Titanium is a transition metal with atomic number 22 and mass number 48. A different isotope of titanium has mass number 46. Explain why both of these titanium atoms have the same chemical properties, and state the number of neutrons in each isotope.

Pearson Edexcel International GCSE Chemistry (4CH1) — 1.3 Atomic structure · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Titanium is widely used in aerospace alloys because of its high strength-to-weight ratio. It has several naturally occurring isotopes.

Model answer (4 marks)

Both isotopes have the same number of protons (22) and therefore the same atomic number. Chemical properties are governed by the number of electrons, and both isotopes have 22 electrons. Titanium‑48 has 48−22=26 neutrons. Titanium‑46 has 46−22=24 neutrons.

Examiner tips

State the common proton number first, then explain that chemical behaviour depends on electrons.
Give the neutron count for each isotope using the mass‑number minus proton number formula.
Use the exact wording ‘same number of protons’ and ‘same number of electrons’ to match the mark scheme.

Common mistakes

Confusing mass number with atomic number; writing 48 and 46 as the number of protons.
Forgetting to calculate the neutron numbers or giving incorrect values.
Using vague phrases like ‘similar properties’ instead of ‘same chemical properties’.

Mark scheme (4 marks)

Both isotopes have the same number of protons (22) / same atomic number
Chemical properties are determined by the number of electrons, and both isotopes have the same number of electrons (22)
Titanium-48 has 26 neutrons (48 − 22 = 26)
Titanium-46 has 24 neutrons (46 − 22 = 24)

Key terms in this question

isotope · atomic number · mass number · neutron