Topic 2 Flashcards

Chemical Bonds

Chemical Bonds: read all 5 questions and answers

1. What is a chemical bond?
   A force of attraction that holds atoms together. Atoms form bonds to achieve a more stable electron arrangement - usually a full outer shell (the octet rule).
2. What is an ionic bond?
   The strong electrostatic attraction between oppositely charged ions. It forms between a metal and a non-metal by the transfer of electrons.
3. What is a covalent bond?
   A shared pair of electrons between two non-metal atoms. Each atom contributes one electron to the shared pair.
4. What is a metallic bond?
   The strong electrostatic attraction between positive metal ions and a 'sea' of delocalised electrons. The outer electrons are free to move throughout the structure.
5. How do you predict the type of bonding?
   Metal + non-metal → ionic bonding. Non-metal + non-metal → covalent bonding. Metal + metal → metallic bonding.

Ionic Bonding

Ionic Bonding: read all 6 questions and answers

1. How does an ionic bond form?
   Step 1: Metal atom LOSES outer electrons → positive ion (cation). Step 2: Non-metal atom GAINS electrons → negative ion (anion). Step 3: Oppositely charged ions attract each other - this is the ionic bond.
2. Describe the formation of NaCl.
   Sodium (2.8.1) loses 1 electron → Na⁺ (2.8). Chlorine (2.8.7) gains 1 electron → Cl⁻ (2.8.8). Strong electrostatic attraction holds the ions together.
3. Describe the formation of MgO.
   Magnesium (2.8.2) loses 2 electrons → Mg²⁺ (2.8). Oxygen (2.6) gains 2 electrons → O²⁻ (2.8). TWO electrons are transferred.
4. Describe the formation of MgCl₂.
   Magnesium loses 2 electrons - one to each of two chlorine atoms. Mg → Mg²⁺. Each Cl → Cl⁻. Ratio: one Mg²⁺ for every two Cl⁻.
5. What is a giant ionic lattice?
   A regular, repeating 3D arrangement of positive and negative ions. Each ion is surrounded by ions of the opposite charge. The strong electrostatic forces act in all directions.
6. What must you show in an ionic dot-and-cross diagram?
   Dots (•) for electrons from one atom, crosses (×) from the other. Square brackets around each ion. The charge on each ion (e.g. [Na]⁺ [Cl]⁻). Only outer shell electrons are needed.

Properties of Ionic Compounds

Ionic Properties: read all 4 questions and answers

1. Why do ionic compounds have high melting points?
   Because of the strong electrostatic forces of attraction between oppositely charged ions. A large amount of energy is needed to overcome these forces.
2. Why don't ionic compounds conduct electricity when solid?
   In the solid state, the ions are held in fixed positions in the lattice and cannot move to carry charge.
3. Why do ionic compounds conduct when molten or dissolved?
   When molten or dissolved in water, the ions are free to move and carry charge through the liquid, allowing electrical conduction.
4. Are ionic compounds soluble in water?
   Many ionic compounds dissolve in water. Water molecules surround the individual ions, breaking down the lattice.

Covalent Bonding

Covalent Bonding: read all 5 questions and answers

1. What is a single covalent bond?
   One shared pair of electrons between two atoms. Examples: H₂, HCl, H₂O, CH₄.
2. What is a double bond?
   Two shared pairs of electrons between two atoms. Example: O₂ (O=O). Each oxygen shares 2 electrons.
3. What is a triple bond?
   Three shared pairs of electrons between two atoms. Example: N₂ (N≡N). Each nitrogen shares 3 electrons.
4. What are intermolecular forces?
   Weak forces of attraction BETWEEN molecules. They are NOT the covalent bonds within molecules. It is these weak forces that are overcome during melting and boiling.
5. What must you show in a covalent dot-and-cross diagram?
   Outer shell electrons only. Dots from one atom, crosses from the other. The shared pair(s) sit between the two atoms. Do NOT use square brackets (those are only for ionic).

Properties of Simple Molecules

Simple Molecules: read all 3 questions and answers

1. Why do simple molecules have low melting and boiling points?
   Because only a small amount of energy is needed to overcome the weak intermolecular forces between molecules. The strong covalent bonds within molecules are NOT broken.
2. Why don't simple molecules conduct electricity?
   Because the molecules have no overall charge - there are no free electrons or ions to carry charge.
3. Give four examples of simple molecular substances.
   H₂ (hydrogen), H₂O (water), CH₄ (methane), Cl₂ (chlorine). All have low boiling points and do not conduct electricity.

Metallic Bonding & Alloys

Metallic Bonding & Alloys: read all 6 questions and answers

1. Describe metallic bonding.
   Metal atoms lose outer electrons → regular lattice of positive ions surrounded by a 'sea' of delocalised electrons. The metallic bond is the strong electrostatic attraction between the positive ions and the delocalised electrons.
2. Why do metals conduct electricity?
   The delocalised electrons are free to move through the structure and carry charge.
3. Why do metals conduct heat?
   The delocalised electrons carry kinetic energy from hotter to cooler regions of the metal.
4. Why are metals malleable?
   The layers of positive ions can slide over each other without breaking the metallic bond, because the sea of delocalised electrons can move with them.
5. What is an alloy?
   A mixture of a metal with one or more other elements (usually metals). The different-sized atoms distort the regular layers, preventing them from sliding. This makes alloys harder than pure metals.
6. Name four common alloys and their compositions.
   Steel: iron + carbon. Stainless steel: iron + chromium + nickel. Bronze: copper + tin. Brass: copper + zinc.

States of Matter

States of Matter: read all 6 questions and answers

1. Describe the particles in a solid.
   Packed tightly in a fixed, regular pattern (lattice). Strong forces hold them in place. Particles vibrate on the spot. Fixed shape and volume.
2. Describe the particles in a liquid.
   Close together but arranged randomly. Weaker forces than solids. Particles can move and slide past each other. Fixed volume but takes the shape of its container.
3. Describe the particles in a gas.
   Very far apart, arranged randomly. Very weak forces. Particles move quickly and randomly in all directions. No fixed shape or volume; easily compressed.
4. Name the changes of state.
   Melting: solid → liquid. Boiling: liquid → gas. Freezing: liquid → solid. Condensing: gas → liquid. Sublimation: solid → gas directly.
5. What are state symbols?
   (s) = solid, (l) = liquid, (g) = gas, (aq) = aqueous (dissolved in water). They are added after chemical formulae in balanced equations.
6. Is a change of state a physical or chemical change?
   Physical change. No new substance is formed. The particles stay the same - only the arrangement and energy change. Mass is conserved.

Giant Covalent & Carbon Allotropes

Giant Covalent & Carbon: read all 7 questions and answers

1. What is a giant covalent structure?
   Huge numbers of non-metal atoms joined by a continuous network of strong covalent bonds. No separate molecules. Very high melting points because many strong bonds must be broken.
2. Describe the structure and properties of diamond.
   Each carbon forms 4 strong covalent bonds in a rigid tetrahedral arrangement. Very hard, very high melting point, does NOT conduct electricity (no free electrons).
3. Describe the structure and properties of graphite.
   Each carbon forms 3 covalent bonds, creating flat layers of hexagonal rings. Layers are held by weak forces so they slide (soft, slippery). One delocalised electron per carbon → conducts electricity along layers.
4. What is graphene?
   A single, one-atom-thick layer of graphite. Each carbon forms 3 bonds with one delocalised electron per atom. Extremely strong, lightweight, and an excellent conductor of electricity and heat.
5. What is buckminsterfullerene (C₆₀)?
   60 carbon atoms arranged in a hollow sphere (like a football). It is a simple molecular structure with weak intermolecular forces between molecules. Uses: drug delivery, catalysts, lubricants.
6. What are carbon nanotubes?
   Graphene rolled into a continuous cylinder. Very high tensile strength, excellent electrical and thermal conductors, huge SA:V ratio. Uses: composites, nanoelectronics, catalysts.
7. Describe the structure of silicon dioxide (SiO₂).
   Similar to diamond. Each silicon bonds to four oxygens, each oxygen to two silicons. Very hard, very high melting point, does not conduct electricity.

Polymers

Polymers: read all 3 questions and answers

1. What is a polymer?
   A very large molecule (macromolecule) made from many smaller repeating units called monomers, joined together by a process called polymerisation.
2. Why are polymers solid at room temperature?
   The intermolecular forces between polymer chains are stronger than in small simple molecules (because the chains are much longer). These forces are strong enough to keep the chains together as a solid.
3. Give two examples of polymers.
   Poly(ethene) - used for plastic bags and bottles. Poly(propene) - used for ropes and crates.

Nanoparticles (Chemistry Only)

Nanoparticles: read all 5 questions and answers

1. What are nanoparticles?
   Particles with a diameter of 1-100 nm (1 nm = 1 × 10⁻⁹ m). They have a very high surface area to volume ratio, giving them unique properties.
2. How does SA:V ratio change with particle size?
   As particles get smaller, the SA:V ratio increases dramatically. A 2 cm cube has SA:V = 3:1. A 1 cm cube has SA:V = 6:1. Halving the size doubles the ratio!
3. What are the three particle size categories?
   Nanoparticles: 1-100 nm. Fine particles (dust): 100-2500 nm. Coarse particles (sand grains): 2500-10,000 nm.
4. Give three uses of nanoparticles.
   Sun creams (TiO₂ blocks UV but is transparent). Silver nanoparticles (antibacterial coatings). Catalysts (huge surface area makes reactions more efficient). Also: drug delivery and self-cleaning surfaces.
5. What are the risks of nanoparticles?
   May enter the body through skin, lungs or ingestion. Long-term health effects not fully understood. Could accumulate in the environment and harm ecosystems. More research is needed.