Molybdenum (Mo)
Molybdenum is element 42, a transition metal in group 6, period 5. A neutral atom has 42 protons, 54 neutrons and 42 electrons, 1 of them valence electrons.
Transition metal- Atomic number
- 42
- Atomic mass
- 95.95 u
- Valence electrons
- 1*
- Protons · neutrons
- 42 · 54
- Electrons per shell
- 2, 8, 18, 13, 1
- At room temperature
- solid
Bohr model of molybdenum
The Bohr model draws molybdenum as a nucleus of 42 protons and 54 neutrons, with its 42 electrons on 5 circular shells: 2 in shell 1, 8 in shell 2, 18 in shell 3, 13 in shell 4, 1 in shell 5. Press Build the atom to watch the shells fill from the inside out. The outer ring (the O shell) is dashed: the electrons there are the ones that take part in chemistry.
Real electrons don't travel in neat circles. They live in fuzzy orbitals, shown below, but the Bohr picture is the quickest way to count shells and valence electrons.
Electron configuration of molybdenum
1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s¹ 4d⁵
Short form (noble gas notation): [Kr] 5s¹ 4d⁵. The [Kr] stands for the electrons of krypton, the noble gas before it.
Molybdenum breaks the usual filling order. The Aufbau rule predicts 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d⁴, but experiments show the configuration above. Moving one electron from the s subshell gives a half-full or full d subshell, which is more stable.
How many valence electrons does molybdenum have?
Molybdenum has 1 valence electron.
Molybdenum is a transition metal, so its valence electrons are less clear-cut than for main-group elements. It has 1 electron in its outermost shell (shell 5), and electrons in its inner d subshell can also take part in bonding.
Protons, neutrons and electrons
| Protons | 42 | equal to the atomic number |
|---|---|---|
| Electrons | 42 | equal to the protons in a neutral atom |
| Neutrons | 54 | mass number 96 − 42 protons |
Atoms of the same element can have different numbers of neutrons (isotopes). The count above uses the rounded atomic mass, the way it's taught in class.
Molybdenum properties
| Symbol | Mo |
|---|---|
| Category | Transition metal |
| Group · period · block | 6 · 5 · d |
| Atomic mass | 95.95 u |
| State at 25 °C | solid |
| Melting point | 2,896 K (2,620 °C, 4,750 °F) |
| Boiling point | 4,912 K (4,640 °C, 8,380 °F) |
| Density | 10.2 g/cm³ |
| Electronegativity (Pauling) | 2.16 |
| Atomic radius | 209 pm |
| First ionization energy | 7.092 eV |
| Electron affinity | 0.746 eV |
| Oxidation states | +6 |
| Common ion charge | +6 |
| Discovered | 1778 by Carl Wilhelm Scheele |
Where molybdenum sits on the periodic table
Group 6: Chromium, Tungsten, Seaborgium.
Questions about molybdenum
How many valence electrons does molybdenum have?
Molybdenum has 1 valence electron in its outer shell; inner d or f electrons can also bond.
How many protons, neutrons and electrons does molybdenum have?
A neutral molybdenum atom has 42 protons and 42 electrons. Its most common form has about 54 neutrons (mass number 96 − 42 protons).
What is the electron configuration of molybdenum?
1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s¹ 4d⁵, written in short form as [Kr] 5s¹ 4d⁵.
What does the Bohr model of molybdenum look like?
A nucleus of 42 protons and 54 neutrons, circled by 5 electron shells holding 2, 8, 18, 13, 1 electrons.
What is the atomic number of molybdenum?
42. The atomic number is the number of protons in the nucleus, and it is what makes an atom molybdenum.