Chemistry C2A
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- Created by: tamannasethi
- Created on: 25-04-17 23:06
what is a compound
a substance where the auto of two or more elements are chemically combined
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group 6 and 7
Non metals - gain electrons to form negative ions
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why do elements lose electrons and where
lose electrons IN THE OUTER SHELL to have a noble has configuration
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Mass number
no. of protons and neutrons
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group 1 and 2
metals and lose electrons to form positive ions
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Giant ionic structure
Closely packed lattice arrangement, Electrostatic forces of attraction between oppositely charged ions in all directions
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GROUP 1
+1 ALKALI METALS
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GROUP 7
-1 HALOGENS (ions called halide)
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GROUP 0
Full outer shell, noble gas, unreactive
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nucleus
made of protons and neutrons
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NEUTRONS
NO CHARGE MASS = 1
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ELECTRONS
-1 CHARGE MASS = TOO SMALL
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ISOTOPES
Different versions of the same element // different no. of neutrons (mass) protons is the same
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Covalent bonding
sharing electrons in OUTER SHELLS - Highest energy level
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CHLORINE
CL2
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OXYGEN
O2 - DOUBLE=BOND, SO TWO PAIRS OF ELECTRONS
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METHANE
CH4
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AMMONIA
NH3
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Ionic compounds [5]
Sodium chloride - Giant ionic lattice // strong electrostatic forces of attraction between all ions // Ionic compounds have high melting and boiling points // Large amount of energy requires to break many strong bonds
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CONDUCTION [4]
Melt sodium chloride = molten sodium chloride=Ions are free to move about in the liquid and the positive ions move to the negative electrode as the negative move to the positive electrode. Current can flow from one electrode to another because of fre
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Dissolve sodium chloride
ions free to move around // able to go from one electrode to another // and carry a current
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why can some substances not conduct electricity
ions are not free to move so cannot carry charge
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Simple covalent molecules / simple molecular [3]
LOW MELTING AND BOILING // atoms held together by covalent bonds and no overall charge so doesn't conduct electricity // strong covalent bonds but attraction between neighbouring particles is weak (intermolecular forces) so low m+b
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Giant covalent structure / macromolecules
Diamond / silica / graphite - no charged ions, all bonded with strong covalent bonds, high mp and bp
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Diamond
Carbon atoms in its structure // strong covalent bonds - high mp and bp // strong rigid structure de to carbon
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silicon dioxide
silica and oxygen covalently bonded, hard rigid structure, high mp and bp bc strong covalent bonds
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Graphite
carbon atoms in structure, liked to 3 , strong covalent bonds, arranged in layers not linked very strongly weak internal // layers can slide over each other easily soft and slippery substance // conducts heat and elec BC each carbon has a free elect
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Metallic bonding [5]
electrons in OUTER SHELL are delocalised, electrons move around positive atoms. SEA OF ELECTRONS - Positive electrons reacting with negative delocalised electrons strong electrostatic attraction //
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metallic bonding exam answer
attraction between opp charged ions hold metal together // atoms can slide over each other to be bent // electrons free to move and these carry current // left - right more electrons in outer shell
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what is a fullerene
hexagonal shapes in tube structure // very light and strong with carbon atoms
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Buckminster fullerene
Deliver drugs to certain cells // lubricants and coatings // catalysts due to large surface area so can increase chemical reactions
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Nanotubes [4]
Reinforces materials // tennis rackets // aircraft materials // v strong
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Carbon structures can conduct electricity [3]
delocalised electrons // one free electron per atom // free elections carry charge
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Nanotubes are strong [4]
have a giant structure with covalent bonds // covalent bonds v strong // lots of energy required to break bonds // can conduct electricity
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Metals structure
atoms are arranged neatly in rows // can slide over each other easily // hammered bent into shape MALLEABLE
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ALLOYS
Mixture of metals to make them harder - original atoms are mixed with other atoms of different sizes which disrupt the shape and columns and CAN NO LONGER SLIDE EASILY
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Shape memory alloys
Can return to remembered shape when warmed
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NITINOL
nickel and titanium // can be bent and shaped and when warmed returns to remembered shape // braces - warmth of mouth - move teeth into place APPLIES EVEN PRESSURE ALL DA TIME
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Conduction in metals
Metals have delocalised electrons in the OUTER SHELL of the atoms that are free to move through the whole structure. Electrons move towards positive side carrying charge
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How particles in a metal can be bent
electrons dont belong to delocalised electrons // metals form positive ions // attraction between oppositely charged particles, golds metal together // no specific bonds exist between adjacent atoms // atoms can slide over each other - to bend
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Metals are good conductors of electricity
they have delocalised electrons // these free electrons carry the electric current (more electrons in outer shell = more free delocalised electrons)
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What are Polymers
strong covalent bonds in long chains and the bonds between the chains determine the properties of the plastic
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LD Low density polythene
heating ethene 200 degrees, under high heat and pressure. Low density is softer and flexible (bags and bottles) weak intermolecular forces free to slide over each other
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HD Polyethe
made at lower temp and pressure with a catalyst, more rigid and is with high mp and bp because if stronger force of attraction as chains are closer w crosslinks
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uses of HD Polyethene
water tanks and drain pipes
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mr relative formula mass
you add all of the ATOMI MASSES TOGETHER -BOTTOM NUMBER
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Paper chromatography use
used for chemical analysis to identify additives in foods (artificial colours)
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Paper chromatography method
Pencil line on paper, spot of food colour on line using pipette, put in solvent keeping line above the solvent, place lid on beaker
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results of paper chromatography
solvent rises up and soaks paper, dissolving sample and the colours separate out, some dissolve easily in the solvent and some more quickly than others, compare samples on a chromatogram, easier and cheaper
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Instrumental methods // using machines
accurate, sensitive, rapid and useful when the SAMPLE IS SMALL
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thermosoftening polymers [9]
tangled chains, no regular structure, easy to operate, no cross links, can melt easily, good for recycling, forces between chains are easy to overcome - can melt and be remoulded (plastics / bottles)
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thermosetting
long chains, crosslinks, covalent bonds are strong and link up diff chains. v strong an hard to melt. crosslinks - hold chains in rigid strong structure
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thermosetting uses
sauce pan handles, plates and spatulas
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why are themosoftening easy to melt and soft
weak intermolecular forces of attraction. polymers separate more easily at low temperatures
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what are thermosofetning
made of long chains of hydrocarbon chains from crude oil
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Nanoscience
1-100nm VERY SMALL - Few 100 atoms in size. Large surface area to volume ratio // large surface area means less catalyst can be used
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uses of nano science
catalysts, deodorant , drug delivery, lubricant coatings
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Gas chromatography
why? used to identify substances by separating out a mixture of compounds and help identify substances present V EXPENSIVE
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Gas chromatography method
gas carries a vaporised substance through a column packed w solid material. Substances travel at diff speeds thru the tube so theyre separated.
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what is the time taken to reach the detector
retention time which is used to identify substances
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gas chromatography step 4 - detector
detects the different chemicals shows them as a perk on a chart and the position on the peaks show the attention time of each substances. Compare the graph peaks/retention times. identify subtances through mass spectrometer which identifies substance
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how to work out the Mr of each substance
molecular ion peak on the graph
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mass spectrometer
creates mass spectrum graph to work out molecular mass // better than paper chromatography because it can identify chemicals quickly accurately and detect very small amounts
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percentage by mass
Ar of element you want /divided by/ Mr of compound x100
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Moles
1 moles = Mr
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how to find the number of moles
mass of element/Mr
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Empirical formula
simple whole number ratio of atoms of each element in a compound
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Empircal formula method
List elements, writeEXPERIMENTAL MASSES, Divide these experimental masses by the Ar and multiply by 2 or 10 etc. get these into the simplest form
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Reacting mass calculations
1. work out the balanced equation 2. work out Mr 3. divide to get one multiply to get all
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percentage yield
actual yield / predicted yield x100 YEILD IS ALWAYS LESS THAN 100%
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Why do you never get 100% yield
product always get lost along the way : Reaction is reversible so the reaction goes both ways 2. product can be lost when speerated form mixture 3. some reactants may react in diff from expectation
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Other cards in this set
Card 2
Front
group 6 and 7
Back
Non metals - gain electrons to form negative ions
Card 3
Front
why do elements lose electrons and where
Back
Card 4
Front
Mass number
Back
Card 5
Front
group 1 and 2
Back
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