Worked example 1
Classify Ge, Ca and S, and predict which conducts electricity as a pure solid.
Try it first: Find each element relative to the staircase before writing anything.
0 of 3 steps revealed.
Types of Solids and IMFSTypes of elementsContent level: Core 15 min
Metals, Nonmetals and Metalloids
What you'll be able to do: Classify any element as a metal, nonmetal or metalloid and predict the properties that follow.
Introduction
Before you can predict how a substance melts, conducts or dissolves, you need to know what kind of elements it is built from. The periodic table sorts that out for you.
These are recommended, not required. You can start this lesson at any time.
Learning objectives
- Locate metals, nonmetals and metalloids on the periodic table
- Describe the physical properties typical of each class
- Predict which class an element belongs to from its position
- Connect element type to the bonding a pair of elements will form
Lesson
The staircase divides the table
A stepped line runs from boron down to astatine. Elements to the left are metals, elements to the right are nonmetals, and the elements touching the line (B, Si, Ge, As, Sb, Te, and often At) are metalloids. Hydrogen is a nonmetal despite sitting in group 1.
Metals make up roughly three quarters of the table, so nonmetal is the shorter list to memorise.
Nonmetals: tight hold on electrons
Nonmetals have high ionization energies and high electronegativities. As solids they are dull and brittle and do not conduct. They form anions with metals and share electrons with other nonmetals.
Metal plus nonmetal points to ionic bonding, nonmetal plus nonmetal points to covalent bonding.
Metalloids: intermediate and useful
Metalloids have properties between the two classes. Silicon and germanium are semiconductors: they conduct much better than nonmetals but far worse than metals, and their conductivity rises with temperature and with doping.
Key ideas
Rule
Position predicts class
Left of the staircase is metal, right is nonmetal, on it is metalloid.
Rule
Metals lose, nonmetals gain
Low ionization energy favours cations, high electronegativity favours anions.
Definition
Semiconductor
A material whose conductivity lies between a metal and an insulator and increases with temperature.
Rule
Bond type shortcut
Metal plus nonmetal gives ionic, nonmetal plus nonmetal gives covalent, metal plus metal gives metallic.
Worked examples
Worked example 2
Predict the bond type in MgO, in CO₂ and in brass (Cu with Zn).
Try it first: Label each element as metal or nonmetal first.
0 of 3 steps revealed.
Common mistakes
Calling hydrogen a metal because it sits in group 1.
Why it's wrong: Hydrogen has a high ionization energy and forms molecular H₂ gas.
Check instead: Treat hydrogen as a nonmetal in every bonding prediction.
Assuming metalloids conduct as well as metals.
Why it's wrong: Semiconductors carry far less current unless heated or doped.
Check instead: Describe metalloid conductivity as intermediate and temperature dependent.
Thinking all nonmetals are gases.
Why it's wrong: Sulfur, phosphorus, carbon and iodine are solids at room temperature.
Check instead: Use position for classification and IMFs for physical state.
Practice this skill
No practice questions are available for this topic yet. You can still practice the whole unit.
What you should now know
Metals sit left of the staircase and lose electrons easily, nonmetals sit right and gain or share them, and metalloids straddle the line with mixed behaviour. Element type predicts conductivity, malleability and the kind of bonding a pair of elements will form.
- The staircase separates metals, nonmetals and metalloids
- Metals conduct and are malleable because electrons delocalise
- Nonmetal solids are brittle insulators
- Element classes predict ionic, covalent or metallic bonding
Sources and further reading
- Chemistry 2e, Section 10.5: The Solid State of MatterOpenStax · Rice University · 10.5View source
CC BY 4.0 License