Platinum

Platinum (Pt) is a transition metal with atomic number 78 and an atomic mass of 195.08. Its electron configuration is [Xe] 4f14 5d9 6s1.

Platinum key data

Symbol	Pt
Atomic number	78
Atomic mass (standard atomic weight)	195.08
Molar mass	195.08 g/mol
Protons	78
Neutrons (most abundant isotope, platinum-195)	117
Electrons (neutral atom)	78
Category	Transition metal
Period	6
Group	10
Block	d-block
Noble gas notation	[Xe] 4f14 5d9 6s1
Full electron configuration	1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d9 6s1
Electrons per shell	2, 8, 18, 32, 17, 1

Atomic mass: IUPAC CIAAW abridged standard atomic weights, 2024. Most abundant isotope: NIST Atomic Weights and Isotopic Compositions.

Measured properties of platinum

From PubChem, the US National Institutes of Health. Public domain. The first ionisation energy is the value for platinum from the NIST Atomic Spectra Database, in place of PubChem’s 9 eV.

Melting point	2041.6 K (1768.4 °C), 17th of 103 by melting point
Boiling point	4098 K (3824.9 °C), joint 16th of 93 by boiling point
Density	21.46 g/cm³, 3rd of 96 by density
State at room temperature	Solid
Electronegativity	2.28 (Pauling), joint 15th of 95 by electronegativity
Van der Waals radius	209 pm, joint 48th of 99 by atomic radius
First ionisation energy	8.9588 eV (864.39 kJ/mol), 27th of 102 by first ionisation energy
Electron affinity	2.128 eV (205.3 kJ/mol), 7th of 57 by electron affinity
Common oxidation states	+4, +2
Discovered	1735

Each rank counts down from the highest value, among the elements PubChem’s table gives one for, and links to that property ranked across the whole table. All of them are collected under periodic trends.

Platinum electron configuration

The full electron configuration of platinum is 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d9 6s1. With the noble-gas core collapsed it is [Xe] 4f14 5d9 6s1, and the outermost subshell is 6s1.

Platinum does not follow the simple filling order. Its measured configuration differs from the one the aufbau rule predicts, because its 5d and 6s subshells lie so close in energy that the simple filling order cannot predict which arrangement is lowest. This is a measured fact about the atom rather than an exception to be derived.

Bohr model of platinum (Pt): a nucleus and six shells holding 2, 8, 18, 32, 17 and 1 electrons from the inside out. — Bohr model of platinum (Pt). Image © ScienceQuest, CC BY 4.0: free to reuse with credit to ScienceQuest and a link to this page, as the image licence explains.

Orbital box diagram of platinum (Pt), [Xe] 4f14 5d9 6s1, with the xenon core drawn as one bar: one box per orbital, filled by Hund’s rule, showing two unpaired electrons, in 5d and 6s. — Orbital diagram of platinum (Pt). Image © ScienceQuest, CC BY 4.0: free to reuse with credit to ScienceQuest and a link to this page, as the image licence explains.

Why group and block follow from this is set out in how the periodic table maps electron configuration, and the electron configuration of every element is listed on one page.

Mass of one platinum atom

A molar mass is grams per mole, so dividing by the Avogadro constant gives the mass of a single atom, or for an element with more than one natural isotope the average mass of its atoms, and the reciprocal gives how many atoms sit in a gram.

Mass of one atom

one atom = 195.08 / (6.02214076 × 10²³)
= 3.2394 × 10⁻²² g

Atoms in one gram

atoms per gram = 6.02214076 × 10²³ / 195.08
= 3.0870 × 10²¹ atoms

Platinum on the periodic table

Platinum is in period 6, group 10, in the d-block.

The other elements of group 10 are nickel, palladium and darmstadtium.