chemical bonding and calculation notes

Chemical bonding ➔Metals ◆Giant metallic lattice structure ◆Form metallic bonds ◆Have giant metallic structures that consist of positive metal ions surrounded by“sea of electrons”that is delocalised from the metal atoms ●Valence electron of each atom are free to move about the overlapping valence shell ●When the valence electron went to the neighbouring shell, a positive metal ion is formed ●Free electrons act as “electronic glue”, as it holds positive metal ions together ●The metal is a lattice of positive ions in a “sea of electrons”

●Thestrong electrostatic forces of attraction between“sea of electrons” and “immobile” positive metal ions that form the structure of the giant metallic lattice is themetallic bonds ●“Sea of electrons” consists of free electrons, mobile electrons and delocalised electrons) ◆Properties: ●Generally exists as a solid at rtp ○Alarge amountof energy has to be absorbed to overcome tostrongmetallic bond ●Havehighmelting and boiling points ●Good heat conductor ○Sea of electrons are free to move to transfer heat ●Conduct electricity inanystate (aka good electrical conductor) ○Sea of electrons are free to move to carry electricity ●Malleable (can bend/be hammered) and ductile (can be drawn out into thin wire without breaking) ○When force is applied, the neatly arranged layers of metal atoms canenvelopeach other easily ➔Giant covalent bonds ◆Formed between thousands and million of atoms extended 3-dimensionally substance

◆ONLY covalent bonds (duh, that’s why they’re called giant covalent bonds) ◆ Giant covalent bonds → Giant covalent substances ◆Example 1 of giant covalent substance:Diamond ●Has a tetrahedral structure ●Each carbon atom covalently bonded to 4 other carbon atoms ◆ Example 2 of giant covalent substance:Graphite ●Formed by many layer of graphene (a grant molecule) ●Has a hexagonal structure ●Each carbon atom covalently bonded to 3 other carbon atoms ○This leaves 1 free electron per carbon atom not bonded ◆ Table of comparisonbetween Diamond and Graphite Diamond Graphite Structure -Tetrahedral structure -Giant molecule -Each carbon atom covalently bonded to 4 other carbon atoms -Hexagonalstructure -Layers of carbon atoms are held by weak force of attractions -Each carbon atom covalently bonded to 3 other carbon atoms, leaving 1 free electron per carbon atom not bonded substance waswas i n a usedforbandit Tu a re gantmilee

Property 1.High melting point 2.High boiling point 3.Low volatility Same applies here ReasonLarge amount of energy to be absorbed to break the strong covalent bonds between the carbon atoms Same applies here Property 4.Non-electrical conductor4. Electrical conductor ReasonNofree moving ion or electron to carry electric current Onefree electron per carbon atom to carry around electric current Property 5.Hard 5. Soft and slippery ReasonLarge forceneeded to break thestrong covalent bonds between the carbon atoms Low forceneeded to break theweak intermolecular forces of attractionto allow to layers to slide over each other easily Uses Used in cutting tools or drill bits due to its hardness (or used in engagement rings #hopelessromantic) ➔Used as a solid lubricant or in pencil lead due to its softness and slippery property

Chemical equations ➔One mole of particles / Avogrado’s number = 6 x 10^23 = 1 mol ➔One mol of any gas occupies a volume of 24 dm^3 at rtp and pressure ➔Formula triangles: ➔Reacting masses: ●1. Write a balanced chemical equation ●2. Compare mole ratio (based on values in the balanced equation; eg. 2 mol of Lithium + 1 mol of Chlorine, write ratio as 2:1) ●3. Convert into number of moles (for known substance) ●4. Find number of moles (for unknown substance)

●5. Convert number of moles into required unit given by the question (eg. mass, volume) ➔Volume of reacting gases: ●Direct proportional relationshipbetween number of mole of gases and volume of gases ○1. Write a balanced chemical equation ○2. Compare mole ratio from balanced equation ○3. Find volume of unknown substance ○4. Find number of moles using volume of unknown substance ○5. Convert number of moles into required unit given by question ➔Concentration of solutions: ●Concentration is theamount of solute dissolvedina given volume of solution ○1. Write a balanced chemical equation ○2. Compare mole ratio from balanced equation ○3. From the question, calculate number of mole (for known substance) ○4. From there, calculate number of moles for unknown substance using the mole ratio ○5. Convert number of moles for unknown substance into required unit given by the question ●mol/dm^3 x Mr = g/dm^3 ●g/dm^3 divided by Mr = mol/dm^3

➔Percentage yield ●No experiment can get 100% yield due to mass loss, contaminations or incomplete reaction along the way in the experiment ●(Actual yield divided by theoretical yield) x 100% ○1. Write balanced chemical equation ○2. Compare mole ratio ○3. Find number of moles for unknown substance ○4. Convert number of moles into mass ○5. Use percentage yield formula to find answer ➔Percentage purity ●(Mass of pure substance ÷mass of impure substance) x 100% ●Do NOTuse impure sample data to calculate number of moles ○1. Write balanced chemical equation ○2. Compare mole ratio ○3. Find number of moles for unknown substance ○4. Convert number of moles into mass ○5. Use percentage purity formula to find answer ➔Limiting reactant ●The limiting reactant is the substance that is completely used up in a reaction

●When the limiting reactant is used up, the reaction stops ●ONLY the limiting reactant should be used for calculation (eg. finding number of moles) ●Whenever there is more than one reactant information, find out what is the limiting reactant by calculating the number of moles (using formulas from the formula triangles) ○1. Write balanced chemical equations ○2. Check if more than 1 reactant information is given. If yes, find the number of moles for both reactants and compare mole ratio using data from the equation and one of the reactants. ○3. From the equation, compare mole ratio between the limiting reactant and the unknown substance ○4. Calculate the number of mole of unknown substance ○5. Convert number of moles into required unit ➔Remember, when in doubt, just find the number of moles! SLAY THE DAY (or exam lol)! :)