It’s important to know how to use a periodic table. The periodic table organizes the elements in a way that allows you to predict element properties and chemical reactions, even if you don’t know anything about an element except what you see on the table. Here’s a look at the information you can find on a standard periodic table of the elements and how to use these facts:
Periodic Table Organization
- Elements are listed in order of increasing atomic number. (Note Mendeleev’s original table organized element by order of increasing atomic weight.)
- Elements are grouped according to periodic properties or trends. On a colored periodic table, the element groups usually are different colors from each other. The main element groups are: alkali metals, alkaline earth metals, transition metals, basic metals, rare earth metals (lanthanides and actinides), metalloids (semimetals), nonmetals, halogens, and noble gases.
- A row of the periodic table is called an element period. A period indicates the highest energy level occupied by the electrons of that element at its ground state.
- A column of the periodic table is called an element group. Members of an element group have the same number of valence electrons.
- The two rows separated from the main body of the table are the rare earth elements, which consist of the lanthanides and actinides. These elements may be considered special transition metals.
How to Read an Element Cell
- The one- or two-letter symbol is the element’s symbol. Usually, the symbol includes the first letter of an element’s name, although there are some exceptions. For example, H is the element symbol for hydrogen. Br is the element symbol for bromine. Yet, Hg is the symbol for mercury. Element symbols are recognized and used internationally, even though countries may use different names for elements.
- Some periodic tables list each element’s full name.
- The integer number is the element atomic number. This is the number of protons in each atom of that element. For example, each bromine atom has 35 protons. Atoms of different elements may have the same number of electrons and neutrons, but never the same number of protons.
- The decimal number is the element’s atomic weight. The atomic weight is a weighted average of the mass of the isotopes of that element. Atomic weight is given in atomic mass units (amu). You can also consider the number as the grams per mole of each element. For example, one mole of bromine atoms would have a mass of 79.904 grams.
How to Use a Periodic Table to See Periodic Table Trends
The table is organized to display trends or periodicity of element properties:
Atomic Radius: one-half the distance between the nuclei of two atoms that are just touching each other.
Ionization Energy: energy needed to completely remove an electron from an atom or ion in the gas phase.
Electron Affinity: measure of an atom’s ability to accept an electron.
Electronegativity: measure of an atom’s ability to form a chemical bond
Summary of Periodic Table Trends
Moving Left → Right Across a Row of the Periodic Table
- Atomic Radius Decreases
- Ionization Energy Increases
- Electron Affinity Generally Increases (except Noble Gas Electron Affinity Near Zero)
- Electronegativity Increases
Moving Top → Bottom Down a Column of the Periodic Table
- Atomic Radius Increases
- Ionization Energy Decreases
- Electron Affinity Generally Decreases
- Electronegativity Decreases