The electron is a negatively charged particle that is part of the atom. All the basic elements are composed of electrons, protons and neutrons. One of the fundamental concepts that must be mastered in chemistry is the ability to determine how many electrons there are in an atom. Thanks to the periodic table of the elements, you will be able to find out without difficulty. Other important concepts involve calculating the number of neutrons and valence electrons (those that occupy the outermost shell of the atom).
Steps
Method 1 of 2: Determine the Number of Electrons of an Atom with Neutral Charge
Step 1. Get a periodic table of elements
It is a color-coded table that organizes all the elements known so far according to their atomic structure. Each element is indicated with an abbreviation consisting of one, two or three letters and is listed according to the weight and atomic number.
The periodic table is featured in all chemistry books and online
Step 2. Find the element in question on the periodic table
The elements are sorted by atomic number and separated into three main groups: metals, non-metals and metalloids (semi-metals). They are also grouped into families which include alkali metals, halogens and noble gases. Each column of the periodic table is called a "group" and each row is called a "period".
- If you know the details of the element that you need to study, for example the group or the period to which it belongs, then you will have no difficulty in finding it on the board.
- If you don't have any information on the item in question, then look for it on the board until you locate it.
Step 3. Find the atomic number of the element
This appears in the upper left corner of the item box, above the symbol. The atomic number indicates that of the protons present in the specific element. Protons are the positively charged particles of the atom. Since electrons are negatively charged, the number of electrons in a neutral atom is equal to that of protons.
For example, boron (B) has an atomic number of 5, which means it has 5 protons and 5 electrons
Method 2 of 2: Determine the Number of Positive and Negative Ion Electrons
Step 1. Find the atomic number of the element
You can read it on the periodic table, in the upper left corner of the element box, above its symbol. This value tells you how many protons there are in an atom of the specific element. Protons are positively charged particles. Since electrons are negatively charged, a neutral atom has as many electrons as protons.
For example, boron (B) has an atomic number of 5, so it has 5 protons and 5 electrons
Step 2. Recognize the charge of the ion
When you add or remove electrons from an atom, you don't change its identity, but you charge it. In this case, we speak of an ion as: K.+, Ca2+ or N3-. In general, the charge is expressed with an apex next to the symbol.
- Since electrons are negatively charged, when you add these types of particles you get a negative ion.
- When you remove electrons, the ion becomes positive.
- For example, N3- has a -3 charge while Ca2+ has a +2 positive charge.
Step 3. Subtract from the atomic number the value of the charge, in the case of a positive ion
If you are dealing with a cation, it means that the atom has lost electrons. To figure out how many have been subtracted, you need to calculate the difference between the atomic number and the charge. In this case the atom has more protons than electrons.
Consider the example of Ca2+ which has a +2 charge and therefore has 2 electrons less than a neutral calcium atom. Its atomic number is 20, so this ion has 18 electrons.
Step 4. Add the charge value to the atomic number, in the case of a negative ion
If you are dealing with an anion, then the atom has gained electrons. To understand how many have been added, you need to calculate the sum between the atomic number and the charge value. In this case, the atom has more electrons than protons.
