Element 33 · Arsenic (As)

Arsenic Bohr model: diagram and electrons per shell

The arsenic Bohr model shows a arsenic atom (As) as a small nucleus with its electrons circling it in 4 shells: 2 in shell K, 8 in shell L, 18 in shell M and 5 in shell N. This page has a rotating 3D arsenic Bohr model, a flat diagram, a table of the electrons in each shell and the steps to draw it yourself.

Rotate the arsenic Bohr model in 3D

Drag to orbit, scroll to zoom.

This is a Bohr model of arsenic (As), a simplified picture of a single arsenic atom. Its nucleus holds 33 protons, and a neutral arsenic atom has 33 electrons, arranged around it in 4 shells (2 in shell K, 8 in shell L, 18 in shell M and 5 in shell N).

As K · 21s² L · 82s² 2p⁶ M · 183s² 3p⁶ 3d¹⁰ N · 54s² 4p³

Arsenic Bohr model diagram

Bohr model diagram of arsenic: a nucleus of 33 protons with 33 electrons on 4 shells, 2 in shell K, 8 in shell L, 18 in shell M and 5 in shell N, each ring labelled with its shell letter. — The arsenic Bohr model drawn flat: each ring is a shell, labelled with its letter, and every dot is an electron (2 in shell K, 8 in shell L, 18 in shell M and 5 in shell N).

Arsenic electrons per shell

A neutral arsenic atom has 33 electrons, one for each of its 33 protons. They fill the shells from the nucleus outwards: 2 in shell K, 8 in shell L, 18 in shell M and 5 in shell N.

Electrons in each shell of the arsenic Bohr model
Shell	Shell number (n)	Electrons	Most it can hold (2n²)	Subshells
K	1	2	2	1s²
L	2	8	8	2s² 2p⁶
M	3	18	18	3s² 3p⁶ 3d¹⁰
N	4	5	32	4s² 4p³

How the arsenic Bohr model builds up, shell by shell

Watch the arsenic Bohr model come together: the nucleus first, then each shell in turn, from the innermost outwards, with its electrons joining the ring. The legend names every shell and counts its electrons, so you can read off the arrangement (2 in shell K, 8 in shell L, 18 in shell M and 5 in shell N) as it forms.

Animation of the arsenic Bohr model being built: a nucleus of 33 protons appears first, then each shell grows in around it and takes its electrons, giving 33 electrons on 4 shells (2 in shell K, 8 in shell L, 18 in shell M and 5 in shell N). — The arsenic Bohr model built up in six seconds: the nucleus first, then each shell with its electrons, ending with 2 in shell K, 8 in shell L, 18 in shell M and 5 in shell N. Protons are red, neutrons yellow and electrons blue.

How to draw the arsenic Bohr model

Find the atomic number. Arsenic has atomic number 33, so a neutral atom has 33 protons and 33 electrons.
Draw the nucleus. Put a circle in the centre and write As in it. The 33 protons sit there with the neutrons.
Draw the shells. Sketch 4 shells as rings around the nucleus. A shell holds at most 2n² electrons: 2 in the first, 8 in the second, 18 in the third and 32 in the fourth.
Place the electrons. Fill from the inside out: 2 in shell K, 8 in shell L, 18 in shell M and 5 in shell N.
Check the total. 2 + 8 + 18 + 5 = 33, the atomic number, so every electron is accounted for.

Atomic data for the arsenic Bohr model

The numbers behind the arsenic Bohr model, grouped by topic. Radii are in picometres (pm) and energies in kilojoules per mole (kJ/mol).

Identity

Symbol: As
Atomic number: 33
Atomic mass: 74.9216 u
Family: Metalloids
Position: group 15, period 4
Block: p-block

Electron configuration

Full: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p³
Shorthand: [Ar] 3d¹⁰ 4s² 4p³
Electrons per shell: 2, 8, 18, 5
Outer-shell electrons: 5 in shell N

Ionisation energies

I₁: 947
I₂: 1798
I₃: 2735
I₄: 4837
I₅: 6043
I₆: 12310

Energy to remove each electron in turn (kJ/mol). A sharp jump means the next electron comes from an inner shell.

Atomic radii

Calculated (pm): 114
Empirical (pm): 115
Covalent (pm): 121
Van der Waals (pm): 185

Electronegativity and electron affinity

Electronegativity (Pauling): 2.18
Electron affinity (kJ/mol): 77.65

Oxidation states

−3 +3 +5

Charges the element commonly takes in compounds.

Physical properties, abundance and history of arsenic

Bulk properties of arsenic, how common it is, who discovered it and some of its compounds.

Physical properties

Phase at room conditions: Solid
Appearance: Metallic grey
Melting point: 816.85°C (1090 K)
Density: 5.727 g/cm³
Specific heat (J/g·K): 0.329
Molar heat capacity (J/mol·K): 24.64
Heat of vaporisation (kJ/mol): 32.4

Abundance

Earth's crust (mg/kg): 1.8
Oceans (mg/L): 0.004

Discovery

Discovered by: Bronze Age
Year: 1250

Common compounds

Arsenic As
Arsanilic Acid C6H8AsNO3
Dimethylarsinic Acid C2H7AsO2
Sodium Arsenite AsNaO2
Arsenic Acid AsH3O4
Gallium arsenide AsGa
Arsenic chloride (AsCl3) AsCl3
Phenylarsine Oxide C6H5AsO

Compounds listed in the PubChem database.

Main isotopes of arsenic

Isotopes of arsenic share the same 33 protons but differ in neutrons. Natural isotopes come first, then the longest-lived others.

Main isotopes of arsenic: mass number, abundance, half-life and decay
Mass number	Natural abundance	Half-life	Decay
71	–	65.3 h	β⁺
73	–	80.3 d	EC
74	–	17.77 d	β⁺, β⁻
75	100 %	stable	–
76	–	1.093 d	β⁻
77	–	38.79 h	β⁻

α = alpha decay, β⁻ = beta-minus, β⁺ = beta-plus, EC = electron capture, SF = spontaneous fission, p / n = proton / neutron emission.

More about arsenic

Arsenic on the periodic table – properties, isotopes, uses and the full arsenic page.
Metalloids – all metalloid elements and their trends.
Bohr model of every element – the Bohr model of all 118 elements.