Matter and materials (III)
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Transcript of Matter and materials (III)
Matter and materials
Properties of matterStrengthThermal and electrical conductivityMagnetic propertiesSolubilityMalleability and ductilityDensityMP and BPAtom that bonds consists ofKinds of bondsForces between bonds
Macroscopic - Observed with sensesMicroscopic Not observed with senses
A mixture is when two or more substances are combined, but each of the substances keep its original properties.Mixtures
Properties of mixturesThe substances keep their original properties.
The substances dont have to be mixed in a fixed ratio.
The mixture can be separated with simple methods.
Two mixturesThe substances are all in one phaseEg airYou cannot identify the different components of the mixture.There are more than one phase.Eg sand and waterSuspension solids that float in liquids. Eg muddy waterEmulsion steady mix of insoluble substances in a liquid.Eg milk, mayonnaise
HomogenousHeterogenous
Because mixtures retain the original properties, we can separate the different substances by physical methodsSeparation methods
Homogenous separation Evaporation
Distillation
Fractional distillation
Chromatography
Centrifugation
Evaporation
Distillation
Taken from regentsprep.orgChromatography
Taken from faqs.orgCentrifuge
Heterogenous separationFiltration
Separating funnel
Decanting
Sorting
Sieving
Separating funnel
Filtration
Taken from codeunit.co.zaSorting
Taken from sbs.utexas.eduSieving
Pure substances are made of only one substance or a compound. Pure substance
Pure substancesAn element only consists of the same atoms.An element cant be separated into simpler substances.Elements are categorised as metals, non-metals and semi-metals.A compound consist of two or more different elements bonded together. Can only be separated by chemical methods.Compounds properties differ from the individual elements.Joined in fixed ratios.Chemical reactions occur during formation.ElementsCompounds
Periodic table
FormulaeH2O is the formula of water
H2O
2 hydrogen atoms 1 oxygen atom
CaO, CaSO4, Ca(OH)2, NH4NO3, CO2, NH3
Diatomic molecules
Ionic bonds
OHH
Ionic bondsGroup 1, 2, 6, 7
Transition metals give off 1, 2, or 3 electrons
Mono-atomic anion ide
Polyatomic ion/radical
Physical differencesMetallic lustreElectrical conductorsThermal conductorsOpaqueMalleable and ductileSolids @ room temperature, except HgHigh MP and BPDull (except graphite & diamonds)Poor electrical and thermal conductorsSome solids = opaque, gases are translucentSolids = brittleLow MP and BPMetalsNon-metals
Semi-metalsGenerally have properties of metals, but a few non-metal properties as well.Ability to conduct electricity increases with heat. (in contrast with metals)
Properties of semi-metalsShiny or dull
Conduct heat and electricity better than non-metals, but weaker that metals
When heated, they can conduct electricity better.
Electrical conductors, Semi-conductors and insulatorsMetals conductors
Non-metals insulators
Semi-metals poor conductors, called semi-conductors
Thermal conductors or insulatorsThermal conduction is the flow of heat from a high temperature to a low temperature.
Metals thermal conductors
Non-metals thermal insulators. All materials that trap air = poor conductors, because air is a poor conductor.
Magnetic and non-magnetic materialsFerromagnetic elements strongly attracted to magnetsFe, Ni, Co, Alnico, ceramic (insulating magnets), magnetite
Phases of matterAnd the kinetic molecular theory
The three phases of matter
SOLIDS
Solids keep its shape and can only be dented, broken or bent.HardHigh densityNo compressibilityFixed volume
Made up of small particlesVibrate onlyVery small spaces between particlesStrong attractive forces causes specific shapeNo diffusionHave crystalline structureHave a specific melting point
Liquid
MeltingSolidification
LIQUIDS
No fixed formNot hardHigh densityNo compressibilityFlowsFixed volume
Particles move in ordered fashionCollisions occurDiffusion occurSmaller spaces between particles than with gasesExerts pressure in all directionsWeak force between particlesSpecific freezing point and boiling point
Gas
EvaporationCondensation
GASES
No fixed formNot hardLow densityEasily compressibleFlowsNo fixed volume
Particles move fastGreater collisionBig open spacesWeak/no forces between particlesInvoluntary motionDiffusion occursExerts pressure in all directions
Kinetic model of matter
Motion of particles
Diffusion
is the movement of particles from a high concentration to a low concentration.
Motion of particles
Kinetic model of matter
1. All matter consist of small particles2. Particles are in constant motion3. Spaces between the particles4. Constant collisions between particles and container5. Temperature is a measure of the kinetic energy of the particles6. Forces between particles7. Phase changes occur when energy changes occur
Phase changes
1. Condensation
4. Evaporation
3. Melting
2. Solidification
1. Condensation
Prior to condensation:* particles slow down* not far apart* less violent collisions
Phase change follows:* Spaces decrease* Forces increase* more orderly arrangement
2. Solidification
Prior to solidification:* particles move very slowly* particles very close to each other* only vibrates
Phase change follows:* very small spaces between particles* forces between particles become very strong* orderly arrangement
3. Melting
Prior to melting:* particles move fast* particles further apart
Phase change follows:* spaces increase* forces decrease* less orderly arrangement
4. Evaporation
Prior to evaporation* particles move very fast* particles very far apart* violent collisions due to high speed
Phase change follows:* spaces between particles are big* forces negligible* disorderly arrangement
Evaporation vs. boiling
EVAPORATION
Occurs @ temp below B.P.
Occurs only on surface
Slow
Causes cooling heat absorbed from environment
BOILING
Occurs @ B.P.
Occurs throughout the liquid
Quicker
Temp remains constant during boiling
Heating curve of water
Heating curve of water
Atomic structureAtomic models
The electrical nature of matter
Michael Faraday
Electrical current through salt solutions
Amount of Q = amount of atoms reacting
Dalton's atomic theory
Michael Faraday
Amount of Q = amount of atoms reacting
Thomsons atomic model
Charge and mass of electrons of all substances are the same.
Thus, electrons in all substances must be the same.
Substances differ because electrons are arranged differently.
-----
Rutherfords atomic model
Bombard thin gold foil with -particles (heavyweight kind of radioactivity).
Fluorecent zinc sulphide screen opposite foil = -particle detector. fluorecent zinc sulphide screen
-particles gold foil
Radioactive source
Rutherford continued
Observations
Most of the -particles showed no diversion. Some were deflected
Some were reflected
ConclusionsElectrons occupy the greatest volume of the atom.
Positive particles are grouped together in the nucleus very heavy, but small.
Atom
++++++++++++++ (+2)
Assumptions
The positive charges are all together in a small volume in the nucleus.
The nucleus is surrounded by a space that contains the e- (v. Small mass) e- are responsible for the great volume of an atom.
Mass is concentrated in the nucleus.
Later investigations predicted that the nucleus ispositively charged. # Protons = # electrons. e- dont move like bees around a hive, e- would collapse into nucleus.
Bohrs atomic model
Electrons move in orbits
Electrons with the same energy move around in the same orbit
Electrons in orbits further away from nucleus have a higher energy
Planetary atomic model
e- move in energy levels
e- with same E values, move in same E levels
Valence orbitals have higher energy than those close to the nucleus
Energy levels closer to the nucleus are filled first with e-
Each energy level can only take a specific amount of e-
e- in orbits close to the nucleus are lower in energy level than orbits further away
If e- are in lowest possible energy level ground state
When e- absorb energy it rises in energy level.
This (excited) state is unstable and e- fall back to lower energy levels
Line spectra
Electrons in the ground state absorb energy. Electrons are now excited, and move to a higher energy level.
This electron is now unstable.
It falls back to its ground state, radiating extra energy as light.
The separate coloured lines of light show electrons only have certain energy. Electrons energy is thus quantised.
Each element has its own unique line spectrum.
Line spectra occur when gases are heated of an electric current is passed through it.
Wave mechanical atomic model
Bohrs atomic model explains the structure of hydrogen, but not those of atoms with more than one electron.
The discovery of wave properties of electrons gave us a more acceptable model.
e- have both particle and wave properties.
Schrodinger stated that moving e- form a 3D wave space that surrounds the nucleus, called an orbital.
Neutron
J. Chadwick discovered a particle with a mass nearly equal to the proton.
Neutral charges, called neutrons.
Atomic mass and diameter
Atoms are extremely small with small masses.
Diameters are also extremely small. Most of the volume of an atom is empty space, the nucleus accounts for most of the mass of an atom at the centre.
ELEMENTAVG ATOMIC MASS
Hydrogen1,673 55 X 10 -27
Carbon1,994 36 X 10 -26
Oxygen2,656 59 X 10 -26
Uranium3,952 33 X 10 -25
Relative atomic mass
Hydrogen is the lightest atom and is chosen as the standard for an atomic mass scale.This mass is equal to 1.Using proportion to find the atomic masses of other elements relative to a mass of 1.
1,673 55 X 10 -27 kg of Hydrogen = 1 on the Hydrogen scaleSo, 2,656 59 X 10 -26 of oxygen = 1x2,656 59 X 10 -26 kg 1,673 55 X 10 -27 kg = 15, 87 on the Hydrogen scale
Structure of the atom
The atom consists of very many small subatomic particles. In chemistry we work with protons, neutrons and electrons.Protons and neutrons are in the nucleus at the centre.Electrons occupy a large region around the nucleus and are 1836 times lighter.When electrons and protons are equal in number, the atom is neutral.When an electron is removed, the atom will be positively charged. An ion is an atom that has a charge on it. Cations are positively charged atoms.Anions are negatively atoms.
Isotopes
Same element, different masses and amount of neutrons.
Nuclide = isotopic nuclei.
Isotopes
Carbon (atomic # 6) has three natural isotopes with atomic weights of 12, 13 and 14.
isotope#p#n========== C-1266 C-1367 C-1468
Tin (Sn, atomic # 50) has ten natural isotopes with atomic masses of 112, 114, 115, 116, 117, 118, 119, 120, 122 and 124. How many protons and neutrons do these isotopes have?
Radioactive or Stable?
Radioactivity is a nuclear phenomenon: it comes as a result of a particular structure in a nucleus.
A radioactive atom is considered unstable. All unstable atoms emit radioactivity (usually by ejecting nuclear particles) in order to reach a stable configuration. This is the process of radioactive decay
So, not all atoms will be radioactive, just a small proportion of isotopes with unstable nuclei. The bulk of isotopes are stable, or non-radioactive.
Stable and Radioactive Isotopes
Carbon (atomic # 6) has three natural isotopes with atomic weights of 12, 13 and 14.
isotope#p#n========== C-1266 C-1367
C-14 is a radioactive isotope; C-12 and C-13 are stable.
Over time the proportion of C-12/C-14 and C-13/C-14 will increase until there is no C-14. (unless some process makes new C-14...)
C-1468
Radioactivity Inside You
Concerned about radioactivity in nature?
To keep things in perspective, consider that 0.01% of all potassium is radioactive K-40.
Potassium is an essential element in the human body. If your body is about 1% K, this means a 70 kg (150 pound) person contains around 1x1021 atoms (thats one billion trillion atoms)of radioactive K-40.
Energy levels in an atom
Energy of an atom is quantized, meaning your electrons all have discrete amounts of energy.Electrons are thus limited to a specific energy level,Which you learned in grade 8 was an orbital.
These main energy levels are indicated by n, and1, 2, or 3 following it.
eg. n = 1
Energy levels in an atom
Each of these main energy levels are then sub-divided into sub-energy levels, which are indicated by the numbers s, p, d and f.
s