This free online atomic element lookup instantly gives you the atomic number, atomic mass, category, period, and group for any of the 118 known chemical elements. Search by element name, chemical symbol, or atomic number.
How to Use the Atomic Element Lookup
Type an element's full name (e.g. "Iron"), chemical symbol (e.g. "Fe"), or atomic number (e.g. "26") into the search field.
Click "Search" to see the element's atomic number, atomic mass, category, period, and group.
If nothing is found, double-check the spelling or try the symbol or atomic number instead.
What Each Result Tells You
Atomic number: the number of protons in the nucleus. It defines the element: every atom with 6 protons is carbon, whatever else it contains. In a neutral atom it also equals the number of electrons.
Atomic mass: the weighted average mass of the element's naturally occurring isotopes, in unified atomic mass units (u). Chlorine shows 35.45 rather than a whole number because natural chlorine is a mix of chlorine-35 and chlorine-37. Elements with no stable isotopes, such as technetium (98) and every element after uranium, are listed with a whole number: the mass number of a well-known long-lived isotope.
Category: the chemical family, such as alkali metal, halogen or noble gas. Elements in the same family tend to react in similar ways. The colours in the periodic table view follow these categories.
Period and group: the period is the row and tells you how many electron shells the atom has; the group is the column. For main-group elements the group predicts the number of outer (valence) electrons: group 1 elements have one, group 17 elements have seven, and group 18 elements have full outer shells, which is why noble gases are so unreactive.
Using Atomic Mass to Find Molar Mass
The atomic mass in u is numerically the same as the molar mass in grams per mole. To find the molar mass of a compound, look up each element, multiply its atomic mass by the number of atoms of that element in the formula, and add the results.
Example, water (H₂O): hydrogen is 1.008 and oxygen is 15.999, so the molar mass is 2 × 1.008 + 15.999 = 18.015 g/mol. That means 18 g of water is very close to one mole, about 6.022 × 10²³ molecules. Hydrogen makes up 2.016 ÷ 18.015, or about 11.2%, of water by mass.
Compound
Working
Molar mass (g/mol)
Common salt, NaCl
22.990 + 35.45
58.44
Carbon dioxide, CO₂
12.011 + 2 × 15.999
44.009
Calcium carbonate (limestone, chalk), CaCO₃
40.078 + 12.011 + 3 × 15.999
100.086
Glucose, C₆H₁₂O₆
6 × 12.011 + 12 × 1.008 + 6 × 15.999
180.156
Board exams and textbooks often use rounded values such as H = 1, C = 12, O = 16, Na = 23 and Cl = 35.5. Use whichever values your syllabus or question paper specifies, as answers can differ slightly in the decimals.
Symbols That Do Not Match the English Name
Most symbols are taken from the English name (O for oxygen, Ca for calcium), but a handful come from Latin or German names. These are the ones students most often get wrong:
Symbol
Element
Origin of the symbol
Na
Sodium (11)
Latin natrium
K
Potassium (19)
Latin kalium
Fe
Iron (26)
Latin ferrum
Cu
Copper (29)
Latin cuprum
Ag
Silver (47)
Latin argentum
Sn
Tin (50)
Latin stannum
Sb
Antimony (51)
Latin stibium
W
Tungsten (74)
German wolfram
Au
Gold (79)
Latin aurum
Hg
Mercury (80)
Latinised Greek hydrargyrum, meaning liquid silver
Pb
Lead (82)
Latin plumbum
Search Tips
Searches ignore capital letters, so "fe", "FE" and "Fe" all find iron. A symbol must be typed in full, though: "F" finds fluorine, not iron.
Names follow IUPAC spelling: Aluminium, Sulfur and Caesium. The common alternatives "sulphur" (used in many Indian textbooks), "aluminum" and "cesium" are also accepted.
Typing a number looks up the element by atomic number, so 79 returns gold. Numbers above 118 return no result because no heavier element has been confirmed.
Hydrogen is placed in group 1 because it has one outer electron, but it is a nonmetal and does not behave like the alkali metals below it.
Frequently Asked Questions
All 118 currently known chemical elements, from Hydrogen (atomic number 1) to Oganesson (atomic number 118).
Atomic mass (or standard atomic weight) is the average mass of an element's atoms, measured in atomic mass units (u). For very heavy, unstable synthetic elements, the mass number of the most stable known isotope is shown instead.
Period is the element's row in the periodic table (1-7), and group is its column (1-18). Lanthanides and actinides are shown with no group number, since they sit outside the standard 18-column layout.
The atomic number counts only protons and is the same for every atom of an element. The mass number counts protons plus neutrons in one particular isotope, so it varies: carbon-12 and carbon-14 both have atomic number 6 but mass numbers 12 and 14. The atomic mass shown by this tool is an average over the natural isotopes, which is why it is usually not a whole number.
They are standard atomic weights rounded to about four or five significant figures, which is more than enough for school, college and most laboratory calculations. The official values are published by IUPAC and a few are revised from time to time. For some elements, such as hydrogen, carbon and oxygen, the true value varies slightly depending on where the sample comes from, so a single conventional figure is shown.