Helium is a noble gas with atomic number 2, which means it has two protons and two neutrons in its nucleus. It is the second element on the periodic table and it is located in the first column of the noble gases. Helium is usually encountered as a gas, but there are also trace amounts of helium found in natural gas deposits and in some minerals.
The electron configuration of helium is 1s2, which indicates that it has two electrons in its first energy level. The first energy level of an atom can hold up to two electrons, and once it is full, any additional electrons have to go into the next energy level. In the case of helium, however, the first energy level is completely filled, which means that all of its electrons are valence electrons.
Valence electrons are the electrons in an atom’s outermost energy level, and they are the ones that are involved in chemical reactions. By knowing how many valence electrons an atom has, we can predict its behavior in chemical reactions and how it will interact with other elements.
In the case of helium, since it has two valence electrons, it is very stable and unreactive. This is due to the fact that its first energy level is completely filled with electrons, and it requires a significant amount of energy to remove one of these electrons. As a result, helium does not form chemical bonds with other elements, and it exists as a monatomic gas.
The stability of helium is also reflected in its physical properties. It has a low boiling point of -268.9°C and a low melting point of -272.2°C, which means that it exists as a gas at room temperature and pressure. Furthermore, its low density makes it rise above other gases, which is why helium is used in balloons and airships.
In addition to its inertness and stability, helium has some interesting and useful properties. It is a very good conductor of heat and electricity, which makes it useful in cooling and refrigeration systems. It is also used in various medical applications, such as MRI machines and respiratory treatments.
In conclusion, helium has two valence electrons, which are located in its first energy level. These electrons give helium its stability and unreactivity, and they also play a role in its physical and chemical properties. Despite its unreactivity, helium has many important applications in science, technology, and medicine, and it continues to be one of the most fascinating and versatile elements on the periodic table.