If the periodic table of the elements seems like a big headache, know that you are not alone in having this problem! Understanding how it works can be difficult, but learning to read it will help you tremendously in science subjects. To begin, look at its structure and the information it gives about the chemical elements, then move on to study each element; finally, it uses the information provided by the table to calculate the number of neutrons in an atom.
Steps
Part 1 of 3: Understanding the Structure of the Periodic Table
Step 1. Read the periodic table starting from the upper left corner and moving towards the lower right corner
The chemical elements are sorted by their atomic number, which increases as you move right and down the table. The atomic number is the number of protons contained in the single atom of an element. You will notice that the atomic weight also increases progressively: this is because the mass of an atom is given by its protons and neutrons, consequently as the number of protons increases, the mass also increases. You can therefore understand a lot of the weight of an element simply by looking at its position on the table.
- Keep in mind that the atomic weight is not expressed in grams, but indicates how many times the mass of an atom is greater than the "atomic mass unit", a reference quantity that corresponds to the twelfth part of the mass of carbon-12.
- Electrons are not included in the atomic weight since they contribute negligibly to the mass of atoms compared to protons and neutrons.
Step 2. Notice how each element has one more proton than the previous one
You can understand this by looking at the atomic number, which as mentioned increases going to the right. However, since the elements are also divided into groups, you will see some discontinuities in the table.
For example, the first line contains hydrogen, whose atomic number is 1, and helium, whose atomic number is 2; however, they are at opposite ends of the table, as they are in different groups
Step 3. Learn to recognize groups of elements
A group, also called a "family", is made up of the elements that share the same column in the periodic table; these have certain physical and chemical properties in common and are generally distinguished by a color. Knowing which elements have similar properties allows you to predict how they will behave. All elements of a certain group have the same number of electrons in the outer orbital of the atom.
- Each element belongs to only one group, with the exception of hydrogen, which is part of both the halogen and alkaline families; in some plates it appears in both.
- In most cases, the columns are numbered from 1 to 18, in Arabic numerals. Numbers can appear along the top or bottom edge of the board. Depending on the convention used, however, the groups may be marked with Roman numerals accompanied by the letters A and B (e.g. IA, IIIB, etc.). The letters differentiate the left part of the table from the right (old IUPAC numbering) or the main elements from the transitional ones (CAS numbering, more used in the United States).
- When you scroll a column of the table from top to bottom, you are "reading a group".
Step 4. Understand why there are gaps in the board
Since the elements are ordered by increasing atomic number, but also vertically according to the group they belong to, not everyone can re-enter a group and progressively increase their number of protons in perfect sequence. It may therefore appear that the table has gaps.
- For example, the first three lines have gaps, because transition metals do not appear on the table until atomic number 21.
- Similarly, elements 57 to 71 (ie the lanthanoids, or rare earths) and 89 to 103 (actinoids) are usually represented in a separate section under the main table.
Step 5. Remember that each row corresponds to a "period"
All the elements of a period have the same number of atomic orbitals, where the electrons are; the number of orbitals corresponds to the period number. In the table there are 7 lines, so 7 periods.
- For example, the elements of the first period have only one orbital, while those of the seventh period have 7.
- In most cases, the periods are numbered 1 to 7 on the left side of the table.
- When you scroll a line from left to right, you are "reading a period".
Step 6. Understand the further distinction in metals, semi-metals and non-metals
It is easier to understand the properties of a chemical element when you know what type of element it is. Most periodic tables specify whether the element is a metal, a semimetal or a non-metal by a different color or other indication. Metals are on the left side of the table, non-metals on the right; the semimetals are sandwiched between these two.
- Keep in mind that hydrogen can be both halogens and alkali metals due to its properties, so it can appear on both sides of the board or be colored differently.
- The elements that have luster, are solid at room temperature, conduct heat and electricity, are malleable and ductile are classified as metals.
- On the other hand, non-metals are considered to be those that lack luster, do not conduct heat or electricity and are not malleable. They are usually found in a gaseous state at room temperature, but they can also become solid or liquid at certain temperatures.
- Finally, elements that have properties typical of both metals and non-metals are classified as semimetals.
Part 2 of 3: Studying the Chemical Elements
Step 1. Learn the symbols of the elements
Each element is identified with a one or two letter symbol, which most often appears large in the center of the box. The symbol abbreviates the element name and is internationally standardized. Element symbols are typically used when experimenting or working with chemical equations, so it's important to learn to recognize them.
The symbols derive largely from the Latin or Greek name, so sometimes the association with the Italian term is not immediate. For example, the symbol of iron is Fe (from the Latin ferrum) and is easily recognizable, while that of potassium is K (from the Latin kalium) and can be more difficult to remember
Step 2. Look for the full names of the items, if any
The more detailed periodic tables also indicate the name of the element (in the language of the country of distribution), for example "helium" or "carbon". This is the name to use when writing the item in full. In most cases it is located just below the symbol, but the location can vary.
Some tables omit the full names, reporting only the symbols
Step 3. Find the atomic number
It is often placed at the top of the box, in the center or in the corner, but it could also be under the symbol or item name. The atomic numbers go in sequence from 1 to 118.
The atomic number is always an integer, not a decimal
Step 4. Remember that the atomic number is the number of protons in an atom
All atoms of an element have the same number of protons. Unlike electrons, an atom cannot acquire or lose protons - otherwise the element would change!
You will need the atomic number to calculate the amount of electrons and neutrons present in the atom of a certain element
Step 5. Keep in mind that the atoms of the elements contain electrons and protons in equal numbers
Protons have a positive charge, while electrons have a negative charge; since normal (neutral) atoms do not have an electric charge, electrons and protons are in equal quantities. Ionized atoms are an exception to the rule: an atom can lose or gain electrons, thus becoming an ion.
- Ions have an electrical charge: they are positive if they contain more protons than electrons (which is indicated by the + sign next to the symbol); they are negative if they have more electrons instead (it is indicated with the sign -).
- If the element is not an ion, the + or - sign will not appear next to the symbol.
Part 3 of 3: Using the Atomic Weight to Calculate the Number of Neutrons
Step 1. Find the atomic weight
It usually appears at the bottom of the box, under the element symbol. In general, the atomic weight (or "relative atomic mass") is determined by the totality of the particles that make up the nucleus and in which the mass of the atom is concentrated, ie protons and neutrons. However, the elements are normally made up of several isotopes, i.e. atoms with a different number of neutrons and therefore with a different mass. Consequently, the atomic weight that appears on the periodic table is actually a weighted average of all possible atomic masses of that element.
- Being an average, it is usually a decimal number.
- While the atomic weight tends to increase as you go right and down along the table, this is not always true.
Step 2. Determine the mass number of the element you are studying
The mass number corresponds to the sum of the protons and neutrons contained in an atom. You can find this by rounding the atomic weight to the nearest whole number.
For example, the atomic weight of carbon is 12,011, which is usually rounded to 12. Similarly, the atomic weight of iron is 55,847, rounded to 56
Step 3. Subtract the atomic number from the mass number to get the number of neutrons
Since the mass number is the sum of protons and neutrons, you can easily calculate how many neutrons are present in an atom by subtracting the protons (i.e. the atomic number) from the mass number.
- Use the following formula: Neutrons = Mass number - Protons.
- For example, carbon has 6 protons and its mass number is 12; since 12 - 6 = 6, it follows that carbon has 6 neutrons.
- To give another example: iron has 26 protons and its mass number is 56; since 56 - 26 = 30, you can deduce that iron has 30 neutrons.
- Don't forget that a given isotope can contain a different number of neutrons and will therefore have a different mass number. For example, the mass number of carbon-14 is not 12 but, in fact, 14. However, the formula does not change.
Advice
- Reading the periodic table is difficult for many people! Don't feel embarrassed if you have a hard time learning how to use it.
- Colors may vary by table, but the information is the same.
- Some periodic tables provide simplified information (for example, they may indicate only the symbol and the atomic number). Look for a board that meets your needs.
