Relate how the arrangement of electrons determines an element’s reactivity
The arrangement of electrons in an atom determines an element's reactivity. Specifically, it is the outermost electrons, known as valence electrons, that play the most significant role in determining chemical reactivity.
To understand this concept, it is important to know about the electron configuration of an atom. The electron configuration identifies how electrons are distributed among the various energy levels or orbitals within an atom.
When two or more atoms engage in a chemical reaction, it is the electrons that interact. Atoms with incomplete valence shells tend to be more reactive because they seek to achieve a stable electron configuration. Stability is achieved by either gaining, losing, or sharing valence electrons.
Elements in Group 1 of the periodic table, also known as alkali metals, have a single valence electron in their outermost shell. These elements are highly reactive because they readily lose this single electron to achieve a stable configuration.
On the other hand, elements in Group 17, known as halogens, have seven valence electrons. They are also highly reactive due to their tendency to gain one electron to achieve a stable configuration.
Noble gases, such as helium, neon, and argon, have complete valence electron shells and are therefore very unreactive. This is because they have achieved a stable electron configuration, meaning they do not readily gain, lose, or share electrons.
In summary, the arrangement of electrons, particularly the number of valence electrons and their distribution among orbitals, determines an element's reactivity. Elements with incomplete valence shells are more reactive as they seek to achieve a stable electron configuration by gaining, losing, or sharing electrons.