033Metalloid · Group 15 · Period 4

Arsenic

Arsenic (As) is element 33, a metalloid in the p-block — group 15, period 4. It is a solid at room temperature with 4 electron shells (2, 8, 18, 5) and an atomic mass of 74.9215956 u.

Atomic mass: 74.92 u
Phase · STP: solid
Melting: —
Boiling: —
Electronegativity: 2.18
Density: 5.727 g/cm³

Photograph — Hi-Res Images ofChemical Elements, CC BY 3.0 <https://creativecommons.org/licenses/by/3.0>, via Wikimedia Commons, source: https://images-of-elements.com/arsenic.php

Identity

Atomic number: 33
Standard atomic weight: 74.92 u
Category: Metalloid
Group: 15 · Pnictogens
Period: 4
Block: p-block
Oxidation states: +5, +3, -3

Physical properties

Melting point: —
Boiling point: —
Density: 5.727 g/cm³
Molar heat capacity: 24.64 J/(mol·K)
Atomic radius: 185 pm
Electron affinity: 77.65 kJ/mol

Atomic structure

33protons

42neutrons

33electrons

5valence e⁻

Noble-gas notation: [Ar] 3d10 4s2 4p3
Full configuration: 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p3
Electrons per shell: 2, 8, 18, 5

Periodic trends

Where Arsenic ranks across all 118 elements.

Electronegativity2.18

Ionization energy947 kJ/mol

Electron affinity77.65 kJ/mol

Density5.727 g/cm³

Atomic radius185 pm

Ionization energies

Energy to remove each successive electron (kJ/mol).

947

1.8k

2.7k

4.8k

6.0k

12.3k

Successive ionization energies (kJ/mol, log scale).

Discovery

Discovered: Ancient
Discovered by: Bronze Age
Named by: —
Appearance: metallic grey