AS Chemistry Unit 1
Terms in this set (192)
A substance that cannot be broken down into two or more different substances
The smallest uncharged particle of an element
Made up of two or more elements
Physical properties of metals
- Electrical conductivity as solid and liquid
- Malleable and ductile
- All solids at room temp. (except Mercury)
Chemical properties of metals
- Form positive cations in compounds
- Reactive metals react with acids to give salt and hydrogen
- React with less reactive cations in displacement reactions
- Increased reactivity down the group
- Oxides and hydroxides act as bases
Chemical properties of non-metals
- Form negative anions in their compounds
- Form covalent bonds with other non-metals
- They increase in reactivity as you ascend the group
- Their oxides are acidic
What are metalloids and what are their properties?
- Element that has properties that belong to metals and non-metals
- Found between metals and non-metals
- Their oxides are weakly acidic
Charged atom or group of atoms
What does the force of electrostatic attraction depend on?
- Size of charge (Larger = Stronger)
- Distance between centres of the two atoms (Shorter distance = Stronger)
How many milligrams are in 1g?
How many nanograms in a gram?
How many grams in a kilogram?
What is 1dm^3 equal to in cm^3 ?
One mole is the amount of substance containing the Avogadro number (L) of atoms, molecules or group of ions.
Relative Atomic Mass
The RAM of an element is the weighted average mass of an atom of that element divided by 1/12 the mass of a carbon-12 isotope
Relative Molecular Mass
The RMM is the average mass of that element or compound divided by 1/12 the mass of a carbon -12 isotope
Relative Isotopic Mass
The RIM is the mass of an of that isotope divided by 1/12 the mass of a carbon-12 isotope
How is the sample in the Mass Spectrometer ionized?
The vapourized sample is bombarded with high-energy electrons in a beam, this will knock off outer-electrons from the atoms to create single-positive charged ions.
How are the positive ions accelerated in the mass spectrometer?
Through the use of an electric field, all the ions will be travelling at the same speed.
How are the ions deflected and what is the relationship between the mass of the ion and the degree of deflection?
- A Magnetic Field.
- The heavier the ion, the less it's deflected
Which ions are detected first?
Lighter ions are detected first
What does the sensor in the Mass Spectrometer measure?
It measures the m/e ratio of each ion and it's abundance relative to the most abundant ion.
What are some of the uses of the Mass Spectrometer?
- To determine RAM of an element
- To detect drugs in urine samples
- In the Pharmaceutical Industry
- Carbon-14 dating
The further away the shell from the nucleus...
- The higher the energy
- The larger the principal quantum number
A region of space where electrons are likely to be found
- Penetration describes the proximity to which an electron can approach the nucleus.
- In a multi-electron system, penetration is defined by an electron's relative electron density near the nucleus of an atom
Trend of Penetration powers?
How many electrons can an orbital hold?
The Aufbau Principle
States that orbitals are filled up from those of the lowest energy and then filled in increasing energies
States that in the event that a sub-shell contains more than one orbital, the electrons fill up so they have parallel spins.
Pauli's Exclusion Principle
States that all the electrons in an atom have to be in different orbitals or have different spins.
What are the two special exceptions when it comes to Electron Configuration?
[Ar] 3d10, 4s1
Why are there exceptions in Chromium and Copper?
This is because an electron is promoted to the d-orbital because the atom is more stable if it's 3d-orbital is half-filled or fully-filled.
- Group 1
- Group 2
- Groups 3 ----> Group 7
- Transitional metals
- 28 elements at the very bottom of the periodic table
States that the magnitude of a force acting on two/between two charged objects is proportional to the product of their charges AND inversely proportional to the square of the distance between their centres
How do you calculate the Effective Nuclear Charge?
Nuclear Charge - Number of Shielding electrons
Effective Nuclear Charge
Is the net charge on the nucleus, after allowing for the electrons in orbit around the nucleus shielding it's full charge.
Trend of Effective Nuclear Charge across a period
- Increases across a period
- Does not increase by as much as +1 between successive elements
Trend of Effective Nuclear Charge in a group
- The effective nuclear charge hardly varies
- Nuclear charge and number of shielding electrons increase similarly
- Cancel out
Periodic Properties - Size of atoms
- Across the period, atomic radii DECREASES
- Extra protons lead to a stronger nuclear charge
- Nuclear attraction is greater
- Draws electron shells closer
- (Increased nuclear charge outweighs the repulsion between the electrons which are being added)
Periodic Properties - Size of Cations
- Cation < Original Atom
- In cation, there's less electron shell(s)
- Missing electrons leads to less electron-electron repulsion
- Less electrons means remaining electrons experience greater nuclear attraction
Periodic Properties - Size of Anions
- Anion > Original Atom
- In anions, there's increased repulsion between existing electrons and added electrons
- This causes ion to expand
- Ion is stable because an equilibrium is established between outward and inward forces
Periodic Properties - Melting Points (Metals)
- Metals; melting point increase across a period
- As you go across, more de-localized electrons
- As you go across, cations have greater charge density
- Thus, electrostatic forces of attraction are stronger
Periodic Properties - Melting Points (Macromolecules)
- Macromolecules will have the largest melting point in their period
- They have a lot of covalent bonds, which require a lot of energy to break
- Carbon, Silicon are examples
Periodic Properties - Melting Points (Simple Molecular Substances)
- Melting point depends on strength of Dispersion Forces
- Forces are generally easy to overcome
- Trend; greater number of electrons = stronger force
First Ionisation Energy
The energy required to remove 1 electron from each atom of a mole of gaseous atoms of the specific element, this creates 1 mol of singly-positive charged ions.
What type of reaction is the 1st IE?
- Energy needs to be added to the electron to remove it from orbit (outweigh attractive forces from the nucleus)
Second Ionisation Energy
The energy required to remove one electron from each ion of a mol of gaseous +1 cations of that element, to create 1 mol of gaseous +2 cations.
What type of reaction is the 2nd IE?
- More endothermic than 1st IE because now there will be a stronger force of nuclear attraction because the same force had been split up over a smaller number of electrons, due to the removal of the previous electron.
What are the 3 factors that affect the magnitude of Ionisation Energy?
1.) ATOMIC RADIUS: Greater atomic radii = smaller Ionisation Energy
2.) NUCLEAR CHARGE: The greater the number of protons, the higher the Ionisation Energy
3.) ELECTRON SHIELDING: The greater the number of electron shells between the outermost electron and the nucleus, the smaller the Ionisation Energy
Successive Ionisation Energies
As you go across the period, the general trend is for ionization energy to increase
- Due to a greater number of protons leading to a stronger nuclear attraction
- there are small drops between Groups 2&3 and 5&6
Why is there a drop in the ionization energies between Groups 2 and 3?
- The electron that is being removed from the element in group 3 is in a p orbital, group 2 is in a s orbital
- The p-orbital is further away from the nucleus
- The electrons in the p-orbitals are shielded more than the electrons in the s-orbitals
- Thus the electrostatic attraction between the nucleus and the outermost electron is weaker
Why is there a drop in the ionization energies between Groups 5 and 6?
- The electrons in the outer shell of the element in the group 6 element is such that one of the p orbitals has a pair of electrons
- This leads to spin-pair repulsion
- This increases the repulsion on the outermost electron, so less energy needed to remove it.
First Electron Affinity
- The First Electron Affinity is the energy change when one electron is added to each atom in a mole of neutral gaseous atoms to create a mole of singly-charged anions
What type of reaction is the 1st EA?
- The forces of attraction between the electron and the nucleus releases energy when they move closer together
Second Electron Affinity
The energy change when one electron is added to each ion in a mole of -1 gaseous anions, to create a mole of -2 gaseous anions
What type of reaction is the 2nd EA?
- This is because when you try to add the second electron, there will be repulsion with the electron you had previously added, thus energy must be applied to overcome that force of repulsion
Patterns and Trends in Electron Affinity
- Across period 2, there is an increase in the energy released because the atomic radii gets smaller and attraction forces increase
- Dip at Beryllium because the electron goes into a singly-occupied 2s-orbital and so repulsion takes place
- Dip at Nitrogen because the electron goes into a singly-occupied 2p-orbital, so repulsion takes place.
The molecular formula of a compound shows the number of atoms of each element in one molecule of that substance
Molar mass is the mass of 1 mole of that substance.
The empirical formula is the simplest whole number ration of the atoms of each element in the substance
How do you calculate Molecular Formula from Empirical Formula?
- Calculate Empirical mass and molar mass of the compound
- Divide molar mass by empirical mass, the number you get is the multiplier you use on the empirical formula to get the molecular formula
Molar Volume of Gases
The molar volume of a gas is the volume occupied by 1 mole of the gas under specified conditions of temperature and pressure
Why may the % yield not 100%?
- Loss in; filtration, evaporating, transfer of liquids
- Competing reactions
- Reversible reactions
- Reactant/Product left in apparatus
- Loss of reactant/product
- Incomplete reaction(s)
Is a measure of the proportion of reactant atoms that are converted into the desired product in the balanced equation
What is the atom economy of addition reactions?
A limiting reagent is the substance that determines the theoretical yield of a product in a reaction.
How do you identify the limiting reagent?
The reactant which produces the least mole number of the specific product is the limiting reagent.
Specific Heat Capacity
The SHC is the heat required to increase the temperature of 1g of the substance by 1 degree celcius
Chemical energy is converted to thermal energy and the temperature of the system rises
Thermal energy is converted into chemical energy, and the temperature of the system falls.
Is the chemical energy in the system at constant pressure that can be converted into thermal energy.
- Denoted by H
What are Standard Conditions?
- 1 atm pressure
- A temperature of 25 degrees celcius
- All solutions at 1 mol/dm^3
- Each substance involved in the reaction is in it's standard physical state
The enthalpy of a substance depends on?
- physical state of the substance
- moles of the substance
- temperature and pressure
Hess' Law states that the total enthalpy change in a chemical reaction is independent of how the reaction took place (the route it took) so long as the starting and ending conditions are the same.
Standard Enthalpy of Formation
The standard enthalpy of formation is the enthalpy change when 1 mole of a substance is formed from its constituent elements in their standard states of 1 atm pressure and 25 degrees celcius
What's the Standard Enthalpy of Formation of any element in it's standard state?
Which direction do arrows point in a Hess Cycle if you are using enthalpy of formation data?
Arrows point upwards
Possible sources of error in a calorimetry of solutions investigation?
- If the reaction is very slow, there will be significant heat loss to the surroundings
- Some heat may be absorbed by apparatus (They have a specific heat capacity too)
- Incomplete reaction due to insufficient stirring
Standard Enthalpy of Combustion
The standard enthalpy of combustion is the enthalpy change when 1 mole of the substance is burnt in excess oxygen under standard conditions of 1 atm pressure and 25 degrees celcius
Possible sources of error in combustion calorimetry investigation?
- Due to the length of experiment, extrapolation doesn't compensate for all the lost heat
- Some of the heat from the burner heats up the surrounding air as opposed to the water
- Beaker absorbs some of the heat
- Incomplete combustion of fuel
- Conditions not being standard; water formed may be vapour as opposed to liquid.
In which direction do the arrows go in the Hess Cycle if you're using enthalpy of combustion data?
Arrows would be pointing downwards
Standard Enthalpy of Neutralisation
The standard enthalpy of neutralization is the enthalpy change when 1 mole of water is produced by the neutralization of an acid by excess base under standard conditions, with all solutions having a concentration of 1 mol/dm^3
Standard Enthalpy of Atomisation
The standard enthalpy of atomization is the enthalpy change when 1 mol of gaseous atoms is formed from the element in it's standard physical state, under standard conditions of 1 atm pressure and 25 degrees celcius
Bond enthalpy is the enthalpy change when a bond in a gaseous molecule is broken
How do you calculate the Bond Enthalpy?
Sum of enthalpy of bonds broken + Sum of enthalpy of bonds made
How do you use the bond enthalpy to work out which bonds are broken first?
The weaker the bond, the earlier it'd be broken.
What does the strength of the metallic bond depend on?
- The charge on the metal ion
- The metallic radius
- The structure of the metallic lattice
Physical properties of Metals - Density and Melting Point
- Group 1 metals have a low density and low melting point
- Group 2 metals have a greater density and melting point than Grp1
- d-block metals are much harder, denser and have higher melting points
The metallic radius is half the distance between the centres of two adjacent metal ions in the metallic structure
Melting Point of Metals across a period
- Melting point increases
- Because metallic radius decreases
Melting Point of Metals down a group
- Melting point decreases
- Because metallic radius increases
Why do metals conduct electricity?
In the metallic structure, there's a sea of de-localized electrons that are mobile and can carry the charge, allowing the metal to conduct electricity
Why do metals conduct heat?
In the metallic structure, the de-localized sea of electrons can conduct heat as kinetic energy because they, and the positive ions vibrate and transfer the heat as kinetic energy through collisions.
Why are metals malleable?
The layers of metal cations can slide over each other whilst retaining strength due to the electrostatic forces of attraction.
Chemical Properties of Metals - IE
Because metals have a lower effective nuclear charge than non-metals, the IE is also lower
What is electronegativity?
Electronegativity is the ability of a particular atom of a particular element, which is covalently bonded to another atom, to attract the bond pair of electrons towards its nucleus.
Chemical Properties of Metals - Electronegativity
Metals have the lowest electronegativity values in the periodic table.
Chemical Properties of Metals - Reaction with Acids
Chemical Properties of Metals - Reaction with Water
Most metals react with COLD water to form;
- Alkaline solution (metal hydroxide)
Electrostatic attraction between the opposite charges on the cations and anions in an ionic compound.
What does the strength of an Ionic Bond depend on?
- CHARGE ON IONS;
The greater the modulus product of the two charges, the stronger the ionic bond.
- RADII OF IONS;
Smaller ions form stronger ionic bonds.
Ions that have the same electronic configuration
What are the isoelectronic ions?
N, O, F, Na, Mg and Al
(Size of ion decreases from left to right)
Results of Copper(II) Chromate U-Tube Investigation
What is evidence for ionic bonding?
A high melting point COMBINED with water solubility.
The Lattice Energy
The lattice energy of a compound is the energy change when 1 mole of the solid s formed from it's constituent gaseous ions.
Factors that affect Lattice Energy
- The magnitude of the charges on the ions
- The sum of the radii of the cation and anion
- The arrangement of the ions in the lattice
- The relative sizes of the ions
- The extent of covalency
Which ionic lattices are the most stable?
The ones composed of cations and anions of a similar size.
How many ions surround a central ion in an ionic compound/lattice
This is the distortion of the electron cloud in an anion by a cation.
What increases Polarising Power?
- Large charge density on cation
- Small radius on cation
- Large charge on anion
- Large radius on anion
If there is polarization in an ionic bond, what does that mean?
There is covalent character in the ionic bond.
How does the magnitude of lattice energy change down a group and why?
- Cations increase in size
- Thus cations are less polarizing due to smaller charge density
Overlap between two s-orbitals leads to?
A sigma bond
Overlap between one s-orbital and one p-orbital leads to?
A sigma bond
Overlap (horizontal) of two p-orbitals leads to?
A sigma bond
Overlap (linear) between two p-orbitals leads to?
A pi bond
What affects the strength of a covalent bond?
- The sum of the ionic radii of the two bonded atoms (smaller atoms form stronger bonds than larger atoms)
- The number of electrons being shared (A double bond is stronger than a single bond)
Dative Covalent Bond
A dative covalent bond is a covalent bond in which both electrons in the shared pair are provided by one atom
Four single bonds contain?
4 sigma bonds
Two single and one double bond contain?
- 3 sigma bonds
- 1 pi bond
One single and one triple bond contain?
- 2 sigma bonds
- 2 pi bonds
Two double bonds contain?
- 2 sigma bonds
- 2 pi bonds
Three single bonds and an ionic bond contain?
- 3 sigma
- 'ionic bond' denotes carbocation being present
Where are the pi and sigma bonds located in a double bond?
- The pi bonds are located above and below the double bond
- The sigma bond(s) are located in between the two carbons
Describe the rotation around a double covalent bond
- You would have to break the bond to rotate it beyond 180 degrees
- A homologous series of compounds is a series of compounds that contain the same functional group and have the same general formula.
- The formula of each member of the series differs by CH2 from the previous one.
A functional group is a small group of atoms or a single halogen atom that gives a compound in the series particular chemical properties
Hydrocarbons are compounds that only contain carbon and hydrogen.
A saturated hydrocarbon in which all the bonds between the carbons are single
1.) Identify longest unbranched carbon chain
2.) Name any substituent groups , in alphabetical order and use number to show location on hydrocarbon.
A cycloalkane is a saturated hydrocarbon with the carbon atoms in a ring
An alkene is a hydrocarbon with one double bond between the carbon atoms
- Must contain any double bonds present in the molecule
- Helps draw the molecule
Must show all the atoms separately and all the bonds in between them.
- Carbon atoms and hydrogen atoms not drawn
- Straight Line = Single bond
- Two Lines = Double bond
- Verticies = Carbon atoms
- Make up vacant bonds with hydrogen
Isomers are compounds with the same molecular formula but a different structural formula.
Compounds have the same number of atoms, but they are structured differently.
Structural Isomerism - Carbon-Chain Isomerism
The isomers differ based on carbon chain length
Structural Isomerism - Positional Isomerism
These isomers differ based on the location of the functional group on the carbon framework
Structural Isomerism - Functional Group Isomerism
This occurs when two compounds have the same molecular formula but belong to two different homologous series, thus they have different functional groups.
- Example; Hexene and Cyclohexane
Geometric isomers are isomers that differ only in the spatial arrangement of atoms in the planar part of the molecule or above and below a ring.
When does Geometric isomerism take place?
When each carbon atoms of the double bond have two different atoms or groups attached to it
Why do Geometric isomers exist?
Due to the restricted rotation around a double bond.
What is used to denote the high priority groups being on the same side in Geometric isomers?
(Z) or cis-
What is used to denote the high priority groups being on opposite sides in Geometric isomers?
(E) or trans-
Alkanes - Boiling Point
- Boiling Point increases with increasing number of carbons
- This is because it leads to an increased number of electrons in the molecule
- As a result, dispersion forces would be stronger
- Stronger dispersion forces mean more energy needed to overcome the forces
Why do branched alkanes have lower boiling points than straight-chained alkanes?
There are fewer points of contact between adjacent molecules; they don't pack closely together.
Alkanes - Solubility
Alkanes are insoluble in water but dissolve in each other
Alkanes - Density
- Liquid Alkanes are less dense than water
- As molar mass increases, density increases
By what mechanism do Alkanes and Halogens react?
Free Radical Substitution
A free radical is an uncharged species with an unpaired electron that is used to form a covalent bond.
A substitution reaction is a reaction in which one atom or group is replaced by another atom or group.
- There's almost always 2 reactants and 2 products
What does a half-headed arrow show?
The movement of a single electron
What condition is needed for initiation?
How are Alkenes manufactured?
What do we call an organic compound with two double bonds?
Alkenes - Physical Properties
- Lower melting and boiling points than alkanes
- This is due to the rigidity of the double bond stopping alkenes from packing closely together
- Insoluble in water
Alkenes - Chemical Reactions
- Alkenes are much more reactive than alkanes
- Alkenes can be combusted, but burn with smoky flame because less hydrogen exists
- Most alkene reactions are addition reactions
What is released when a pi bond breaks?
2 new sigma bonds
Which is stronger, pi or sigma bonds?
Alkene Reactions - Hydrogen
Conditions: Nickel Catalyst, 150 degrees
Product: Alkane (e.g ethene ---> ethane)
Reaction Type: Addition
Alkene Reactions - Halogens
Conditions: Mix at room temperature
Product: 1,2dibromoalkane (e.g 1,2dibromoethane)
Reaction Type: Electrophillic Additon
An electrophile is a species that bonds to an electro-rich site in a molecule. It accepts a pair of electrons from that site and froms a new covalent bond.
Alkene Reactions - Hydrogen Halides
Reagent: Hydrogen Halide (HBr)
Conditions: Mix gases at room temperature
Product: Haloalkane (e.g Bromoethane)
Reaction Type: Electrophillic addition
What does a full-headed arrow denote?
Movement of a pair of electrons
When HX adds to an asymmetrical alkene, the hydrogen atom goes to the carbon which already had the most hydrogen atoms directly attached
Which carbocation is most stable and why?
- Secondary or Tertiary (depends on molecules)
- The carbocations are stabilized by the inductive effect of the nearby alkyl groups, the more alkyl groups present around the carbon, the more stable it's carbocation will be
Alkene Reactions - Potassium Manganate (VII) Solution
Reagent: Neutral Potassium Manganate (VII) sol.
Conditions: Shake together at room temp
Product: Alkane-1,2-diol (e.g ethane-1,2-diol)
Reaction Type: Oxidation
What colour change would be visible when the alkene reacts with the potassium manganite solution?
Purple to colourless
What is the atom economy of polymerization reactions?
What are the problems associated with polymers?
Probability of something unfavourable happening - depends on how equipment is being handled and used.
Known risk associated with a specific chemical that can be mitigated through advised use
Give some examples of Hazards
- Absorption through skin
- Highly Flammable
By considering the strength and structure of the pi bond, explain why alkenes are more reactive than alkanes
- pi bonds are weaker than sigma bonds
- pi bonds are more accessible to electrophilic attack
Explain why, in moving from Na to Ar, the general trend is for the first ionization energy to increase?
- Nuclear charge is increasing
- The number of electron shells stay the same
- Shielding remains the same
- Distance from nucleus is less
Suggest why a small amount of UV light can result in the formation of a large amount of product
Because the chlorine radicals are regenerated during the propagation reactions.
Explain why the melting temperature of silicon is very much greater than that of white phosphorous
- You are breaking covalent bonds in Silicon
- Silicon is a macromolecule
- Phosphorous is a simple molecules
- Phosphorous only held by weak Dispersion forces
In an experiment to measure the enthalpy change of a reaction involving gases, which condition needs to be always kept constant?
What type of reaction is hydration?
Addition and oxidation
State and explain how electron affinity values change as you go down Group 7
- EA become less exothermic
- The added electron is further away from the nucleus
- There's more shielding from the nucleus
Suggest, with a reason, how a reactant should be added to boiling sulfuric acid
- In small portions
- To prevent the mixture from boiling over
State what is meant by the term cracking
- Breaking a C-C bond
- Breaking the molecule into smaller molecules
- Breaking the hydrocarbon into a smaller hydrocarbon
Ions are separated in the mass spectrometer by?
A magnetic field
What type of structure is Sulfur and what is the melting point (low/high)?
- Simple molecular
- Low melting point
The bonding in solid ammonium chloride is?
Ionic, covalent and dative covalent
A chemical compound has a high melting temperature and a high boiling temperature; from this it can be deduced that its bonding could be?
Either ionic or covalent