1 - This question is about the periodic table.
In the 19th century, some scientists tried to classify the elements by arranging them in order of their atomic weights.
Figure 1 shows the periodic table Mendeleev produced in 1869.
His periodic table was more widely accepted than previous versions.
Figure 1
1-1 The atomic weight of tellurium (Te) is 128 and that of iodine (I) is 127. Why did Mendeleev reverse the order of these two elements?
[1 mark]
ANSWER
Mendeleev swapped around the order of iodine (atomic weight 127) and tellurium (atomic weight 128). He placed iodine after tellurium so that it was in the same group as fluorine, chlorine and bromine which have very similar properties. Mendeleev actually believed that the atomic weights must have been measured incorrectly.
1-2 Mendeleev left spaces marked with an asterisk *.
He left these spaces because he thought missing elements belonged there.
Why did Mendeleev’s periodic table become more widely accepted than previous versions?
[3 marks]
ANSWER
Mendeleev had predicted properties of missing elements. After some time, some elements were discovered whose properties matched Mendeleev’s predictions.
1-3 Mendeleev arranged the elements in order of their atomic weight.
What is the modern name for atomic weight?
[1 mark]
Tick () one box.
ANSWER
Relative Atomic Mass
1-4 Complete the sentence.
In the modern periodic table, the elements are arranged in order of _______ proton number.
ANSWER
In the modern periodic table, the elements are arranged in order of increasing proton number.
1-5 Chlorine, iodine and astatine are in Group 7 of the modern periodic table. Astatine (At) is below iodine in Group 7.
Predict:
• The formula of an astatine molecule
• The state of astatine at room temperature.
[2 marks]
ANSWER
Formula of astatine molecule is At2
State at room temperature is Solid
1-6 Sodium is in Group 1 of the modern periodic table.
Describe what you would see when sodium reacts with chlorine.
[2 marks]
ANSWER
We will see that sodium burn with a flame and we will then see a white powder.
