Which electrons experience a greater effective nuclear charge: the valence electrons in beryllium or the valence electrons in nitrogen? Why?

Valence electrons are the electrons in the outermost shell, or energy level, of an atom. They are significant because these electrons predominantly contribute to the chemical properties of an element, including how it will bond with other atoms. These are the electrons used during chemical reactions.
When comparing elements, the number of valence electrons determines the element's placement in the periodic table and its ability to form certain types of bonds. For example, beryllium has two valence electrons and nitrogen has five, making nitrogen more chemically versatile in forming compounds. It's this configuration of valence electrons that also impacts the effective nuclear charge they experience, a concept that is directly tied to the trends in the periodic table.

The atomic number of an element is a fundamental property that corresponds to the number of protons in its nucleus. It's denoted by the symbol 'Z'.
As atomic number increases, the number of protons in the nucleus also increases, leading to a stronger charge in the core of the atom. This is why nitrogen, which has an atomic number of 7, will exert a stronger force on its valence electrons compared to beryllium, with an atomic number of 4. The atomic number is key in understanding the effective nuclear charge because it directly indicates the degree of positive charge acting upon the electrons.

The periodic table is a systematic arrangement of elements ordered by their atomic number, electron configuration, and recurring chemical properties. Elements are laid out in rows, called periods, and columns, called groups. As you move across a period from left to right, elements gain protons and electrons, and typically the effective nuclear charge increases. This is because the additional protons create a stronger positive charge in the nucleus, attracting electrons more strongly.
Both beryllium and nitrogen are found in the same period, which means they have the same number of electron shells. However, due to nitrogen's higher position in the periodic table (further to the right), it signifies a stronger effective nuclear charge on its valence electrons.

The shielding effect describes how core electrons--those that lay between the nucleus and the outermost electrons--diminish the force exerted by the nucleus on the valence electrons. Inner electrons repel valence electrons due to their negative charge, effectively reducing the net positive charge the valence electrons experience from the nucleus, known as the effective nuclear charge.
In comparing beryllium and nitrogen, both have the same electron shells that provide the shielding effect. However, the number of shielding electrons does not sufficiently offset the increased positive charge that nitrogen's nucleus has due to more protons. Thus, the shielding effect plays a crucial role in determining effective nuclear charge but does not change proportionally across a period.

Electron shells are layers of electrons that surround the nucleus of an atom. Each shell can hold a specific maximum number of electrons and are filled from the innermost shell outward.
The number of electron shells an element has influences its chemical properties and the distance valence electrons are from the nucleus. Elements with the same number of electron shells are placed in the same period in the periodic table. Beryllium and nitrogen, despite having different numbers of protons and valence electrons, share the same principal electron shell. This is why they both have similar shielding effects, but due to nitrogen's additional protons, its valence electrons are held more tightly, showcasing the nuanced interplay between electron shells and effective nuclear charge.