Metals, Non-metals and Metalloids

The Three Broad Classes of Elements

The periodic table groups elements not only into s, p, d, and f blocks, but also into three broad categories based on their physical and chemical properties: metals, non-metals, and metalloids (also called semi-metals). This classification is one of the oldest and most intuitive ways to understand the behaviour of elements.

Metals dominate the table — they make up more than 78% of all known elements. They occupy the left side of the periodic table. Non-metals are clustered at the top right. Between them lies a diagonal band of elements that show mixed behaviour.

---

Metals — Location and General Properties

Metals are found on the left side of the periodic table. In any horizontal row (period), the leftmost elements are metallic, and the metallic character gradually weakens as you move right.

Physical properties of metals:

1. State at room temperature: Most metals are solids. There are three notable exceptions:

   • Mercury (Hg) is a liquid at room temperature.
   • Gallium (Ga) melts at 303 K (about 30 °C) — it can melt in your hand.
   • Caesium (Cs) melts at 302 K (about 29 °C).

2. Melting and boiling points: Generally high. This is because metallic bonds are strong and require a lot of energy to break.

3. Electrical and thermal conductivity: Metals are good conductors of both heat and electricity. This is due to the presence of delocalised electrons that can move freely through the metallic lattice.

4. Malleability: Metals can be hammered or rolled into thin sheets without breaking. For example, gold can be beaten into extremely thin foils.

5. Ductility: Metals can be drawn into long, thin wires. Copper and aluminium are common examples.

---

Non-Metals — Location and General Properties

Non-metals are located at the top right of the periodic table. In a given period, the elements change from metallic on the left to non-metallic on the right.

Physical properties of non-metals:

1. State at room temperature: Most non-metals are either solids or gases. There are exceptions:

   • Boron and carbon are solids with very high melting points (unusually high for non-metals).
   • Many non-metals like oxygen, nitrogen, and chlorine are gases.

2. Melting and boiling points: Generally low. The forces between molecules (van der Waals forces) are weak, so little energy is needed to separate them.

3. Electrical and thermal conductivity: Non-metals are poor conductors. They are often insulators. (Graphite, a form of carbon, is an exception — it conducts electricity.)

4. Brittleness: Most solid non-metals are brittle. They shatter or crumble when struck. They are neither malleable nor ductile.

---

Trends in Metallic and Non-Metallic Character

Two clear trends emerge from the periodic table:

• Down a group: Metallic character increases. As you go down, atoms get larger, the outermost electrons are farther from the nucleus and are held less tightly. They are more easily lost, which is a hallmark of metallic behaviour.
• Across a period (left to right): Metallic character decreases and non-metallic character increases. The nuclear charge increases, pulling electrons in more tightly. Atoms become less willing to lose electrons and more willing to gain them.

These trends are not abrupt. The change is gradual, which is why there is a diagonal band of elements with mixed properties.

---

Metalloids (Semi-Metals)

The elements that lie along the zig-zag line separating metals from non-metals show properties of both metals and non-metals. They are called metalloids or semi-metals.

The textbook lists these specific metalloids:

• Silicon (Si)
• Germanium (Ge)
• Arsenic (As)
• Antimony (Sb)
• Tellurium (Te)

Characteristic behaviour of metalloids: …