20
Ca
Calcium
40.078
Calcium
Alkaline earth metal
Calcium is element 20, symbol Ca. It sits in period 4, group 2, and weighs 40.078.
Metals that give up two electrons — vigorous, but less so than the alkali metals.
- Atomic number
- 20
- Atomic weight
- 40.078
- Period
- Period 4
- Group
- Group 2
- Block
- s block
- Electron configuration
- [Ar] 4s2
- Outer-shell electrons
- 2
- Neutrons
- 20
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 Calcium's number and symbol?
Element 20, symbol Ca, atomic weight 40.078.
Q. Where does it sit in the table?
Period 4, group 2 — a alkaline earth metal.
Q. What is its electron configuration?
1s2 2s2 2p6 3s2 3p6 4s2, or [Ar] 4s2 for short.
Q. How many neutrons does it have?
Rounding the atomic weight and subtracting the atomic number gives 20. The exact count depends on the isotope.