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Chemical Bonding (Ionic, Covalent and Metallic): Question 1

Syllabus 2.4

Multiple choice Core 1 mark

Lithium fluoride (LiF) crystals are used as windows in some ultraviolet spectrometers, because thin slices of the crystal let UV light pass through them. Which statement correctly describes what happens when lithium atoms and fluorine atoms react together to form lithium fluoride?

Choose an answer to check it, then compare with the worked solution below.
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Worked solution

Step 1: Identify the group of each element

Lithium is in Group I, so it has 1 electron in its outer shell. Fluorine is in Group VII, so it has 7 electrons in its outer shell.

Step 2: Work out the direction and number of electrons transferred

A metal atom (lithium) reacting with a non-metal atom (fluorine) forms an ionic bond by electron transfer, not sharing. Lithium only needs to lose its single outer electron to reach a stable, full-shell arrangement (like a noble gas):

Li→Li++e−\text{Li} \rightarrow \text{Li}^+ + e^-

Fluorine needs just one more electron to complete its outer shell:

F+e−→F−\text{F} + e^- \rightarrow \text{F}^-

Step 3: Combine the ions

The resulting Li+\text{Li}^+ ion and F−\text{F}^- ion are held together by a strong electrostatic attraction between the oppositely charged ions. This is the ionic bond.

Why the other options are wrong

  • A: describes a covalent bond (sharing electrons), which happens between non-metal atoms, not between a metal and a non-metal.
  • C: reverses the transfer. Fluorine (Group VII) gains an electron, it does not lose one, and lithium (Group I) loses an electron, it does not gain one.
  • D: lithium has only one electron in its outer shell, so it can transfer only one electron, not two.

Final answer

The correct statement is B\boxed{\text{B}}: lithium transfers one electron to fluorine, forming Li+\text{Li}^+ and F−\text{F}^- ions held together by a strong electrostatic attraction.