Science & Chemistry

Periodic Table Chart

Compare all 118 chemical elements by atomic number, symbol, period, group, block, family, and standard atomic-weight notation; then use periodic patterns to connect position with electron structure and chemical behavior.

Periodic-table layouts and educational category colors can differ. Atomic number, element name, symbol, and IUPAC group numbering are standardized; some classification boundaries and Group 3/f-block display conventions vary by table.

Periodic Table Chart showing all 118 elements, groups, periods, blocks, families, atomic numbers, and broad periodic trends

How the periodic table works

The IUPAC periodic table recognizes 118 elements and uses group numbers 1 through 18. The modern table is arranged by increasing atomic number, which equals the number of protons in an atom's nucleus.

Elements in the same group often share related valence-electron patterns. Elements in the same period occupy the same broad principal-shell level as the row develops. These repeating electron-structure patterns are why chemical properties recur periodically.

Atomic number defines the element. Atomic weight does not. Isotopes of one element share the same proton number but differ in neutron number, so natural isotopic composition can make standard atomic weight a measured average or interval rather than an integer.

Recognized elements

118

Hydrogen is atomic number 1 and oganesson is atomic number 118.

Long-form structure

18 groups · 7 periods

Groups are vertical columns; periods are horizontal rows.

Primary ordering

Atomic number

The modern periodic table is ordered by proton number, not atomic weight.

Atomic weights

Not always one fixed number

Natural isotope variation and radioactivity affect how atomic-weight information is reported.

Periodic Table of All 118 Elements

All recognized elements in atomic-number order. Atomic weights use the CIAAW abridged standard values where available; an em dash means no standard atomic weight is assigned.

Swipe horizontally inside the table to view every column.

All recognized elements in atomic-number order. Atomic weights use the CIAAW abridged standard values where available; an em dash means no standard atomic weight is assigned.
Atomic no.	Symbol	Element	Period	Group	Block / series	Family	Abridged standard atomic weight
1	H	Hydrogen	1	1	s	Nonmetal	1.0080 ± 0.0002
2	He	Helium	1	18	s	Noble gas	4.0026 ± 0.0001
3	Li	Lithium	2	1	s	Alkali metal	6.94 ± 0.06
4	Be	Beryllium	2	2	s	Alkaline-earth metal	9.0122 ± 0.0001
5	B	Boron	2	13	p	Group 13	10.81 ± 0.02
6	C	Carbon	2	14	p	Group 14	12.011 ± 0.002
7	N	Nitrogen	2	15	p	Group 15	14.007 ± 0.001
8	O	Oxygen	2	16	p	Chalcogen	15.999 ± 0.001
9	F	Fluorine	2	17	p	Halogen	18.998 ± 0.001
10	Ne	Neon	2	18	p	Noble gas	20.180 ± 0.001
11	Na	Sodium	3	1	s	Alkali metal	22.990 ± 0.001
12	Mg	Magnesium	3	2	s	Alkaline-earth metal	24.305 ± 0.002
13	Al	Aluminium	3	13	p	Group 13	26.982 ± 0.001
14	Si	Silicon	3	14	p	Group 14	28.085 ± 0.001
15	P	Phosphorus	3	15	p	Group 15	30.974 ± 0.001
16	S	Sulfur	3	16	p	Chalcogen	32.06 ± 0.02
17	Cl	Chlorine	3	17	p	Halogen	35.45 ± 0.01
18	Ar	Argon	3	18	p	Noble gas	39.95 ± 0.16
19	K	Potassium	4	1	s	Alkali metal	39.098 ± 0.001
20	Ca	Calcium	4	2	s	Alkaline-earth metal	40.078 ± 0.004
21	Sc	Scandium	4	3	d	Transition metal	44.956 ± 0.001
22	Ti	Titanium	4	4	d	Transition metal	47.867 ± 0.001
23	V	Vanadium	4	5	d	Transition metal	50.942 ± 0.001
24	Cr	Chromium	4	6	d	Transition metal	51.996 ± 0.001
25	Mn	Manganese	4	7	d	Transition metal	54.938 ± 0.001
26	Fe	Iron	4	8	d	Transition metal	55.845 ± 0.002
27	Co	Cobalt	4	9	d	Transition metal	58.933 ± 0.001
28	Ni	Nickel	4	10	d	Transition metal	58.693 ± 0.001
29	Cu	Copper	4	11	d	Transition metal	63.546 ± 0.003
30	Zn	Zinc	4	12	d	Group 12	65.38 ± 0.02
31	Ga	Gallium	4	13	p	Group 13	69.723 ± 0.001
32	Ge	Germanium	4	14	p	Group 14	72.630 ± 0.008
33	As	Arsenic	4	15	p	Group 15	74.922 ± 0.001
34	Se	Selenium	4	16	p	Chalcogen	78.971 ± 0.008
35	Br	Bromine	4	17	p	Halogen	79.904 ± 0.003
36	Kr	Krypton	4	18	p	Noble gas	83.798 ± 0.002
37	Rb	Rubidium	5	1	s	Alkali metal	85.468 ± 0.001
38	Sr	Strontium	5	2	s	Alkaline-earth metal	87.62 ± 0.01
39	Y	Yttrium	5	3	d	Transition metal	88.906 ± 0.001
40	Zr	Zirconium	5	4	d	Transition metal	91.222 ± 0.003
41	Nb	Niobium	5	5	d	Transition metal	92.906 ± 0.001
42	Mo	Molybdenum	5	6	d	Transition metal	95.95 ± 0.01
43	Tc	Technetium	5	7	d	Transition metal	—
44	Ru	Ruthenium	5	8	d	Transition metal	101.07 ± 0.02
45	Rh	Rhodium	5	9	d	Transition metal	102.91 ± 0.01
46	Pd	Palladium	5	10	d	Transition metal	106.42 ± 0.01
47	Ag	Silver	5	11	d	Transition metal	107.87 ± 0.01
48	Cd	Cadmium	5	12	d	Group 12	112.41 ± 0.01
49	In	Indium	5	13	p	Group 13	114.82 ± 0.01
50	Sn	Tin	5	14	p	Group 14	118.71 ± 0.01
51	Sb	Antimony	5	15	p	Group 15	121.76 ± 0.01
52	Te	Tellurium	5	16	p	Chalcogen	127.60 ± 0.03
53	I	Iodine	5	17	p	Halogen	126.90 ± 0.01
54	Xe	Xenon	5	18	p	Noble gas	131.29 ± 0.01
55	Cs	Caesium	6	1	s	Alkali metal	132.91 ± 0.01
56	Ba	Barium	6	2	s	Alkaline-earth metal	137.33 ± 0.01
57	La	Lanthanum	6	—	f series	Lanthanoid	138.91 ± 0.01
58	Ce	Cerium	6	—	f series	Lanthanoid	140.12 ± 0.01
59	Pr	Praseodymium	6	—	f series	Lanthanoid	140.91 ± 0.01
60	Nd	Neodymium	6	—	f series	Lanthanoid	144.24 ± 0.01
61	Pm	Promethium	6	—	f series	Lanthanoid	—
62	Sm	Samarium	6	—	f series	Lanthanoid	150.36 ± 0.02
63	Eu	Europium	6	—	f series	Lanthanoid	151.96 ± 0.01
64	Gd	Gadolinium	6	—	f series	Lanthanoid	157.25 ± 0.01
65	Tb	Terbium	6	—	f series	Lanthanoid	158.93 ± 0.01
66	Dy	Dysprosium	6	—	f series	Lanthanoid	162.50 ± 0.01
67	Ho	Holmium	6	—	f series	Lanthanoid	164.93 ± 0.01
68	Er	Erbium	6	—	f series	Lanthanoid	167.26 ± 0.01
69	Tm	Thulium	6	—	f series	Lanthanoid	168.93 ± 0.01
70	Yb	Ytterbium	6	—	f series	Lanthanoid	173.05 ± 0.02
71	Lu	Lutetium	6	—	f series	Lanthanoid	174.97 ± 0.01
72	Hf	Hafnium	6	4	d	Transition metal	178.49 ± 0.01
73	Ta	Tantalum	6	5	d	Transition metal	180.95 ± 0.01
74	W	Tungsten	6	6	d	Transition metal	183.84 ± 0.01
75	Re	Rhenium	6	7	d	Transition metal	186.21 ± 0.01
76	Os	Osmium	6	8	d	Transition metal	190.23 ± 0.03
77	Ir	Iridium	6	9	d	Transition metal	192.22 ± 0.01
78	Pt	Platinum	6	10	d	Transition metal	195.08 ± 0.02
79	Au	Gold	6	11	d	Transition metal	196.97 ± 0.01
80	Hg	Mercury	6	12	d	Group 12	200.59 ± 0.01
81	Tl	Thallium	6	13	p	Group 13	204.38 ± 0.01
82	Pb	Lead	6	14	p	Group 14	207.2 ± 1.1
83	Bi	Bismuth	6	15	p	Group 15	208.98 ± 0.01
84	Po	Polonium	6	16	p	Chalcogen	—
85	At	Astatine	6	17	p	Halogen	—
86	Rn	Radon	6	18	p	Noble gas	—
87	Fr	Francium	7	1	s	Alkali metal	—
88	Ra	Radium	7	2	s	Alkaline-earth metal	—
89	Ac	Actinium	7	—	f series	Actinoid	—
90	Th	Thorium	7	—	f series	Actinoid	232.04 ± 0.01
91	Pa	Protactinium	7	—	f series	Actinoid	231.04 ± 0.01
92	U	Uranium	7	—	f series	Actinoid	238.03 ± 0.01
93	Np	Neptunium	7	—	f series	Actinoid	—
94	Pu	Plutonium	7	—	f series	Actinoid	—
95	Am	Americium	7	—	f series	Actinoid	—
96	Cm	Curium	7	—	f series	Actinoid	—
97	Bk	Berkelium	7	—	f series	Actinoid	—
98	Cf	Californium	7	—	f series	Actinoid	—
99	Es	Einsteinium	7	—	f series	Actinoid	—
100	Fm	Fermium	7	—	f series	Actinoid	—
101	Md	Mendelevium	7	—	f series	Actinoid	—
102	No	Nobelium	7	—	f series	Actinoid	—
103	Lr	Lawrencium	7	—	f series	Actinoid	—
104	Rf	Rutherfordium	7	4	d	Transactinide	—
105	Db	Dubnium	7	5	d	Transactinide	—
106	Sg	Seaborgium	7	6	d	Transactinide	—
107	Bh	Bohrium	7	7	d	Transactinide	—
108	Hs	Hassium	7	8	d	Transactinide	—
109	Mt	Meitnerium	7	9	d	Transactinide	—
110	Ds	Darmstadtium	7	10	d	Transactinide	—
111	Rg	Roentgenium	7	11	d	Transactinide	—
112	Cn	Copernicium	7	12	d	Transactinide	—
113	Nh	Nihonium	7	13	p	Transactinide	—
114	Fl	Flerovium	7	14	p	Transactinide	—
115	Mc	Moscovium	7	15	p	Transactinide	—
116	Lv	Livermorium	7	16	p	Transactinide	—
117	Ts	Tennessine	7	17	p	Transactinide	—
118	Og	Oganesson	7	18	p	Transactinide	—

Atomic number is dimensionless. Standard atomic weight is a relative quantity; displayed uncertainties follow the CIAAW abridged table.

• Lanthanoids and actinoids are shown as detached f-series entries here rather than forcing one Group 3 layout convention.
• Family labels are educational summaries; detailed classifications can vary at boundaries and for superheavy elements.

Table sources: International Union of Pure and Applied Chemistry — Periodic Table of Elements; Commission on Isotopic Abundances and Atomic Weights — Abridged Standard Atomic Weights; Royal Society of Chemistry — Periodic Table

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Interactive reference

Periodic Table Element Finder

Enter an atomic number, element symbol, or full element name to retrieve its position and reference data.

Atomic number, symbol, or name

Element

Iron (Fe)

Period

Group

Block / series

Family

Transition metal

Abridged standard atomic weight

55.845 ± 0.002

Atomic number is the table's backbone

Moving one place forward in atomic number adds one proton. Carbon is 6 because every carbon nucleus has six protons; oxygen is 8 because every oxygen nucleus has eight.

Periodic Table Periods Chart

The seven periods are horizontal rows. Period lengths reflect the subshells that become occupied as atomic number increases.

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The seven periods are horizontal rows. Period lengths reflect the subshells that become occupied as atomic number increases.
Period	Element count	Span	Electron-structure idea
1	2	H → He	Only the 1s shell is being filled.
2	8	Li → Ne	2s and 2p subshells fill.
3	8	Na → Ar	3s and 3p subshells fill.
4	18	K → Kr	4s, 3d, then 4p are occupied across the period.
5	18	Rb → Xe	5s, 4d, then 5p are occupied.
6	32	Cs → Rn	Includes the lanthanoid series and 4f filling.
7	32	Fr → Og	Includes the actinoid series and superheavy elements through atomic number 118.

Periods are numbered 1 through 7.

• The detached lanthanoid and actinoid rows belong to periods 6 and 7, not to separate periods.

Table sources: International Union of Pure and Applied Chemistry — Periodic Table of Elements; Royal Society of Chemistry — Periodic Table

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Periodic Table Groups and Families

Groups are vertical columns numbered 1 through 18. Familiar family names emphasize shared chemistry within selected columns.

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Groups are vertical columns numbered 1 through 18. Familiar family names emphasize shared chemistry within selected columns.
Group	Family / region	Examples	Key note
1	Alkali-metal column	H, Li, Na, K, Rb, Cs, Fr	Hydrogen sits in Group 1 but is a nonmetal and chemically distinct from the alkali metals.
2	Alkaline-earth metals	Be, Mg, Ca, Sr, Ba, Ra	Typical main-group metals with two valence electrons.
3	Transition-region convention	Sc, Y; f-block placement varies by table	Group 3 presentation differs among long-form periodic-table conventions.
4	Transition metals	Ti, Zr, Hf, Rf	d-block family.
5	Transition metals	V, Nb, Ta, Db	d-block family.
6	Transition metals	Cr, Mo, W, Sg	d-block family.
7	Transition metals	Mn, Tc, Re, Bh	d-block family.
8	Transition metals	Fe, Ru, Os, Hs	d-block family.
9	Transition metals	Co, Rh, Ir, Mt	d-block family.
10	Transition metals	Ni, Pd, Pt, Ds	d-block family.
11	Coinage-metal column	Cu, Ag, Au, Rg	Group 11 d-block.
12	Group 12	Zn, Cd, Hg, Cn	Often treated separately from the transition-metal definition in strict contexts.
13	Boron group	B, Al, Ga, In, Tl, Nh	p-block.
14	Carbon group	C, Si, Ge, Sn, Pb, Fl	p-block.
15	Pnictogen group	N, P, As, Sb, Bi, Mc	p-block.
16	Chalcogens	O, S, Se, Te, Po, Lv	p-block.
17	Halogens	F, Cl, Br, I, At, Ts	p-block.
18	Noble gases	He, Ne, Ar, Kr, Xe, Rn, Og	Helium is placed in Group 18 although its occupied shell is 1s².

IUPAC group numbers run from 1 to 18.

• Hydrogen is placed in Group 1 but is not an alkali metal.
• Group 3 and detached f-series placement can be drawn differently in long-form tables.

Table sources: International Union of Pure and Applied Chemistry — Periodic Table of Elements; Royal Society of Chemistry — Periodic Table

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s, p, d and f Regions

Blocks organize the table by broad electron-configuration patterns. Detached f-series rows keep the conventional long form compact.

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Blocks organize the table by broad electron-configuration patterns. Detached f-series rows keep the conventional long form compact.
Region	Typical location	Subshell idea	Interpretation
s block	Groups 1–2 plus He	s subshell	Usually 1–2 electrons in the differentiating s subshell.
p block	Groups 13–18 except He	p subshell	Main-group region containing nonmetals, metalloids, and metals.
d block	Groups 3–12 region	d subshell	Transition region; the exact formal definition of transition metal is narrower than simply being in the d block.
f series	Lanthanoids and actinoids	f subshell	Usually displayed as two detached rows to keep the conventional table compact.
Lanthanoid series	La–Lu	4f region	Period 6 inner-transition series in the detached-row convention.
Actinoid series	Ac–Lr	5f region	Period 7 inner-transition series; all actinoids are radioactive.

Block labels are structural categories, not units.

• Helium is chemically a noble gas in Group 18 even though its occupied shell is 1s².

Table sources: Royal Society of Chemistry — Periodic Table

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The detached rows still belong to periods 6 and 7

Lanthanoids are normally drawn below the main body to shorten period 6, and actinoids are drawn below it to shorten period 7. Detaching them is a layout choice, not a separate part of the periodic law.

Periodic Trends Chart

Broad directional trends help compare elements, but they are not exception-free laws and depend on the property definition.

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Broad directional trends help compare elements, but they are not exception-free laws and depend on the property definition.
Property	Across a period →	Down a group ↓	Main reason	Caution
Atomic radius	Generally decreases	Generally increases	Greater effective nuclear attraction across a period; added shells down a group.	Broad trend with exceptions.
First ionization energy	Generally increases	Generally decreases	Electrons are held more strongly across a period and are farther from the nucleus down a group.	Subshell and pairing effects create exceptions.
Electronegativity	Generally increases toward F	Generally decreases	Effective nuclear attraction and atomic size both matter.	Scale and element availability matter; noble gases often lack standard Pauling values.
Metallic character	Generally decreases	Generally increases	Electron loss becomes less favorable across a period and more favorable down many groups.	Not a single measured quantity.
Valence-shell principal level	Usually unchanged within a period	Increases	Moving down introduces a higher principal shell.	Useful for main-group reasoning.
Shielding	Changes modestly across	Generally increases	More occupied inner shells lie between valence electrons and the nucleus.	Detailed shielding is orbital-dependent.
Reactivity	No single universal direction	Family-specific	Chemical reactivity depends on electron configuration and reaction partner.	Use group-specific chemistry rather than one global trend.

Qualitative trends only.

• Use property-specific charts for numerical comparison because definitions and exceptions matter.

Table sources: Royal Society of Chemistry — Periodic Table

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Periodic trends are directions, not perfect staircases

Atomic radius generally decreases across a period, while ionization energy and electronegativity generally rise. Subshell structure, electron pairing, oxidation state, bonding environment, and the exact property definition create important exceptions.

Main-Group Valence Patterns

Representative outer-shell patterns help explain recurring main-group chemistry. Actual oxidation states and bonding depend on the element and compound.

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Representative outer-shell patterns help explain recurring main-group chemistry. Actual oxidation states and bonding depend on the element and compound.
Group	Elements	Broad outer pattern	Common chemistry clue
1	H; Li, Na, K, Rb, Cs, Fr	ns¹	Alkali metals commonly form +1 ions; hydrogen is a special case.
2	Be, Mg, Ca, Sr, Ba, Ra	ns²	Common +2 oxidation state for the alkaline-earth metals.
13	B, Al, Ga, In, Tl, Nh	ns²np¹	+3 is important; heavier members also show lower oxidation states.
14	C, Si, Ge, Sn, Pb, Fl	ns²np²	Oxidation states from −4 to +4 occur across the group.
15	N, P, As, Sb, Bi, Mc	ns²np³	−3, +3, and +5 are important patterns, with element-specific behavior.
16	O, S, Se, Te, Po, Lv	ns²np⁴	−2 is common for lighter chalcogens; positive states also occur for heavier members.
17	F, Cl, Br, I, At, Ts	ns²np⁵	Halogens commonly form −1; fluorine is especially electronegative.
18	He; Ne, Ar, Kr, Xe, Rn, Og	filled outer shell	Noble gases are comparatively unreactive, but heavier members can form compounds.

ns and np represent valence-shell subshells.

• These are broad patterns, not complete electron configurations or guaranteed oxidation states.

Table sources: International Union of Pure and Applied Chemistry — Periodic Table of Elements

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Element Symbols That Are Easy to Misread

Several symbols reflect Latin or historical names rather than the modern English element name.

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Several symbols reflect Latin or historical names rather than the modern English element name.
Symbol	Element	Historical root	Memory clue
Na	Sodium	natrium	The symbol preserves a Latin-derived name.
K	Potassium	kalium	K comes from kalium.
Fe	Iron	ferrum	Fe comes from ferrum.
Cu	Copper	cuprum	Cu comes from cuprum.
Ag	Silver	argentum	Ag comes from argentum.
Sn	Tin	stannum	Sn comes from stannum.
Sb	Antimony	stibium	Sb comes from stibium.
W	Tungsten	wolfram	W reflects the name wolfram.
Au	Gold	aurum	Au comes from aurum.
Hg	Mercury	hydrargyrum	Hg derives from a historical Greek/Latin form meaning liquid silver.
Pb	Lead	plumbum	Pb comes from plumbum.
Cs	Caesium	caesius	The symbol follows the element name; US English often spells the name cesium.

Chemical symbols are standardized identifiers.

• Element symbols are case-sensitive: Co is cobalt, while CO is a chemical formula for carbon monoxide.

Table sources: International Union of Pure and Applied Chemistry — Periodic Table of Elements

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Element symbols are case-sensitive

Co means cobalt. CO means carbon monoxide. The second character of a two-letter element symbol is lowercase, and several symbols such as Na, K, Fe, Ag, Au, Hg, and Pb reflect historical names rather than modern English spelling.

Atomic Number, Mass and Weight Notation

Atomic number, mass number, atomic mass, standard atomic weight, and molar mass are related but distinct quantities.

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Atomic number, mass number, atomic mass, standard atomic weight, and molar mass are related but distinct quantities.
Term	Meaning	Example	Key distinction
Standard atomic weight	Recommended relative atomic weight for normal terrestrial materials	H, C, O, Fe	Can be a single value with uncertainty or an interval.
Abridged standard atomic weight	Simplified CIAAW value for routine use	Fe 55.845 ± 0.002	Useful when full uncertainty detail is unnecessary.
Interval atomic weight	Range caused by natural isotopic-composition variation	H, Li, B, C, N, O	A single exact value is not appropriate for all normal samples.
No standard atomic weight	No characteristic isotopic abundance in normal terrestrial material	Tc, Pm, many radioactive elements	Periodic tables may instead show a bracketed mass number for a selected nuclide.
Atomic number Z	Number of protons in the nucleus	O has Z = 8	Atomic number defines the element.
Mass number A	Protons + neutrons in one nuclide	¹²C has A = 12	Mass number belongs to a specific isotope, not to an element as a whole.
Atomic mass	Mass of a particular atom or nuclide	Mass of ¹²C	Expressed in daltons for individual atoms/nuclides.
Molar mass	Mass per amount of substance	g/mol	Numerically close to familiar atomic-weight values for elemental atoms, but it is a different quantity and unit.

Atomic number and relative atomic weight are dimensionless; atomic mass can be expressed in Da; molar mass is mass per amount of substance.

• Do not treat the number shown in a periodic-table atomic-weight field as a universal isotope mass.

Table sources: Commission on Isotopic Abundances and Atomic Weights — Abridged Standard Atomic Weights; International Union of Pure and Applied Chemistry — Periodic Table of Elements

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Not every element has a standard atomic weight

The CIAAW abridged table assigns standard atomic weights only where characteristic terrestrial isotopic abundances support them. Technetium, promethium, and many radioactive or synthetic elements therefore have no standard atomic weight.

How to Read a Periodic-Table Cell

Most periodic-table cells combine identity information with one or more reference properties.

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Most periodic-table cells combine identity information with one or more reference properties.
Cell field	Typical format	What it tells you	Reading tip
Atomic number	Integer	Number of protons	Atomic number orders the modern periodic table.
Symbol	One- or two-letter identifier	C, Fe, Og	First letter uppercase; second letter lowercase.
Element name	Official element name	Carbon	Names and symbols are standardized by IUPAC.
Atomic weight / mass notation	Relative atomic-weight information	12.011 ± 0.002 or —	Interpret the notation rather than assuming every element has one fixed natural atomic weight.
Group	Vertical column	1–18	Elements in a group often share valence-electron patterns.
Period	Horizontal row	1–7	Period tracks the principal shell structure of the ground-state atom.
Block	s, p, d, or f region	p block	Block reflects the type of subshell being filled in the broad electron-configuration pattern.
Family / series	Chemical grouping	Halogen, noble gas, lanthanoid	Family labels summarize useful similarities but are not substitutes for actual properties.

Field formatting varies by periodic-table edition.

• Always read the legend because color categories and extra properties differ between periodic tables.

Table sources: International Union of Pure and Applied Chemistry — Periodic Table of Elements; Royal Society of Chemistry — Periodic Table; Commission on Isotopic Abundances and Atomic Weights — Abridged Standard Atomic Weights

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Periodic Table Terminology Chart

Useful terms for discussing positions, families, and series without confusing layout conventions with chemical definitions.

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Useful terms for discussing positions, families, and series without confusing layout conventions with chemical definitions.
Term	Meaning	Example	Important nuance
Group	Vertical column numbered 1–18	Group 17 contains the halogens	IUPAC recommends Arabic group numbers 1 through 18.
Period	Horizontal row	Period 4 runs K through Kr	Periods reflect repeating electron-shell structure.
Family	Common chemical grouping	Alkali metals, halogens, noble gases	Family names emphasize shared chemistry.
Lanthanoids	La through Lu in common usage	Period 6 detached series	IUPAC prefers the collective name lanthanoids.
Actinoids	Ac through Lr	Period 7 detached series	All actinoids are radioactive.
Transition element	Element whose atom has an incomplete d subshell, or can form cations with an incomplete d subshell	Fe is a classic example	This definition is narrower than simply saying every Group 3–12 element is a transition metal.
Metalloid	Informal boundary classification	B, Si, Ge, As are commonly included	Metalloid lists vary among sources; the term has no single universally fixed membership.
Transactinide	Element with Z > 103	Rf through Og	These are synthetic superheavy elements beyond the actinoid series.

Terminology reference.

• Some educational category labels, especially metalloid membership, are not defined by one universally fixed list.

Table sources: International Union of Pure and Applied Chemistry — Periodic Table of Elements; Royal Society of Chemistry — Periodic Table

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How to use the periodic table

Start with identity, then position, then property. Atomic number tells you which element you have. Group and period provide structural context. Block connects position with electron configuration. Only then should you apply property-specific trends or numerical charts.

1. Read atomic number

This is the proton count and uniquely identifies the element.

2. Check symbol and name

Use standardized symbols exactly; capitalization changes meaning.

3. Locate group and period

Groups compare vertical families; periods compare horizontal sequences.

4. Identify the block or series

s, p, d, and f regions connect position with electron configuration.

5. Interpret atomic-weight notation

A standard atomic weight is not the mass number of one isotope.

6. Apply a specific trend carefully

Use atomic-radius, electronegativity, ionization-energy, or oxidation-state data when you need a numerical comparison.

The Royal Society of Chemistry periodic table is useful when you want to switch from positional information to element-by-element property data and trend views.

Periodic table FAQs

How many elements are in the periodic table?

The periodic table contains 118 recognized elements, from hydrogen with atomic number 1 through oganesson with atomic number 118.

What determines an element's position in the periodic table?

Atomic number determines the order. Atomic number equals the number of protons in the nucleus.

How many groups are in the periodic table?

The conventional long-form periodic table has 18 numbered groups.

How many periods are in the periodic table?

The periodic table has seven periods.

What is a group in the periodic table?

A group is a vertical column. Elements in the same group often share related valence-electron patterns and chemical behavior.

What is a period in the periodic table?

A period is a horizontal row. Moving across a period increases atomic number one proton at a time.

What are the s, p, d, and f blocks?

They are broad regions associated with the type of subshell involved in the electron-configuration pattern across the table.

Why are lanthanoids and actinoids shown below the main table?

They are usually detached to keep the conventional 18-column table compact. They belong to periods 6 and 7 respectively.

Does every element have a standard atomic weight?

No. Elements without a characteristic natural terrestrial isotopic abundance, including many radioactive elements, do not have a standard atomic weight.

Is atomic number the same as atomic weight?

No. Atomic number counts protons. Atomic weight reflects isotope masses and abundances in an element's normal terrestrial material.

Why do some atomic weights have uncertainty or ranges?

Natural isotopic composition can vary, and measured quantities carry uncertainty. CIAAW therefore reports uncertainties and, for some elements, intervals.

Which element has the highest atomic number?

Oganesson has atomic number 118, the highest atomic number among the currently recognized elements.

Why is helium in Group 18 if it has an s-shell configuration?

Helium has a filled 1s shell and behaves chemically as a noble gas, so it is conventionally placed in Group 18 even though its occupied subshell is s.

Are metalloid classifications identical on every periodic table?

No. Metalloid is an informal classification and different educational tables can draw the boundary differently.

Does atomic radius always decrease perfectly from left to right?

No. Atomic radius generally decreases across a period, but detailed values depend on radius definition and electronic structure.

What is the best way to read a periodic-table cell?

Start with atomic number, symbol, and name. Then use group, period, block, and atomic-weight notation to interpret structure and periodic relationships.

Sources

Element names, symbols, group numbering, periodic-table conventions, atomic-weight data, and property organization are grounded in IUPAC, CIAAW, and the Royal Society of Chemistry.

International Union of Pure and Applied Chemistry — Periodic Table of Elements

Provides IUPAC element names, symbols, group numbering guidance, periodic-table conventions, and official background on the 118 recognized elements.

https://iupac.org/what-we-do/periodic-table-of-elements/

Commission on Isotopic Abundances and Atomic Weights — Abridged Standard Atomic Weights

Provides the current abridged standard atomic weights and identifies elements for which no standard atomic weight is assigned.

https://ciaaw.org/abridged-atomic-weights.htm

Royal Society of Chemistry — Periodic Table

Provides an interactive 118-element table with groups, periods, blocks, classifications, element data, and property-trend views.

https://periodic-table.rsc.org/

How the periodic table works

Periodic Table of All 118 Elements

Periodic Table Element Finder

Atomic number is the table's backbone

Periodic Table Periods Chart

Periodic Table Groups and Families

s, p, d and f Regions

The detached rows still belong to periods 6 and 7

Periodic Trends Chart

Periodic trends are directions, not perfect staircases

Main-Group Valence Patterns

Element Symbols That Are Easy to Misread

Element symbols are case-sensitive

Atomic Number, Mass and Weight Notation

Not every element has a standard atomic weight

How to Read a Periodic-Table Cell

Periodic Table Terminology Chart

How to use the periodic table

1. Read atomic number

2. Check symbol and name

3. Locate group and period

4. Identify the block or series

5. Interpret atomic-weight notation

6. Apply a specific trend carefully

Related chemistry charts

Periodic table FAQs

Sources