chemistry exam s2

what is covalent bonding?

what is covalent bonding?

an intramolecular bond, between non-metals that share electrons to achieve full(er) valence shell

how is covalent bonding held?

electrostatic force of attraction between positive nucleus and negative shared electrons

linear molecular geometry

no lone pairs on central atom, 1/2 bonding electron pairs

v shaped (bent) molecular geometry

1/2 lone pairs on central atom, 2 bonding electron pairs

trigonal planar

no lone pairs on central atom, 3 bonding electron pairs

trigonal pyramidal

1 lone pair on central atom, 3 bonding electron pairs

tetrahedral

no lone pairs on central atom, 4 bonding electron pairs

lewis dot diagram

1 electron = 1 dot

valence diagram / structural formula

1 electron pair = 1 line

polarity

difference in electronegativity between atoms either side of bond, uneven pull of electron distribution (dipoles)

polar covalent molecules

asymmetrical dipoles; always v-shaped and trigonal pyramidal

dipole-dipole attractions

polar, opposite dipoles attract, strength increases with polarity (electronegativity difference), relatively weak

hydrogen bonding

polar, molecules containing hydrogen (slightly positive) covalently bonded to nitrogen/ oxygen/ fluorine (slightly negative), relatively strong

dispersion forces

polar or non, instantaneous dipole (from constant electron movement), induces in surrounding molecules, relatively weakest

properties of covalent bonding

low melting/ boiling points, soft/ malleable, poor electrical conductors

what is ionic bonding?

an intramolecular bond, between metals and non-metals in fixed proportions that exchange electrons to achieve full(er) valence shell

how is ionic bonding held?

electrostatic forces of attraction between positive cations and negative anions

properties of ionic bonding

high melting/ boiling points, hard, brittle, conduct electricity (only in molten/ aqueous)

what is metallic bonding?

an intramolecular bond, between metals that ‘lose’ electrons to achieve full(er) valence shell

how is metallic bonding held?

electrostatic forces of attraction between positive cations and negative delocalised electrons

properties of metallic bonding

high melting/ boiling points, hard/ dense, malleable / ductile, lustrous, conduct heat and electricity

structural isomers

molecules with same molecular formula (i.e. they have the same number of each atom type) but different semi/ structural formulas (atoms attached together differently), branched or postitional

branched (chain) isomers

some carbon and hydrogen atoms exist as alkyl groups (-yl)

positional isomers

functional groups differ in location in molecule

alkanes

all single C-C bonds, saturated, H=Cx2+2

alkenes

minimum 1 double C-C bond, unsaturated, H=Cx2

alkynes

minimum 1 triple C-C bond, unsaturated, H=Cx2-2

alcohols

molecules with hydroxyl group (-ol), a carbon single bonded to OH

carboxylic acids

molecules with carboxyl group (-oic acid), carbon atom double bonded to oxygen (C=O) and single bonded to a hydroxyl group (-OH).

esters

esterification reaction between alcohol and carboxylic acid, forms water molecule product

properties of water

naturally exists in 3 states, liquid at room temp, solid less dense than liquid, high surface tension, relatively high melting/ boiling point, high latent heat values/ specific heat capacity

solubility

maximum amount of solute (g) that can be dissolved in given amount of water (100g) at particular temperature. generally a positive correlation with temperature

concentration

relative amount of solvent and solute in solution, high solute = concentrated, low = dilute

precipitation reaction

collision of insoluble oppositely charged ions

soluble ions (SNAPE)

Sodiums, Nitrates, Ammoniums, Potassiums, Ethanoates

insoluble ions (CHOPS)

Carbonates, Hydroxides, Oxides, Phosphates, Sulphides

soluble + exceptions

I’m Clear and Brief, Probably Agnes; So…, Agnes Probably Battered her Cat

insoluble + exceptions

Company Policy is, Never-Hurt G1; Oh Oxygen, Never-Hurts G1 Barely Cares; Seriously, G1 Never-Hears G2

acids

donates hydrogen ions, pH<7, ionise in water to form hydronium ions (H3O+)

bases

receives hydrogen ions, pH>7, dissociates in water to form hydroxide ions (OH-)

strength of acids

readiness to donate; ability to completely ionise ∴ weakens with each donated ion. eg strong: HCl, H2SO4, HNO3

strength of bases

readiness to receive; ability to completely dissociate. eg strong: NaOH, KOH, LiOH, Ca(OH)2

conjugate acid-base pair

product formed from reactant. eg: acid HCl donates, conjugate base Cl-

strength of conjugate pair

inverse correlation. eg: strong acid - weak conjugate base

self-ionisation of water

forms H3O+ and/or OH-. in pure water (pH7), equal concentration proportion of 10^-7 M, total 10^-14

acidic (+ basic) solutions

concentration of H3O+ > 10^-7 M, OH- < 10^-7 M. vice versa for bases.

reaction (not acid-base): acid + reactive metal →

salt + H2

reaction (acid-base): acid + metal oxide/ hydroxide →

salt + H2O

reaction (acid-base): acid + metal (hydrogen) carbonate →

salt + H2O + CO2

calculating pH with hydronium

pH = -log10[H3O+]; 10^-pH = [H3O+]

properties of gases

low density, fill containers completely and uniformly, compressible, exert uniform pressure on inner container, easily mix/ diffuse

qualities of gases

constant and random moving particles, increasing speed with heat, no forces of attraction or repulsion, perfectly elastic collisions (no KE lost)

pressure measurement conversions

1atm: 101.3kPa: 760mmHg

boyle’s law

pressure is inversely proportional to volume. p1v1=p2v2

charles’ law

volume is directly proportional to temperature. v1/t1=v2/t2

molar volume formula (at SLC)

n=V/ 24.8

universal gas equation

PV=nRT

limiting agent

need > given. use amount given in subsequent equations

excess agent

given > need

temperature conversion

K = C + 273, C = K - 273

reduction reaction

the oxidant chemical gains electrons

oxidation reaction

the reductant chemical loses electrons

reductant

reactant that causes reduction by losing electrons

oxidant

reactant that causes oxidation by gaining electrons

OIL RIG

Oxidation Is Loss (e-) Reduction Is Gain (e-)

balancing complex half equations (KOHES)

balance Key element, balance Oxygens (add H2O), balance Hydrogens (add H+), balance charge (add Electrons), States

oxidation number: free elements

zero (0)

oxidation number: ions

the overall charge

oxidation number: main group metals (Mg)

equal to valency (Mg = +2)

oxidation number: oxygen

-2 (except peroxides, -1; and fluorine, +2)

oxidation number: hydrogen

+1 (except metal hydroxides, -1)

oxidation number: neutral compound

zero (0), sum of components’ charge

assigning oxidation numbers to elements when calculating

only write charge of 1 atom, regardless of subscript (eg. O2 = -2, not -4)

concentration (formulas)

c1v1=c2v2

c=m/V

what is the salt bridge’s purpose?

to prevent accumulation of charge in half cell solutions, by enabling free ion flow to balance

converting mol L-1 to g L-1

multiply or divide by molar mass

specific heat capacity: definition

amount of energy (j) required to increase temperature of substance certain amount (1g) by 1ºC

specific heat capacity: formula

q=mcΔT

latent heat value: definition

amount of energy required to initiate a substance’s state change (ie. break intermolecular bonds)

latent heat value: formula

q=nL