1.1 Simple Model of the Atom

This question is about atomic structure.

A group of students looks at the diagram below showing the arrangement of electrons in a chemical substance.

The students make the following incorrect or incomplete conclusions:

• Student 1 states that the substance is fluorine, neon or sodium
• Student 2 states that it is not possible to determine which atom or ion the diagram represents
• Student 3 states that the mass number is 10

Explain how students 1 and 2 could combine their ideas to produce one possible correct conclusion with an appropriate justification.

Evaluate student 1's suggestions of fluorine and sodium.

Correct student 3's statement. Explain your reasoning.

The students are told that the diagram represents  .

Describe the additions that should be made to the diagram to show this.

A scientist produces silicon.

In the first step, the scientist first heats a mixture of sand (silicon dioxide) and magnesium powder. 

In the second step, after cooling, the resulting mixture containing magnesium oxide and silicon is placed into a beaker and hydrochloric acid is added.

Write a balanced symbol equation, including state symbols, for the reaction in the first step.

Write the word equation for the reaction that occurs in the second step.

Explain how the silicon can be removed from the final reaction mixture.

During the second step, several gases are also produced.

One of the gases produced is silane, SiH₄, which has a similar structure to methane, CH₄.

Silane spontaneously reacts with oxygen.

 SiH₄ (g) + 2O₂ (g) → SiO₂ (s) + 2H₂O (l)

Compare, in terms of energy, the strength of the Si-H bond in silane compared to the C-H bond in methane.

This question is about mixtures.

Figure 1 shows a chromatogram of the food dyes in a black food colouring.

Figure 1

Describe how a student could obtain a chromatogram similar to the one shown in Figure 1.

Chromatography is performed on another black food colouring. 

This new food colouring contains the same individual dyes as those shown in Figure 1 but in different proportions.

Predict the appearance of this chromatogram. Justify your answer.

A student prepares a sample of butan-1-ol, which has a boiling point of 118 ^oC.

The sample contains an impurity with a boiling point of 125 ^oC.

The student plans to purify the sample using the equipment shown in Figure 2.

Explain why this equipment is unsuitable for separating the reaction mixture.

Explain why cold water should enter the condenser at the lowest point.

This question is about chlorine.

Explain the information given by the numbers in the chemical symbol for chlorine.

Calculate the number of atoms that are present in one mole of chlorine gas.

Complete the dot and cross diagram to show the covalent bonding in a chlorine molecule, Cl₂.

Show only the electrons in the outer shell.

The radius of a chlorine atom is approximately 1 x 10^-10 m.

State and explain the difference, if any, between the radius of a chlorine atom and a chloride ion.

The many millions of different substances in the world are all made from elements.

Define the term ‘element’.

Most of the substances that we come across everyday are compounds.

What is a compound?

The series of diagrams in Figure 1 below shows different ways of representing the atom.

Figure 1

Which diagram represents the plum pudding model of the atom?

Tick (✔) one box.

Which diagram represents the model that is based on the alpha particle scattering experiment?

Tick (✔) one box.

Which diagram represents the model of the atom according to Bohr's work?

Tick (✔) one box.

Write down the definition for the mass number of an atom.

Element Z has two isotopes. Their masses are 57  and 59.

The percentage abundance of each isotope is:

• 75% of ⁵⁷Z
• 25% of ⁵⁹Z

Estimate the relative atomic mass of element Z.

Tick (✔) one box.

The work that Chadwick carried out in his experiments allowed for a better understanding of isotopes.

Explain how his work made advances in our understanding of isotopes.

This question is based on atoms.

What does the number 24 represent in ²⁴Mg?

The nuclear model of the atom was based on experimental work involving the alpha particle scattering experiment. 

This model replaced the older plum pudding model. 

Compare both of these models.

The mass numbers and percentage abundance of three isotopes of an element are shown in Table 1.

Table 1

Calculate the relative atomic mass (A_r) of the element.

Give your answer to 3 significant figures.

The second row of the periodic table holds eight elements starting with lithium and ending with neon.

Figure 2 shows an atom with two electron shells or energy levels.

Figure 2

Complete Figure 2 to represent the electronic structure of an atom of boron, using X’s to represent the electrons.

Name the part of the atom labelled Z in Figure 2.

Give the name of the subatomic particles in part Z of a boron atom.

State the relative charges of these subatomic particles.

The electronic structure in Figure 3 is of a neon atom and it is not correct.

Explain what is wrong with the electronic structure shown in Figure 3.

This question is based on chlorine.

What is the group number of chlorine?

Complete the table below showing the properties of the subatomic particles.

Use the correct word from the box to complete the sentence below.

alkalis         alloys         isotopes 

Atoms of chlorine with different numbers of neutrons are called _____________ .

Sodium reacts with chlorine to form common table salt.

Complete the word equation for this reaction.

Sodium     +    _______________   →     ______________

Write the half equation to show sodium metal becoming a sodium ion.

Complete the half equation to show a molecule of chlorine becoming chloride ions.

 Cl₂ + _____  →  _____

Complete the following sentences.

Substances in which atoms of two or more different elements are chemically combined are called _______________.

Substances that are placed together in the same container, that do not react with each other and can be separated by physical means are called _____________. 

Rock salt is a mixture of sand and salt. Salt dissolves in water while sand does not. 

A group of students separated rock salt. 

They used the following method.

1. Add the rock salt to a beaker.

2. Add 250 cm³ of water.

3. Leave without disturbing to allow the sand to settle to the bottom.

4. After a while, decant the salt water into an evaporating dish.

5. Heat the evaporating dish with a Bunsen burner until salt crystals begin to form.

Suggest one improvement to step 2 that the students could have done to make sure all the salt is dissolved.

The salty water in step 4 still contained a very small amount of sand grains. 

Suggest one improvement to step 4 that could successfully remove the sand.

Suggest one safety precautions the students should take in step 5.

Another student separated water from salty water using the apparatus in the diagram below.

By referring to points 1 and 2 in Figure 4, describe how this technique works.

What is the reading on the thermometer during this process?

Reading: _______