8.2 Modern Periodic Table of Elements
The Modern Periodic Table of Elements contains 118 known elements organised systematically based on their atomic structure. By arranging elements according to their proton numbers, scientists can easily predict their chemical and physical properties.
Learning Objectives
- State the principle of arrangement of elements in the Modern Periodic Table of Elements.
- Identify the groups, periods, and special series (lanthanoids and actinoids) in the Modern Periodic Table.
- Describe the changes in properties of elements across a period from left to right.
- Determine the electron arrangement of atoms for elements with proton numbers 1 to 20.
- Explain the formation of positive ions and negative ions to achieve stable duplet or octet electron arrangements.
Formation of Positive and Negative Ions
Metal atoms donate their valence electrons while non-metal atoms accept electrons to achieve a stable octet electron arrangement.
Short Explanation
Arrangement Principle
Elements are arranged from left to right and top to bottom in ascending order of their proton number.
The Modern Periodic Table of Elements contains 118 types of elements. In each element's box, information typically shown includes the proton number, symbol of element, name of element and relative atomic mass.
Groups and Periods
Groups are the 18 vertical columns. Periods are the 7 horizontal rows. The lanthanoids and actinoids are placed separately at the bottom of the table.
Changes Across a Period
Moving from left to right across any period, metallic properties decrease while non-metallic properties increase, properties of oxides change from basic to acidic, and electrical conductivity of the elements decreases.
Electron Arrangement
In a neutral atom, the number of protons equals the number of electrons. Electrons fill the shell closest to the nucleus first. The first shell can hold up to 2 electrons, the second shell up to 8 electrons, and the third shell can hold up to 18 electrons. For atoms with proton numbers 1 to 20, the first shell is filled with 2 electrons, the second shell with 8 electrons, and the third shell with 8 electrons.
Formation of Ions
Most atoms have an unstable electron arrangement and tend to achieve stability. A duplet electron arrangement has 2 electrons in the first shell, while an octet electron arrangement has 8 electrons in the outermost shell. Metal atoms donate electrons to form positive ions, while non-metal atoms accept electrons to form negative ions.
Try to Answer First
Answer in your mind, then press “Check Answer”.
What is the fundamental principle used to arrange elements in the Modern Periodic Table?
State the family names of the elements located in Group 17 and Group 18.
An atom of element \(X\) has 12 electrons with an electron arrangement of 2.8.2. How does this atom form an ion and what type of ion is produced?
Common Mistakes
- Confusing groups (vertical columns, 18 in total) with periods (horizontal rows, 7 in total).
- Writing the electron arrangement of an ion when asked for the neutral atom's arrangement, or omitting the periods/dots between shell numbers, for example writing 286 instead of 2.8.6.
- Thinking that positive ions are formed by gaining protons, rather than losing negatively charged electrons.
- Forgetting that the third shell for atoms with proton numbers 1 to 20 only accommodates up to 8 electrons before the next shell begins.
Concept Misunderstandings
An atom gains positive charge by taking in extra protons into the nucleus.
Protons remain unchanged inside the nucleus during chemical reactions. A positive ion is formed strictly because a neutral atom donates negatively charged electrons, leaving more protons than electrons.
All periods have the exact same properties.
Moving across a period results in continuous trends: metallic nature decreases, oxide nature turns from basic to acidic, and electrical conductivity decreases.
Summary
- The Modern Periodic Table organizes 118 elements by increasing proton number (number of protons in an atom's nucleus).
- It consists of 18 groups (vertical columns) and 7 periods (horizontal rows), along with the lanthanoids (proton numbers 57–71) and actinoids (proton numbers 89–103) at the bottom.
- Across a period (left to right): metallic character decreases, electrical conductivity decreases, and oxide character changes from basic to acidic.
- For elements 1 to 20, electron shell capacities are 2, 8, 8.
- Atoms donate or accept electrons to achieve a stable duplet (2 electrons in the first shell) or octet (8 valence electrons) configuration: metals donate electrons → positive ions; non-metals accept electrons → negative ions.
Short Activity
A. Objective Quiz
1 What is the definition of the proton number of an element?
2 A chlorine atom has an electron arrangement of 2.8.7. How does it achieve a stable electron arrangement?
B. Fill in the Blanks
3 Each of the vertical columns in the Modern Periodic Table of Elements is called a .
4 Positive ions are formed when the atoms of elements donate their outermost electrons.
C. Drag and Drop: Match Each Group to Its Name
Drag each group to its specific group name. On a phone, tap an answer first, then tap a matching box. Tap the Answer Choices area to return a selected item.
C. Match Each Group to Its Name
Write the correct group name next to each group.
| Group in Periodic Table | Name of Group |
|---|---|
| Group 1 | |
| Group 2 | |
| Group 17 | |
| Group 18 |
Answer choices: Alkali metals • Alkaline earth metals • Halogens • Inert gases
