4.2The Arrangement in the Periodic Table of Elements
The modern Periodic Table of Elements is a systematic classification of chemical elements arranged in ascending order of their proton numbers from left to right and from top to bottom. By knowing the proton number of an atom, its electron arrangement can be determined, which directly reveals its group and period in the Periodic Table.
Learning Objectives
- Describe briefly the modern Periodic Table of Elements.
- Generalise the relationship between the proton number and the position of elements in the Periodic Table of Elements (groups and periods).
Determining Group and Period from Electron Arrangement
Use the number of valence electrons and the number of filled shells to locate an element in the Periodic Table.
3 to 8 valence electrons → Group = valence electrons + 10
Brief Explanation
Understand how groups and periods are determined.
Groups
Vertical columns in the Periodic Table are called Groups. There are 18 groups. The number of valence electrons determines the group of an element.
- 1 or 2 valence electrons → Group 1 or 2.
- 3 to 8 valence electrons → Group = valence electrons + 10.
Periods
Horizontal rows in the Periodic Table are called Periods. There are 7 periods. The number of shells filled with electrons determines the period of an element.
- Period = number of shells filled with electrons.
| Element | Proton number | Electron arrangement | Valence electrons | Group | Period |
|---|---|---|---|---|---|
| Lithium, Li | 3 | 2.1 | 1 | 1 | 2 |
| Calcium, Ca | 20 | 2.8.8.2 | 2 | 2 | 4 |
| Aluminium, Al | 13 | 2.8.3 | 3 | 13 | 3 |
| Silicon, Si | 14 | 2.8.4 | 4 | 14 | 3 |
| Nitrogen, N | 7 | 2.5 | 5 | 15 | 2 |
| Oxygen, O | 8 | 2.6 | 6 | 16 | 2 |
| Bromine, Br | 35 | 2.8.18.7 | 7 | 17 | 4 |
| Krypton, Kr | 36 | 2.8.18.8 | 8 | 18 | 4 |
Try to Answer First
Answer mentally, then check the explanation.
What determines the period of an element in the Periodic Table of Elements?
An element has a proton number of 14. What is its group and period?
How are elements arranged in the modern Periodic Table of Elements?
Common Mistakes
Avoid these errors when determining the position of an element.
Concept Misunderstandings
Compare each misconception with the correct fact.
Elements in the modern Periodic Table are arranged according to their relative atomic mass.
In the modern Periodic Table, elements are arranged in ascending order of their proton numbers.
All elements take their group number directly from the number of valence electrons.
Only elements with 1 or 2 valence electrons have a group number equal to their valence electrons; elements with 3 to 8 valence electrons must add 10 to determine their group number (Groups 13 to 18).
Summary
Key facts to remember.
- The modern Periodic Table arranges elements in ascending order of proton numbers.
- Groups are the 18 vertical columns determined by the number of valence electrons.
- 1 or 2 valence electrons → Group 1 or 2.
- 3 to 8 valence electrons → Group = valence electrons + 10.
- Periods are the 7 horizontal rows determined by the number of shells filled with electrons.
Short Activity
Complete all parts before checking your score.
A. Objective Quiz
An atom of element X has a proton number of 7. In which group and period is element X located in the Periodic Table of Elements?
What factor determines the period of an element in the Periodic Table of Elements?
B. Fill in the Blanks
The vertical columns in the Periodic Table of Elements are called _____.
For an element with 3 to 8 valence electrons, its group number is calculated by adding the number of valence electrons to _____.
C. Match Each Element to Its Position
Drag each element on desktop. On mobile, tap an element and then tap the matching box.
Element
Lithium, Li (proton number 3) Calcium, Ca (proton number 20) Aluminium, Al (proton number 13) Krypton, Kr (proton number 36)Position in Periodic Table
Keywords
Tap or hover over a term to read its meaning.
