Valence electrons and electron dot diagrams for atoms

Answer Key - Grade 10 Science Worksheet - Challenge Me

Circle the best answer, or write your answer on the line.

1. 1.

   In N₂, each nitrogen has 5 valence electrons, 2 nonbonding and 6 shared in a triple bond. Formal charge = valence − nonbonding − shared ÷ 2. What is it, Bo?

   0
2. 2.

   Jun draws ozone, O₃ (18 valence electrons), as O=O=O with two lone pairs on each end oxygen and none on the center. What is wrong?

   • It uses 20 electrons: one lone pair should be removed from each end oxygen atom here
   • It uses 16 electrons, not 18: one bond must become single so the center gets a lone pair
   • Nothing: double bonds on both sides are the way to give each oxygen a full octet of 8
3. 3.

   NO has 11 valence electrons. Why can't both atoms get a full octet, Kira?

   • Nitrogen's 5 and oxygen's 6 must add to 12, so one electron is missing
   • 11 is odd, so one electron stays unpaired and one atom has 7 electrons
   • A triple bond N≡O gives both atoms an octet with electrons to spare
4. 4.

   Phosphorus forms PCl₅, but nitrogen cannot form NCl₅. Why, Luz?

   • Phosphorus has more valence electrons than nitrogen does, so it bonds more
   • Phosphorus is in period 3 and can hold more than 8; nitrogen is limited to 8
   • Nitrogen has 5 valence electrons and chlorine 7, so 3 bonds can fit

5. Read this first

   Ionization energies of sodium (real data, CRC)

   electron removed	energy (kJ/mol)
   first	496
   second	4562

6. 5.

   Sodium's first ionization energy is 496 kJ/mol and its second is 4562 kJ/mol. What does the jump show, Milo?

   • The second electron comes from a full inner shell, so sodium forms Na⁺, not Na²⁺
   • Sodium wants to lose two electrons, but the second is just a little harder to remove
   • The jump shows that sodium has 2 valence electrons, with the second being tight

7. Successive ionization energies of element X (real data, CRC)

   electron removed	energy (kJ/mol)
   first	738
   second	1451
   third	7733
   fourth	10543

8. 6.

   Element X has the ionization energies in the table. Which group is it in, Noah?

   • Group 1: the first energy is the smallest in the list
   • Group 2: the big jump comes after the second electron
   • Group 4: four energies are listed, so four electrons come off
9. 7.

   A chloride ion (181 pm) is much bigger than a chlorine atom (99 pm). Why, Pia?

   • The ion has gained a proton, which pulls its outer shell farther outward
   • The ion has gained a whole extra shell of electrons around its nucleus
   • Both have 17 protons, but 18 electrons repel each other and spread out
10. 8.

    Helium has 2 valence electrons yet is as unreactive as neon, which has 8. Why, Ren?

    • Helium has 8 electrons around it, counting both of its shells
    • Helium is unreactive because it is a very light gas, lighter than any other
    • Helium's only shell holds 2, so its outer shell is already full
11. 9.

    Iron forms both Fe²⁺ and Fe³⁺. Why can transition metals form more than one ion, Tala?

    • Iron has 2 valence electrons for 2+, and air supplies the extra electron for 3+ ions
    • Iron has 3 valence electrons, so it can form just a 3+ ion
    • Their s and next-to-outer d electrons are close in energy, so they can lose 2 or 3
12. 10.

    N₂ has 10 valence electrons. Which Lewis structure gives both nitrogen atoms an octet, Zee?

    • N–N with three lone pairs on each nitrogen: 2 + 12 = 14 electrons
    • N=N with two lone pairs on each nitrogen: 4 + 8 = 12 electrons
    • N≡N with one lone pair on each nitrogen: 6 + 4 = 10 electrons