Ch.2 - Atoms & ElementsWorksheetSee all chapters
All Chapters
Ch.1 - Intro to General Chemistry
Ch.2 - Atoms & Elements
Ch.3 - Chemical Reactions
BONUS: Lab Techniques and Procedures
BONUS: Mathematical Operations and Functions
Ch.4 - Chemical Quantities & Aqueous Reactions
Ch.5 - Gases
Ch.6 - Thermochemistry
Ch.7 - Quantum Mechanics
Ch.8 - Periodic Properties of the Elements
Ch.9 - Bonding & Molecular Structure
Ch.10 - Molecular Shapes & Valence Bond Theory
Ch.11 - Liquids, Solids & Intermolecular Forces
Ch.12 - Solutions
Ch.13 - Chemical Kinetics
Ch.14 - Chemical Equilibrium
Ch.15 - Acid and Base Equilibrium
Ch.16 - Aqueous Equilibrium
Ch. 17 - Chemical Thermodynamics
Ch.18 - Electrochemistry
Ch.19 - Nuclear Chemistry
Ch.20 - Organic Chemistry
Ch.22 - Chemistry of the Nonmetals
Ch.23 - Transition Metals and Coordination Compounds

Solution: What are the numbers of electrons, sequentially, in each of the following ions?    Ca2+, Fe2+, I-, O2-       a) 20e-, 26e-, 53e-, 8e-b) 18e-, 26e-, 54e-, 8e-c) 22e-, 28e-, 52e-, 6e-d) 18e-, 24e-, 54e-


What are the numbers of electrons, sequentially, in each of the following ions?    

Ca2+, Fe2+, I-, O2-       

a) 20e-, 26e-, 53e-, 8e-

b) 18e-, 26e-, 54e-, 8e-

c) 22e-, 28e-, 52e-, 6e-

d) 18e-, 24e-, 54e-, 10e-

e) 20e-, 20e-, 53e-, 8e-


We’re being asked to determine number of electrons in the ions given.  Recall that the symbol for an element or ion is as follows:

  • The atomic number tells us the number of protons
  • Recall that in a neutral element the number of protons and electrons are equal
  • So we have to find the atomic number of each from the periodic table. 
  • But here we have ions so we have to modify it. 
    • Every (+) charge removes 1 electron. 
    • Every (-) charge adds 1 electron. 
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