Shiny foil, yellow powder
Aluminum foil is shiny, bends without breaking, and conducts electricity. Sulfur is a pale yellow powder that crumbles at a touch and doesn’t conduct at all. Based on properties like these, the 118 elements fall into a few big categories.
Kinds of elements
Metals金属 make up most of the periodic table: more than 90 elements. Metals have a shiny luster, conduct heat and electricity well, and are malleable (they can be hammered into sheets) and ductile (they can be drawn into wires). All metals are solids at room temperature except mercury.
Nonmetals非金属 are only a dozen or so elements, such as hydrogen, carbon, nitrogen, oxygen, sulfur, and chlorine. Most are dull and don’t conduct electricity (graphite, a form of carbon, is an exception), and the solid ones are brittle. At room temperature, some are gases (oxygen, nitrogen, chlorine), some are solids (carbon, sulfur, phosphorus), and bromine is a liquid.
Metalloids准金属 lie along the “staircase” line between the metals and nonmetals: boron, silicon, germanium, arsenic, antimony, and tellurium. Their properties fall in between. Silicon, for example, looks shiny like a metal but is brittle, and it conducts electricity only somewhat, which makes it a semiconductor.
The noble gases稀有气体 make up group 18: helium, neon, argon, krypton, xenon, and radon. All are gases at room temperature, and they hardly react with anything, because their atoms’ outer shells already hold a stable arrangement of electrons (lesson 1.3.6). Their uses come from that unreactivity:
- Helium is light and doesn’t burn, so it fills balloons and airships.
- Neon glows red when electricity passes through it, which is how neon signs work.
- Argon protects hot metal from the air during welding, and it fills light bulbs so the filament doesn’t react.
| Metals | Nonmetals | |
|---|---|---|
| Luster | Shiny | Usually dull (graphite is shiny) |
| Conduct heat and electricity | Well | Usually poorly (graphite conducts) |
| Hammered | Flattens (malleable) | Solids shatter (brittle) |
| State at room temperature | Solid (mercury is liquid) | Gases and solids; bromine is liquid |
Where they are on the table
Metals fill the left side and the middle of the periodic table. Nonmetals cluster in the upper right, with the metalloids along the staircase between them, and the noble gases form the last column, group 18. Periods 2 and 3 show it clearly: lithium, beryllium, sodium, magnesium, and aluminum are metals; boron and silicon are metalloids; carbon, nitrogen, oxygen, fluorine, phosphorus, sulfur, and chlorine are nonmetals; and neon and argon are noble gases.
Switch the coloring to see where each kind of element sits, and which elements are gases or liquids at room temperature:
The table is wide: swipe sideways to see all of it.
Click any element in the table.
Here are four unlabeled solid elements: copper, aluminum, sulfur, and graphite. Run some tests to identify them, and notice how graphite is like a metal and how it isn’t:
Click a test above. The results will be recorded in this table.
A chemical property only shows up during a chemical change, so after a test like this, that portion of the sample has turned into something else.
Example 1: Classify by position
Use the periodic table to classify lithium, boron, fluorine, bromine, and krypton, and give the state of each at room temperature.
- Lithium. Group 1, on the far left: a metal, and a solid.
- Boron. On the staircase line: a metalloid, and a solid.
- Fluorine. Group 17, upper right: a nonmetal, and a gas.
- Bromine. Also group 17: a nonmetal, and one of only two elements that are liquids at room temperature.
- Krypton. Group 18: a noble gas.
Example 2: Graphite conducts, so is carbon a metal?
A student says, “Graphite conducts electricity and is shiny, so carbon must be a metal.” Is that right?
- One property isn’t enough. Metals share a whole set of properties: luster, conductivity, malleability, and ductility.
- Graphite fails the hammer test. It breaks apart instead of flattening, and it can’t be drawn into a wire.
- Check the position. Carbon sits in group 14, in the upper right, among the nonmetals.
- Answer. No. Carbon is a nonmetal; graphite’s conductivity is an exception.
- Mercury
Mercury is the only metal that's a liquid at room temperature.
- Bromine
Bromine is the only nonmetal that's a liquid at room temperature.
- Nitrogen
Nitrogen gas makes up about 78% of the air.
- Sulfur
Sulfur is a pale yellow solid.
- Helium
All the noble gases are gases at room temperature.
- Iron
Every metal except mercury is a solid at room temperature.
- Chlorine
Chlorine is a yellow-green gas.
- Iodine
Iodine is a dark purple-black solid.
- Sodium
Sodium is a silvery solid metal, soft enough to cut with a knife.
Common mistakes
Mistake 1: “Anything that conducts electricity is a metal.” Graphite conducts, but carbon is a nonmetal. Look at the whole set of properties, and above all at the element’s position on the table.
Mistake 2: “All metals are solids at room temperature.” Mercury is a metal and a liquid. That’s why it was once used in thermometers.
Mistake 3: “Noble gases never react with anything, which is why they’re called inert gases.” They’re very unreactive, but not completely: chemists have made compounds of xenon. That’s why the old name “inert gases” has been replaced by “noble gases.”
Quick check
Which of these elements is a metal?
Mercury is a metal that happens to be a liquid at room temperature. Silicon is a metalloid; bromine and iodine are nonmetals.
Which nonmetal is a liquid at room temperature?
Bromine is the liquid nonmetal. Mercury is also a liquid, but it's a metal; iodine is a solid and chlorine is a gas.
Summary
- Metals (most elements, on the left and in the middle) are shiny, conduct, and are malleable and ductile; all are solids except mercury.
- Nonmetals (upper right) are usually dull, poor conductors (graphite is an exception), and brittle as solids; bromine is the only liquid. Metalloids along the staircase are in between.
- The noble gases in group 18 already have a stable outer shell, so they’re very unreactive. They’re used in balloons, neon signs, and as protective gases.
On to AP (for later)
Topic 1.7 uses atomic structure to explain why elements become more metallic toward the lower left of the table and more nonmetallic toward the upper right. Topic 2.4 explains metals’ conductivity and malleability with metallic bonding: positive ions held together by a “sea” of shared electrons.