Where to find the number of electrons

If an atom doesn't have 36 protons, it can't be an atom of krypton. Adding or removing protons from the nucleus of an atom creates a different element. For example, removing one proton from an atom of krypton creates an atom of bromine. By definition, atoms have no overall electrical charge. That means that there must be a balance between the positively charged protons and the negatively charged electrons.

Atoms must have equal numbers of protons and electrons. In our example, an atom of krypton must contain 36 electrons since it contains 36 protons. Electrons are arranged around atoms in a special way.

If you need to know how the electrons are arranged around an atom, take a look at the ' How do I read an electron configuration table? An atom can gain or lose electrons, becoming what is known as an ion. An ion is nothing more than an electrically charged atom. Adding or removing electrons from an atom does not change which element it is, just its net charge.

The plus sign means that this is a positively charged ion. It is positively charged because a negatively charged electron was removed from the atom. The atomic weight is basically a measurement of the total number of particles in an atom's nucleus.

In reality, it isn't that clean cut. The atomic weight is actually a weighted average of all of the naturally occurring isotopes of an element relative to the mass of carbon Didn't understand that? Doesn't matter. The different isotopes of an element are identified by writing the mass number of the atom in the upper left corner of the symbol for the element.

If the atoms are neutral, they also must contain six electrons. The only difference between these isotopes is the number of neutrons in the nucleus. Click here to check your answer to Practice Problem 1. Much of what is known about the structure of the electrons in an atom has been obtained by studying the interaction between matter and different forms of electromagnetic radiation.

Electromagnetic radiation has some of the properties of both a particle and a wave. Particles have a definite mass and they occupy space. Waves have no mass and yet they carry energy as they travel through space. In addition to their ability to carry energy, waves have four other characteristic properties: speed, frequency, wavelength, and amplitude. The frequency v is the number of waves or cycles per unit of time. The frequency of a wave is reported in units of cycles per second s -1 or hertz Hz.

The idealized drawing of a wave in the figure below illustrates the definitions of amplitude and wavelength. The wavelength l is the smallest distance between repeating points on the wave. The amplitude of the wave is the distance between the highest or lowest point on the wave and the center of gravity of the wave. If we measure the frequency v of a wave in cycles per second and the wavelength l in meters, the product of these two numbers has the units of meters per second.

The product of the frequency v times the wavelength l of a wave is therefore the speed s at which the wave travels through space. Atoms form molecules and compounds by sharing electrons to create chemical bonds. Understanding the nature of this bonding begins by knowing the number of electrons associated with each atom. With the information from a periodic table of the elements, and some straightforward arithmetic, you can calculate the number of electrons based on the chemical formula of a material.

Analyze the chemical formula and write down the element types that comprise the compound as well as the number of atoms of each type. The second example, SO 4 2- , contains the elements sulfur S—1 atom and oxygen O—4 atoms. Navigate to the periodic table of the chemical elements see Resources and find out the integer atomic number for each element identified in Step 1—the number that appears just above the chemical symbol for each element.

In our example, the atomic numbers of the elements potassium K , nitrogen N , oxygen O and sulfur S are 19, 7, 8 and 16, respectively. Repeat for all elements in the molecule, then add up all the products to calculate the number of electrons. Subtract the charge value from the number of electrons obtained in Step 3 if the ion has a positive charge. Add the charge value to the number of electrons Step 3 if the ion has a negative charge.