Flash Cards- Edexcel: Chemistry Unit 2 2013

-Arranged elements (known at the time) and placed them onto the periodic table by their properties and compounds

-Used it to predict the existence of properties of some elements that had not yet been discovered yet

-Noble gases had not been discovered as they are unreactive/inert (full outer-most shell)

-VERY SMALL Nucleus in the center (with Protons and Neutrons)

-Electron shells surrounding nucleus holding electrons (2 on the 1st and 8 on the 2nd+)

-Atoms ALWAYS contain the same amount of electrons and protons.

Atomic No. = no. of protons (electrons)

Mass No.= No. of protons, electrons and neutrons

- Electrons -  (mass)1/2000  (charge) -1

- Protons - 1 (mass) 1           (charge) +1

- Neutrons- 1 (mass) 1          (charge) 0

-Periods are rows in which elements are arranged in order of their increasing atomic number,

-Groups are vertical columns in which elements with similar properties are placed.

- To work out the Relative Atomic Mass (Mr)

(%isotope x Mass) + (%isotope2 x Mass) / 100

-Different elements can combine to form compounds, by forming new chemical bonds

- Ionic Bonds  are formed by the transfer of electrons to produce cations and anions.

- Cations are positivley chared ions from losing electrons (group 1 and 2- alkali metals)

-Anions are negatively charged ions from gaining electrons (group 6 and 7 non metals)

- Ionic compounds have a regular lattice structure 'closely packed' held together by strong electrostatic forces (ionic bonds) from oppositely charged ions.

-Ionic compounds had high melting&boiling points because of the strong  bonds between the ions.

- When molten or aqueous  they are able to conduct electricity  because ions separate and are free to move so electric current can be carried.

-Common Sodium (Na) , Potassium (K) and Ammonium salts (NH4) are soluble.

-All Nitrates are soluble

- All Common Chlorides  except for Silver (Ag) and Lead  (Pb)

- All common Sulfates are soluble except for Lead,Barium (Ba) and Calcium (Ca)

- All common Carbonates and Hydroxides except for Sodium, Potassium and Ammonium.

- Insoluble salts can be formed as precipitates from soluble salts :

• Mix solutions of the reactants E.g. Lead nitrate + Sodium Chloride
• Filter the precipitate
• Wash the Precipitate with distilled water
• Scrape the insoluble salts off the filter paper and dry in an oven

- Barium Sulfate is given as a 'meal' to X-ray patients (with gut problems) because:

• It is opaque to the x-ray
• It is insoluble ; it will not be absorbed into the bloodstream so it is safe.

-Sodium (Na+) ions give Yellow/Orange Flame

-Potassium (K+) ions gives a Lilac Flame

-Calcium (Ca+2) and Lithium (Li+) gives a Brick Red Flame

-Copper (Cu+2) gives a Blue-Green Flame

-Strontium (Sr2+) gives a Bright Red Flame

These are all to test if ions are present in solids or solutions

• Add a few drops of dilute nitric acid to the sample and shake
• Add a few of drops of Silver Nitrate to the solution
• A White Precipitate is Formed.

(Sample+Dilute Nitric Acid) +Silver Nitrate----->White Precipitate

• Add a few drops of Dilute HCL acid to the sample and shake
• Add a few drops of Barium Chloride to the solution
• A White precipitate is formed so the sample contains SO4- ions

• Add any acid to the sample
• Salt, water and CO2 is formed
• Use a pipe and connect it from the bung to a tube of limewater (so CO2  released turns the water milky)

- Bunsen and Kirchoff Invented a device called a spectroscope

- A spectroscope used light from the bunsen burner that passed through a prism revealing all colours from a specific mineral emmitted.

- They discovered Rubidium and Caesium because of the Reddish light from the Rubidium (hence the name 'ruby' meaning red) and a Blue light emmitted from Caesium ('caesius' latin for bluish-grey)

-A Covalent Bond  is a bond created when two atoms share electrons (non-metals only)

-It results in forming molecules

-Simple Molecular Covalent Substances have:

• Low melting and Boiling Points (because of the weak inter-molecular forces)
• Strong Covalent Bonds (intra-molecular)
• Does Not Conduct Electricity because there are no ions

-Giant Molecular Substances are billions of atoms joined together by covalent bonds and have:

• High Melting&Boiling points
• Cannot conduct electricity (except for graphite).

Some Examples of Giant molecular substance are:

GRAPHITE

• Used as a lubricant and in pencils
• For every carbon atom there are three covalent bonds; has delocalised electrons
• able to conduct electricty
• layers formed;held loosley;can slide over eachother;can rub off in pencils

DIAMOND

• Hard
• Does not conduct electricity
• Has 4 covalent bonds for every carbon atom
• Good for cutting tools

-Miscible liquids/solutions are harder to separate

-Immiscible liquids/solutions are easier to separate e.g water & oil

Methods of Separation

• Fractional Distillation- using different boiling points to create different products
• Simple distillation- the liquid that has the lower boiling point will condense first.
• Chromatography- Rf=distance travelled by compound/distance travelled by solvent
• Separating Funnel
  
  

Fractional distillation

• Air is Filtered to remove dust
• It is cooled at -200 degrees celsius. to become liquid
• During its cooling , water condenses and is removed
• CO2 freezes and is removed
• Liquified air enters the fractioning column and is slowly heated
• Remaining gases (e.g.nitrogen) are seperated ; Oxygen and Argon comes out

-Group 1 : Alkali Metals

-Group 7 : Halogens

-Group 0 : Noble Gases

Metals

-Regular arrangement of ions (held together by strong metallic bonds)

-Giant metallic structure from metallic bonds

-Surrounded by a sea of delocalised electrons (allowing the ability to conduct electricity)

-Malleable - layers of atoms allow them to slide over eachother

-(Most metals are transition metals) have high melting and boiling points 

-Form colourful compounds

Alkali Metals

- Soft

- Low melting points

- Reacts Vigourously with water (forms hydroxides [alkaline] and hydrogen gas)

As you go down along group 1, the reactivity increases because there are more electron shells, further away from the nucleus, so there are weaker forces between the electron/shell and the nucleus

Halogens

-Soluble to form acidic solutions:

• Halogen + Hydrogen ----> Hydrogen Hallide
• Halogen + Metal ----> Metal Hallide

Cl2 (g) + H2 (g) ----> 2HCl (g)

At room tempuratures:

• Chlorine - is Green,Reactive, Poisonous gas
• Bromine- Dense,Poisonous, Orange Liquid
• Iodine- Dark, Grey, Crystalline Solid

Noble Gases

• Chemically Inert (does not react much)
• Fills the electron shells fully
• Boiling Points and Densities increase as you move down the group

Its Uses.....

• Inertness- atomosphere for welding (stop hot metal from  reacting with oxygen and protects it) and filament lamps (to stop hot filament from burning away as argon is non-flammable)
• Low Density - To fill Balloons
• Non- Flammable

Discovery of Noble Gases

-Chemists noticed that the density of nitrogen made in a reaction was different from nitrogen in the air

- They hypothesised that nitrogen in the air had other gases mixed in with it.

- Experiments were perforemd to test this hypothesis and eventually discovered other noble gases through methods such as Fractional distillation.

Elements and Compounds can be:

• Ionic
• Simple/Giant Mollecular Covalent
• Metallic

Displacement Reactions

• The Higher the element is in group 7, then the more reactive it is
• When Hallides dissolve in water, the ions are free to react
• If there is a more reactive halogen is a reaction with a solution with hallide ions, then it will 'push out' or displace the least reactve halogen

Exothermic Reactions

• Is when heat energy is given out so the temperature of surroundings increase
• Examples of Exothermic Reactions : Neutralisation , Explosions, Combustion
• There is more energy of the reactants at the start of the reaction which the decreases so the products have less energy. 

Endothermic Reactions

• Takes in heat energy
• Examples of Endothermic Reactions : Dissolving Ammonium Nitrate, Electrolysis, Photosynthesis.
• There is Less energy of the reactants at the starts however it increases/gains energy so the products have more energy

Breaking covalent bonds is ENDOTHERMIC

Forming bonds is EXOTHERMIC

Heat Energy Change

• Exothermic - more heat energy is released making bonds in products
• Endothermic - less heat energy is released making bonds in products

Chemical Reactions can be:

• Very slow, VERY VERY Fast, Explosive

Collision Theory- Reactions occur when particles collide

Factors Affecting the Rate of a Reaction:

• Concentration- more reactants in the same volume increases collisions
• Surface Area- More area is exposed increasing particle collisions
• Temperature- Particles have more energy to move faster increasing collisions and the chances of successful collisions
• Catalysts- Speed the rate of reactins without being used up

• Used in vehicles to remove/reduce the amount of hydrocarbons being released
• Converts Carbon Monoxide (CO) + Unburnt fuel to Carbon Dioxide (CO2) + Water Vapour
• Catalysts lower temperatures & pressures and is also cheaper so it is saving money
• Has a high surface area (honeycomb structure) to make it more efficient and use less expensive metals (Platinum,Rhodium,Palladium)
• Works best at higher temperatures because rate of reactions increase at higher temperatures 

Relative Atomic Mass (Ar)= top number of element

Relative Formula Mass (Mr) = Ar x no. of atoms of element

Percentage Composition= Ar x No. of atoms of element/Mr of compound then multiply by 100

Empirical Formula= 1. list elements 2. write their masses from the experiment 3.divide by their Ar  4. divide by the lowest value and convert answers to ratio form (don't forget to write the elements as a ratio first e.g. Mg:O)

Masses in reactions = 1. calculate the Mr  2.divide to get to one 3. then multiply to get all

Percentage Yield = Actual yield / theoretical yield x 100

Actual Yield is always less than the theoretical yield becuase:

• Chemicals lost between containers, filters etc. (practical losses)
• Incomplete reactions or unwanted reactions