c3 revision (chemistry unit 3)

CHEMISTRY 3

PERIODIC TABLE

EARLY PERIODIC TABLE

•Early 1800s - LESS THAN 40 ELEMENTS

•NEW ELEMENTS discovered REGULARLY

•Noticed patterns in the way they worked - PROPERTIES

•Worked out Atomic Weight

JOHN NEWLAND

•In order of ATOMIC MASS

•LAW OF OCTAVES - Similarities in PROPERTIES of every 8TH ELEMENT

JOHN NEWLAND - Problems

•Some groups had a MIX of METAL and NON METAL

•Only worked for FIRST FEW ELEMENTS

•Elements still being discovered

DMITRI MENDELEEV

•Arranged in PERIODIC way

•LEFT GAPS for UNDISCOVERED ELEMENTS

•otherwise elements wouldn’t have SIMILAR PROPERTIES

•predicted Atomic Mass and Properties to undiscovered elements.

AFTER MENDELEEV...

•... These were discovered:

•Noble Gases

•Electrons

•Atomic Structure

•accuracies in atomic number ordering

•Groups and Periods (modern table)

MODERN PERIODIC TABLE

MODERN PERIODIC TABLE

•Order by ATOMIC NUMBER - Makes all elements fit into groups with SIMILAR PROPERTIES

•GROUPS tell us the number of electrons in the OUTER SHELL

GROUP 1 - ALKALI METALS

•All LOW DENSITY

•React w/ NON-METALS = IONIC COMPOUNDS

•React w/ WATER = RELEASE HYDROGEN

•Form HYDROXIDES that dissolve in water = ALKALINE SOLUTION

GROUP 1 - ALKALI METALS

•The FURTHER DOWN THE GROUP the MORE REACTIVE THE ELEMENT

•The LOWER the MELTING&BOILING POINT

•Purple flame - SODIUM AND ONWARDS

GROUP 2 TRANSITION

METALS•COMPARED TO GROUP 1 - HIGHER

MELTING&BOILING POINTS except for mercury.

•HARDER&STRONGER

•LESS reactive, don’t react as much with WATER&OXYGEN

GROUP 2 TRANSITION

METALS•Build buildings due to being LESS

REACTIVE

•Form IONS with different charges

•Form COLOURED compounds [COPPER SULFATE - BLUE]

•Useful as CATALYSTS

GROUP 7 HALOGENS

•Bad conductors

•POISONOUS

•Coloured vapours

•React with METALS to form IONIC COMPOUNDS [ SODIUM CHLORIDE]

GROUP 7 HALOGENS

•ION produced called HALIDE

•E.G. Fluorine - Fluoride etc.

•Each has -1 Charge

•FURTHER DOWN - LESS reactive

•HIGHER Melting & Boiling points

GROUP 7 HALOGENS

•DIATONIC MOLECULES

•Higher the reactivity , in DISPLACEMENT reaction, element with HIGHER reactivity will displace lower reacivity.

TRENDS IN REACTIVITY

TRENDS IN REACTIVITY

•GROUP 1 DOWN - MORE reactive

•GROUP 7 DOWN - LESS reactive

•The HIGHER the energy level of the OUTER ELECTRONS:

•The easier electrons are LOST

•The LESS easily electrons are GAINED

TRENDS IN REACTIVITY

•GROUP 1 elements need to LOSE electrons to react.

•LESS ENERGY LEVELS:

•STRONGER attraction [ To NUCLEUS]

•Less SCREENING/SHIELDING by INNER ELECTRONS

•Electrons lost LESS easily

TRENDS IN REACTIVITY

•MORE ENERGY LEVELS:

•Outer Electron FURTHER from nucleus

•WEAKER attraction [ TO NUCLEUS]

•MORE screening/Shielding by inner electrons

•Electron lost EASILY

GROUP 7 REACTIVITY

•Needs to GAIN electron

•LESS energy levels :

•Outer electron CLOSER to nucleus

•Stronger attraction [ TO NUCLEUS]

•LESS screening/shielding by INNER ELECTRONS

GROUP 7 REACTIVITY

•MORE energy levels :

•Outer electron FURTHER to nucleus

•Weaker attraction [ TO NUCLEUS]

•MORE screening/shielding by INNER ELECTRONS

HARD AND SOFT WATER

INTRO•SOFT water : can LATHER [produce

bubbles when soaped]

•HARD water : CAN’T Lather : creates SCUM&SCALE

•contains DISSOLVED COMPOUNDS

• AND MAGNESIUM&CALCIUM compounds [river flows over substances]

HARD WATER

•SCUM : INSOLUBLE precipitate

•Formed by REACTION with SOAP

•CA2+ [Calcium Ion] REACTS with HARD WATER

•MORE soap needed [more expensive]

•SOAPLESS detergents made to avoid scum [no Sodium Stearate won’t react]

HARD WATER•SCALE : INSOLUBLE SOLID

•REDUCES efficiency

•E.G. Kettle - SCALE is POOR CONDUCTOR OF HEAT - Kettle has to work harder to heat water.

•BENEFITS : Bone development ; Teeth development ; Reduce Heart Disease

HARD WATER

•TEMPORARY - Softened by Heating/Boiling

•PERMANENT - Remains hard even when Heated / Boiled

SOFTENING HARD WATER

•Contains CA2+ [CALCIUM IONS]

•Contains MG2+ [MAGNESIUM IONS]

•TO SOFTEN - Add WASHING SODA (Sodium Carbonate) =

SOFTENING USING WASHING SODA

•1. TO SOFTEN - Add WASHING SODA (Sodium Carbonate) =

•Calcium Ions + Carbonate ions = Calcium Carbonate + Sodium

SOFTENING USING ION EXCHANGE

•2. Use ION EXCHANGE COLUMN

•Cylinder containing RESIN containing SODIUM (NA+) or HYDROGEN (MG2+) ions

•Magnesium&Calcium ions exchange with Sodium/Hydrogen ions

•Sodium/Hydrogen Ions left in water

TEMPORARY HARD WATER

•Softened when HEATED

•contains HCO₃⁻ - Hydrogen Carbonate Ions

•HCO₃⁻ DECOMPOSES to CARBONATE IONS

•Carbonate Ions REACT with magnesium ions / Calcium Ions to form carbonates

TITRATION

TITRATION METHOD

•The METHOD to see how much ACID or ALKALI is needed to create a NEUTRAL SOLUTION.

•1. measure and add volume of ALKALI into CONICAL FLASK using a PIPETTE

•2. measure drops of Phenolphthalein/ Methyl Orange

TITRATION METHOD

•3. Pour acid in BURETTE and RECORD READING

•4. OPEN TAP in Burette, add little acid, swirl conical flask to mix.

•5. ADD ACID until solution is NEUTRAL (shown by indicator)& repeat

•Pheno - Pink to Colourless

TITRATION CALCULATION

•Should be able to calculate QUANTITIES in titrations involving :

•concentrations - MOLES per dm³

•masses - GRAMS per dm³

•If conc. of one reactant is known, it can be used to find the conc. of the other reactant.

TITRATION CALCULATION

•1 decimetre cubed = 1000cm³ = 1 LITRE

•CONC. OF SOLUTION = Moles per dm³ [ 3 moles per 1 dm³ ]

•MOLES - mass [g] of 1 MOLE of a substance is it’s RELATIVE FORMULA MASS in Grams. [ Add all relative atomic masses in a compound together = 1 mole]

TITRATION CALCULATION E.G.•Make 1 mole per dm³ solution of

Sodium Hydroxide NaOH

•Relative atomic masses =

•Na=23 O=16 H=1 1 MOLE = 40g

• Take 1dm³ [1000 cm³ ] of water and put 40g of NaOH in it

TITRATION CALCULATION

E.G.2•Put 40g in 500cm³ of water , what

is the Concentration in Moles/dm³?

•500cm³ is half 1dm³ , so you Double the mass = 80g = 2 moles/dm³

TITRATION CALCULATION

E.G.3•What MASS of sodium hydroxide

is there in 250 cm³ of a 2 moles/dm³ solution?

•2 mol = 80g

•250cm³ = 1/4 of 1000

•1/4 x 80g = 20g

TITRATION CALCULATION

E.G.4•We have 45cm³ of Sodium Hydroxide solution, and 0.2 mol/dm³ which has neutralised 15cm³ of Ethanoic acid.

•What is : The conc. of Ethanoic Acid in

•a) mol/dm³

•b) grams/dm³ = Mᵣ Ethanoic Acid = 60

TITRATION CALCULATION

E.G.4•a)

•4

TITRATION CALCULATION

E.G.4•b) Mᵣ ETHANOIC ACID = 60g

•Use moles/dm³ answer from previous question =

TITRATION PRACTICE QUEST

•25.0 cm³ of ACID is placed into a conical flask. The concentration of acid = ?

•The ACID was Neutralised (reacted completely) with 13.5cm³ of sodium Hydroxide of conc. 0.10 mol/dm³

•Calculate the Conc. in mol/dm³

•1 mole Sodium Hydroxide = 1 mole acid

TITRATION PRACTICE QUEST

TITRATION PRACTICE 2

•Titration is done to find concentration of SULPHURIC ACID. 25.0cm³ of the sulphuric acid solution was NEUTRALISED by 34.0cm³ of a POTASSIUM HYDROXIDE solution of 2.0 mol/dm³

•Equation for reaction is =

TITRATION PRACTICE 2

ENERGY LEVEL DIAGRAMS

ENERGY LEVEL DIAGRAM

•The reaction is either ENDOTHERMIC or EXOTHERMIC

•Energy needs to be supplied to the atoms to BREAK THE BONDS and this takes energy from the environment.

•When making bonds, energy is RELEASED to the environment.

ENERGY LEVEL DIAGRAM

•If the graph shows a higher energy going to a lower energy level, it is EXOTHERMIC, as energy is released.