87
Fr
Francium
223
Francium
Alkali metal
Francium is element 87, symbol Fr. It sits in period 7, group 1, and weighs 223.
They give up their single outer electron so readily that water sets them off.
- Atomic number
- 87
- Atomic weight
- 223
- Period
- Period 7
- Group
- Group 1
- Block
- s block
- Electron configuration
- [Rn] 7s1
- Outer-shell electrons
- 1
- Neutrons
- 136
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 Francium's number and symbol?
Element 87, symbol Fr, atomic weight 223.
Q. Where does it sit in the table?
Period 7, group 1 — a alkali metal.
Q. What is its electron configuration?
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s1, or [Rn] 7s1 for short.
Q. How many neutrons does it have?
Rounding the atomic weight and subtracting the atomic number gives 136. The exact count depends on the isotope.