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Bonding, structure and properties of matter (Allotropes of carbon…
Bonding, structure and properties of matter
Formation of ions
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Group 1 and 2 are metals; lose electrons to form cations.
Group 6 and 7 are non-metals; gain electrons to form anions.
Ionic bonding
When metals and non-metals react together, metal atom loses electrons to become positively charged ion and non-metal gains electrons to become negatively charged ion.
Dot and cross shows this- useful for showing how ionic compound formed but don't show structure of compound, size of ions or how arranged.
Ionic compounds
Ions form closely packed regular lattice arrangement with strong electrostatic forces of attraction between oppositely charged ions in all directions in lattice. Have a structure of giant ionic lattice.
Have high mp and bp due to strong bonds between ions so a lot of energy required to overcome attraction.
- When solid- ions held in place so cannot conduct electricity.
- When melted ions are free to move and carry electric current.
- Ionic compounds dissolve easily in H2O. The ions separate and are free to move in solution so carry electric current.
Ball and stick model shows regular pattern of ionic crystal and shows how ions are arranged. But model isn't to scale so relative sizes of ions may not be shown. Also not actually gaps between ions.
Covalent bonding
Sharing of electrons between non-metal electrons in outershell. The positively charged nuclei of bonded atoms are attracted to shared pair of electrons by electrostatic forces, making bonds strong.
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Dot and cross diagrams show bonding in covalent compounds- useful in showing which atoms the electrons in covalent bond come from but don't show relative sizes of atoms, or how arranged in space.
Displayed formula shows covalent bonds as single lines between atoms- show how electrons are connected in large molecules but don't show 3D structure of molecule or which atoms, electrons in covalent bond come from.
3D model shows atoms, covalent bonds and arrangement. But can get confusing for larger molecules with more atoms. Don't show where electrons have come from.
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Allotropes of carbon
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Diamond- giant covalent structure made of carbon atoms that form 4 covalent bonds; hard- take a lot of energy to break and have high mp. Don't conduct electricity- no free electrons or ions.
Graphite- each carbon atom forms 3 covalent bonds creating sheet of carbon atoms arranged in hexagons. Aren't covalent bonds between layers; held together weakly so free to move past each other. Makes it soft and slippery - ideal as lubricating material. Has high mp. Has 1 delocalised electron as only 3 of 4 outer electrons are used in bonds- conducts electricity and thermal energy.
Graphene- sheet of carbon atoms joined in hexagons. Sheet is one atom thick; 2-D compound. Network of covalent bonds make it very strong. Very light- added to composite materials to improve strength without weight. Has 1 delocalised electron- conduct electricity through whole structure- be used in electronics.
Silicon dioxide (silica)- what sand is made of. 1 grain of sand is 1 giant structure of silicon and oxygen.
Fullerenes- molecules of carbon shaped like closed tubes or hollow balls. Made up of carbon atoms arranged in hexagons, pentagons or heptagons. Can be used to cage other molecules- help deliver a drug (forms around other atom or molecules which is then trapped inside). Have huge surface area -great industrial catalyst- individual catalyst molecule could be attached to fullerenes. Also make great lubricants. Can form nanotubes- tiny carbon cylinders. Ratio between length and diameter of nanotube is very high. Can conduct electricity and thermal energy. Have high tensile strength- don't break when stretched. Technology that uses small particles of nanotubes- nanotechnology- can be used in electronics without adding weight- tennis racket frames.
Metallic bonding
Metals consist of giant structure. Electrons in outershell of metal atoms are delocalised- strong forces of eletrostatic attraction between positive metal ions and shared negative electrons.
Forces hold atoms in regular structure- metallic bonding- strong. These include metallic elements and alloys. Delocalised electrons produce properties of metals. Most compounds with metallic bonds have high bp and mp- solid at room temperature.
Layers of atoms in metal ion slide over each other- malleable- bent, hammered, rolled into shape.
Pure meals too soft when pure. Alloys- mixture of 2 or more metals or metal and other element.- harder than metal. When element added to pure metal, distorts layers, making harder to slide over each other.
States of matter
How strong forces are depends on material, temperature and pressure.
- Solids- strong forces of attraction between particles; close together in fixed position- regular lattice arrangement. Keep definite shape and volume. Particles vibrate in positions- the hotter; more vibrations- expand slightly when heated.
- Liquids- weak forces of attraction between particles. Randomly arranged; free to move past each other.. definite volume but not definite shape. the hotter, the more faster they move- expand slightly when heated.
- Gas- very weak forces of attraction-move and travel in straight lines. Don't keep definite shape or volume- fill an container. Move in random motion. Hotter, faster- expand or pressure increases.
Particle model explains states of matter. but aren't really solid, inelastic or spheres- actually atoms, ions or molecules. It also doesn't show forces between particles.