What's the difference between a 1s² and a 2s² electron configuration?

The difference between a 1s² and a 2s² electron configuration lies in the energy level and spatial distribution of the electrons.

In atomic physics, electron configuration refers to the distribution of electrons of an atom or molecule in atomic or molecular orbitals. The 1s² and 2s² configurations refer to the placement of electrons in different energy levels and orbitals of an atom. The number before the 's' (1 and 2 in this case) represents the principal quantum number, or energy level. The 's' denotes the type of orbital, and the superscript number (²) indicates the number of electrons in that orbital.

In a 1s² configuration, the two electrons occupy the first energy level (n=1) in an s orbital. This is the lowest energy level and is closest to the nucleus. The s orbital is spherical in shape, and in this case, it is completely filled as it can hold a maximum of two electrons.

On the other hand, a 2s² configuration means the two electrons are in the second energy level (n=2) in an s orbital. This energy level is at a higher energy and further from the nucleus than the 1s orbital. The 2s orbital is also spherical but is larger and encompasses a greater volume than the 1s orbital. It also contains a nodal plane where the probability of finding an electron is zero.

The energy levels and spatial distribution of electrons in an atom determine its chemical properties and reactivity. Electrons in higher energy levels are more reactive because they are less tightly bound to the nucleus and more accessible for chemical reactions. Therefore, understanding the difference between 1s² and 2s² electron configurations is crucial in predicting the behaviour of atoms in chemical reactions.