Healthy Atomic Structure Competition

What two aspects of atomic structure are the same for atoms of phosphorus-26 and phosphorus-27?

• the number of neutrons and the number of electrons

• the number of neutrons and the number of protons

• the number of protons and the number of electrons

• the atomic number and the mass number

Answer explanation

The only difference in composition between isotopes is the number of neutrons present in the nucleus of the atoms

A sample of an element is analysed in a mass spectrometer and the spectrum produced is shown below. What is the relative atomic mass of the element?

• 65.0

• 66.0

• 64.5

• 65.5

Answer explanation

Relative atomic mass = [(64 × 40) + (66 × 30) + (67 × 30)]/100 = 65.5

How many neutrons are there in an atom of oxygen represented by the following symbol?

• 18

• 8

• 16

• 10

Answer explanation

the difference between the mass number (18) and the atomic number (8) is 10. This is an isotope of oxygen.

An atom of any element contains equal numbers of which of the following sub-atomic particles?

• Electrons and neutrons

• Electrons and protons

• Electrons, neutrons and protons

• Neutrons and protons

Answer explanation

atoms are electrically neutral as they contain equal numbers of protons and electrons. If these are not equal then the particle concerned is not an atom but an ion. 

Which sub-atomic particle(s) is/are located in the nucleus of an atom?

• protons only 

• protons and electrons 

• protons and neutrons 

• neutrons and electrons 

Answer explanation

The nucleus of an atom contains the protons and neutrons (collectively known as nucleons). Together, they are responsible for the majority of the mass of an atom. 

Which species has the following composition of subatomic particles: 19 protons, 20 neutrons, and 18 electrons?

• ³⁹₁₉K⁺ 

• ⁴⁰₂₀Ca²⁺

• ³⁹₁₉K

• ⁴⁰₁₈Ar

Answer explanation

³⁹₁₉K⁺ has 19 protons, 20 neutrons and 18 electrons. Note that it has one less electron than protons because it is a positive ion with a 1+ charge.

Cadmium is an element that has several isotopes. One of these isotopes is ¹¹²₄₈Cd. Which of the species in the table is also an isotope of cadmium?

• iv

• ii

• i

• iii

Answer explanation

The answer must be either i or ii because 48 is the atomic number of cadmium. The number of neutrons in the isotope given in the question is 112 - 48 = 64 so a different isotope would have a similar (but different) number of neutrons. So 66 is the correct answer.

Naturally occurring hydrogen consists of two different isotopes. These are ¹₁H and ²₁H. Which diagram shows the arrangement of particles in the two isotopes?

• 
• 
• 
• 

Answer explanation

The only difference is an extra neutron in the heavier isotope.

Which line in the following table is correct for the properties of these regions of the electromagnetic spectrum?

• iii

• i

• ii

• iv

Answer explanation

UV radiation has high energy, high frequency and short wavelength. Infrared has longer wavelength, lower energy and lower frequency.

Which statement regarding the electron transitions that result in the formation of an emission line spectrum is correct?

• Electrons absorb energy as they transition from higher to lower energy levels.

• Electrons absorb energy as they transition from lower to higher energy levels.

• Electrons emit energy as they transition from higher to lower energy levels.

• Electrons emit energy as they transition from lower to higher energy levels.

Answer explanation

emission line spectra are produced by electron transitions from higher energy levels to lower energy levels. These electron transitions release energy in the form of electromagnetic radiation. Absorption line spectra are produced when electrons absorb energy and transition to higher energy levels. Like emission spectra, the energy is absorbed in the form of electromagnetic radiation.