SEM 1 EXAM Flashcards
how does nucleus stay together
electrostatic repulsion forces protons apart, but strong nuclear force attracts nuclear particles together
if nuclear force is balanced, atoms is stable
what happens if nuclear forces are unbalanced
then the nucleus will be unstable and decay over time
isotopes
atoms of an element with the same number of protons, but different number of neutrons.
chemical properties are similar (atom behaviour in chem reaction is based on arrangement and number of electrons.
different physical properties (mass and nuclear stability)
chemical and physical properties
how elements participate in chemical reaction
feature one can measure and observe
radioactive decay of isotopes
if forces in atom are balanced, atom is stable
if not balanced, atom is unstable and nucleus undergoes radioactive decay to become stable.
in radioactive decay, radiation is emitted, which is useful for radioactive dating and medical diagnosis and treatment
half-life
time taken for half the original sample to decay
relative atomic mass
compares the mass of atom to the mass of another atom
all atoms are compared to carbon 12
isotopes have different masses and abundances on earth
weighted average of the relative masses of the isotopes of an element relative to carbon12
Democritus
disagreed with the idea of infinitely divisible matter, proposed that matter consisted of tiny particles with nothing between them but empty space called “atomos”
dalton
elements composed of atoms
an atom of same element have a same properties, atoms of different elements have different properties
atoms not created nor destroyed or changed into different types during reactions
c reaction is separation, combination , rearrangement of atoms
compounds are combinations of atoms in specific ratio
thomson
found electrons
realised that atoms could be divided further
plum pudding model: electrons embedded in positively changed mass
rutherford
proposed the atom consisted mostly of empty space
electrons orbited around nucleus. most of mass was in the nucleus, all positive charge was located in the nucleus carried by protons
bohr
electrons were in electrons shells around the nucleus, each shell has a specific amount of energy
Chadwick
discovered the existence of neutrons that accounted for around half the mass of the nucleus, had neutral charge
Electrostatic attraction
related to distance the valence electrons are from the nucleus
strength of attraction of protons and electrons
shielding effect
related to number of inner shell electrons, shield the effect of the protons from valence electrons.
reduces ionisation energy
correlates to number of inner electron shells and attraction of valence electrons to nucleus
core charge
how defective the charge of the nucleus is at holding the valence electrons in
increases going towards noble gases
atomic radii
decrease going right
increase going down
electronegativity
ability of atom to attract electron
increases going right
decrease going down as electron is further from nucleus so it is harder to attract
ionisation energy
energy required to remove loosely bound electron
depends on
nuclear charge: more nuclear charge means more protons in nucleus which increases ionisation energy because valence electrons are tightly held on.
distance form nucleus: further distance decreases electrostatic attraction between valence electrons and nucleus. valence electrons are loosely held.
increases towards right
decreases going down because valence shell is further away making it easier to lose electrons
electron affinity
ability to accept electron and from a negative ion
metallic character
set of properties associated with metals
depends on ability to lose valence electrons
decrease going right
increase going down
ground state
shells next to nucleus are taken up by electrons
when electron is at its lowest possible energy levels
how electrons jump
atoms absorb energy, electron around nucleus gain this extra energy and move up to higher energy levels.
electrons can be so excited that they leave (ionisation)
energy levels are discreet. electrons can only exist in specific energy levels
electrons cannot exist between energy levels, therefore
amount of energy absorbed and emitted = difference in one energy level and another. electrons could be excited from one energy level to another by specific amounts of energy that corresponds to the difference in energy levels.
amount of energy absorbed by any sample of one element is the same
excited state
an atom in which electrons occupy higher energy levels than the lowest possible energy levels.
as it moves back to ground state, emits light
atomic emission spectroscopy
absorption and emission of light help identify element
process of analysing light emitted by electron as it return to ground state
spectroscope: takes emitted light and separates it into its component wavelengths to produce a line emission spectrum.
sample to analysed is heated to much higher temperatures, and light emitted is passed through a prism. the prism disperses light into its component colours. the monochromatic allows single wavelengths to pass at a time, then spectra is recorded
fingerprint
AAS
uses absorption of light by electrons to measure how much of an element is present. used AAS
- element analysed is determined: there could be many element in a sample but we need to focus on one. thus the lamp is made of the same element being tested. current passes through gaseous sample of element in lamp and emits light. has unique wavelengths to other elements
- vaporised: changing substances in sample to atoms. when light passes through, only the element being tested will absorb the light because it has the same energy levels as atoms that emitted light from lamp.
- detection: light passed through sample enters monochromator-> selects one wavelength of light for analysis by detector-> measures intensity of light and turns it into a number.
compared to known samples by constructing a calibration curve. concentration against absorbance value.
absorbance value
measure of amount of light that passed through sample without being absorbed, lets you know concentration
what is mass spectrometry
based on different masses of atoms in sample
determine what elements are present in a sample or what isotope and their abundance in a sample.
determines mass relative to carbon12 and calculates relative abundance of the isotope
determine isotopic composition of an element.
method of mass spectrometry
sample vaporised then…
1. ionisation: sample is bombarded with high energy electrons/ UV LIGHT.
removes valence electrons leaving atom with positive charge
does this with ALL atoms.
- acceleration: cations accelerated through electrical field at very high speeds according to mass-charge ratio
- deflection: pass through a magnetic field where they undergo deflection according to their mass. ions separated according to mass and charge
lighter= more deflection - detection: detectors measure amount of ions that strike them
graphed in a mass spectrum.
why does lamp pulsate in atomic absorption spectroscopy
light from the lamp is pulsed so that the detector can distinguish between the light from the cathode lamp that is left over after absorbance and the continuous light naturally emitted gaseous atoms in the flame/burner returning back to their ground state.
finds extent of lamp light being absorbed and to what extent
material
substances that make other objects. often mixtures of many substances. can be pure (elements and compounds)
pure substance
Pure substances are defined as substances that are made of only one type of atom or molecule.
properties cannot be altered
distinct and measurable properties for any given arrangement of atoms or molecules
pure substance vs homogeneous mixture
homogeneous mixture: components can be separated
pure substances: can’t be separated
elements
substances made of one type of atom
compounds
pure substance made up of more than one type of atoms
chemically combined, uniform composition
pure substances
properties cannot be altered. properties are distinct and measurable for any given arrangement of atoms or molecules
mixtures
properties can be changed depending on how much of each component is added mixture.this useful as properties can be controlled.
individual components keep their properties
variable composition
alloy
mixture of metal with other metals or small amount of non metals
e.g. iron is soft an sprone to corrosion. but adding some carbon creates steel which is stronger and corrosion resistant
polymer
material with a molecular structure that is composed of many repeating smaller units bonded together.
compared to metals, they are less dense, electrical insulator, corrosion resistant
natural: wool, silk, paper
synthetic: polystyrene
ceramics
inorganic, non metallic solid. composed of metals, nonmetals, metalloids held together by ionic and covalent bonds.
can be highly ordered (crystalline)or highly irregular (amorphous)
natural: kaolinite (makes porcelain)
synthetic: silicon carbide (used as an abrasive)
properties: hard, high compressive strength, able to withstand high temperatures. most are good insulators, but some have semi/super conducting properties
composite materials
combination of two or more distinct materials with significantly different chemical and physical properties.
creates a range of properties that would be unobtainable with using one of the individual components.
e.g. reinforce concrete = concrete matrix +embedded steel bars
low tensile strength of concrete counteracted with high tensile of steel
maintains high compressive strength of concrete
heterogenous mixture
non uniform mixtures that contain physically separate materials
not pure or uniform
mixtures can have different proportions of the same components .
eg. granite has 3 different minerals, each piece has a different amount but it is still granite
homogenous material
materials that have uniform composition throughout
breaking it smaller = would be identical
homogenous solution
consists of solute and solvent, solute is distributed throughout the solvent as very small particles, so it appears uniform
nanoscale
structure between 1 and 100 nm
nanometer = 10 ^-9
nanomaterial
substances (natural and synthetic) that are composed of single units that exist in ten nanoscale
very large surface area compared to the volume they occupy
adsorption of nano-materials
where molecules stick to surface of of a solid or liquid
can be used to remove unwanted chemicals and gases
large surface area means that a small volume of nanoparticles can adsorption a large number of molecules
transportation of nano materials
can transport molecules that are adsorbed
small size and large surface area mean that they can transport chemicals through air, skin and even cells
used in chemotherapy treatments for cancer as it can transport drugs to specific cells
nano materials as catalysts
can speed up rate of reaction without being altered or destroyed in the process. provide surface for reaction to occur
reactant molecules absorb onto the surface of the nanoparticles which allows reactant molecules to combine to form the product
large sa means many reactions can occur at once. ->increases rate of reaction
gold as nanoparticles
properties can change as nanoparticles
gold changes its colour
melt at lower temperatures and appear red in solution
zinc oxide in sunscreen
good absorbers of uv radiation and appear transparent because the particle size is much smaller than the wavelength of visible light, so light can go through it with very little being affected
other metal oxides tend to be milky white
having nanoparticles means that it’s distributed evenly so uv radiation is absorbed/scattered by zinc oxide. if they were bigger it means that it wouldn’t be evenly distributed and up rays could pass through
Nanoparticles in medicine
colloidal gold: labeling antigens, optimises distribution of drugs to cells in difficult areas (brain, retina, tumours), targets tumors and provides detection
silver: antibacterial and antifungal properties, due realease of silver ion from surface of metal
sa enhances antibacterial effectiveness
safety risks of nanoparticles
can travel through air, bloodstream, skin, cells
can interact with inside body (biomolecules) to cause unwanted reactions
composite nanomaterial
small size and unique properties are useful for them to be composite nanoparticles
stain resistant cotton: cotton fibres covered with water resistant nanoparticles
tyres: added carbon improved resistance and abrasion. increase electrical conductivity, prevents build up of static electricity
fullerenes
3d structures formed by networks or carbon atoms
nanotube: cylindrical tube, reinforcement in composite nanomaterial
graphene: flat 2d layer of carbon atoms arranged in hexagons
buckyball: soccer ball shaped 3d structure
top down method to make nanoparticles
size of material is progressively reduced , by grinding until size is achieved.
+: large quantities produced, cheap, uniform
-: limited to simple structures
sieving
based on particle size
separates mixtures of different particles, smaller particles pass through holes, large ones are trapped
filtration
particles not dissolved in solvent
separates suspended solid from a liquid using a filter funnel and paper.
Evaporations
particles dissolved in liquid
boiling/evaporating solvent away from solute
distillation
differences in boiling point
separates two liquids with different boiling points or a soluble solid and the solvent
distillation flask, condenser, receiving flask
fractional distillation
vapour passes through a column packed with glass beads. less volatile component component condenses on the glass beads and drips back to distillation flask
can be used to separate miscible liquids
separating funnel
difference in density
immiscible liquids separate into layers due to density
tap is opened to let the more dense component out of the mixture
metallic bonding
chemical bonding that results from attraction between metal atoms and the surrounding sea of electrons
metals have low ionisation energy that is why they lose electrons easily
high MP and BP of metals
forces of electrostatic attraction between metal cation and delocalised electrons are very strong so it requires more energy to break them
why do metals conduct electricity
delocalised electrons are free to flow through the metal and so carry a current.
why are metals malleable
bonding in metals is not rigid. as metals are metal with a force, the atoms slide through electron sea to new positions while continuing to maintain their connections to each other. this also makes the ductile.
attractive forces stronger than repulsive.
non directional bonding
why are metal dense
particles are closely packed together
why are metals shiny and opaque
freely moving and delocalised electrons are present so metals can reflect light and appear shiny.
close packing of cations prevent light from slipping through making it opaque
what does a greater core charge in a metal mean in terms of bonding
atoms packed tightly with stronger bonds
metallic bond structure
- cations are closely packed in 3d network. cations occupy fixed positions in lattice
- delocalised electrons moving freely. they belong to the lattice as a whole, not an individual atom
- these electrons come from valence electrons not inner shell ones
- cations held in position due to ESF of attraction between cations and electrons (metallic bonding)
limitations to metallic bonding
structure can't explain: variations in properties magnetic nature differences in electrical conductivities *more complex model needed
ways to modify metals
alloy production
heat treatment
formation of nanoparticles
metal alloys
mixing metals with other substances (metal/carbon). substances are melted, mixed and cooled.
harder and lower MP: since atoms of different sizes are now included, the properties may differ. lattice doesn’t move in the same way (lower MP)
iron and carbon
steel
harder and less corrosive, but less malleable because atoms are slightly different in size and lattice can’t move past each other as easily.
ionic bonds
when a metal and non metal come into contact and a electron is lost from the metal and given to non metal. cations and anions formed. held together by electrostatic forces of attraction between ions (ionic bonding)
ions have inert gas electron configuration
each cation is surrounded by anion and vice versa (attractive forces outweigh repulsive forces)
high MP and BP of ionic bonds
large amount of thermal energy to overcome attraction between oppositely charged ions and allow them to move freely
bricks in furnace made of MgO
why are ionic compounds brittle and hard
strong forces of electrostatic attraction hold ions together, so a strong force is required to break them
brick in houses CaPO4
when a force is applied ions move in the direction of the force, like ions are forced together causing them to repel (repulsion causes it to shatter)
ionic compounds and electrical conductivity
solid: not free to move, can’t conduct current
ceramic insulators
solution/liquid: lattice dissociates in water into charged ions that move freely in solution
cations -> cathode
anions -> anode
ammonium chloride in dry cell batteries as electrolytes
ionic compounds and solubility
soluble: ions break away and mix with water molecules
insoluble: ions remain bonded and don’t form a solution
depends on:
1. attraction between cation and anion
2. ion and water molecule
why are metals good conductors of heat
cations vibrate vigorously and are able to transfer thermal energy to each other
delocalised electrons readily transfer thermal energy as they move through the lattice
why do metals form cations
low ionisation energy
interstitial alloy
when atoms of element that is supposed to be mixed with metal is much smaller and fill spaces between lattice
Substitutional alloy
larger, similar property metal added to lattice
covalent molecular bonds
sharing of electrons to attain full valence shell. molecules are discrete (individual)
if atoms have similar electronegativities than they are like to form covalent bonds because they have the same affinity for electrons and don’t want to donate.
positively charged nuclei attracted to shared electrons
low MP of covalent molecular bonds
Intermolecular forces are weak so not much energy is required to break them
non conductive of covalent molecular
no mobile particles
electrons locked in covalent bonds
softness of covalent molecular
intermolecular forces are weak
molecules can be moved out of position easily
hence soft
covalent networks and properties
only intramolecular forces made form network of repeating lattices of covalently bonded atoms (intramolecular) eg silicon dioxide, carbon, silica properties: hard high MP + BP solid @room temp non conductive (except graphite)
