The periodic table looks like a wall of boxes, but it is really a map. Each box is one element, and its position tells you how that element behaves. Elements in the same column share outer electrons, so they react in similar ways. The table is ordered by atomic number, the count of protons, and that single number explains why iron sits with the transition metals while chlorine sits with the halogens. This lookup tool lets you jump straight to any of the 118 elements without hunting through the grid.
Type a symbol, a name, or an atomic number. Iron, Fe, and 26 all lead to the same box: atomic number 26, atomic mass about 55.845, group transition metal. The symbol is the fastest route, because symbols are unique. Names can trip you up: aluminium is spelled aluminum in the United States, and caesium is spelled cesium. Numbers never have that problem, which is why teachers often ask for the atomic number first and the name second.
Atomic number and atomic mass answer different questions. The atomic number counts protons, and it never changes for an element. The atomic mass is an average of the masses of its isotopes, weighted by how common each isotope is, which is why it is usually not a whole number. Chlorine is about 35.45 because most chlorine is mass 35 with a good share of mass 37. For formula maths, use the mass the tool shows, and keep two or three decimal places at most.
Groups are the shortcut to chemistry. Alkali metals in the first column react strongly with water. Halogens in the second-to-last column are eager to gain an electron. Noble gases in the last column barely react at all, because their outer shells are full. Transition metals in the middle block form coloured compounds and often work as catalysts. When you meet a new element, its group gives you a first guess about its behaviour before you read anything else.
A worked example shows the habit to build. Suppose a question asks about bromine. Look up Br: atomic number 35, mass about 79.904, group halogen. From the group you predict it forms salts like chlorine and iodine, and from the mass you can use it in formula calculations. Now look up potassium, K, atomic number 19, alkali metal. Pairing a halogen with an alkali metal is the classic salt-forming combination, and potassium bromide is exactly the kind of compound that pattern predicts.
Two common mistakes are worth naming. The first is mixing up atomic number and mass number: the number of protons is fixed, while the mass number of one isotope is a whole number that changes between isotopes. The second is reading the symbol wrong: Co is cobalt, while CO is carbon monoxide, a compound of two elements. Case matters in symbols, and this tool matches symbols exactly as written, so Fe works and FE does not pretend to be the same thing.
Use this lookup as a study aid, not as a lab authority. It is an educational practice tool, and its masses are standard average values for homework and revision. Real lab work uses a current reference and the safety data sheet for each chemical, and no lookup replaces those. When a value matters for a real measurement, check it against a second source, and when a chemical is hazardous, follow your supervisor and your safety rules first.
Trends across the table turn lookup into prediction. Atomic size shrinks as you move left to right across a period, because the growing nuclear charge pulls the same shell closer, and it grows as you move down a group, because each row adds a new shell. Reactivity follows the same logic in reverse for metals and nonmetals: metals on the left lose electrons more easily as you go down, while nonmetals on the right gain them more eagerly as you go up. Electronegativity, the pull an atom has on shared electrons, rises toward fluorine at the top right. When you look an element up, note its neighbours too, because the trend between neighbours often answers a question faster than any single value.