33
As
Arsenic
74.922
Arsenic
Metalloid
Arsenic is element 33, symbol As. It sits in period 4, group 15, and weighs 74.922.
Part metal, part nonmetal — which is what makes semiconductors possible.
- Atomic number
- 33
- Atomic weight
- 74.922
- Period
- Period 4
- Group
- Group 15
- Block
- p block
- Electron configuration
- [Ar] 4s2 3d10 4p3
- Outer-shell electrons
- 5
- Neutrons
- 42
The periodic table
Rows are periods, columns are groups. Tap any square to open that element.
1H2He3Li4Be5B6C7N8O9F10Ne11Na12Mg13Al14Si15P16S17Cl18Ar19K20Ca21Sc22Ti23V24Cr25Mn26Fe27Co28Ni29Cu30Zn31Ga32Ge33As34Se35Br36Kr37Rb38Sr39Y40Zr41Nb42Mo43Tc44Ru45Rh46Pd47Ag48Cd49In50Sn51Sb52Te53I54Xe55Cs56Ba57La58Ce59Pr60Nd61Pm62Sm63Eu64Gd65Tb66Dy67Ho68Er69Tm70Yb71Lu72Hf73Ta74W75Re76Os77Ir78Pt79Au80Hg81Tl82Pb83Bi84Po85At86Rn87Fr88Ra89Ac90Th91Pa92U93Np94Pu95Am96Cm97Bk98Cf99Es100Fm101Md102No103Lr104Rf105Db106Sg107Bh108Hs109Mt110Ds111Rg112Cn113Nh114Fl115Mc116Lv117Ts118Og
Others in the same group
Neighbours by number
How to read this
- A row (period) is the number of electron shells. Elements in period 3 carry three of them.
- A column (group) tells you how many electrons sit in the outer shell — which is why a group behaves alike.
- Atomic weight runs at roughly twice the atomic number: about as many neutrons as protons.
- The 28 lanthanides and actinides are drawn below the table. Slotting them in would stretch it to 32 columns.
Frequently asked questions
Q. What are Arsenic's number and symbol?
Element 33, symbol As, atomic weight 74.922.
Q. Where does it sit in the table?
Period 4, group 15 — a metalloid.
Q. What is its electron configuration?
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p3, or [Ar] 4s2 3d10 4p3 for short.
Q. How many neutrons does it have?
Rounding the atomic weight and subtracting the atomic number gives 42. The exact count depends on the isotope.