Electrons

Energy Levels (remember that electrons are found in orbitals)

• orbitals in an atom form a series of energy levels in which electrons may be found.

• Each electron in an atom has its own distinct amount of energy that corresponds to the energy level that it occupies.

• Electrons can gain and lose energy and move to different energy levels.

Ground states

• Electrons occupying the lowest available orbitals, the atom is in ground state.

• Electrons in a ground state atom have filled the available spaces from the lowest energy level to higher levels until all electrons are accounted for.

Excited State

• When electrons are subjected to stimuli such as heat, light, or electricity, an electron absorbs energy and temporarily moves to a higher energy level. This unstable condition is called an excited state.

• An excited electron will then return to its available level by emitting the same amount of energy it absorbed.

  • Emitted energy

    • The energy emitted may be in the form of infrared, ultraviolet, or visible light.

    • While the light appears as one color to our eyes, it is actually composed of many different wavelengths, Each of which is seen as a different line when viewed through an instrument called a spectroscope.

    • The visible light produced by electrons is confined to narrow lines of color called bright-line Spectra. Each atom has its own distinct pattern of bright-line spectrum and the Spectra are used to identify elements.

Energy Levels

The chemical properties of an element are based on the number of valence electrons of its atoms.

• Each energy level has sub-levels. The number of sub-levels is determined by the number of the energy levels.

  • E.g. Energy level 3 has 3 sub-levels.

• Sub-levels are represented by letters. The first sub-level of any energy level is represented as the s sub-level. The second sub-level is p. The third is d, and the fourth is f.

• Sub-levels are described by using the number of the principal energy level together with the letter of each sub-level

  • E.g. 3s represents the first sub-level of the third energy level.

Electron Configuration

• In an electron configuration, the electrons of an atom are described by identifying the energy level of each electron and its sub-level.

  • E.g. 3s represents the first sub-level of the third energy level.

• A superscript is added to show the number of electrons in the sub-level.

  • E.g.  4p 5 tells the reader that there are five electrons in the 4p sub-level.

Writing electron configuration

The electron configurations of the elements can be read in order of increasing atomic number, starting with hydrogen, by adding an additional electron for each new atom.

The order in which sub-levels are filled in the figure above use the following rules:

• Each added electron is placed into the sub- level of the lowest available energy

• No more than two electrons can be placed in any orbital.

• A single electron must be placed into each orbital of a given sub-level before any pairing takes place

• the outermost principal energy level can only contain electrons in S And P orbitals