C2 Flashcards
What is relative atomic mass
The mass of an atom compared to 1/12th of a carbon12 atom, defined as 12 exactly
Its symbol is Ar
Ar is the greater number seen on an atom in the periodic table a
What is a chemical formula
A description of a compound or an element that uses symbols to describe the atoms present. The numbers show how many atoms are present
What is relative formula mass
Mr
The total of all relative atomic masses in a substance
What is the empirical formula
The simplest whole number ratio of the atoms of each element in a compound
How do we calculate the empirical formula, when masses are given
Divide the mass by the ar number of each element
Divide these answer by the smallest one
Then we have the simplest ratio
If give a percentage we can change the percent into grams as necessary
(E.g 70% = 70g)
What is a balanced equation
When the relative formula mass is equal on both sides of the equation.
There are an equal number of each element atom on both sides
What is a mixture
Material consisting of two or more or more different substances not chemically joined together
What is a pure substance
Consisting of just one element or compound
What is an impure substance
Material consisting of two or more different elements or compounds
How are mixture useful?
Mixtures such as alloys (mixture of metal and another element) are used in many items including jewellery (gold and copper alloy)
How do you determine if something is pure or not
All pure elements will have a fixed boiling /boiling point. On a temperature and time line graph we can easily see this as the temperature will not increase with the time when the substance is melting / boiling
E.g pure water will stay at 100°C when boiling
What are the main differences in melting and boiling points between impure and pure substances
Impure will have a lower melting point
Impure will melt over a range if temperatures
(Or boil)
How do you determine a melting point.
By heating it
You measure the temperature when it has melted OR measure the temperature at regular time intervals (better)
Remember when doing this heat the substance slowly and stir it slowly
What is a solution (not solution e.g a maths problem)
A mixture formed when one substance dissolves in another
What is a solute
Substance that dissolved in a solvent (emg salt)
What is a solvent
A substance that can dissolve a solute to form a solution (e.g water)
What does it mean when something dissolves
The process in which a solute and solvent mix to form a solution
What does it mean if something is soluble or insoluble
Soluble = A substance that will dissolve in a given solvent
Insoluble =(this describes) a substance that will not dissolve
What is filtration + how is it done
A ‘separating technique’ that separates an insoluble substance (in its solid form) from substances in the liquid state.
This is done by pouring it through a funnel into filter paper into a beaker (normally a conical flask). The insoluble solid will not pass through as the filter paper contains microscopic holes it can’t fit through.
What is filtrate
Liquid that passes through the filter during filtration
What is residue
Insoluble material left behind (on the filter paper) during filtration
What is crystalisation
The process in which crystals are formed during evaporation of a solvent from a solution
The solution is heated until saturated, as it cools down crystals form
How dose crystallization work
Heat the solutions so the solvent evaporates slowly, leaving behind crystals (too fast and a powder will be left)
The solution must be heated untill it becomes a saturated solution.
Once this has happened crystals begin to form.
As the temp decreases solubility decreases so more crystals form
What is Solubility
A measure of how much solute can dissolve in a given amount if solvent at a temperature
What is a saturated solution
A solution containing the maximum mass of solute at any given temperature
What is distillation
A method to separate a solvent from a solution (through heating)
How does distillation work?
A solvent and solute in solution will have different boiling points
The solvent will have a lower boiling point than the solute so it will evaporate.
It leaves the solution in its gas state and rises, it then travels down the condenser and turns back into a liquid
This leaves the two substances in there own beakers seperate from ine another
In distillation what is the condenser
A tube which the solvent will travel through as a gas and turn into a liquid.
This tube is kept cold by a constant flow of water; the water enters on the top side and exits on the bottom
What is fractional distillation
A method for separating a mixture of liquids with different boiling points into different fractions (sections)
What is a fractionating column
A piece of apparatus used to improve the separation of solvents during fractional distillation
How does fractional distillation work
It relies on the mixture of substances in having different boiling points
Boil both the mixtures like usual
In the fractionating column:
Vapour condenses on the inside surface, heating it up
When the temperature inside the tube reaches the substance’s boiling point (substance with the lower boiling point) it can no longer condense but the other substance can.
The substance which condensed more falls back as droplets into the flask, the vapour then passes down through the condenser
(Then the substances have been seperated)
How dose the fractional column improve distillation
It improves the separation of the mixture.
It has a large surface area so the vapour can continually condense.
The column is its hottest at the bottom and coolest at the top
What is chromatography
A separation method that relies on the distribution of a substance between a mobile phase and a stationary phase.
What is the mobile stage
A substance in a liquid or gas state that moves during chromatography
What is the stationary phase
A substance in the solid or liquid state that does not move during chromatography
What is paper chromatography
A separation which uses paper as its stationary phase and and a solvent in the liquid as the mobile phase
What is TLC
Thin layer chromatography
A type of chromatography which uses silica or alumina spread on a plate as its stationary phase and a solvent in the liquid state as the mobile phase
How do we use paper chromatography
Get your chromatography paper and at its base draw a line in PENCIL (ink will smudge and ruin the experiment)
Place your samples on the line (e.g a purple pen)
Next put it in water until the top if the water is just below your drawn line.
The water will travel up the paper separating the blue and red from the purple
How do we use TLC
Stationary phase - thin layer of silica or alumina powder on a plate
Mobile phase - solvent
Fill the chromatography tank to a depth of 1cm and heat , if the solvent is flammable ensure there are no naked flames
Add a small amount of your sample on the baseline (ensuring you dont damage the powder / silica)
Put the plate in the tank
Let the solvent travel through the powder and take the blate out before it reaches the top.
Analyse the coloured spots
What is a chromatogram
The pattern produced when separating a mixture using chromatography
What is and how do you calculate Rf value
Relative distance travelled by a substance during chromatography
Distance travelled by substance (measured at its mid point) ÷ distance travelled by solvent (measured from your pencil line to the end)
What is gas chromatography
A type of chromatography which uses silica or alumina packed in a metal tube for the stationary phase and an inert carrier gas as the mobile phase
The inert gas pushes your sample through the column (in a gas form), different substances bond to the stationary phase differently and a detector sends signles when the leave the column
E.g of carrier gas could be nitrogen
How does gas chromatography work
The sample is turned into a gas when injected into the column.
The carrier gas then pushes it through.
Different components take different amounts of time to travel through the column, depending on how long they travel through the stationary phase.
A detector sends signals to a computer when each substance leaves the column.
The computer produces a chromatogram in which each component is a peak plotted against travel time
How can we tell if a substance is pure (using chromatography and gas chromatography)
There will only be one coloured spot (chromatography)
If two chromatograms have the same shape / size they are the same substances
How to choose which separation method to use.
If the mixture contains:
Insoluble and soluble substances - dissolving followed by filtration
A solute dissolved by in a solvent- crystallisation to obtain the solute and simple distillation to obtain the solvent
Two or more substances in the liquid state - fractional distillation
Coloured soluble substances - paper chromatography ot TLC
What are the physical properties of metals
Shiny
High melting/boiling point
Solid at room temperature
Malleable (bend without shattering)
Ductile (can be pulled into wires)
Its a good conductor of heat and electricity
What are the physical properties of non metals
Dull
Usually low melting / boiling point
Half are solid and half are gas (roughly)
Brittle (shatter when hammered)
Non ductile (snap when pulled)
Poor conductors (they are insulators)
What is the periodic table arranged in
Periods and groups
Increasing atomic mass
Chemical properties of metals
They lose ions to become positive
They dont react with each other (but mix to form alloys)
They react with oxygen to form oxides. When dissolved in water these are alkaline
What are the chemical properties of non-metals
They gain electrons to form negative ions
Non metals react with each other to form compounds
They react with oxygen to form oxides, these form acidic solutions whej dissolved in water
What is a period and a group
A horizontal row (period)
A vertical row (group)
What is the electronic structure
How electrons are arranged in its atoms
What electron shell must be full to have a neutral atom
The outer shell
How does the electronic structure relate to the periodic table
The group they are in tells us how many electrons are in their outer shell
The period they are in tell us how many electron shells there are (starting with one in hydrogen)
What is an ion
A positively / negarively charged atom which has lost or gained electrons
How does the electronic structure change in ions
Take the electronic structure of the atom and change accordingly
E.g Na = 2,8,1
Na+ = 2,8
What are electron diagrams
These diagrams show the electronic configuration of an atom.
They also display the charge of an ion
What is an ionic compound
A compound containing oppositely charged ions from different elements
What is an ionic bond
Strong electrostatic forces of attraction between oppositely charged ions
How do ionic compounds form
When a metal reacts with a non metal it transfers electrons to the non metal in order to give itself a full outer shell.
This process can be seen in a dot cross diagram (similar two electronic diagrams except it shows electrons being transferred and only the outer shell is drawn)
How are ionic compounds arranged in their solid state
They contain positive and negative ions arranged in a regular way.
What is a giant ionic lattice
A structure of ionic compounds in which oppositely charged ions are held in a regular way and have a repeating arrangement by strong electrostatic (intermolecular) forces of attraction
What are ionic bonds
Bonding between a metal and non metal with strong electrostatic forces of attraction between oppositely charged ions.
How can we model giant ionic lattices
Using the ball and stick model we can represent each ball as an oppositely charged ion and the sticks represent the electrostatic forces of attraction
What are the limitations of the ball and stick model
They don’t represent the distance between each particle
It doesn’t represent the bonding
Doesn’t show the size of each particle
What is a covalent bond
A strong force of attraction between the nuclei of two atoms that are sharing electrons
They occur between two non-metals
What is a simple molecule
A particle that consists of few non-metal atoms joined together with covalent bonds .
Examples of simple molecules are hydrogen, oxygen, water and carbon dioxide.
How are covalent bonds shown
Using dot cross diagrams where electrons are shared between the atoms (like a venn-diagram) usually only the outer shell is shown.
All of the outer shells will be full
What is the bonding and structure in simple covalent molecules like
The forces between each nuclei of the atoms are strong but the intermolecular forces between molecules are weak
Due to these weak intermolecular forces simple covalent bonds often have low melting points
(Requires little energy to break the bonds)
What are intermolecular forces
Weak forces of attraction which exist between simple molecules
What are giant covalent structures
An arrangement of non-metal atoms joined by covalent bonds in a regular arrangement
What is the chemical formulae for giant covalent structures
As these contain too many atoms, their formula is always written in the empirical formula.
This is why we see the formula for a diamond written as just C
What are polymers
Substance with molecules made of many repeat units
What are monomers
Small molecules which join together to form polymer molecules
What is a displayed formula for simple covalent molecules (shows bonding)
A diagram where atoms are displayed as symbols and covalent bond by lines
H2O would be:
H-O-H
02 would be
0=0
(Two lines show a double bond so each atom shared two electrons)
How are polymer molecules modelled
They consist of few non metal atoms bonded to each other through covalent bonds.
They are usually modled using dot cross diagrams
How are thermosofteningpolymers arranged
Each polymer molecule is represented by a wavy line
In thermosoftening polymers the lines appear like a tangled web and is very easy to separate
How are thermosetting polymers arranged
The polymer molecules are joined by strong covalent bonds.
This is called cross linking
What is a repeating unit
A section of a polymer molecule that is repeated many times within the molecule
How are metals structured
At a solid state the atoms are packed together in a giant metallic lattice
Positive metal ions are joined to a sea of delocalised electrons
What is a giant metallic lattice
The repeating regular arrangement of metal ions or atoms in a solid state
What are metallic bonds like
Electrons leave the outer shell of the metal and they are free to move throughout the metal (delocalised)
There are strong electrostatic forces of attraction between the layers of electrons and layers of positive metal ions
+ + + + +
- - - - - -
+ + + + +
(Not entirely accurate (app cant add photos) just remember each positive ion has a delocalised electeon next to it
What did Mendeleev do
He organised elements into what we know
as the periodic table
He arranged all elements based on their atomic weight
He group elements with similar properties together
He left space for elements that had not been found yet but he predicted were there
He realised argon and potassium had similar weights but different properties so he created the noble gasses
He swapped iodine and tellurium around to better fit their chemical properties
How were Mendeleev’s predictions correct
Gallium was discovered and fit perfectly into the period table
Who was john Newlands and what did he do
He was an English Scientist
(Before Mendeleev)
He noticed each 8th element had a similar property he organised them into 8 groups (law of octaves)
He still organised them by atomic weight
People mocked him as elements with different properties where in the same group
He believed all elements had been discovered
What did john Dalton do (relative to the periodic table)
(before Newlands)
He measures the atomic weight of elements
He then organized a table of known elements by their atomic weight
He also gave each element its own symbol
Difference between atomic mass and atomic weight
Atomic weight is the average weight of an element (including isotopes)
Atomic mass is the number of protons + neutrons in an atom
Who discovered what the atomic number actually was
Henry Moosley
Discovered the atomic number was the number of protons in the nucleus
How is the periodic table arranged today
In groups and periods
Elements are arranged in order of increasing atomic number
The atomic number is the number of protons in an atom
The number of electrons in an atom is equal to the number of protons
Electronic structure is determined by the number of electrons
The electronic structure determines its chemical properties (and therefore is group and period)
What are alletropes
Different forms of an element in the same state but with different atomic arrangements
What is diamond like
Diamond is an allotrope of carbon, it is a giant covalent structure where each carbon atom is joined by 4 others
These bonds are very strong so diamond has a high melting / boiling point
They are very hard
What is graphite like
A giant covalent structure where each carbon atom is bonded to 3 other carbon atoms
It has a layered structure, but these layers are held together by weak intermolecular forces
This makes graphite slippery
High melting / boiling point (due to strong covakent bonds in each layer)
Delocalised electrons allow them to conduct electricity
What is graphene
A carbon allotrope that resembles a single layer of graphite
Its almost transparent, extremely strong and conducts electricity
What are fullerenes
Family of carbon allotropes with tubes or balls of atoms
What is a buckyball
Buckminsterfullerene
Its a hollow ball
They can be used as lubricants, as molecules act like tiny ball bearings
They are small enough to pass through cell membranes, so may one day be used to deliver medical drugs directly to cells
It is an allotrope of carbon
What is a nano tube
A sheet of graphene rolled into a tube
Its strong and sometimes used to reinforce sports equipment
Conducts electricity
Why can nano tubes and graphene conduct electricity
As they have delocalised electrons
Why do buckyballs not conduct electricity
Although they have delocalised electrons, these are held by forces which inhibit their movement.
Vanderwall forces (electrostatic)
Why do buckyballs not conduct electricity
Although they have delocalised electrons, these are held by forces which inhibit their movement.
Vanderwall forces
Why do buckyballs not conduct electricity
Although they have delocalised electrons, these are held by forces which inhibit their movement.
Vanderwall forces
What bonds hold together and what is their strength :
A metal
An ionic compound
A giant covalent structure
Simple molecule
A metal - metallic bonds (strong)
An ionic compound - ionic bonds (strong)
A giant covalent structure - covalent bonds (strong)
Simple molecule - (atoms connected through covalent bonds) intermolecular forces (weak)
What is sublimation
When a solid changes directly to a gass
What does it mean if a compound has strong bonds
The bonds need more energy to break - more energy is needed to break the bonds
(Changing state)
Why does sublimation happen
Simple molecules are attracted to each other by intermolecular forces
The molecules pack together in a regular way
When heat is applied these bonds are fully broken - causing the molecule to become a gas
What is needed to change a substances state
Bonds need to be broken
What is a lattice
A regular arrangement of ions, atoms or molecules
Why are some substance brittle and some malleable
It depends on how easily the particles in a lattice can change their positions
Why are metals malleable
Metal ions are held in a lattice by forces that attract them to a sea of electrons
When a large enough force is applied layers of metal ions slide over each other
What are nano particles
A particle between 1nm and 100nm across
Contains just a few hundred atoms
1nm is 1×10^-9
How do we describe a material made from nanoparticles
A nanoparticulate
(Made of nanoparticles)
What are nanoparticles useful for
Paints
Cosmetics (suncream)
New catalysts
Self-cleaning ovens / windowsb
Why are nanoparticles so usefull
They have an extremely small size
They have a very large surface area to volume ratio
What are the possible risks of using nanoparticles
They may be breathed into or absorbed into the body
Toxic substances may stick to them
They may take a long time to break down
Their effects on the body / environment are difficult to determine
What are the properties of metal bonds
Strong bonds
High melting and boiling points
Conduct electricity when solid or liquid
What are the properties of ionic bonds
Strong bonds
High melting and boiling points
Does not conduct electricity (except graphite)
What are the properties of simple molecules
Weak
Low melting / boiling points
They conduct electricity
What is effervescence
Bubbling or fizzling observed in a reaction
What is a formulation
A useful mixture with a precise purpose
What type of test is a flame test
A physical test
What type of test is a hydroxide precipitate test
Chemical test
How do fractional distillation columns improve the rate of distilation
They have a larger surface area so more can condense
What is a formulation
A mixture of chemicals that do not react
The chemicals are measured out in specific quantities to give desired properties
