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Chemistry - key concepts in chemistry (periodic table - mendeleev and…
Chemistry - key concepts in chemistry
chemical equations
formulas
water - H2O
ammonia - NH3
carbon dioxide - CO2
hydrogen - H2
chlorine - Cl2
oxygen - O2
ions
ammonium - NH4^+
nitrate - NO3^-
hydroxide - OH^-
carbonate - CO3^2-
sulfate - SO4^2-
balanced equations
word equations
state symbols - (s)(l)(g)(aq)
ionic equations
hazards
oxidising e.g. liquid oxygen
environmental hazard e.g. mercury
toxic e.g. hydrogen cyanide
harmful e.g. bleach
:
highly flammable e.g. petrol
corrosive e.g. concentrated sulfuric acid
history of atom
Dalton - atoms were solid spheres, different spheres were different elements
Thompson - atoms must contain smaller negatively charged particles, electrons (plum pudding)
Rutherford - plum pudding must be wrong. Positively charged nucleus in the centre, cloud of electrons, most of atom empty space
Bohr - electrons in shells, each shell fixed distance from nucleus, with fixed energy
the atom
nucleus
middle of atom
contains protons and electrons, has positive charge because of protons
very small within atom but contains most of its mass
electrons
orbit around nucleus in shells
negatively charged and negligible mass
very small but shells cover most of atoms space
same amount of protons as neutrons, so atoms are neutral
mass number - atomic number = no. of neutrons
isotopes and RAM
isotopes
different forms of the same element which have same no. of protons but different no. of neutrons
same atomic number but different mass number
e.g. carbon-13 has 6 protons and electrons but 7 neutrons
RAM
average mass of 1 atom of the element, compared to 1/12 of the mass of 1 atom of carbon-12
RAM is average mass number of the elements' isotopes. But it does take into account the abundance of the isotope.
RAM isotope calculations
periodic table - mendeleev and electronic configurations
sorted elements into groups based on properties
sorted them according to atomic mass
some elements ended up in wrong columns as atomic mass he had was wrong
he left gaps in the table - he predicted the proprties of elemens not discovered then e.g. he predicted properties of germanium
mendeleev tried to order using atomic mass instead of atomic number
1st shell: 2 electrons, 2nd: 8, 3rd: 8
can work out electronic configuration using position in periodic table - group is outer shell electrons and period is number of shells
ionic bonding
ions are charged particles, formed when atoms lose or gain electrons to form ions
anions formed when atoms gain electrons, cations formed when atoms lose electrons
groups 1, 2 (cations), 6 and 7 (anions)are most likely to form ions
ionic compounds
dont conduct electricity because ions cant move. when molten/aqueous they do conduct
high melting & boiling points due to strong attraction between ions
dissolve easily in water
regular lattice structure
covalent bonding
H2, H2O, CH4, HCl, O2, CO2
simple molecular substances
very weak intermolecular forces
low melting and boiling points, usually gases or liquids at room temp.
as molecules get bigger intermolecular forces become stronger
dont conduct electricity
some are soluble, some aren't
giant covalent structures
bonded together by strong covalent bonds
very high melting/boiling points
dont conduct electricity except for graphite/ene
not soluble in water
diamond - carbon based giant covalent structure
network of carbon atoms with 4 covalent bonds
strong covalent bonds require lots of energy to break - high m.p.
rigid lattice makes diamond extremely hard - used in cutting tools e.g. saw teeth and drill bits
does not conduct electricity - no free electrons or ions
graphite - carbon based giant covalent structure
3 covalent bonds creating sheets of carbon atoms arranged in hexagons
no bonds between layers so held together weakly. makes graphite soft/slippery - ideal as lubricatant
high m.p. and conducts electricity (so is used in electrodes) because there is 1 delocalised/free electron
graphene - carbon based giant covalent structure
one layer of graphite and it is a fullerene
sheet of carbon atoms joined together in hexagons
2D because sheet is 1 atom thick
fullerenes
molecules of carbon atoms with hollow shapes
based on hexagonal rings of carbon atoms (sometimes pentagons or heptagons)
C60 buckminsterfullerene first discovered fullerene looks like a sphere
carbon nanotubes
high tensile strength - strengthens materials without adding much weight
cylinders of graphene so conduct electricity
they make tennis rackets lightweight and strong
used to deliver drugs to body - cages other molecules. used as a catalyst - high surface area
polymers
long chains of covalently bonded carbon atoms
intermolecular forces strong so high melting points
formed when lots of monomers join e.g. ethene joins to make polyethene
metallic bonding
giant structure with regular pattern - very strong
electrons in outer shell of atom are delocalised. strong attraction between positive metal ions and negative electrons
compounds include metallic elements and alloys. delocalised electrons produce all the properties of metallic compounds
properties
very high m.p./b.p.
generally shiny solids at room temp and not soluble in water
generally more dense as ions are more packed
layers of atoms in metal can slide over each other making them malleable - can be hammered/rolled into flat sheets
delocalised electrons carry current so they are good conductors of electricity
