Valence electrons and electron dot diagrams for atoms
Grade 10 Science Worksheet
Circle the best answer, or write your answer on the line.
Nitrogen has 5 valence electrons and oxygen has 6. How many valence electrons go into the Lewis structure of nitrate, NO₃⁻, Ari?
Nitrogen has 5 valence electrons and hydrogen has 1. How many valence electrons go into the Lewis structure of ammonium, NH₄⁺, Bo?
Sulfur and oxygen each have 6 valence electrons. How many valence electrons go into the Lewis structure of sulfate, SO₄²⁻, Esme?
CO₂ has 16 valence electrons. Which Lewis structure uses all 16 and gives every atom an octet, Jun?
- O=C=O, with one lone pair on each oxygen, so just 12 are used
- O–C–O, with three lone pairs on each oxygen, so carbon has just 4
- O=C=O, with two lone pairs on each oxygen
NH₃ has 8 valence electrons. How many lone pairs does the nitrogen atom hold in its Lewis structure, Kira?
- 0, because nitrogen's electrons are used up in the bonds themselves
- 3, one lone pair for each bond
- 1: three N–H bonds use 6 electrons, leaving one pair
In H₂O, which statement about electrons around each atom is right, Luz?
- Oxygen has 8 electrons around it, and each hydrogen has 2
- Oxygen has 6 electrons around it, its valence count
- Each atom needs 8 electrons, so each hydrogen atom has 8 as well
Calcium (2-8-8-2) and nitrogen (2-5) form an ionic compound. What is its formula, Noah?
- Ca₃N₂: three Ca give 6 electrons and two N take 6
- CaN: one Ca gives 2 electrons to one N atom, so they balance
- Ca₂N₃: two Ca and three N balance the charges
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Successive ionization energies of magnesium (real data, CRC)
electron removed energy (kJ/mol) first 738 second 1451 third 7733 Why does magnesium form Mg²⁺ and not Mg³⁺, Pia?
- Removing the third electron costs about the same as the second, so Mg³⁺ is possible
- Magnesium atoms have just 2 electrons in total, so no electrons remain to lose
- The third electron comes from a full inner shell and costs 7733 kJ/mol
First ionization energy of group 1 metals (real data, CRC)
metal energy (kJ/mol) lithium 520 sodium 496 potassium 419 rubidium 403 cesium 376 Group 1 metals react more fiercely down the group. What explains it, Ren?
- Each has 1 valence electron, but it sits farther out and is easier to remove
- Each metal has more valence electrons down the group, so more of them can react
- Each nucleus has more protons, so it holds its outer electron less tightly
First ionization energy in period 3 (real data, CRC)
element valence electrons energy (kJ/mol) sodium 1 496 chlorine 7 1251 argon 8 1521 Argon has the highest first ionization energy of these three. Why, Tala?
- Argon has more valence electrons than sodium, and a bigger group is harder to remove
- Argon has fewer shells than sodium, so its electrons sit closer to the nucleus
- Its outer shell is a full octet with 18 protons pulling, so it costs the most