Sodium ions

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Definition and electronic structure

A sodium atom that has lost an electron becomes the monatomic charged sodium ion and is denoted by the symbol Na+. Sodium ions have the electronic structure[1] 1s22s22p6, as they have become oxidised, having lost the lone electron in its 3s subshell: this is why sodium ions have a +1 charge overall.

Sodium ions in the human body

Sodium ions are present in the human body playing key roles in several processes, such as in the primary active transport carried out by the Na+/K+-ATPase[2], during the depolarisation of neuronal cell membranes during an action potential and as an important component in the secondary active transport of glucose which is completed by the Na+-glucose symporter.

When a stimulus causes membrane potential to rise from its resting potential of -70 mV to threshold frequency of -55 mV. It causes the voltage gated sodium channels to open allowing the flow of sodium ions into the cell resulting in depolarisation. Once the neurone reaches peak polarisation the sodium channels close and the potassium channels open allowing the flow of potassium ions out of the cell – this is called repolarization. During repolarisation, too many potassium ions move out of the cell causing the membrane potential to fall too low therefore resulting in hyperpolarisation. When hyperpolarisation occurs, the membrane must restore the potential back to its resting potential by transporting 3 Na+ out of the cell and 2K+ into the cell via the sodium potassium pump using ATP[3].

In compounds

Sodium ions also form ionic compounds with negative ions, a common example being the neutral ionic compound sodium chloride (NaCl), where the sodium ion has a positive +1 charge (Na+) and the chloride ion has a negative -1 charge (Cl-1).


  1. Chemguide. Electronic Structures Of Ions. 2012 [cited 30/11/2016]. Available from:
  2. Georgia State University, HyperPhysics. The Sodium-Potassium Pump. Published: N/A [cited 30/11/2016]. Available from:
  3. Hyper Physics, Ka Xiong Charand,
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