30 questions · 6 topics
Periodic table FAQ: answers to common questions
Short, accurate answers to the questions people ask most about the periodic table, grouped by topic. Each answer is one short paragraph.
Periodic table basics
Start here: what the table is, what an element is, how many there are and what the table is used for.
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How many elements
There are 118 confirmed elements: how many are natural, man-made, metals or gases, and whether more are coming.
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What elements are
Elements are pure substances made of one kind of atom, defined by their number of protons.
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Purpose of the table
It organizes the elements so their properties can be compared and predicted from position alone.
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The 5 elements
Earth, water, fire, air and aether (or the Chinese and Hindu versions) are ancient ideas, not chemical elements.
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The first element
Hydrogen, atomic number 1, is the first element and the lightest and most abundant in the universe.
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Rows, columns and layout
How periods, groups and families divide the table, and how to read any tile on it.
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What a period is
A period is a horizontal row; there are seven, and the row number is the number of electron shells.
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What a group is
A group is a vertical column; there are 18, and members share valence electrons and chemical behavior.
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How many groups
There are 18 groups in the modern table; older systems counted eight A and eight B groups.
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How many periods
There are 7 periods holding 2, 8, 8, 18, 18, 32 and 32 elements, adding up to 118.
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How it is organized
By atomic number, in periods and groups, with blocks, families and a metal-to-nonmetal diagonal.
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What a family is
A family is a set of elements with similar properties, often but not always one group.
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How to read it
Read each tile's atomic number, symbol and mass, then use its row and column for period and group.
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What the numbers mean
Atomic number, atomic mass, group and period numbers: each number on the table has its own meaning.
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Atoms, numbers and electrons
Atomic number, atomic mass, particles in the atom, valence electrons and ion charges.
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Atomic number
The number of protons in an atom's nucleus: it defines the element and its place in the table.
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Valence electrons
For main-group elements, read the group number: 1 and 2, or the group number minus 10 for groups 13 to 18.
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Finding neutrons
Neutrons = mass number minus atomic number, where mass number is the atomic mass rounded.
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Atomic mass
It is the decimal number in each tile: the average mass of the element's isotopes in atomic mass units.
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Atomic symbol
A one- or two-letter abbreviation for an element, some from Latin names such as Na, K, Fe and Au.
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Properties and trends
Where metals and nonmetals sit, which elements are gases, and how reactivity and electronegativity change across the table.
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Where metals are
Metals fill the left and center of the table, to the lower left of the stair-step line.
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Where metalloids are
Metalloids lie along the diagonal staircase between metals and nonmetals, from boron to tellurium.
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Where nonmetals are
Nonmetals fill the upper right of the table, to the right of the staircase line, plus hydrogen at the top left.
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How many metals
About 92 of the 118 elements are metals, though the exact count depends on how borderline elements are classed.
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Most unreactive group
Group 18, the noble gases, because their outer shells are full.
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Most dangerous element
There is no single answer, but polonium, plutonium, fluorine, mercury and arsenic are leading candidates.
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History, names and symbols
Who built the table, why it is called periodic, and where element symbols and names come from.
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Who invented it
Dmitri Mendeleev published the first accepted table in 1869, building on earlier work by others.
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Why it is called periodic
Because element properties repeat at regular intervals when listed by atomic number.
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The chemistry chart
The chart of all the elements is called the periodic table, or the periodic chart.
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Study tips and curiosities
Ways to memorize the table, record-setting elements, and a few popular questions that are not about chemistry alone.
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What is 67
Element 67 is holmium (Ho); the slang '67' is a separate 2025 meme.
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How to memorize it
Chunk it by group, use mnemonics, songs, flashcards and quizzes, and learn patterns before names.
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Is water on the table
No: water is a compound of hydrogen and oxygen, and the table lists only elements.
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