Water - Preliminary Module 3

26-March-2016 Definitions - Solution - homogenous mixture of 2 or more substances Solute - substances dissolved by the solvent - (or also know as the component with a lower amount in mixture)Solvent - substance in which the solute is dissolved - (or also know as the component with the greater amount in the mixture)Solute dissolves into the solvent to form the solution. CONCENTRATION The concentration of a solution is the amount of solutes present in the a specific amount of solution. It is calculated in the form of a ratio. concentration = solute / solution units used to calculate the concentration - g/ml (use normal formula = solute/solution) - but remember to make the units the same grams / millilitres - g/g sometimes referred to as w/w (convert to grams over grams then plus the solvent to the solution so that formula = solute / solvent + solution) - %w/w (units of the weight are chosen by choice) - but what ever you choose make sure to use above formal as it is mass over mass hence plus the solvent and solution) - in final answer always mention (% * w(unit)/w(unit) so that marker knows what units are used.- %w/v (means % multiply by the weight /volume) e.g. g/ml - make sure units are consistent- mol / L ( for this situation the formula is concentration -= solute /solution = mol / L ) this is known as MOLARITY (in this formula make sure to convert all volume measurements to L) ** DO PRACTICE QUESTIONS CONCERNING APPLICATION OF FORMULA AND DIFFERENT THINGS THAT CAN BE FOUND USING THE FORMULA**

2 - April - 2016 1. DILUTION - adding of more solvent to the solution definition - process of reducing the concentration of a solution by adding in greater amounts of the solvent.However when changing the concentration, the number of particles of the solute do not change, henceforth the number of moles doesn't change.Hence this formula is derived ; C(1)V(1) = C(2)V(2) because n1 = n2 **important note to remember = because final volume, is the entire volume of the solution it is equivalent to initial volume plus the final volume. 2. CHEMICAL BONDING Intramolecular bonds - any force which holds together the atoms making up a molecule or a compound- Ionic - Ionic bonding is the complete transfer of valence electron(s) between atoms. It is a type of chemical bond that generates two oppositely charged ions.- Metallic - Metallic bonding is the strong attraction between closely packed positive metal ions and a 'sea' of delocalised electrons.- Covalent - Covalent bond is a chemical bond that involves the sharing of electron pairs between atoms.Intermolecular bonding - The force of attraction which act between neighbouring molecules. These are what makes the physical properties of covalent molecular.- Dispersion forces = These forces are the result of the movement of electrons which cause slight polar moments.- Dipole-Dipole attraction = are attractive forces between the positive end of one polar molecule and the negative end of another polar molecule.- Hydrogen bonding = is the electrostatic attraction between polar groups that occurs when a hydrogen (H) atom bound to a highly electronegative.ELECTRONEGATIVITY (SIDE - TRACKING A BIT) Definition - the electron attracting power of an atom of an element (metals have low), (non-metals have high)Trend - across a period increases, decreases down a group. IONIC COMPOUND - - An ionic bond is formed when the two elements have a large difference is electronegativity - the two elements usually need to have a change in electronegativity above 1.7 COVALENT COMPOUND - - Is formed when the non-metallic elements have a small difference in electronegativity, each electron has similar amount of pull on electrons hence causing them to be shared. - change in electronegativity usually needs to be in between : 0 - 0.4 - an electron cloud an be used to represent the route of the electrons, and the equality/inequality of the time spent with each element. **consider however _ what if there is a change in electronegativity? what does this mean? what happens when elements have similar but different electronegativity?- electrons will be shared unequally = electrons will spend more time around the element with a higher electronegativity. If electronegativity is different then it is called a polar covalent bond in which the change in electronegativity needs to be in between 0.4 - 1.7POLAR COVALENT MOLECULES- When two atoms of similar but different electronegativity, share electrons unequally. electron clouds is used to visibly show this, where the cloud is bigger it is indicated that the electron spends more time around that element, when the cloud around the element is smaller it means that the electron spends less time around that electron.- when electrons spend more time around a specific element they make that element slightly negative, hence making the other element slightly positive.- the area of the slightly negative element is known as the electro-negative part of the cloud. - the area of the slightly positive element is known as the electro positive part of the cloud.- slightly is an important term to use because it identifies that this is a covalent compound not an ionic compound, if it was indefinitely classified as positive and negative then it would be considered to be an ionic compound. - this bond between the two slightly different electronegativity holding elements is know as a bond dipole.- resulting uneven covalent bond is known is known as a - polarity - having two distinctly opposite sides or ''poles'' SUMMARY - bond dipole : difference in charges due to separation of positive and negative charges. - polarity : separation of opposite electric charges.- polar molecule : one that has oppositely charged ends.

9 - April - 2016Non Polar Covalent Molecule in covalent compounds when the difference EN is between 0/4 and 1.7, it forms a polar covalent molecule, but when difference is less than 0.4 it forms a non-polar covalent molecule.a polar covalent molecule is shown by the arrowhead and the plus sign '' bond dipole'' a non polar covalent molecule is shown by a simple dash between the atoms.Non polar polar covalent bonds exist where the atoms have a similar EN (0 - 0.4), a molecule with non-polar covalent bonds is always non-polar.Shape of a Molecule - bond dipole refers to when theres is difference in charges due to separation of positive and negative charges. Hence, the dipoles of a molecule determine the polarity of the molecule. Hence, this is called the net dipole which refers to the polarity of the molecule. dipoles should be treated like vectors when calculating polarity. the shape is very important in determining the net dipole (polarity of molecule). if there is a net dipole in ANY direction, the molecule will still be considered polar. however when the net dipole = 0 and the molecule is hence non-polar it means that the electrons in that molecule are shared equally. so if molecule is polar it means that electrons are unequally shared. vsepr theory