Chemical Elements Periodic Table

Last updated: February 8, 2026Reviewed date: February 8, 2026Reading time: 4 min read

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Article Summary

The periodic table, also known as the periodic table of the elements, is an ordered arrangement of the chemical elements into rows ("periods") and columns ("groups"). It is an icon of chemistry and is widely used in physics and other sciences. It is a depiction of the periodic law, which states that when the elements are arranged in order of their atomic numbers an approximate recurrence of their properties is evident. The table is divided into four roughly rectangular areas...

Key Takeaways

This article explains Why Arrange Elements in a Table? in simple medical language.
This article explains Does the Modern Periodic Table Change? If So, How and Who Does That? in simple medical language.
This article explains Chemical Element Data in PubChem in simple medical language.
This article explains Tabular Atomic Mass Data in simple medical language.

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The periodic table, also known as the periodic table of the elements, is an ordered arrangement of the chemical elements into rows (“periods”) and columns (“groups”). It is an icon of chemistry and is widely used in physics and other sciences. It is a depiction of the periodic law, which states that when the elements are arranged in order of their atomic numbers an approximate recurrence of their properties is evident. The table is divided into four roughly rectangular areas called blocks. Elements in the same group tend to show similar chemical characteristics.

Why Arrange Elements in a Table?

Seeing chemical elements arranged in the modern periodic table is as familiar as seeing a map of the world, but it was not always so obvious.

The creator of the periodic table, Dmitri Mendeleev, in 1869 began collecting and sorting known properties of elements, like he was playing a game, while traveling by train. He noticed that there were groups of elements that exhibited similar properties, but he also noticed that there were plenty of exceptions to the emerging patterns.

Incredibly, instead of giving up, he tried altering the measured property values to better fit the patterns! He also predicted that certain elements must exist which didn’t at the time – again, in an effort to get the patterns in his “game” to work out.

There were plenty of skeptics and it took years to gain international acceptance, but once newly-discovered elements matched the ones that Mendeleev predicted, his patterns could not be dismissed. In addition, some of the properties that he “fudged” were later recalculated and found to be much closer to his predictions.

Chemical Elements Periodic Table

Does the Modern Periodic Table Change? If So, How and Who Does That?

The periodic table as we know it today is managed by the International Union of Pure and Applied Chemistry, or IUPAC (eye-you-pack).

While much of what is in the periodic table is stable and unlikely to change, the IUPAC organization is responsible for deciding what needs to be changed. They have created criteria for what constitutes the discovery of a new element.

In addition, any new element must be assigned a temporary name and symbol, and if validated, given an official name. Such was the case when IUPAC recently reviewed elements 113, 115, 117 and 118, and decided to give them official names and symbols (goodbye, ununseptium and hello, tennessine!).

Atomic weights found within a periodic table one might think are constant. The truth is that atomic weights have changed as a function of time. Since 1899 the IUPAC Commission on Isotopic Abundances and Atomic Weights (CIAAW) has been evaluating atomic weights and abundances. For example, Carbon had an atomic weight of 12.00 in 1902 but today it is [12.0096, 12.0116]! Times sure have changed as the source of the sample will determine the value.

Finally, IUPAC assigns collective names (lanthanoids and actinoids) and group numbering (1 to 18) and has investigated the membership of the group 3 elements.

PubChem is working with IUPAC to help make information about the elements and the periodic table machine-readable. (The machine-readable data used to render the periodic table on this page, are available for download by clicking the Download button at the top of this page.)

Chemical Element Data in PubChem

PubChem is providing this periodic table page in order to help navigate abundant chemical element data available in PubChem. When exploring the table or list views on this page, please note the links to dedicated pages for each element. These individual element summary pages contain a lot of additional information as well as references. Please refer to them for details about provenance of the element property information.

Tabular Atomic Mass Data

Atomic Number	Symbol	Name	Atomic Mass [u]
1	H	Hydrogen	1.0080
2	He	Helium	4.00260
3	Li	Lithium	7.0
4	Be	Beryllium	9.012183
5	B	Boron	10.81
6	C	Carbon	12.011
7	N	Nitrogen	14.007
8	O	Oxygen	15.999
9	F	Fluorine	18.99840316
10	Ne	Neon	20.180
11	Na	Sodium	22.9897693
12	Mg	Magnesium	24.305
13	Al	Aluminum	26.981538
14	Si	Silicon	28.085
15	P	Phosphorus	30.97376200
16	S	Sulfur	32.07
17	Cl	Chlorine	35.45
18	Ar	Argon	39.9
19	K	Potassium	39.0983
20	Ca	Calcium	40.08
21	Sc	Scandium	44.95591
22	Ti	Titanium	47.867
23	V	Vanadium	50.9415
24	Cr	Chromium	51.996
25	Mn	Manganese	54.93804
26	Fe	Iron	55.84
27	Co	Cobalt	58.93319
28	Ni	Nickel	58.693
29	Cu	Copper	63.55
30	Zn	Zinc	65.4
31	Ga	Gallium	69.723
32	Ge	Germanium	72.63
33	As	Arsenic	74.92159
34	Se	Selenium	78.97
35	Br	Bromine	79.90
36	Kr	Krypton	83.80
37	Rb	Rubidium	85.468
38	Sr	Strontium	87.62
39	Y	Yttrium	88.90584
40	Zr	Zirconium	91.22
41	Nb	Niobium	92.90637
42	Mo	Molybdenum	95.95
43	Tc	Technetium	96.90636
44	Ru	Ruthenium	101.1
45	Rh	Rhodium	102.9055
46	Pd	Palladium	106.42
47	Ag	Silver	107.868
48	Cd	Cadmium	112.41
49	In	Indium	114.818
50	Sn	Tin	118.71
51	Sb	Antimony	121.760
52	Te	Tellurium	127.6
53	I	Iodine	126.9045
54	Xe	Xenon	131.29
55	Cs	Cesium	132.9054520
56	Ba	Barium	137.33
57	La	Lanthanum	138.9055
58	Ce	Cerium	140.116
59	Pr	Praseodymium	140.90766
60	Nd	Neodymium	144.24
61	Pm	Promethium	144.91276
62	Sm	Samarium	150.4
63	Eu	Europium	151.964
64	Gd	Gadolinium	157.2
65	Tb	Terbium	158.92535
66	Dy	Dysprosium	162.500
67	Ho	Holmium	164.93033
68	Er	Erbium	167.26
69	Tm	Thulium	168.93422
70	Yb	Ytterbium	173.05
71	Lu	Lutetium	174.9668
72	Hf	Hafnium	178.49
73	Ta	Tantalum	180.9479
74	W	Tungsten	183.84
75	Re	Rhenium	186.207
76	Os	Osmium	190.2
77	Ir	Iridium	192.22
78	Pt	Platinum	195.08
79	Au	Gold	196.96657
80	Hg	Mercury	200.59
81	Tl	Thallium	204.383
82	Pb	Lead	207
83	Bi	Bismuth	208.98040
84	Po	Polonium	208.98243
85	At	Astatine	209.98715
86	Rn	Radon	222.01758
87	Fr	Francium	223.01973
88	Ra	Radium	226.02541
89	Ac	Actinium	227.02775
90	Th	Thorium	232.038
91	Pa	Protactinium	231.03588
92	U	Uranium	238.0289
93	Np	Neptunium	237.048172
94	Pu	Plutonium	244.06420
95	Am	Americium	243.061380
96	Cm	Curium	247.07035
97	Bk	Berkelium	247.07031
98	Cf	Californium	251.07959
99	Es	Einsteinium	252.0830
100	Fm	Fermium	257.09511
101	Md	Mendelevium	258.09843
102	No	Nobelium	259.10100
103	Lr	Lawrencium	266.120
104	Rf	Rutherfordium	267.122
105	Db	Dubnium	268.126
106	Sg	Seaborgium	269.128
107	Bh	Bohrium	270.133
108	Hs	Hassium	269.1336
109	Mt	Meitnerium	277.154
110	Ds	Darmstadtium	282.166
111	Rg	Roentgenium	282.169
112	Cn	Copernicium	286.179
113	Nh	Nihonium	286.182
114	Fl	Flerovium	290.192
115	Mc	Moscovium	290.196
116	Lv	Livermorium	293.205
117	Ts	Tennessine	294.211
118	Og	Oganesson	295.216

Safety note: This is not a prescription or diagnosis. For severe symptoms, pregnancy danger signs, children with serious illness, chest pain, breathing difficulty, stroke-like weakness, or major injury, seek urgent care.

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Start with a registered doctor or the nearest qualified health center.

What to tell the doctor

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Bring old prescriptions, investigation reports, and current medicines.
Write allergies, pregnancy status, diabetes, kidney/liver disease, and major past illnesses.
Bring one family member if the patient is weak, elderly, confused, or a child.

Questions to ask

What is the most likely cause of my symptoms?
Which danger signs mean I should go to hospital quickly?
Which tests are necessary now, and which can wait?
How should I take medicines safely and what side effects should I watch for?
When should I come for follow-up?

Tests to discuss

Vital signs: temperature, pulse, blood pressure, oxygen saturation
Basic physical examination by a clinician
CBC, urine test, blood sugar, or imaging only when clinically needed

Avoid these mistakes

Do not use antibiotics, steroid tablets/injections, or strong painkillers without proper medical advice.
Do not hide pregnancy, kidney disease, ulcer, allergy, or blood thinner use.
Do not delay emergency care when danger signs are present.

Medicine safety and first-aid guide

This section is for patient education only. It does not replace a doctor, pharmacist, or emergency care.

Safe first steps

Avoid heavy lifting, sudden bending, and prolonged bed rest.
Use comfortable posture and gentle movement as tolerated.
Discuss physiotherapy, X-ray, or MRI only when clinically needed.

OTC medicine safety

For mild back pain, pain-relief medicine may be discussed with a doctor or pharmacist.
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Avoid these mistakes

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For rural patients and family caregivers

Patient health record and symptom diary

Write your symptoms, medicines already taken, test results, and questions before visiting a doctor. This note stays on your device unless you print or copy it.

Doctor to discuss: Doctor / qualified healthcare provider

Tests to discuss with doctor

Basic vital signs: temperature, pulse, blood pressure, oxygen level if needed
Relevant blood, urine, imaging, or specialist tests only after clinical assessment

Questions to ask

What is the most likely cause of my symptoms?
Which warning signs mean I should go to emergency care?
Which tests are really needed now?
Which medicines are safe for my age, pregnancy status, allergy, kidney/liver/stomach condition, and current medicines?

Emergency warning signs such as chest pain, severe breathing difficulty, sudden weakness, confusion, severe dehydration, major injury, or loss of bladder/bowel control need urgent medical care. Do not wait for online information.

Go to emergency care if you notice:

Severe or rapidly worsening symptoms
Breathing difficulty, chest pain, fainting, confusion, severe weakness, major injury, or severe dehydration

Doctor / service to discuss: Qualified healthcare provider; specialist depends on symptoms and examination.

Step 1
Check danger signs first
If danger signs are present, seek emergency care and do not wait for online information.
Step 2
Record the symptom story
Write when symptoms started, severity, medicines already taken, allergies, pregnancy status, and test results.
Step 3
Visit a qualified clinician
A doctor, nurse, or qualified healthcare provider can examine you and decide which tests or treatment are needed.
Step 4
Do only useful tests
Do tests after clinical assessment. Avoid unnecessary tests, random antibiotics, or repeated medicines without diagnosis.
Step 5
Follow up and return early if worse
If symptoms worsen, new warning signs appear, or treatment is not helping, return for review quickly.

Rural patient practical tips

Take a written symptom diary and all previous prescriptions/test reports.
Do not hide medicines already taken, even herbal or over-the-counter medicines.
Ask which warning signs mean urgent referral to hospital.

This roadmap is for education. A real diagnosis and treatment plan requires history, examination, and clinical judgment.

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Write your symptom story. A health professional or site editor can review it before any answer is prepared. This box is not for emergency care.

Emergency first: Severe chest pain, breathing trouble, unconsciousness, stroke signs, severe injury, heavy bleeding, or rapidly worsening symptoms need urgent local medical care now.

Frequently Asked Questions

Why Arrange Elements in a Table?

Seeing chemical elements arranged in the modern periodic table is as familiar as seeing a map of the world, but it was not always so obvious. The creator of the periodic table, Dmitri Mendeleev, in 1869 began collecting and sorting known properties of elements, like he was playing a game, while traveling by train. He noticed that there were groups of elements that exhibited similar properties, but he also noticed that there were plenty of exceptions to the emerging patterns. Incredibly,…

Does the Modern Periodic Table Change? If So, How and Who Does That?

The periodic table as we know it today is managed by the International Union of Pure and Applied Chemistry, or IUPAC (eye-you-pack). While much of what is in the periodic table is stable and unlikely to change, the IUPAC organization is responsible for deciding what needs to be changed. They have created criteria for what constitutes the discovery of a new element. In addition, any new element must be assigned a temporary name and symbol, and if validated, given an official name.…

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Chemical Elements Periodic Table

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