Bismuth: Atomic Mass 208.98, Properties, Uses and Myths
Here you will learn how to find bismuth on the interactive periodic table and read its tile correctly.
You will also get its data, a short history, its uses, three myths and one worked calculation.
Find bismuth on the interactive periodic table
Open the interactive periodic table and look for the tile with 83, 208.98 and Bi on it. Tap the tile. A quick-view card opens with the atomic mass, electron configuration, physical state and oxidation states. Choose Read all data to open the full profile of the element.
You can also use the search box. It accepts a name, a symbol or an atomic number, so "bismuth", "Bi" and "83" all work.
To see the family, use the Category filter. Pick post-transition metal and compare bismuth with the other members. Do this once yourself. A tile teaches more than a memorised number, because you see where the element sits and what its neighbours look like.
Look at polonium, the next tile, too. Its mass is written as [209], in square brackets. Bismuth's mass, 208.98, has no brackets. We will see why below.
Bismuth data at a glance
The table below uses values from the bismuth tile and the isotope facts we checked. Open the full profile for the electron configuration, physical state and other data.
| Item | Bismuth | How to read it |
|---|---|---|
| Symbol | Bi | Short form of the element's name |
| Atomic number | 83 | Number of protons in every atom |
| Atomic mass | 208.98 | Average mass of an atom, in atomic mass units (u) |
| Category | Post-transition metal | A metal placed after the transition metals |
| Nearly stable isotope | Bismuth-209 | The isotope that gives the standard atomic mass |
| Half-life of bismuth-209 | 2.01 × 1019 years | Time for half of the atoms to decay |
An isotope is a form of an element with the same number of protons but a different number of neutrons. A half-life is the time in which half of a sample of a radioactive isotope decays.
What "post-transition metal" tells you
A post-transition metal is a metal that lies to the right of the transition metals in the table. Tin and bismuth are examples. These metals are generally softer than typical transition metals such as iron and have weaker metallic character.
The category reminds you that metals are not all alike. In exams, place bismuth by its tile and category. Do not guess from its name or from how heavy it feels.
A short history of bismuth
Bismuth has been known as a metal for a very long time. Early on, it was confused with lead and tin, because all three are soft and heavy. Later, chemists showed that it is a separate element with its own properties.
In more recent times, scientists studied its nucleus closely. They found that bismuth-209, its natural isotope, is very slightly radioactive. The half-life is so long that nobody saw it decay for many years. We come back to this in the myths.
Main uses of bismuth
- Stomach medicine: A compound called bismuth subsalicylate is used to treat temporary stomach upset. It can turn the stool or tongue black for a short time. The reason is that bismuth reacts with trace sulfur compounds and forms black bismuth sulfide. The colour change is temporary and harmless. This is general information, not advice. Take any medicine only as your doctor or pharmacist directs.
- Alloys: Bismuth is commonly mixed with other metals to make alloys that melt at low temperatures.
- Cancer research: The isotope bismuth-213 has been used in targeted alpha therapy, a treatment that aims alpha radiation at cancer cells. Trained medical teams use it. It is produced through a decay chain, not taken from ordinary bismuth.
People often choose bismuth when they want a heavy metal that is gentler than lead. That is the practical meaning of "low toxicity". Low does not mean zero, so safe handling still matters.
Three common misconceptions
Myth 1: Bismuth is completely stable
Not exactly. Bismuth-209 is now known to be radioactive. Its half-life is 2.01 × 1019 years, which is more than a billion times the age of the universe. So it is called nearly stable. For lab work and school problems, you can treat it as stable. Strictly, bismuth has no truly stable isotope.
Myth 2: Every heavy metal is as poisonous as lead
Many students think a heavy metal is always dangerously toxic. Bismuth is the usual counter-example, since it has low toxicity. But this is no licence to be careless. Using bismuth medicine for more than six weeks may lead to build-up in the body. That is why such medicines are taken only with proper guidance.
Myth 3: The mass 208.98 is an average of many natural isotopes
For many elements, such as chlorine, the atomic mass is a weighted average of several isotopes. Bismuth is different. Its standard atomic mass is given from one isotope, bismuth-209. That is why 208.98 is so close to the whole number 209. This also explains the brackets: polonium has no stable or nearly stable isotope to base a fixed value on, so its tile shows [209], the mass number of a chosen isotope.
Worked example: moles and percentage using tile values
Question: Find (a) the mass of 0.5 mol of bismuth, and (b) the percentage of bismuth in bismuth(III) oxide, Bi2O3. Use the tile values: Bi = 208.98 and O = 15.999.
Step 1. The molar mass of an element in g/mol has the same number as its atomic mass in u. So 1 mol of bismuth has a mass of 208.98 g.
Step 2 (part a). Mass = moles × molar mass = 0.5 × 208.98 = 104.49 g.
Step 3 (part b). Molar mass of Bi2O3 = (2 × 208.98) + (3 × 15.999) = 417.96 + 47.997 = 465.957 g/mol.
Step 4. Percentage of bismuth = (417.96 ÷ 465.957) × 100 = about 89.70%.
Check: Bismuth is far heavier than oxygen, so most of the mass should come from bismuth. An answer near 90% makes sense.
Now try the same steps for another oxide of your choice. Take the atomic masses from the tiles. Compare the two percentages and explain the difference.
Key takeaways
- Bismuth is Bi, atomic number 83, atomic mass 208.98, a post-transition metal.
- Its standard atomic mass comes from bismuth-209, which is nearly stable with a half-life of 2.01 × 1019 years.
- Bismuth has low toxicity, but low is not the same as none.
- Use the tile, the Category filter and Read all data to check each value yourself.
- In calculations, use the atomic mass in u as the molar mass in g/mol.
Frequently asked questions
What is the atomic mass of bismuth?
It is 208.98, as shown on bismuth's tile. Its atomic number is 83 and its symbol is Bi.
Which category does bismuth belong to?
Bismuth is a post-transition metal. You can confirm this with the Category filter on the interactive table.
Is bismuth radioactive?
Bismuth-209 is radioactive in a technical sense, but its half-life is 2.01 × 1019 years, so it is considered practically stable. Other bismuth isotopes decay faster, and they do not occur in nature in useful amounts.
Why does bismuth medicine blacken the stool?
Bismuth reacts with trace sulfur compounds and forms bismuth sulfide, which is black and highly insoluble. The change is temporary and harmless. If you have any doubt, ask a doctor.
Why is polonium's mass in square brackets but bismuth's is not?
Square brackets show an element with no stable form to base a fixed value on. Bismuth's mass is given from bismuth-209, so it is written plainly as 208.98.
What to do next. Try it yourself on the page below.
Interactive Periodic Table — All 118 Elements →
