Complete the table below by determining both the number of valence electrons and the…

CHEMISTRY · Multi-part · A Level · Chemistry · Atomic structure · Atomic structure

Problem

Complete the table below by determining both the number of valence electrons and the number of core electrons for each species listed. Use the ground-state electron configuration for every species.

Species	Atomic number (Z)	Charge	Number of valence electrons	Number of core electrons
(i) Br	35	0	?	?
(ii) Se $^{2-}$	34	–2	?	?
(iii) Ca $^{2+}$	20	+2	?	?
(iv) K	19	0	?	?
(v) Al $^{3+}$	13	+3	?	?

(a) For each species, write its complete ground-state electron configuration in spectroscopic (orbital) notation. (b) Using your configurations from part (a), fill in the last two columns of the table with the correct numbers of valence and core electrons. (c) For the pair consisting of Ca

^{2+}

and K, explain why they have the same total number of electrons but different numbers of valence electrons.

Related theory

Atomic Structure
Electronic Configuration
Electron Configurations
Structure of Atom
Atomic Structure and Electron Configuration

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