Question 1 Medium
An element has the electronic structure 2,8,1. Give its period number.
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Answer: 3
- Three shells contain electrons.
- So it is in Period 3.
The periodic table and electronic structure: GCSE Combined Science Chemistry practice questions
A second set of questions on the periodic table and electronic structure. They are different from the ones on the topic page. Try each, then open the answer and compare your working.
More questions
Question 2 Medium
Which element has the electronic structure 2,8,8? Its atomic number is 18.
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Answer: argon
- Atomic number 18 is argon.
- Its outer shell is full, so it is a noble gas.
Question 3 Medium
An element has atomic number 14. Give its electronic structure.
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Answer: 2,8,4
- 2 in the first shell and 8 in the second.
- 14 − 10 = 4 in the third shell.
Question 4 Medium
An element is in Group 3 and Period 2. Give its electronic structure.
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Answer: 2,3
- Period 2 means two shells, so the first has 2.
- Group 3 means 3 outer electrons, so 2,3.
Question 5 Hard
Magnesium forms an ion by losing electrons. Write the formula of the ion, including its charge.
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Answer: Mg²⁺
- Magnesium is 2,8,2.
- It loses 2 outer electrons.
- The ion is Mg²⁺.
Question 6 Hard
Oxygen has the electronic structure 2,6. State the charge on an oxide ion.
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Answer: 2−
- Oxygen needs 2 more electrons for a full outer shell.
- Gaining 2 electrons gives a charge of 2−.
Question 7 Hard
Why does helium have 2 outer electrons but sit in Group 0?
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Answer: its outer shell is full
- Its first shell holds only 2 electrons.
- The outer shell is full, like the other noble gases.
Question 8 Hard
Mendeleev swapped the order of tellurium and iodine in his table. Give one reason why.
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Answer: so they fitted the groups with similar properties
- Their atomic masses suggested the opposite order.
- The properties fitted better in the swapped order.
Quick checks
Short questions with options. Choose one before you open the answer.
Check 1
What is a group in the periodic table?
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A column. Elements in a group have similar properties.
Check 2
What is a period in the periodic table?
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A row.
Check 3
In what order are the elements arranged?
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Increasing atomic number.
Check 4
Where are metals in the periodic table?
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To the left of the stepped line.
Check 5
What does the group number tell you?
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The number of electrons in the outer shell.
Check 6
What does the period number tell you?
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The number of shells that contain electrons.
Check 7
How many electrons can the first shell hold?
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2.
Check 8
How many electrons can the second shell hold?
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8.
Check 9
What is the electronic structure of sodium?
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2,8,1.
Check 10
What is the electronic structure of chlorine?
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2,8,7.
Check 11
What type of ion do metals form?
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Positive ions, by losing electrons.
Check 12
What do non-metals do in reactions?
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Gain electrons to form negative ions, or share electrons.
Check 13
Why did Mendeleev leave gaps in his table?
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For elements not yet discovered, whose properties he predicted.
Check 14
What was Mendeleev’s table arranged by?
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Atomic mass, with elements with similar properties in the same column.
Check 15
Name a non-metal that conducts electricity.
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Graphite, a form of carbon.
Check 16
Describe the typical appearance of a solid non-metal.
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Dull and brittle.
Check 17
What is the electronic structure of magnesium?
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2,8,2.
Check 18
How many electrons can the third shell hold, in the first 20 elements?
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8.
Check 19
Why is helium in Group 0 and not Group 2?
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Its outer shell is full with 2 electrons.
Check 20
What ion does a Group 1 metal form?
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A 1+ ion, by losing 1 electron.
Check 21
What ion does a Group 7 element form?
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A 1− ion, by gaining 1 electron.
Check 22
What charge is on the ion of a Group 2 metal?
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2+.
Check 23
Which scientist arranged elements by atomic mass in 1869?
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Mendeleev.
Check 24
Which two elements did Mendeleev swap in his table?
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Tellurium and iodine.
Check 25
What does brittle mean for a solid?
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It breaks or shatters when hit.
Check 26
What does atomic number tell you about an atom?
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The number of protons, which is also the number of electrons in a neutral atom.
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