Hafnium (Hf)
Hafnium is element 72, a transition metal in group 4, period 6. A neutral atom has 72 protons, 106 neutrons and 72 electrons, 2 of them valence electrons.
Transition metal- Atomic number
- 72
- Atomic mass
- 178.49 u
- Valence electrons
- 2*
- Protons · neutrons
- 72 · 106
- Electrons per shell
- 2, 8, 18, 32, 10, 2
- At room temperature
- solid
Bohr model of hafnium
The Bohr model draws hafnium as a nucleus of 72 protons and 106 neutrons, with its 72 electrons on 6 circular shells: 2 in shell 1, 8 in shell 2, 18 in shell 3, 32 in shell 4, 10 in shell 5, 2 in shell 6. Press Build the atom to watch the shells fill from the inside out. The outer ring (the P 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 hafnium
1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d²
Short form (noble gas notation): [Xe] 6s² 4f¹⁴ 5d². The [Xe] stands for the electrons of xenon, the noble gas before it.
How many valence electrons does hafnium have?
Hafnium has 2 valence electrons.
Hafnium is a transition metal, so its valence electrons are less clear-cut than for main-group elements. It has 2 electrons in its outermost shell (shell 6), and electrons in its inner d subshell can also take part in bonding.
Protons, neutrons and electrons
| Protons | 72 | equal to the atomic number |
|---|---|---|
| Electrons | 72 | equal to the protons in a neutral atom |
| Neutrons | 106 | mass number 178 − 72 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.
Hafnium properties
| Symbol | Hf |
|---|---|
| Category | Transition metal |
| Group · period · block | 4 · 6 · d |
| Atomic mass | 178.49 u |
| State at 25 °C | solid |
| Melting point | 2,506 K (2,230 °C, 4,050 °F) |
| Boiling point | 4,876 K (4,600 °C, 8,320 °F) |
| Density | 13.3 g/cm³ |
| Electronegativity (Pauling) | 1.3 |
| Atomic radius | 212 pm |
| First ionization energy | 6.825 eV |
| Electron affinity | — |
| Oxidation states | +4 |
| Common ion charge | +4 |
| Discovered | 1923 by Dirk Coster |
Where hafnium sits on the periodic table
Group 4: Titanium, Zirconium, Rutherfordium.
Questions about hafnium
How many valence electrons does hafnium have?
Hafnium has 2 valence electrons in its outer shell; inner d or f electrons can also bond.
How many protons, neutrons and electrons does hafnium have?
A neutral hafnium atom has 72 protons and 72 electrons. Its most common form has about 106 neutrons (mass number 178 − 72 protons).
What is the electron configuration of hafnium?
1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d², written in short form as [Xe] 6s² 4f¹⁴ 5d².
What does the Bohr model of hafnium look like?
A nucleus of 72 protons and 106 neutrons, circled by 6 electron shells holding 2, 8, 18, 32, 10, 2 electrons.
What is the atomic number of hafnium?
72. The atomic number is the number of protons in the nucleus, and it is what makes an atom hafnium.