Atoms and Reactions

Atoms and Reactions

Redox Reactions
1. Oxidation is the gain of oxygen
2. Reduction is the loss of oxygen
3. Metals tend to be oxidised, losing electrons to form positive ions
4. Reactive metals undergo redox reactions with many acids. The metal is oxidised, forming positive metal ions and the hydrogen is reduced.
Oxidation Numbers
1. Uncombined elements:0
2. Combined Oxygen: -2
3. Combined Oxygen in Peroxides: -1
4. Combined Hydrogen: +1
5. Combined Hydrogen in metal hydrides: -1
6. Simple Ion: charge in ion
7. Combined Fluorine: -1
8. Transition elements form ions with different oxidation numbers. The number written in the bracket is its oxidation number.
Titrations
1. The unknown information may be: the concentration of a solution, a molar mass, a formula or the number of molecules of water of crystallisation
2. How to carry out a titration: Using a pipette, add a measured volume of one solution to a conical flask. Add a suitable indicator. Place the other solution in a burette. Add the solution in the burette to the solution in the conical flask until the reaction has just completed, measure the volume of solution added from the burette, you now know the volume of one solution that exactly reacts with the volume of the other solution
3. Calculating an unknown concentration: Calculate the moles of bith, then calculate the concentration using C=n/v
4. Moles= Mass/RFM
Formulae for Crystals and Salts
1. Hydrated: the crystalline form containing no water
2. Anhydrous: the form containing no water
3. Water of crystallisation: when a compound crystallises within water, the water can become part of the resulting crystalline structure.
4. Hydrated crystals can contain different amounts of water, the amount of water contained is shown by a dot formula
5. The dot formula of hydrated salts can be determined using the empirical formula or experimental results
6. Using empirical formula: Step 1: Use the number of hydrogen atoms to work out how many water molecules are present Step 2: Use the remaining atoms to determine the formula of the main salt and how many molecules are present. Step 3: Construct the dot formula
7. Using experimental data: Step 1: Calculate moles of anhydrous Step 2: Calculate moles of water Step 3: Determine the formula of the hydrated salt.
Salts
1. A salt is an ionic compound with the following features:
  1. The positive ion, or cation in a salt is usually a metal ion or an ammonium ion
  2. The negative ion, or anion, is derived from an acid
  3. The formula of a salt is the same as that of the parent acid, except that a H+ ion has been replaced by the positive ion
2. Acid Salts: If one H+ ion is replaced, an acid salt is formed, for example sodium hydrogen sulfate.
  1. The acid salt can behave as an acid, because the other H+ ion can be replaced to form a conventional salt, eg Sodium Sulfate
3. Formation of salts: They can be produced by neutralising acids with bases such as carbonates, metal oxides or alkalis.
4. Acid+carbonate= Salt+ CO2 +H2O
5. Acid+ metal oxide= Salt+ H2O
6. Acid+Alkali= Salt +H2O
7. Acid+metal=Salt +H2
Acids and Bases
1. Acids in Aq solution: When an acid is added to water, the acid releases H+ ions. This ion is the active ingredient in acids
2. Acids and dissociations: Strong acids are very good at giving up H+ ions, they fully dissociate. Weak acids are not very good at giving H+ ions, once these ions are released they are quickly taken back again
3. A base us a proton acceptor which neutralises acids.
4. Alkalis in Aq solution: A special type of base that is able to dissolve in water to form aq hydroxide ions
5. Ammonia as a weak base: Ammonia is a gas that dissolves in water to form a weak alkaline solution. Ammonia is a weak base because only a small proportion of the dissolved NH3 reacts with water.
6. Amphoteric Substances: Behave as acids and bases, for example an amino acid molecule which contains a carboxyl acid which is able to donate a proton and an amino basic group which could accept a proton
Atom Economy
1. Molecular mass of desired product/ sum of molecular masses of all products x 100
Percentage Yields
1. actual amount in mol/ theoretical amount in mol x 100
Moles and Reactions
1. Stochiometry studies the amounts of substances that are involved in a chemical reaction
2. moles= Mass/RFM
3. C= n/v
Chemical Equations
1. A species is a type of particle that takes part in a reaction. It could be an atom, ion molecule, empirical formula or electron.
2. Giant structures are formed when many atoms or ions bond together in a repeating fashion.
Moles and Solutions
1. Concentration: How much solvent is dissolved in a given amount of solvent.
2. 1000cm3 = 1dm3
3. n=c x V
4. Standard Solution: A solution of known concentration, normally used in titrations to determine unknown information about other substance.
5. Concentrated- a large amount of solute per dm3
6. Dilute- a small amount of solute per dm3
Moles and gas volumes
1. Molar gas volume- at room temp and pressure, one mole of a gas occupies 24dm3.
2. Ideal gas equation: pV= nRT
  1. P= pressure
  2. V= volume
  3. n=number of moles
  4. R= gas constant (8.314mol-1K-1)
  5. T= temperature
Types of Formulae
1. Empirical formula- the simplest way of showing a chemical formula. It shows the ratio between elements
  1. Calculating: Divide amount by molar mass to work out molar ratio, divide answers by smallest. Use ratio for empirical formula
2. Molecular formula- Used for compounds which exist as simple molecules, it tells you the number of each type of atom that make up a molecule.
  1. Calculating molecular formula:relative molecular mass/ Mass of empirical formula, times empirical formula by answer.
Amount of Substance and the mole
1. Amount of substance: The quantity that has moles as its unit.
2. Mole: the amount of substance containing as many particles as there are carbon atoms in exactly 12g of the carbon-12 isotope
3. Avogadro constant: the number of atoms per mole of the carbon-12 isotope
4. moles= mass/RFM
Ions and the periodic table
1. Elements is the same group of the periodic table have the same number of outer shell electrons and react in similar ways.
2. Atoms of metals in groups 1-3: Lose electrons to form positive ions with the electron configuration of the previous noble gas in the period table.
3. Atoms of Non-metals in groups 5-7: Gain electrons to form negative ions with the electron configuration of the next noble gas in the periodic table
4. Atoms of Be, B, C and Si do not normally form ions because it requires too much energy to transfer the outer shell electrons to form ions
Determining masses using mass spectrometry
1. A mass spectrometer is a piece of apparatus that can be used to find out about molecules, for example it can be used to identify an unknown compound, find the relative abundance of each isotope of an element or determine structural information about molecules.
2. Calculating the relative atomic mass from a mass spectrum: times percentages by mass number over 100
3. Calculating Abundance from graph: Measure total heights of all peaks, put height of one peak over the total heights of all peaks and times by 100.
Atomic Masses
1. Relative Isotopic Mass- The mass of an atom of an isotope compared with 1/12 of the mass of an atom of carbon-12.
2. Relative Atomic Mass- The weighted mean mass of an atom of an element compared with 1/12 of the mass of an atom of carbon-12.
Atomic Structure
1. Proton 1+, neutron 0, electron 1-
2. Isotopes of the same element have different masses, the same number of protons and electrons but different numbers of neutrons in the nucleus.
The Changing Atom
1. Modern Day- Protons and neutrons are made up of even smaller particles called quarks,
2. Fifth century- You can divide a sample of matter only a certain number of times
3. Early 1800s- Atomic theory- atoms are tiny particles made of elements which can be divided. All atoms of a given element are the same.
4. JJ Thomson- Cathode rays were a stream of particles that had a negative charge and could be deflected by both a magnet and an electric field. They had a very small mass. Plum pudding model- Negatively charged particles in a sea of positive charge.
5. Rutherfords Gold-leaf: Plum pudding atom hardly deflected any alpha particles, most of them were not deflected however a small percentage were through large angles. Some particles were deflected towards the source. The positive charge of an atom and most of its mass are concentrated in the nucleus, the negative electrons orbit the nucleus.
6. 1918- Rutherford discovered the proton
7. Niel Bohr's planetary model and Moseley's work on atomic number: Bohr's model helped to explain some periodic properties such as spectral lines seen in emission spectra and the energy of electrons. Moseley discovered the link between x-ray frequencies and an elements atomic number.
8. 1923-26- Louis de Broglie suggested that particles could have the nature of both a wave and a particle. Schrödinger suggested that an atom has orbitals.
9. Chadwick discovered the neutron

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