Atomic Structure and Isotopes: Chemistry 0620 (Cambridge O Level / IGCSE)

A science museum's touring exhibition includes a large mechanical model of an atom for visitors to explore. A small plaque fixed to one of the modelled particles reads:

relative charge = 0, relative mass = 1

Which particle does this plaque describe?

A hydroponics company grows lettuce indoors and tests a nutrient solution before it is pumped to the plants. One test measures the potassium content of the solution using the isotope of potassium shown below.

${}^{39}_{19}\text{K}$

(a) State what the numbers 39 and 19 represent in this symbol. [2]

(b) For one atom of this isotope, state the number of protons, the number of neutrons and the number of electrons. [3]

(c) In the nutrient solution, potassium is present as $\text{K}^+$ ions rather than as atoms. State the number of electrons in one $\text{K}^+$ ion of this isotope. [1]

A sports-drink manufacturer is writing a technical data sheet explaining the electrolyte ions in a new product: sodium ions, $\text{Na}^+$, and chloride ions, $\text{Cl}^-$. Sodium has proton number 11 and chlorine has proton number 17.

(a) Write the electronic configuration of a sodium atom and of a chlorine atom. [2]

(b) Write the electronic configuration of a $\text{Na}^+$ ion and of a $\text{Cl}^-$ ion. [2]

(c) State the name of the noble gas that has the same electronic configuration as (i) the $\text{Na}^+$ ion, and (ii) the $\text{Cl}^-$ ion. [2]

(d) Magnesium, proton number 12, is also used in some sports-drink formulations, as $\text{Mg}^{2+}$. Use the electronic configuration of a magnesium atom to state which group of the Periodic Table magnesium is in, and explain your reasoning. [2]

A hospital radiology department uses two different forms of iodine: iodine-123, used in small amounts as a tracer for thyroid imaging, and iodine-131, used in larger doses to treat an overactive thyroid. Both are the same element, but with different mass numbers. Iodine has proton number 53.

(a) Define the term isotope. [2]

(b) State the number of neutrons in one atom of iodine-123 and in one atom of iodine-131. [2]

(c) Explain, in terms of subatomic particles, why iodine-123 and iodine-131 have the same chemical properties. [2]

A battery-recycling plant extracts lithium metal from used batteries and analyses a sample using a mass spectrometer. The results show the sample contains only two naturally occurring isotopes of lithium, lithium-6 and lithium-7, in the relative abundances shown in the table. Lithium has proton number 3.

(a) State the number of protons and the number of neutrons in one atom of lithium-7. [2]

(b) Calculate the relative atomic mass, $A_r$, of this lithium sample. Give your answer to 3 significant figures. [3]

(c) Explain why lithium-6 and lithium-7 can be extracted and used together as the same element, even though their atoms are not identical. [2]

A dental clinic uses a fluoride varnish containing the isotope shown below:

${}^{19}_{9}\text{F}$

Which row correctly states the numbers of protons, neutrons and electrons in one atom of this isotope?

A structural engineer is testing an aluminium bracket that has a thin phosphorus-based fireproof coating. Separately, an agricultural chemist is checking the potassium content of a soil fertiliser. Aluminium has proton number 13, phosphorus has proton number 15, and potassium has proton number 19.

(a) Write the electronic configuration of an aluminium atom and of a phosphorus atom. [2]

(b) State the number of outer-shell electrons in an aluminium atom and in a phosphorus atom, and hence give the group number of each element. [2]

(c) Write the electronic configuration of a potassium atom and state which group of the Periodic Table potassium is in. [2]

An analytical laboratory identifies four atoms, W, X, Y and Z, in a mineral sample. The table shows the proton number and nucleon number of each atom.

Which two atoms are isotopes of each other?

A geologist analyses a magnesium-rich mineral sample in a mass spectrometer and finds three naturally occurring isotopes of magnesium present in the abundances shown in the table. Magnesium has proton number 12.

(a) State the number of protons and the number of neutrons in one atom of magnesium-26. [2]

(b) Calculate the relative atomic mass, $A_r$, of this magnesium sample. Give your answer to 3 significant figures. [4]

(c) Magnesium-24 and magnesium-26 have different masses. Explain, in terms of subatomic particles, why samples of pure magnesium made from only magnesium-24 atoms or only magnesium-26 atoms would react identically with dilute hydrochloric acid. [2]

A metallurgist analyses a sample of pure copper wire and finds it contains only two naturally occurring isotopes, copper-63 and copper-65. The relative atomic mass of this copper sample is found to be $63.55$. Copper has proton number 29.

(a) State the number of protons and the number of neutrons in one atom of copper-65. [2]

(b) Let the percentage abundance of copper-63 in the sample be $x$. Write an expression, in terms of $x$, for the percentage abundance of copper-65. [1]

(c) Using your expression from (b) and the relative atomic mass given above, calculate the percentage abundance of copper-63 and of copper-65 in this sample. [3]

(d) Copper-63 and copper-65 have different numbers of neutrons. Explain, in terms of subatomic particles, why they can be extracted and used together as a single element, copper. [2]