Interactive Periodic Table: Element Inspector

Hover or click any element to instantly inspect its full technical data. Search by name, symbol, or atomic number. Filter by category. 100% client-side, no data sent anywhere.

Filter by category:

Hover or click any element tile to inspect its data

Alkali Metal
Alkaline Earth
Transition Metal
Post-Transition
Metalloid
Nonmetal
Halogen
Noble Gas
Lanthanide
Actinide
Unknown
Key Terms Explained
Atomic Number
The count of protons in an atom's nucleus. This number uniquely identifies every element and never changes for a given element.
Atomic Mass
The weighted average mass of all naturally occurring isotopes of an element, expressed in atomic mass units (u). It is almost never a whole number.
Isotope
Atoms of the same element that have the same number of protons but different numbers of neutrons, giving them different masses but nearly identical chemical behavior.
Electron Configuration
A notation describing how electrons are distributed across an atom's orbitals. Example: Sodium is 1s2 2s2 2p6 3s1, meaning 1 electron in the outer s-orbital.
Valence Electrons
Electrons in the outermost energy shell. These are the only electrons available for bonding. The number of valence electrons determines an element's reactivity and bonding patterns.
Halogen
Group 17 elements (fluorine, chlorine, bromine, iodine, astatine). They have 7 valence electrons and are highly reactive nonmetals that readily form salts when combined with metals.
Noble Gas
Group 18 elements with a full outer electron shell. Because they are already stable, they rarely form compounds and exist as single atoms in nature at standard conditions.
Transition Metal
d-block elements in Groups 3-12. They are characterized by variable oxidation states, the ability to form colored compounds, and often serve as catalysts in industrial chemistry.
Electronegativity
A measure of how strongly an atom attracts electrons in a chemical bond. Fluorine has the highest electronegativity (4.0). Electronegativity generally increases across a period and decreases down a group.
Alkali Metal
Group 1 elements (except hydrogen). They have one valence electron, are very soft, shiny metals with low melting points, and react violently with water to produce hydrogen gas and a strong base.

The Complete Guide to the Periodic Table

The periodic table is the single most powerful reference tool in all of chemistry. Understanding its structure, patterns, and organization unlocks the ability to predict how elements behave and react before ever running an experiment. This guide covers everything from the basic layout to the quantum mechanics behind why the table is shaped the way it is.

How to Use This Tool

Type any element name (e.g., "calcium"), symbol (e.g., "Ca"), or atomic number (e.g., "20") into the search bar to instantly highlight matching elements and dim everything else. Click a category filter button to highlight all elements in that group. Hover over or click any element tile to populate the Inspector Panel on the left with its full technical profile: atomic mass, electron configuration, block, period, group, and standard state. The physical table structure is always preserved, so spatial relationships remain visible even when filtering.

Why the Table Has Its Shape

Dmitri Mendeleev arranged the first periodic table in 1869 by atomic mass and noticed that chemical properties repeated in a periodic pattern. The modern table is arranged by atomic number instead, which eliminated the anomalies in Mendeleev's version. The shape of the table directly reflects quantum mechanics: the s-block (Groups 1-2 and 18 for helium) fills s-orbitals; the p-block (Groups 13-18) fills p-orbitals; the d-block (Groups 3-12) fills d-orbitals; and the f-block (Lanthanides and Actinides) fills f-orbitals. Each block corresponds to a type of orbital being filled as electrons are added.

Reading Trends Across the Table

Several key properties change predictably as you move across or down the table. Atomic radius generally decreases left to right across a period (more protons pull electrons in tighter) and increases top to bottom down a group (each new period adds an electron shell). Ionization energy - the energy needed to remove an electron - generally increases left to right. Electronegativity increases left to right and decreases top to bottom. Metals sit to the left, nonmetals to the right, and metalloids form a staircase-like boundary between them.

The Lanthanide and Actinide Series

Elements 57-71 (Lanthanides) and 89-103 (Actinides) technically belong in Periods 6 and 7 between Groups 2 and 3. They are shown in a separate block below the main table only for space reasons. All Lanthanides are shiny, silvery metals with very similar chemical properties to each other because their 4f electrons are shielded from chemical interactions by outer shells. Actinides are all radioactive; only thorium and uranium occur in meaningful natural quantities. Elements beyond uranium (atomic number 92) are all synthetic and increasingly unstable.

Electron Shell Capacity Guide: The 2n2 Rule

Every electron shell has a maximum number of electrons it can hold, determined by the formula 2n2, where n is the shell number. This is one of the most tested concepts in introductory chemistry.

Shell (n) Name Max Electrons (2n2) Subshells Example Element that fills this shell
1 K shell 2 electrons 1s Helium (2 total)
2 L shell 8 electrons 2s, 2p Neon (10 total)
3 M shell 18 electrons 3s, 3p, 3d Argon fills 3s and 3p (18 total); 3d fills later
4 N shell 32 electrons 4s, 4p, 4d, 4f Krypton fills through 4p (36 total)
5 O shell 50 electrons 5s, 5p, 5d, 5f, 5g* Xenon fills through 5p (54 total)
6 P shell 72 electrons 6s, 6p, 6d, 6f* Radon fills through 6p (86 total)
7 Q shell 98 electrons 7s, 7p, 7d* Oganesson fills through 7p (118 total)

* Subshells marked with an asterisk exist theoretically but are not filled by any currently known element. Important note: in practice, the order electrons fill subshells does not follow simple shell order. The 4s subshell fills before 3d, and 6s fills before 4f. The 2n2 rule describes the theoretical maximum capacity of each shell, not the order of filling. Use the Aufbau principle, Hund's rule, and the Pauli exclusion principle for filling order.

Frequently Asked Questions

The periodic table is arranged in 18 vertical columns called groups (or families) and 7 horizontal rows called periods. Elements in the same group share the same number of valence electrons, giving them similar chemical properties. For example, all elements in Group 1 (the alkali metals) have one valence electron and react vigorously with water. Elements in the same period share the same highest electron shell being filled. As you move left to right across a period, the atomic number increases by one each step, the atomic radius generally shrinks, and electronegativity generally increases.
Valence electrons are the electrons in the outermost energy shell of an atom. They are the only electrons involved in chemical bonding, reactions, and the formation of ions. The number of valence electrons determines how an element behaves: elements with 1 valence electron (like sodium) tend to lose it easily and form +1 ions; elements with 7 valence electrons (like chlorine) tend to gain one electron and form -1 ions; elements with 8 valence electrons (like neon) are already stable and rarely react. Understanding valence electrons is the single most important concept for predicting how elements combine to form compounds.
Noble gases (helium, neon, argon, krypton, xenon, and radon) are unreactive because their outermost electron shell is completely full. Helium has 2 electrons filling its first shell; all others have 8 electrons filling their outermost shell. This full-shell configuration, sometimes called an octet, represents a state of maximum stability. There is no energetic incentive for a noble gas to gain, lose, or share electrons with another atom, so they exist almost entirely as single atoms in nature. Under extreme conditions, heavier noble gases like xenon and krypton can be forced to form compounds, but this is rare.
The atomic number is the number of protons in the nucleus of an atom. It is a whole number that uniquely identifies an element: carbon always has 6 protons, oxygen always has 8. Atomic mass (also called atomic weight) is the weighted average mass of all naturally occurring isotopes of that element, expressed in atomic mass units (u or Da). Because isotopes have different numbers of neutrons, the atomic mass is almost never a whole number. For example, chlorine has an atomic number of 17 but an atomic mass of approximately 35.45 because it is a mixture of about 75% chlorine-35 and 25% chlorine-37 in nature.
The Lanthanides (elements 57-71) and Actinides (elements 89-103) are placed in a separate block at the bottom purely for practical layout reasons. They belong to Period 6 and Period 7 respectively, and technically should be inserted between Group 2 and Group 3. However, including them inline would make the table 32 columns wide, which is unwieldy to print or display. Because these elements fill the f-subshell (the f-block) and have very similar chemical properties to each other within each series, separating them causes minimal confusion while making the table far more compact and readable.
This tool is for educational reference only. Atomic mass values are IUPAC 2021 standard atomic weights. All calculations and data are processed entirely in your browser.