Chemistry Flashcards
What are elements
substances that contain only one type of atom
what is a compound
substance made of more than one type of element chemically combined
what is a mixture
two or more elements or compounds not chemically combined
how do you separate an insoluble solid from a liquid
you filter it
crystallisation method
- add an impure solid to a solvent
- place the mixture in an evaporating basin
- until crystals start to appear
- leave the liquid to evaporate
- separate soluble solid from solvent to collect solid
when is fractional distillation used
to separate a mixture of liquids
distillation method
- heat the mixture
- evaporate the solvent
- pass vapours into the condenser
- collect the condensed liquid
- separate soluble solid from solvent to collect liquid
when is paper chromatography is used
used to separate a mixture of solids dissolved in a solvent
- solids with more attraction to solvent moves further up paper
what is the earliest idea of atoms
that atoms are the smallest particles which could not be divided
what is a plum-pudding model
a ball of positive charge with electrons embedded within
what is the nuclear model
- Made by Rutherford and Marsden
- positively charged nucleus surrounded by electrons
Alpha scattering experiment
- most alpha particles passed through atom
- those that hit centre were repelled
What did Bohr suggest?
electrons were in energy shells around nucleus
What did James Chadwick discover?
discovered the nucleus had positive protons and neutrons surrounded by electrons
what are ions
an atom that has gained or lost electrons
what is the atomic number and mass number
- atomic number : proton
-mass number : proton + neutron
how to calcutulate RAM
∑ isotope mass x isotope abundance / 100.
what is the charge of each subatomic particle
- proton : +1
- neutron : 0
- electron : -1
How did Dalton organise periodic table?
in order of atomic weight
what are isotopes
elements with the same proton number but different neutron number
Wat do elements in the same group have?
- same outer shell
- similar properties
what are the meanings of columns and rows?
- columns = groups
- rows = periods
What did Newland notice?
every eighth element was similar
What was Medeleev’s order?
- ordered atomic weight in rows
- elements with similar properties in same column
How is modern table organised?
-has atomic nu,mber in rows
- similar properties in same column
Formation of table
- metals on left
- non metals on right
What type of ions do they form?
- metals form + ions
- non metals form - ions
What are the properties for Group 0 elements?
- noble gases
- full outer shell
- boiling point increases as you go down
- unreactive
What are the properties of group 7 elements
- halogens
- mass, bpt, mpt gets higher as you go down
- less reactive as you go down
- more reactive halogens displaces less reactive from a solution of its salt
What is ionic bonding
- happens between metal and non-metal
- is an electrostatic force of attraction between oppositely charged ions
what are the properties of group 1 elements?
- alkali metals
- more reactive as you go down
- when reacts with water, metal hydroxide and hydrogen is produced
why do different particles have different mpt and bpt?
strength of the forces between the particles is responsible
- stronger forces = higher mpt and bpt
what are the properties of transition metals?
- have higher mpt, bpt
- more dense than group 1 metals
- less reactive than alkalis
- form ions of many charges
-compound are often coloured
-often used as catalysts
Topic 2
what happens at the mpt and bpt?
- at mpt : melting and freezing takes place
- at bpt : boiling and condensing takes place
The structure of ionic bonds
- giant ionic lattice
- held together by strong electrostatic forces of attraction
What happens in ionic bonds?
-metal loses electron = becomes + charged
- non metal gains electrons = becomes - charged
properties of ionic bonds
- hgh mpt and boiling point = loads of energy needed to break bond
- will not conduct electricity when solid, will when molten or dissolved in water
(when solid ions are not free to move, when molten or dissolved thy can move and carry charge)
What are covalent bonds?
- between non metals
- atoms share electrons for full outer shell
Properties of simple covalent molecules
-small number of atomes held together by covalent bond
- low mpt and bpt = have weak intermolecular forces, do not require a lot of energy to overcome
- do not conduct electricity = no overall charge, no free electrons
structure and properties of a diamond
- each carbon atom has 4 covalent bonds
- very hard, stron structure
- high mpt and bpt = strong covalent bond
- does not conduct electricity
what is a polymer?
very large molecules formed when many smaller molecules bond together covalently
properties of giant covalent molecules
- large number of atoms covalently bonded together in huge structure
- high mpt and bpt
- held together by strong covalent bond = requires loads of energy to break
-the bigger the size, the bigger the intermolecular force
what is graphene?
single layer of graphite with properties making it useful for electronics and composites
wha tare fullerenes?
- molecules of carbon atoms with hollow shape
- used in nanotechnology, electronics and materials
sturcture and properties of graphite
- each carbon atom has 3 covalent bonds
- hexagonal layers with delocalised electrons between
- high mpt and bpt = strong covalent bond
- conducts electricity = free electrons
- slippery = layers can slide over eachother
what are cations and anions?
- cations : + charged ions
- anions : - charged ions
what happens when a metallic bond is formed?
- each metal atom loses it outer shell and electrons
- become delocalised around cations
- electrostatic forces between cations and electrons hold it together
what is the structure of a metal?
- giant structure of cations in regular patter
- cloud of delocalised electrons
properties of metals
- high mpt and bpt = strong metallic bond
- malleable = atoms can slide over eachother
- good conductors of heat and electricity =delocalised electrons carry both charge and heat
what are nano particles
particles between 1-100nm in size
what are the uses and possible risks for nanoparticles?
uses
- sunscreen, self cleaning windows
- cosmetics and antimicrobes
risks
- small = can be breathed in
- can affect environment
Topic 3
what is law of conservation of mass
no atoms are lost or gined during a reaction
formula for moles
moles = mass/ mr
concentration formula
concentration = amount of solute/volume of solution
what are limiting reactants?
- reactant that is used up completely
- once used up reaction stops
`titration experiment
- measure 25cm3 of alkali using pipetter into conical flask
- add a few drops of indicator ( phenolphthalein is pink)
- slowly add acid from burette , swirling
-when indicator changes (phenolphthalein goes colourless) , stop adding acid - record volume used
- repeat til concordant results are found
percentage yield facts
- 100% % yield never occurs as reaction may not go to completion as it is reversible
- some product may be lost during separation
- may have unexpected reactions
percentage yield formula
% yield = (product mass/ theoretical mass) x 100
what is atom economy
- measure of starting materl that way is useful
- high atom economy is preferred as less raw material is wasted = less energy wasted
atom economy formula
atom economy = relative formula mass x 100
concentration formulas
- concentration = mass/ volume
- concentration = moles/volume
chromatography rf value
= distance moved by substance/ distance moved by solvent
what happens during reaction of metal with acid
- metal atoms lose electrons
- hydrogen ions gain electrons
what is oxidation and reduction
- oxidation = loss of electron
- reduction = gain of electrons
topic 4
when metals react with oxygen
produce metal oxides
reactive metals
- more reactive displaced by less reactive
- less reactive found in native state
elements below carbon are reduced at high temp - more reactive extracted by electrolysis
when metals react with salt
metal + acid = salt + hydrogen
what are alkalis
- types of bases
- metal oxides and carbonates are bases
- salts produced
what are bases
bases are compounds that can neutralise an acid
acids and alkalis
Acids
- less pH than 7
Alkalis
- higher pH than 7
general equation of metal carbonate
metal carbonate + acid = salt + water + CO2
different types of salts
- hydrochloric acid = chlorides
- sulfuric acid = sulfates
- nitric acid = nitrates
how to make clean dry salts
- add excess base to warmed acid
- filter off excess base
- place solution in evaporating basin
- heat over water bath til crystals appear
- leave for water to fully evaporate
What is electrolysis?
breaking down of substance using direct surrent
Differene between strong and weak acids
Strong
- completely ionise in aqueous solutions
weak
- partially ionise
what is an electrolyte?
- molten or dissolved ionic compund
- meant to be elctrolysed
what happens in electrolysis?
- negative ions move to anode + where they lose electrons
- positive ions move to cathode - where they gain electrons
what happens at the anode and cathode ?
- at anode = non metals form
- at cathode = metals form
steps of electrolysis in aluminium oxide
- bauxite ore is purifief to get aluminium oxide
- aluminium oxide is dissolved in molten cryolite
- mixture is electrolysed and aluminium forms cathode
why is cryolite used?
to reduce mpt of aluminium oxide = save energy
