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20 Ca Calcium 40.0784

Calcium

ALKALINE EARTH METAL
Bohr Model: Electrons arranged in energy shells around the nucleus.

Calcium is a chemical element with symbol Ca and atomic number 20. Calcium is a soft gray alkaline earth metal, fifth-most-abundant element by mass in the Earth's crust. The ion Ca2+ is also the fifth-most-abundant dissolved ion in seawater by both molarity and mass, after sodium, chloride, magnesium, and sulfate.

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Quick Facts

Atomic Number 20
Period 4
Group 2
Phase Solid
Appearance Unknown
About Alkaline Earth Metals

Alkaline earth metals (Group 2) are reactive metals, though less so than alkali metals. They typically lose two electrons to form cations with a +2 charge.

History

Discovered By Humphry Davy
Named By Unknown

Physical Properties

Atomic Mass 40.0784
Density 1.55 g/L
Molar Heat 25.929 J/(mol·K)
Phase Transition (Melting & Boiling Points)

Calcium melts at 1115 K and boils at 1757 K.

Atomic Properties

Electron Config [Ar] 4s2
Electronegativity 1
Electron Affinity 2.37 kJ/mol
Ionization Energy 589.8 kJ/mol
Orbital Filling Diagram
This diagram visualizes electron configuration according to the Aufbau principle and Hund's rule. Boxes represent orbitals (s, p, d, f), while arrows indicate electrons with spin up or down. Electrons fill lower energy levels first and occupy orbitals singly before pairing.
Emission Spectrum Emission spectrum of Calcium

Photograph

Image of Calcium Source: Wikipedia

External Resources

Wikipedia PubChem Royal Society of Chemistry Periodic Videos (YouTube)

Study Guide

Atomic Number

The number of protons in the nucleus, which defines the element.

Atomic Mass

The average mass of an atom, including protons and neutrons.

Electronegativity

A measure of how strongly an atom attracts electrons in a bond.

Ionization Energy

The energy required to remove an electron from an atom.

Electron Config

The arrangement of electrons in the atom's energy shells.