101
Md
Mendelevium
258
Mendelevium
Actinide
Mendelevium is element 101, symbol Md. It sits in period 7, in the rows below the table, and weighs 258.
The second row below the table. All radioactive, and most of them made by people.
- Atomic number
- 101
- Atomic weight
- 258
- Period
- Period 7
- Group
- set below the table
- Block
- f block
- Electron configuration
- [Rn] 7s2 5f13
- Neutrons
- 157
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 Mendelevium's number and symbol?
Element 101, symbol Md, atomic weight 258.
Q. Where does it sit in the table?
Period 7, among the actinides drawn below the table.
Q. What is its electron configuration?
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f13, or [Rn] 7s2 5f13 for short.
Q. How many neutrons does it have?
Rounding the atomic weight and subtracting the atomic number gives 157. The exact count depends on the isotope.