Terry Livingston, age 13, of Nashville, Tennessee, for his question:
What is meant by the K energy level?
Our first concept of the world of atoms is concerned with size. The mind needs time to grasp its submicroscopic scale. But this picture is a bare skeleton until we enliven it with the concept of energy. The K energy level is but one of the disciplined forces within the busy atom.
A sizable atom, such as calcium, has four energy levels K and L, M and N. Larger atoms have more energy levels, while smaller ones may have only one or two. But in all atomic elements, K is the ground level of lowest energy. This type of energy is not the same as the nuclear force in the core of the minuscule atom. It is a property of the shells of electrons that orbit the atomic nucleus. Of course, since the atom is an orderly system of particles and interrelated energies, the K and other energy levels are associated with the dynamic energy of the nucleus and affected by it.
An electron, of course, is a particle of matter bearing one unit of negative electri¬city. Each atomic element has its quota of orbiting electrons and every corner of the universe has stray unattracted electrons. Each of these negative particles has the same size and mass as all the others. Its negative charge is opposite and precisely equal to the positive charge of a proton in the atomic nucleus.
A normal atom is electrically neutral because the number of its positive protons equals the number of its negative electrons.. The atom has been compared to a miniature solar system, with a nuclear sun and planetary electrons. Modern physicists accept only part of this picture. For one thing, electrons do not trace orbits on a neat plane more,,•or less level with their solar equator. Their paths swoop this way and that around the surface of invisible spheres.
Electrons orbit at set distances from the nucleus and a spherical shell has room for more than one of them. Scientists name these electron shells with letters, beginning with K as the inside shell. The orderly structure of the atom dictates a set number of electrons for each shell. The lowest K level can hold one or two electrons but no more. The larger L level outside it is completely filled with eight. The N level of a larger atom can hold up to 32 swirling electrons.
Energy from the central nucleus acts as a binding force on the swarming electrons, somewhat as the sun's gravity holds the planets in their places. The K level, being closest, feels the strongest pull. This detracts from the whirling freedom of the energetic electrons The K sphere is the closest of the electron shells and has the lowest energy level.
This complicated concept explains why and how atoms with incomplete outer shells combine with suitable partners to form molecules. It also led to the quantum theory. An electron can get an extra jolt of energy from outside the atom. It may use it to hop out¬ward for a brief spin in the next shell. When it drops back, it emits a measurable quantum unit of light energy. A drop back of two shells yields two quanta. These whole quantum numbers suggest the existence of unified packages of light energy called photons.