States of Matter and Chemical Bonds

States of Matter

• Three states: solids, liquids, and gases
• Particle arrangement: solids – tightly packed, vibrating; liquids – close, random motion; gases – widely spaced, free movement
• Energy transfer: melting/boiling – energy from surroundings; freezing/condensing – energy to surroundings
• Particle model limitations: doesn't account for forces between particles or their non-spherical nature

Melting and Boiling Points

• Melting point: temperature stops rising until all solid melts
• Melting process: enough energy breaks forces between particles
• Boiling point: temperature remains constant as energy transfers
• Cooling effects: particles move closer, leading to condensation and freezing
• Sublimation – some solids directly change to gases without melting

Compounds and Bonds

• Compounds: formed when elements chemically combine
• Ionic bonds: electron transfer between metals and non-metals
• Positive ions (cations): atoms lose electrons (e.g., Na⁺)
• Negative ions (anions): atoms gain electrons (e.g., Cl⁻)
• Dot and cross diagrams: show electron transfer in ionic bonding
• Noble gases: stable electron arrangements, unreactive
• Mixing vs. reacting: mixing doesn't change composition, reacting does
• Electron structures: crucial for ion formation
• Group 1 & Group 7 reactivity: Group 1 loses electrons, Group 7 gains electrons
• Stability: Atoms react to achieve stable electron configurations
  • Group 1 ions: form 1+ ions
  • Group 2 ions: form 2+ ions
  • Group 3 ions: form 3+ ions
  • Group 5-7 ions: form 3-, 2-, and 1- ions respectively
  • Group 0 elements: do not form ions

Ionic Compounds

• Ionic compounds: held together by strong electrostatic attraction (ionic bonding) between oppositely charged ions
  • Ion formation: metals form positive ions, nonmetals form negative ions
• Giant ionic structures: large numbers of ions in a repeating pattern
• Properties: high melting/boiling points, conduct electricity when molten or dissolved (not in solid form), typically hard and brittle
• Examples: MgO, CaCl₂, NaCl, etc.
  • Lattice structure: 3D arrangement of ions
  • Electrical conductivity in different states (solid, molten, dissolved)

Covalent Compounds

• Covalent bonds: atoms share electron pairs to achieve stability
• Simple molecules: molecules like H₂, O₂, N₂
  • Bond types: single, double, triple bonds
• Examples: H₂O, NH₃, CH₄ (methane)
• Properties of simple molecular compounds: low melting/boiling points, non-conductors of electricity, various shapes.
• Intermolecular forces: weak forces between molecules influencing properties like melting and boiling points
• Giant covalent structures: very hard substances (e.g., diamond, each carbon atom forms four covalent bonds making it exceptionally hard)

Polymers

• Polymers: long chains of small reactive molecules bonded together
• Example: polyethylene (from ethene molecule)

Fullerenes and Graphene

• Fullerenes: carbon molecules forming hollow cages (e.g., C60, Buckyball)
• Graphene: single layer of carbon atoms arranged in a hexagonal lattice
• Properties: high tensile strength and electrical conductivity
• Applications: in specific cases like drug delivery, lubricants, catalysts, and flexible displays, etc.

Metallic Compounds

• Giant metallic structures: regular arrangement of metal atoms
• Delocalized electrons: free to move throughout the structure
• Properties: high melting/boiling points, malleable, ductile, good conductors of heat and electricity
• Alloys: mixtures of metals, often harder than pure metals
  • Different sized atoms distort layers, hindering sliding, improving strength.
  • Examples of metals: copper (good electrical conductivity)

Nanoscience

• Nanoscience: study of structures on a nano-scale (1-100 nm).
• Nanoparticles: particles with nano-scale dimensions
• High surface area to volume ratio (SA:V): leads to high reactivity compared to larger particles
• Applications of nanoparticles: drug delivery, cosmetics, catalysts, electronics, and more.
• Potential health risks: possible effects from entering bloodstream through cosmetic products.
• Examples and their applications: drug delivery systems (e.g., cancer), sunscreens (e.g., higher UV protection), and more.