4.6 Electron Energy Levels A rainbow forms when light passes through water droplets. Learning Goal Describe the energy levels, sublevels, and orbitals for the electrons in an atom.

Electromagnetic Radiation We experience electromagnetic radiation in different forms, such as light, the colors of a rainbow, or X-rays. Electromagnetic radiation consists of energy particles that move as waves of energy. The distance between the peaks of waves is called the wavelength. High-energy radiation has shorter wavelengths. Low-energy radiation has longer wavelengths.

Atomic Spectrum When light from a heated element passes through a prism, it separates into distinct lines of color separated by dark areas called an atomic spectrum. Each element has its own unique atomic spectrum. In an atomic spectrum, light from a heated element separates into distinct lines.

Electron Energy Levels The lines in an atomic spectrum are associated with the changes in energies of the electrons. In an atom, each electron has a specific energy, known as its energy level, which is assigned principal quantum numbers (n) = (n = 1, n = 2, …). increases in energy as the value of n increases and electrons are farther away from the nucleus. The energy of an electron is quantized—electrons can have only specific energy values.

Electromagnetic Spectrum The electromagnetic spectrum shows the arrangement of wavelengths of electromagnetic radiation, with the visible range from 700 to 400 nm.

Electrons and Energy Levels Electrons with the same energy are grouped in the same energy level. Energy levels are assigned values called principal quantum numbers (n), (n = 1, n = 2, …). An electron can have only the energy of one of the energy levels in an atom.

Changes in Electron Energy Level Electrons move to a higher energy level when they absorb energy. When electrons fall back to a lower energy level, light is emitted. The energy emitted or absorbed is equal to the differences between the two energy levels.

Sublevels It is the arrangement of electrons that determines the physical and chemical properties of an element. Each energy level consists of one or more sublevels. The number of sublevels in an energy level is equal to the principal quantum number n of that energy level. The sublevels are identified as s, p, d, and f. The order of sublevels in an energy level is s < p < d < f

Sublevels

s Orbitals The location of an electron is described in terms of probability. Orbitals are a three-dimensional volume in which electrons have the highest probability of being found. The s orbitals are shown as spheres. (a) The electron cloud of an s orbital represents the highest probability of finding an s electron. (b) The s orbitals are shown as spheres. The sizes of the s orbitals increase because they contain electrons at higher energy levels.

p Orbitals There are three p orbitals, starting with n = 2. Each p orbital has two lobes, like a balloon tied in the middle, and can hold a maximum of two electrons. The three p orbitals are arranged perpendicular to each other along the x, y, and z axes around the nucleus.

p Orbitals A p orbital has two regions of high probability, which gives a “dumbbell” shape. (a) Each p orbital is aligned along a different axis from the other p orbitals. (b) All three p orbitals are shown around the nucleus.

d Orbitals Each of the d sublevels contains five d orbitals. Four of the five d orbitals consist of four lobes that are aligned along or between different axes. One d orbital consists of two lobes and a doughnut-shaped ring around its center.

Orbital Capacity and Electron Spin The Pauli exclusion principle states that each orbital can hold a maximum of two electrons. electrons in the same orbital repel each other. electrons in the same orbital must have their magnetic spins cancel (they must spin in opposite directions). We can represent magnetic spins with an arrow An orbital can hold up to two electrons with opposite spins.

Number of Electrons in Sublevels There is a maximum number of electrons that can fill each sublevel. Each s sublevel has one orbital and can hold a maximum of two electrons. Each p sublevel has three orbitals and can hold a maximum of six electrons. Each d sublevel has five orbitals and can hold a maximum of 10 electrons. Each f sublevel can has 7 orbitals and can hold a maximum of 14 electrons.

Number of Electrons in Sublevels

Study Check Which of the following elements are likely to have electrons in the 3p sublevel? C Si O As

Solution Which of the following elements are likely to have electrons in the 3p sublevel? C fills only the energy level n = 2. Si has electrons in the 3p sublevel. O fills only the energy level n = 2. As has electrons in the 3p sublevel. Si and As will have electrons in the 3p sublevel.