Difficulty: Introductory | Prerequisites: None, though familiarity with the periodic table layout helps.
This topic sits right at the start of general chemistry. You are learning how to observe and classify elements by their physical properties: colour, lustre, and whether they behave as metals, metalloids, or nonmetals. These distinctions underpin everything that follows in bonding, reactivity, and materials science. If you can look at an element and place it in the right category, you have the foundation for predicting how it will behave chemically.
Elements have observable physical properties (colour, lustre) that correlate with their classification as metals, metalloids, or nonmetals. Metals are typically shiny, nonmetals are typically dull or colourless, and metalloids sit somewhere in between. Knowing the category lets you predict properties before you even see the sample.
Element
A pure substance made of only one type of atom, defined by its atomic number. In simple terms, it is a substance that cannot be broken down into anything simpler by chemical means.
Lustre
The way a surface reflects light. Metals tend to have a shiny (metallic) lustre; nonmetals are dull or have no lustre at all. Think of it as whether the sample looks polished or chalky.
Metal
An element that is typically shiny, conducts heat and electricity, and is malleable (can be hammered into shape). Most elements on the periodic table are metals. In simple terms, metals are the shiny, bendy, conductive ones.
Nonmetal
An element that is typically dull or colourless, does not conduct electricity well, and is brittle (if solid). Think of it as the opposite set of physical traits from metals.
Metalloid (semimetal)
An element with properties intermediate between metals and nonmetals. Silicon is the classic example: it looks shiny like a metal but conducts electricity only under certain conditions (hence its use in semiconductors). Think of metalloids as the elements that could not quite decide which side to join.
Physical property
A characteristic of a substance that can be observed or measured without changing its chemical identity. Colour, lustre, density, melting point, and state of matter are all physical properties.
Metals are shiny (high lustre), conduct heat and electricity, and are generally malleable and ductile.
Most metals appear light grey or silvery in their pure, solid form. Copper (orange) and gold (yellow) are the well-known exceptions.
All the metals in Lab 6 were classified as shiny: aluminium, copper, iron, magnesium, nickel, silver, tin, zinc.
Nonmetals are dull or colourless and poor conductors.
Gases such as nitrogen and oxygen are colourless with no lustre at all.
Solid nonmetals vary: carbon is black and dull, sulfur is yellow and dull, phosphorus (red allotrope) is deep red and dull.
Note that nonmetals can exist in very different physical forms depending on their allotrope (carbon as graphite vs. diamond, for instance).
Metalloids sit along the "staircase" line on the periodic table (boron, silicon, germanium, arsenic, antimony, tellurium, and sometimes polonium).
Silicon, the only metalloid in Lab 6, is grey/black and shiny, so it looks metallic at first glance.
The giveaway is electrical conductivity: metalloids are semiconductors, not full conductors.
If an element is a metal or a metalloid, predict shiny.
If it is a nonmetal, predict dull (or no lustre if it is a gas).
In Lab 6, every prediction matched reality (chromium, gold, lead, cadmium: all metals, all shiny; silicon: metalloid, shiny).
Students often assume that anything shiny must be a metal. It is not: metalloids such as silicon are shiny too, but they are not metals.
Students sometimes think colour alone tells you the classification. Colour is an observable property, but it does not reliably sort metals from nonmetals. Iron is grey/black and so is silicon, yet one is a metal and the other a metalloid.
"Dull" and "colourless" are not the same thing. Sulfur is dull (it reflects light poorly), but it has a strong yellow colour. Nitrogen is colourless (a gas with no visible hue) and also has no lustre.
A common slip is labelling silicon as a nonmetal because it looks dark. Its position on the periodic table (right on the staircase) makes it a metalloid.
⚠️ You will almost certainly be asked to classify an element as M, ML, or NM based on its position on the periodic table. Know where the staircase is.
⚠️ Predicting physical properties (shiny vs. dull) from classification is a standard lab-exam question. The rule is simple: metals and metalloids are shiny, nonmetals are dull or have no lustre.
⚠️ Be ready to identify elements whose symbols do not match their English names: Fe (iron), Cu (copper), Ag (silver), Sn (tin), Au (gold). These come from Latin names and are a favourite exam trick.
The metal/nonmetal distinction is why copper wiring conducts electricity in your walls while the rubber (polymer of nonmetals) insulates it. Silicon's metalloid nature, sitting between conductor and insulator, is the entire basis of semiconductor electronics.
True or false: All metals are shiny.
True (by definition, metals have metallic lustre).
True or false: Silicon is a nonmetal.
False. Silicon is a metalloid.
Fill in the blank: An element that is colourless and has no lustre is most likely a ______.
Nonmetal (specifically a gaseous nonmetal, such as nitrogen or oxygen).
True or false: The symbol for tin is Ti.
False. Ti is titanium. Tin is Sn (from the Latin stannum).
Fill in the blank: Metals are good conductors of ______ and ______.
Heat and electricity.
Q: An element is grey/black, shiny, and sits on the staircase of the periodic table. Is it a metal, metalloid, or nonmetal?
A: Metalloid. The staircase position is the deciding factor.
Q: You observe a deep red, dull solid. What classification would you predict?
A: Nonmetal. Dull lustre strongly suggests nonmetal (this matches phosphorus).
Q: What is the chemical symbol for silver, and why does it not start with "S"?
A: Ag, from the Latin argentum. S is already taken by sulfur.
Q: Name two elements from Lab 6 that are colourless gases with no lustre.
A: Nitrogen (N) and oxygen (O).
Q: If you were told an unknown element is a metal, what lustre would you predict?
A: Shiny (metallic lustre). All metals exhibit lustre.
This material connects directly to the periodic table topic (Doc 2 in this set), where you learn the group and period structure that determines whether an element is a metal, metalloid, or nonmetal. It also feeds into chemical bonding: metals lose electrons to form cations, nonmetals gain electrons to form anions, and metalloids can go either way depending on the bonding partner.
Later in the course, physical properties such as conductivity and malleability come back when you study metallic bonding and crystal structures.
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