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Lanthanum and actinium, because of their similarities to the other members of the series, are included and used to name the series, even though they are transition metals with no f electrons.

Electron configurations of ions

We have seen that ions are formed when atoms gain or lose electrons. A cation (positively charged ion) forms when one or more electrons are removed from a parent atom. For main group elements, the electrons that were added last are the first electrons removed. For transition metals and inner transition metals, however, electrons in the s   orbital are easier to remove than the d   or f   electrons, and so the  highest   ns   electrons are lost, and then the ( n – 1) d   or  ( n – 2) f electrons are removed. An anion (negatively charged ion) forms when one or more electrons are added to a parent atom. The added electrons fill in the order predicted by the Aufbau principle.

Predicting electron configurations of ions

What is the electron configuration and orbital diagram of:

(a) Na +

(b) P 3–

(c) Al 2+

(d) Fe 2+

(e) Sm 3+


First, write out the electron configuration for each parent atom. We have chosen to show the full, unabbreviated configurations to provide more practice for students who want it, but listing the core-abbreviated electron configurations is also acceptable.

Next, determine whether an electron is gained or lost. Remember electrons are negatively charged, so ions with a positive charge have lost an electron. For main group elements, the last orbital gains or loses the electron. For transition metals, the last s orbital loses an electron before the d orbitals.

(a) Na: 1 s 2 2 s 2 2 p 6 3 s 1 . Sodium cation loses one electron, so Na + : 1 s 2 2 s 2 2 p 6 3 s 1 = Na + : 1 s 2 2 s 2 2 p 6 .

(b) P: 1 s 2 2 s 2 2 p 6 3 s 2 3 p 3 . Phosphorus trianion gains three electrons, so P 3− : 1 s 2 2 s 2 2 p 6 3 s 2 3 p 6 .

(c) Al: 1 s 2 2 s 2 2 p 6 3 s 2 3 p 1 . Aluminum dication loses two electrons Al 2+ : 1 s 2 2 s 2 2 p 6 3 s 2 3 p 1 =

Al 2+ : 1 s 2 2 s 2 2 p 6 3 s 1 .

(d) Fe: 1 s 2 2 s 2 2 p 6 3 s 2 3 p 6 4 s 2 3 d 6 . Iron(II) loses two electrons and, since it is a transition metal, they are removed from the 4 s orbital Fe 2+ : 1 s 2 2 s 2 2 p 6 3 s 2 3 p 6 4 s 2 3 d 6 = 1 s 2 2 s 2 2 p 6 3 s 2 3 p 6 3 d 6 .

(e). Sm: 1 s 2 2 s 2 2 p 6 3 s 2 3 p 6 4 s 2 3 d 10 4 p 6 5 s 2 4 d 10 5 p 6 6 s 2 4 f 6 . Samarium trication loses three electrons. The first two will be lost from the 6 s orbital, and the final one is removed from the 4 f orbital. Sm 3+ : 1 s 2 2 s 2 2 p 6 3 s 2 3 p 6 4 s 2 3 d 10 4 p 6 5 s 2 4 d 10 5 p 6 6 s 2 4 f 6 = 1 s 2 2 s 2 2 p 6 3 s 2 3 p 6 4 s 2 3 d 10 4 p 6 5 s 2 4 d 10 5 p 6 4 f 5 .

Check your learning

Which ion with a +2 charge has the electron configuration 1 s 2 2 s 2 2 p 6 3 s 2 3 p 6 3 d 10 4 s 2 4 p 6 4 d 5 ? Which ion with a +3 charge has this configuration?


Tc 2+ , Ru 3+

Got questions? Get instant answers now!

Key concepts and summary

The relative energy of the subshells determine the order in which atomic orbitals are filled (1 s , 2 s , 2 p , 3 s , 3 p , 4 s , 3 d , 4 p , and so on). Electron configurations and orbital diagrams can be determined by applying the Pauli exclusion principle (no two electrons can have the same set of four quantum numbers) and Hund’s rule (whenever possible, electrons retain unpaired spins in degenerate orbitals).

Electrons in the outermost orbitals, called valence electrons, are responsible for most of the chemical behavior of elements. In the periodic table, elements with analogous valence electron configurations usually occur within the same group. There are some exceptions to the predicted filling order, particularly when half-filled or completely filled orbitals can be formed. The periodic table can be divided into three categories based on the orbital in which the last electron to be added is placed: main group elements ( s and p orbitals), transition elements ( d orbitals), and inner transition elements ( f orbitals).

Questions & Answers

how to complete and balance ionic equation?
what is molar mass?
Wendy Reply
Molar mass is defined as the mass of a sample of a compound divided by the amount of substance of that sample.
or M=m\n mathematically.
atom is the smallest indivisible part of an element that takes place in chemical reaction
Obinna Reply
An atom is the smallest indivisible part of an element
what is chemistry?
Mathias Reply
what is an atom
what is an atom?
is the study of matter and the changes it under goes.
under goes through three state they are solid liquid and gas
in a sturctural way formula for C6H12
sorry ,it's properties and structures
please what is hydroxyl group
Gold Reply
the hydroxyl group is a functional group consisting of a hydrogen atom covalently bonded to an oxygen atom.
Names are of homologous series
Josiah Reply
what's an hydroxyl group?
A hydroxy or hydroxyl group is the entity with the formula OH. It contains oxygen bonded to hydrogen. In organic chemistry, alcohols and carboxylic acids contain hydroxy groups. The anion [OH⁻], called hydroxide, consists of a hydroxyl group. 
what are the steps to follow when writing the condensed formula of elements
Jessicafaith Reply
What is organic chemistry
John Reply
what's organic chemistry?
Mr Reply
why do electrons have no mass
Skynetic Reply
hello there
hi and who say electrons has no mass ? it does have but most at time consider negleable
please what is maa
yeah i will calculate it
Because it's mass it very very small compare with mass of atom
it's simple
consider the rxn of butadiene .Butadiene is prepared by the gas phase catalytic dehydrogenation of 1-butene , at 900K and 1 bar. c4H8 (g)_ C4H6 (g) + H2 (g) (a) In order to suppress side reactions , the butane is diluted with steam before it passes into the reactor.Estimate the conversion
Estimate the conversion of 1-butene for a feed consisting of 10 moles of steam per mole of 1-butene. (b) find the conversion if the inerts were absent and side reactions are ignored .
help me please I have tried
wat is the difference between electrochemical chemical corrosion
please how can i solve this project work..modern aid science process and product
what is the definition of chemistry
Sophia Reply
Sophia pls check on fb u will see transcendence Internationale is a group from here just join over, and ask any question in science from there we here created it
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U will see it
for now chemistry is the study of matter and it properties, why and how element combined to form other substances
Chemistry is a group that identifies properties of matter and many more
Wow and chemistry also is the systematic study of nature
chemistry is the study of the structure, properties of matter and the effect of addition or removal of heat from substances.
calculate the relative molecular Mass of the following 1 ZnCl2 2 NaNo3 3 HNO3 4 CaO
Reuben Reply
2) 23+14+(16×3)= 3)1+14+(16×3)= 4) 40+16= 1) Zn+71= that's how they do it but for Zn I don't know its mass number
Reuben u are welcome to join the group transcendence Internationale on fb we created it for science students is a question and answering platform for all science subjects
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hi guys I'm new here, please I need definition of acid and base
please some one should tell me the meaning of hydro carbon
What is radioactivity
Aaron Reply
radioactivity is the spontaneous disintegration of the nucleus of an atom of an element to emmit radiation
When dividing a certain and uncertain number, you still use sig figs? Ex: 12.86g divided by 12 M&Ms
Kristen Reply
Practice Key Terms 7

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Source:  OpenStax, Chemistry. OpenStax CNX. May 20, 2015 Download for free at http://legacy.cnx.org/content/col11760/1.9
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