Learning Objectives
- State the periodic law and explain the organization of elements in the periodic table
- Predict the general properties of elements based on their location within the periodic table
- Identify metals, nonmetals, and metalloids by their properties and/or location on the periodic table
Core Concepts & Principles
Early chemists noticed that certain elements share similar chemical and physical behaviors. For instance, lithium, sodium, and potassium are shiny, conduct electricity well, and react vigorously, while calcium, strontium, and barium share similar metallic traits but show distinct reactivity and bonding ratios.
Dmitri Mendeleev and Lothar Meyer independently recognized these recurring patterns, publishing early tables organized by atomic mass. Mendeleev notably used his table to successfully predict undiscovered elements like gallium and germanium.
In modern chemistry, the underlying organizing principle is atomic number rather than mass.
The Periodic Law & Table Organization
- Periodic Law: The physical and chemical properties of the elements are periodic functions of their atomic numbers.
- Structure: The modern periodic table arranges elements in order of increasing atomic number across 7 horizontal rows (periods or series) and 18 vertical columns (groups).
- Reactivity Trends: Elements within the same vertical group share similar chemical properties because they possess similar valence electron configurations.
Broad Element Classifications
Elements are broadly divided into three categories based on appearance and conductivity:
- Metals: Shiny, malleable, ductile, and excellent conductors of heat and electricity.
- Nonmetals: Dull, brittle, and poor conductors of heat and electricity.
- Metalloids: Intermediate conductors that possess a mix of metallic and nonmetallic properties.
Further structural subdivisions include main-group elements (or representative elements in columns 1, 2, and 13–18), transition metals (columns 3–12), and inner transition metals (the bottom two rows, separated into lanthanides and actinides).
Specific Group Families
Several vertical columns have dedicated family names based on their chemical behavior:
- Alkali metals (Group 1): Highly reactive metals that form 1:1 compounds with hydrogen/oxygen (excluding hydrogen itself).
- Alkaline earth metals (Group 2): Reactive metals that form 1:2 compounds with hydrogen.
- Pnictogens (Group 15)
- Chalcogens (Group 16): Also known as the oxygen family; famously utilized in medicinal chemistry (e.g., sulfur and oxygen analogs used by Elion and Hitchings to disrupt cell replication).
- Halogens (Group 17): Highly reactive nonmetals.
- Noble gases (Group 18, or inert gases): Unreactive gases with full outer shells.
Problem-Solving Routines & Methods
How to Classify Elements on the Periodic Table
- 1Locate the element symbol on the periodic table using its atomic number.
- 2Observe its horizontal row (period) and vertical column (group) to identify its family.
- 3Determine its broad classification (metal, nonmetal, or metalloid) based on its position relative to the zig-zag dividing line.
Pro-Tip: Remember that hydrogen is a unique nonmetal often displayed near Group 1 or 17, but it does not belong to the alkali metal family.
Practice & Concept Checks
Concept Check
What specific group family name applies to the element chlorine (Cl)?
Concept Check
Would you expect calcium (Ca) to be a good conductor of heat and electricity?
Key Terms & Vocabulary
MendeleevHistory
Russian chemist widely credited with creating the first periodic table arranged by atomic mass and predicting missing elements.
MeyerHistory
German chemist who independently published a periodic table ordered by atomic mass around 1870.
periodic lawPrinciples
The principle stating that the properties of the elements are periodic functions of their atomic numbers.
periodic tableStructure
A tabular arrangement of elements ordered by atomic number, highlighting recurring chemical patterns.
periodsStructure
Horizontal rows of elements across the periodic table (also referred to as series).
seriesStructure
Alternative term for horizontal rows or periods in the periodic table.
groupsStructure
Vertical columns of the periodic table containing elements with similar chemical behaviors.
metalsElement Classes
Elements that are shiny, malleable, ductile, and good conductors of heat and electricity.
nonmetalsElement Classes
Elements that appear dull and are poor conductors of heat and electricity.
metalloidsElement Classes
Elements with intermediate conductivity and a mixture of metallic and nonmetallic properties.
main-group elementsSubdivisions
Elements in columns 1, 2, and 13–18 of the periodic table (also called representative elements).
representative elementsSubdivisions
Alternative term for main-group elements in columns 1, 2, and 13–18.
transition metalsSubdivisions
Metallic elements located in columns 3–12 of the periodic table.
inner transition metalsSubdivisions
Elements in the two bottom rows of the periodic table (lanthanides and actinides).
lanthanidesSubdivisions
The top row of inner transition metals, spanning atomic numbers 57–71.
actinidesSubdivisions
The bottom row of inner transition metals, spanning atomic numbers 89–103.
alkali metalsGroup Families
Reactive metals in Group 1 (excluding hydrogen) that form 1:1 ratio compounds with oxygen.
alkaline earth metalsGroup Families
Reactive metals in Group 2 that form compounds with a 1:2 ratio to hydrogen.
pnictogensGroup Families
Elements located in Group 15 of the periodic table.
chalcogensGroup Families
Elements located in Group 16 of the periodic table, also known as the oxygen family.
halogensGroup Families
Reactive nonmetals located in Group 17 of the periodic table.
noble gasesGroup Families
Unreactive, chemically stable elements in Group 18 of the periodic table.
inert gasesGroup Families
Alternative term for Group 18 noble gases, referencing their historical lack of reactivity.