Cadmium (Cd)
Cadmium is element 48, a transition metal in group 12, period 5. A neutral atom has 48 protons, 64 neutrons and 48 electrons, 2 of them valence electrons.
Transition metal- Atomic number
- 48
- Atomic mass
- 112.41 u
- Valence electrons
- 2*
- Protons · neutrons
- 48 · 64
- Electrons per shell
- 2, 8, 18, 18, 2
- At room temperature
- solid
Bohr model of cadmium
The Bohr model draws cadmium as a nucleus of 48 protons and 64 neutrons, with its 48 electrons on 5 circular shells: 2 in shell 1, 8 in shell 2, 18 in shell 3, 18 in shell 4, 2 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 cadmium
1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰
Short form (noble gas notation): [Kr] 5s² 4d¹⁰. The [Kr] stands for the electrons of krypton, the noble gas before it.
How many valence electrons does cadmium have?
Cadmium has 2 valence electrons.
Cadmium 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 5), and electrons in its inner d subshell can also take part in bonding.
Protons, neutrons and electrons
| Protons | 48 | equal to the atomic number |
|---|---|---|
| Electrons | 48 | equal to the protons in a neutral atom |
| Neutrons | 64 | mass number 112 − 48 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.
Cadmium properties
| Symbol | Cd |
|---|---|
| Category | Transition metal |
| Group · period · block | 12 · 5 · d |
| Atomic mass | 112.41 u |
| State at 25 °C | solid |
| Melting point | 594.2 K (321 °C, 610 °F) |
| Boiling point | 1,040 K (767 °C, 1,410 °F) |
| Density | 8.69 g/cm³ |
| Electronegativity (Pauling) | 1.69 |
| Atomic radius | 158 pm |
| First ionization energy | 8.994 eV |
| Electron affinity | — |
| Oxidation states | +2 |
| Common ion charge | +2 |
| Discovered | 1817 by Karl Samuel Leberecht Hermann |
Where cadmium sits on the periodic table
Group 12: Zinc, Mercury, Copernicium.
Questions about cadmium
How many valence electrons does cadmium have?
Cadmium has 2 valence electrons in its outer shell; inner d or f electrons can also bond.
How many protons, neutrons and electrons does cadmium have?
A neutral cadmium atom has 48 protons and 48 electrons. Its most common form has about 64 neutrons (mass number 112 − 48 protons).
What is the electron configuration of cadmium?
1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰, written in short form as [Kr] 5s² 4d¹⁰.
What does the Bohr model of cadmium look like?
A nucleus of 48 protons and 64 neutrons, circled by 5 electron shells holding 2, 8, 18, 18, 2 electrons.
What is the atomic number of cadmium?
48. The atomic number is the number of protons in the nucleus, and it is what makes an atom cadmium.