Copper

Copper (Cu) is a transition metal with atomic number 29 and an atomic mass of 63.546. Its electron configuration is [Ar] 3d10 4s1.

Copper key data

Symbol	Cu
Atomic number	29
Atomic mass (standard atomic weight)	63.546
Molar mass	63.546 g/mol
Protons	29
Neutrons (most abundant isotope, copper-63)	34
Electrons (neutral atom)	29
Category	Transition metal
Period	4
Group	11
Block	d-block
Noble gas notation	[Ar] 3d10 4s1
Full electron configuration	1s2 2s2 2p6 3s2 3p6 3d10 4s1
Electrons per shell	2, 8, 18, 1

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

Measured properties of copper

From PubChem, the US National Institutes of Health. Public domain.

Melting point	1357.8 K (1084.6 °C), 42nd of 103 by melting point
Boiling point	2835 K (2561.9 °C), 46th of 93 by boiling point
Density	8.933 g/cm³, 32nd of 96 by density
State at room temperature	Solid
Electronegativity	1.9 (Pauling), joint 36th of 95 by electronegativity
Van der Waals radius	140 pm, joint 95th of 99 by atomic radius
First ionisation energy	7.726 eV (745.4 kJ/mol), 39th of 102 by first ionisation energy
Electron affinity	1.228 eV (118.5 kJ/mol), 18th of 57 by electron affinity
Common oxidation states	+2, +1
Discovered	Ancient

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.

Copper electron configuration

The full electron configuration of copper is 1s2 2s2 2p6 3s2 3p6 3d10 4s1. With the noble-gas core collapsed it is [Ar] 3d10 4s1, and the outermost subshell is 4s1.

Copper does not follow the simple filling order. Its measured configuration differs from the one the aufbau rule predicts, because a filled d subshell sits lower in energy than the arrangement the rule would give. This is a measured fact about the atom rather than an exception to be derived.

Bohr model of copper (Cu): a nucleus and four shells holding 2, 8, 18 and 1 electrons from the inside out. — Bohr model of copper (Cu). 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 copper (Cu), 1s2 2s2 2p6 3s2 3p6 3d10 4s1: one box per orbital, filled by Hund’s rule, showing one unpaired electron, in 4s. — Orbital diagram of copper (Cu). 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 copper 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 = 63.546 / (6.02214076 × 10²³)
= 1.0552 × 10⁻²² g

Atoms in one gram

atoms per gram = 6.02214076 × 10²³ / 63.546
= 9.4768 × 10²¹ atoms

Copper on the periodic table

Copper is in period 4, group 11, in the d-block.

The other elements of group 11 are silver, gold and roentgenium.