbell-shaped and can hold a total of 6 electrons, housing three p orbitals (each holding 2 electrons). p orbitals start from the second shell. These two types of orbitals, occupied by the valence electrons of an element, are extremely significant in chemical bonding and the overall behavior of elements.

An understanding of s and p orbitals helps us make sense of the periodic table layout and why certain groups contain elements with similar properties. For instance, Group 1 elements possess a single s orbital electron outside their noble gas core, leading to similar reactivity patterns among them.