Third Year Flashcards
Element
A substance containing only 1 type of atom
Compound
A substance contains 2 or more types of atoms chemically combined
Mixture
Two or more types of atoms mixed together but not chemically combined
What is simple distillation?
Obtaining water from a solution
Boil the water then condense the vapours
What is fractional distillation?
Separating mixtures of liquids
What is filtration?
Obtaining a solid from a suspension
Solid left on the paper is called the residue, the liquid that passes through the filtrate paper is called the filtrate
What is crystallisation?
As the water from a solution evaporates, the solution can no longer hold as much dissolved solute and so some of the solute crystallises out
Why doesn’t the temperature rise when boiling ethanol?
The energy is used to overcome forces rather than heat it up
What is paper chromatography?
Separating mixtures of different coloured dyes from each other
What 3 things does paper chromatography show?
How many dyes there are
How soluble each dye is
Whether a pen is permanent
How to calculate the rf value ?
Measure to the middle of the spot
Chromatography process
1) draw a pencil line 2cm from the bottom of the paper
2) draw a spot on the paper for each pen
3) label each spot
4) place 1cm depth of water in the beaker
5) place chromatography paper in bracket
6) leave paper in the beaker until the water is near the top
Atom
A particle of matter containing a single nucleus (number of protons is balanced by equal number of electrons)
Molecule
Two or more atoms joined together with covalent bonds
Atomic number
Number of protons in the nucleus
Mass number
Number of protons and neutrons in the nucleus
Isotopes
Atoms of the same element with different numbers of neutrons
Relative atomic mass
The average mass of all the different isotopes of an element on a scale where 12C atoms have a mass of exactly 12
How to calculate the relative atomic mass?
Times the mass number by the abundance % for each element, add, then divide by 100
Groups
Columns - how many are in the outer shell
Periods
Rows - how many shells are occupied
Metal oxides that dissolve in water form ?
Alkaline solutions
Non metal oxides that dissolve in water form ?
Acidic solutions
What are ions?
Contain full outer shells of electrons - in reactive
Metal atoms lose electrons to form ?
Cations
Non metal atoms gain electrons to form?
Anions
What is ionic bonding
The force of attraction between oppositely charged ions
Why do compounds with giant ionic lattices have high melting and boiling points?
Oppositely charged ions attract each other
Strong force of attraction
Lots of these ions in a solid, therefore lots of energy is needed to overcome these forces
MP and BP very high
Why don’t ionic compounds conduct electricity when solid?
No freedom to move - only conduct electricity when molten and in aqueous solutions
Diamond ?
Covalent bonding
Giant covalent structure (each carbon atom is covalently bonded to 4 other atoms)
Very poor conductivity - no ions, no electrons capable of moving away from atoms
Very hard - very rigid lattice
Graphite ?
Covalent bonding
Giant covalent (each carbon atom is covalently bonded to 3 other atoms )
Very good conductivity - extra electron can move
Very soft - only weak forces between layers, layers can slide over each other easily
C60 fullerene ?
Covalent bonding
Simple molecular (each molecule has 60 carbon atoms joined together, forces between molecules are weak, but forces within molecules are strong)
Very poor conductivity - no ions, no electrons capable of moving away
Not very hard - only weak force between molecules, forces are easy to break
What is covalent bonding between
Non metals and non metals
What happens in covalent bonding
Electrons are shared between the atoms to produce full outer shells
Atoms join together to make a molecule
Each pair of shared electrons is a covalent bond
The compound formed is made of molecules (molecules arent joined together)
What is the ‘bond’?
The bond is the electrostatic attraction between the negatively charged pair of electrons shared between the 2 atoms and the positively charged nucleus
What are the diatomic elements with single bonds?
H2, F2, Cl2, Br2, I2
What are the diatomic element le with double or triple bonds?
O2, N2
What are the diatomic compounds
HCl
What are the inorganic molecules
H2O
NH3
CO2
What are the organic molecules
CH4, C2H6 (ethane), C2H4 (Ethene)
What are the organic molecules containing halogen atoms?
C2H5Cl (chloroethane)
C2H3Cl (chloroethene)
Simple molecular substances
Melting or boiling of them does not involve braking strong covalent bonds
Only weak forces are broken
Not much energy is required to overcome the forces, therefore the MP and BP is low
Giant covalent
No molecules - all atoms are linked via a series of covalent bonds
Large number of bonds have to be broken in order to melt or boil
High mp and bp
General word equation for Alkali metals
Metal + water = metal hydroxide + hydrogen
When metals react and lose electrons, they become?
Oxidised
What happens in group 1
The atoms of each element get larger going down the group
The outer shell of electrons gets further away from the nucleus - shielded by more shells
Yeh further the electron is from the positive nucleus, the easier it can be lost in reactions
Reactivity of alkali metals increases going down group 1
Down group 1
Element becomes more reactive, MP decreases (suggesting the metabolic bonding becomes weaker)
Element becomes denser
Lithium
Fizzes and floats
Sodium
Melts into a ball, fizzes and floats
Potassium
Burns with lilac flame
Fizzes and floats
Rubidium
Sinks, vigorous reaction
Caesium
Sinks
Explosive
Metal + oxygen
= metals oxide
Metal + acid
= salt + hydrogen
Reactivity series
Potassium Sodium Lithium Calcium Magnesium Aluminium Zinc Iron Nickel Tin Lead Copper mercury Silver Gold Platinum
Displacement
A more reactive element will displace the positive ion of a less reactive element from a compound
Practical for displacement
Add a small amount of each metal on the spotting tile
Add each solution of metal salt to each of the metals
Record the results
What does iron need to rust
Oxygen and water
What are 3 ways to prevent rusting
Galvanising
Sacrificial protection
Barrier methods
What is galvanising
Iron is coated in thin layer of zinc
What is sacrificial protection
Magnesium and zinc are used as sacrificial protection
Should be periodically replaced
They are more reactive than iron
What is barrier methods ?
Coating iron in oil or paint
What is oxidation
Loss of electrons and gain or oxygen
What is reduction
Gain of electrons and loss of oxygen
Oxidising agent
= reduction (usually a non metal)
What is reducing agent
=oxidation (usually a metal or negative ion)
What are group 7 non metals called
Halogens
Colours of halogens
F - pale green gas Cl - green gas Br - brown/red liquid I - grey solid (sublimates to purple vapour) At - black solid (radioactive)
What happens going down group 7
Melting and boiling points increase
Molecules become larger
Intermolecular forces get stronger
More energy is needed to overcome these forces
Halogen + metal
= salt
Halogens become …… reactive going down the group?
Less reactive
Displacement reactions for halogens
A more reactive halogen can displace a less reactive halogen from solutions of its salt
Add bromide water to each test tube containing KCl, KBr, KI
% gases in atmosphere
Nitrogen - 78
Oxygen - 21
Argon - 0.9/1
Carbon dioxide - 0.04
Element + air
Volume always decreases to 79%
21% is used up for oxygen
Mg in oxygen
Bright blue flame
Sulfur in oxygen
Bright blue flame, smoke created
Hydrogen in oxygen
Louder explosion than in air
Equation for thermal decomposition
Metal carbonate - metal oxide + carbon dioxide
