Question

Explain why the \(s\) block in the periodic table has only two columns while the \(p\) block has six.

Short answer

The 's' block has only two columns because an 's' orbital can contain only two electrons, whereas the 'p' block has six because there are three 'p' orbitals, each able to hold two electrons, for a total of six electrons.

Step-by-step solution

Understanding Electron Orbitals

The periodic table is arranged according to the electron configuration of elements. The 's' and 'p' in the 's' block and 'p' block refer to the types of atomic orbitals: 's' orbitals are spherical, and 'p' orbitals are dumbbell-shaped. An orbital can hold a maximum of two electrons.

Explaining the 's' Block

The 's' block contains elements where the 's' orbital is being filled with electrons. There are only two columns because an 's' orbital can have only two electrons, and there are two 's' orbitals in a period (one for each spin orientation).

Explaining the 'p' Block

The 'p' block elements have their 'p' orbitals being filled. There are three 'p' orbitals (px, py, pz), each capable of holding two electrons, which sums up to six electrons in total for the three orbitals. Therefore, the p block has six columns, corresponding to the six possible electron positions in the three p orbitals.

Key concepts

Electron Orbitals

Electron orbitals are regions around an atom's nucleus where electrons are most likely to be found. They are depicted by different shapes that represent the mathematical probability of finding an electron in a given space. These shapes vary according to the energy levels and types of orbitals (s, p, d, f).

Atoms are constructed in layers or shells, and electrons fill these shells in a specific order determined by the principles of quantum mechanics. The first shell is filled first, then the second, and so on, with each shell having subshells consisting of orbitals. Understanding orbitals is crucial to grasping the arrangement of elements in the periodic table since this arrangement reflects the order in which orbitals are filled.

S Orbital

The 's' orbital is the simplest type of electron orbital and is spherical in shape. Each energy level of an atom has one 's' orbital, beginning with the 1s orbital closest to the nucleus. Because of their shape, 's' orbitals don't have directional properties that p, d, or f orbitals have.

The s orbital is significant because it’s the first to be filled as you move across a period in the periodic table. Its capacity to hold only two electrons leads to the creation of the 's' block in the periodic table, which consists simply of two groups. This is due to the Pauli exclusion principle, which states that an orbital can hold only two electrons with opposite spins.

P Orbital

The 'p' orbital is a more complex orbital with a dumbbell or lobed shape. There are three mutually perpendicular p orbitals in each energy level, designated as px, py, and pz. Each of these orbitals can also hold two electrons, meaning that a set of p orbitals (consisting of all three px, py, and pz) can hold a total of six electrons.

This accounts for the six columns of the 'p' block on the periodic table. The different orientations of the p orbitals give them unique spatial properties, affecting the chemical bonding and reactivity of the atoms. Elements of the p block are known for their involvement in covalent bonding where the shape of the p orbital plays a critical role.

Electron Configuration

Electron configuration is the arrangement of electrons around the nucleus of an atom in its orbitals. It is a detailed description of each electron's position within an atom, which is essential for understanding an element's chemical behavior. The Aufbau principle, Hund's rule, and the Pauli exclusion principle dictate the order in which electron shells and subshells are filled.

For instance, hydrogen has an electron configuration of 1s1, meaning it has one electron in the 1s orbital. For calcium, with an electron configuration of [Ar]4s2, after argon's configuration all the subshells are filled, and it has two electrons in the 4s orbital. This information helps describe the reactivity and bonding characteristics of each element and is a fundamental tool for chemists.