Properties of metals Revision Notes

Metals are excellent conductors of heat because their atoms are arranged in a lattice with free-moving electrons. These free electrons transfer kinetic energy rapidly throughout the metal, allowing heat to spread quickly. For example, a copper saucepan heats evenly on a stove because copper’s free electrons carry heat efficiently.

In contrast, non-metals generally lack free electrons and have more localized electrons involved in covalent bonds. Heat transfer in non-metals occurs mainly through vibrations of atoms (phonons), which is less efficient. For instance, wood or plastic handles on cooking utensils remain cool because these materials conduct heat poorly, protecting the user from burns.

• Metals conduct heat via free electrons and lattice vibrations.
• Non-metals conduct heat poorly due to lack of free electrons.
• Example: Copper conducts heat well; plastic does not.

Electrical conductivity depends on the ability of charged particles to move freely. Metals have delocalised electrons that can move throughout the metal lattice, allowing electric current to flow easily. This is why metals like copper and aluminium are used for electrical wiring.

Non-metals usually have electrons tightly bound in covalent bonds, so they do not have free electrons to carry charge. As a result, most non-metals are electrical insulators. For example, rubber and glass do not conduct electricity and are used as insulating materials.

Some non-metals, such as graphite (a form of carbon), are exceptions because their structure allows some electron mobility, but these are special cases.

• Metals conduct electricity due to free-moving electrons.
• Non-metals are generally electrical insulators.
• Graphite is a non-metal that conducts electricity due to its structure.

Malleability is the ability to be hammered or rolled into thin sheets, and ductility is the ability to be drawn into wires. Metals exhibit both properties because their atoms are arranged in layers that can slide over each other without breaking the metallic bonds, thanks to the sea of delocalised electrons.

For example, gold can be hammered into very thin sheets (gold leaf) and drawn into fine wires for jewellery and electronics.

Non-metals are generally brittle when solid because their atoms are held in fixed positions by directional covalent bonds. When force is applied, these bonds break rather than allowing layers to slide, causing the material to shatter. For example, sulfur crystals break easily under stress.

• Metals are malleable and ductile due to non-directional metallic bonding.
• Non-metals are brittle because of rigid covalent bonds.
• Example: Gold is malleable; sulfur is brittle.

Metals typically have high melting and boiling points because strong metallic bonds require significant energy to break. The strength of these bonds depends on the number of delocalised electrons and the charge of metal ions. For example, iron melts at 1538°C, reflecting strong bonding.

Non-metals usually have lower melting and boiling points because their atoms are held together by weaker intermolecular forces (such as van der Waals forces) or covalent bonds within molecules that require less energy to overcome. For example, oxygen is a gas at room temperature with a boiling point of -183°C.

However, some non-metals with giant covalent structures, like diamond or silicon, have very high melting points due to strong covalent bonds throughout the lattice.

• Metals have high melting and boiling points due to strong metallic bonds.
• Non-metals generally have lower melting and boiling points due to weaker intermolecular forces.
• Exceptions: Giant covalent non-metals like diamond have high melting points.

Most metals react with dilute acids to produce a salt and hydrogen gas. This occurs because metals can displace hydrogen from acids due to their ability to lose electrons and form positive ions.

For example, zinc reacts with dilute hydrochloric acid as follows:

Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g) (zinc + hydrochloric acid → zinc chloride + hydrogen gas)

• The metal atom loses electrons to form metal ions in solution.
• Hydrogen ions (H⁺) from the acid gain electrons to form hydrogen gas (H₂).
• The salt formed depends on the acid used (e.g., hydrochloric acid forms chlorides).

Some metals react with cold water to form metal hydroxides and hydrogen gas. This reaction is more vigorous for highly reactive metals such as alkali metals.

For example, sodium reacts with cold water: 2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g)

Less reactive metals like magnesium do not react noticeably with cold water because their reactivity is insufficient to displace hydrogen from water at room temperature.

• Alkali metals (e.g., sodium, potassium) react rapidly and often violently with cold water.
• The products are metal hydroxides dissolved in water and hydrogen gas.
• Safety precautions are important due to the flammable hydrogen gas and exothermic nature of the reaction.

Some metals that do not react with cold water will react with steam (hot water vapour) to form metal oxides and hydrogen gas.

For example, magnesium reacts with steam: Mg(s) + H₂O(g) → MgO(s) + H₂(g)

This reaction requires higher temperature and energy to proceed compared to reaction with cold water.

• Steam provides more reactive water molecules due to higher temperature.
• Metal oxides formed are usually solid and less soluble than hydroxides.
• This reaction demonstrates the increased reactivity of metals at elevated temperatures.

The reactivity of metals can be ranked by their ability to react with acids, cold water, and steam.

Highly reactive metals like potassium and sodium react vigorously with cold water.

Moderately reactive metals like magnesium react with steam but not cold water, and less reactive metals like zinc react with acids but not water.

• Reactivity decreases down the group for alkali metals but increases across the periodic table for transition metals.
• This trend helps predict which metals will react with acids or water under given conditions.
• Understanding these reactions is essential for applications such as metal extraction and corrosion prevention.