Structure

Physical Properties of Metals

• Strong
• High melting and boiling points
• Conduct electricity (delocalised electrons free to move throughout structure)
• Good conductors of heat (delocalised electrons)

Workability of Metals

• When subjected to small force, metal stretches then returns to original position - elastic
• Large force applied, particles slide over each other and stay in new positions
• Malleable - easily beaten to shape
• Ductile - easily pulled into wires

Alloys

• Can make harder by alloying with other metals
• Mixture of metals
• Brass for e.g. --> mixture of copper and zinc

Giant Ionic Structures

• ALL GIANT STRUCTURES DON'T HAVE FIXED NUMBER OF PARTICLES
• All ionic compounds have huge lattices of positive and negative ions packed in regular way
• Lattice is regular array of particles
• Lattice held together by strong attractions between opposite charged ions
• Examples:
• NaCl
• MgO

Properties of Ionic Substances

• High melting points due to strong forces holding lattices together
• High boiling points due to reason above
• Crystalline
• Brittle because any small distortion of crystal will bring ions with same charge alongside each other, like charges repel, crystal splits itself apart
• Soluble in water
• Insoluble in organic solvents
• Don't conduct electricity when solid because no mobile electrons
• Conduct electricity when dissolved in water or melted because ions free to move

Giant Covalent Structures - Diamond

• Form of pure carbon
• Four unpaired electrons in each atom so each carbon bonds strongly to four other carbons in tetrahedral arrangement
• Very hard, very high melting and boiling point because of very strong carbon-carbon covalent bonds
• Doesn't conduct electricity - all electrons in valence shell tightly held in covalent bonds between atoms so no delocalised electrons
• Isn't soluble in water of any solvent because of powerful covalent bond

Giant Covalent Structures - Graphite

• Form of carbon
• Layer structure, each layer strong but individual layers easily separated
• Soft material with slimy feel because forces holding atoms together in each layer strong but attractions between layers much weaker so layers can be flaked off
• High melting and boiling point
• Insoluble in any solvents
• Less dense than diamond because graphite layers relatively far apart
• Conducts electricity because each carbon atom only joined to three others

Simple Molecular Structures

• Fixed numbers of atoms joined by strong covalent bonds
• Simple molecular structures tend to be gases, liquids or solids with low melting point
• Insoluble in water unless react with it
• Often soluble in organic solvents
• Don't conduct electricity because no overall electrical charge and no electrons mobile enough to move from molecule to molecule

Elements

• Substances which can't be split into anything more simple
• All atoms in element have same atomic number

Compounds

• Combination of two or more elements in fixed proportions, joined by strong bonds
• Doesn't matter whether compound molecular, giant covalent or giant ionic

Mixtures

• Various components in any proportions

Differences between mixtures and compounds

• Properties: In mixture of elements, each element has its own properties but properties of compound different.
• Ease of Separation: Mixtures can be separated by physical means i.e. changing temperature, dissolving part of the mixture in solvent like water. Compounds can't.
• Energy Changes: When making mixtures, there aren't energy changes for example temperature change. But during compounds, there are energy changes such as explosion.