En anglais

Ionic bonding: electron transfer and charged lattices

Science · Matter & Materials · ages 14-16

Name ______________________ Date ____________

Why does an ionic solid have such a high melting point?
- its ions are unusually heavy for their size
- the ions are glued together by the electrons in between
- the lattice traps air that has to be driven out of it first
- every ion is pulled on by all the opposite ions around it
A magnesium atom is 2,8,2. How many electrons does it lose to become an ion?
Answer: ______________
What charge does an ion formed by a group 7 non-metal carry?
- 7-, one for each of its outer electrons
- 1+, because it loses one electron
- 1-, because it gains one electron
- 7+, because it loses all seven
A group 3 metal forms an ion. What is the size of its charge?
Answer: ______________
In a dot-and-cross diagram for sodium chloride, what do the dots and the crosses show?
- they mark which atom each electron started on
- dots are protons and crosses are electrons
- dots are full shells and crosses are empty ones
- dots show the electrons that moved and crosses the ones that stayed
After sodium and chlorine react, which particle has the arrangement 2,8,8?
- the sodium ion, which lost one of its electrons
- the sodium atom, before it reacted
- the chlorine atom, before it reacted
- the chloride ion, which gained one electron
A calcium atom is 2,8,8,2. What ion does it form?
- Ca2-, by gaining two electrons from a non-metal
- Ca6+, by emptying its outer two shells
- Ca2+, by losing its two outer electrons
- Ca8+, by losing everything above the first shell
Calcium ions are 2+ and nitride ions are 3-. How many calcium ions balance two nitride ions?
Answer: ______________
The ions in a molten ionic compound are held as firmly as they are in the solid.
Circle one: True False
Magnesium oxide melts at 2852 degrees and sodium chloride at 801. What explains the gap?
- magnesium oxide's formula holds more ions than sodium chloride's
- sodium chloride is a solution rather than a solid
- 2+ and 2- pull on each other harder than 1+ and 1- do
- magnesium oxide has no lattice, so it melts differently

Answer key

For grown-ups. Fold this page away before handing over the rest.

Ionic bonding: electron transfer and charged lattices W1-mt_sf24C4YLtN-s1

every ion is pulled on by all the opposite ions around it · A lattice is not a set of pairs. Each ion is held by every oppositely charged neighbour, and melting has to beat all of those attractions at once.
2 · The outer shell holds 2, and losing both leaves the full 2,8 underneath. That makes the ion 2+.
1-, because it gains one electron · A group 7 atom has 7 outer electrons and needs one more for a full shell. Gaining that one electron makes it 1-.
3 · Group 3 means three outer electrons. Losing all three leaves a full shell underneath and a charge of 3+.
they mark which atom each electron started on · Dots and crosses are just two ways of drawing an electron. Using both lets you see which atom each electron started on, so the transfer is visible.
the chloride ion, which gained one electron · Chlorine starts at 2,8,7 and takes one electron, reaching 2,8,8. Sodium starts at 2,8,1 and drops one, so its ion is 2,8.
Ca2+, by losing its two outer electrons · Two outer electrons make calcium a group 2 metal. Losing both leaves the full 2,8,8 underneath and a charge of 2+.
3 · Two nitride ions come to 6-. Each calcium ion offers 2+, so three of them give 6+ and the formula is Ca₃N₂.
False · Melting is exactly the process of beating those attractions. In the melt the ions still attract each other, but they are no longer locked in place, which is why the melt conducts.
2+ and 2- pull on each other harder than 1+ and 1- do · Both are giant ionic lattices. Magnesium oxide is built from 2+ and 2- ions, and bigger charges attract more strongly, so more heat is needed to pull the lattice apart.