Chemistry - S2.1-2.3 & S3.2

what is the ionic bond?

between a metal (cation) and a non-metal (anion)

how is the ionic bond formed?

by electrostatic attractions between oppositely charged ions

how are ionic compounds named?

(cation)(anion + ide)

polyatomic ionic compounds to remember

ammonium - NH₄⁺

hydroxide - OH¯

nitrate - NO₃-

hydrogen carbonate - HCO₃-

carbonate - CO₃²⁻

sulfate - SO₄²-

phosphate - PO₄³⁻

transition metals to remember

Fe^2+, Fe³⁺ and Cu²⁺, Cu⁺

the ionic compound structure

ionic compounds exist as 3D lattice structures held together by ionic bonds - represented by ratio of ions bcz there is no fixed number of ions)

what is lattice enthalpy? (and effect of ionic charge and radius on lattice enthalpy?)

lattice enthalpy (a measure of the strength of the ionic bonds in different compounds)

• as ionic charge increases, lattice enthalpy increases

• as ionic radius increases, lattice enthalpy decreases

the ionic properties

• high MP and BP and low volatility: bcz of their strong attractions and bonds

• generally soluble in water but not in non-polar liquids: polar water attracts cations and anions

• high electrical conductivity in liquid and aqueous state: ions are mobile when not in lattice form (solid)

what is the covalent bond?

between two non-metals

how is a covalent bond formed?

by the electrostatic attractions between a shared pair of electrons and the positive nucleus

what is the octet rule?

the tendency of atoms to gain a valence shell of 8 electrons

steps for drawing Lewis structures

1. calculate the total valence electrons of all atoms

2. identify the skeletal structure

3. add more electron pairs to complete the octet

4. check valence electrons are the same as previously calculated

exceptions to the octet rule

Be - 2 pairs

B - 3 pairs

H - 1 pair

not enough electrons to make 4 pairs

when are there double and triple bonds

if there are not enough electrons to achieve octets on all the atoms in a molecule (O=O, N₂ (triple), O=C=O)

what is every covalent bond characterized by? (+ trend on PT)

bond length (distance between two bonded nuclei) and bond strength (the measure of energy needed to break the bond)

• down a group - bond length increases, bond strength decreases

difference between bond length and strength between single and multiple bonds

the more bonds, the more shared electrons and stronger force of electrostatic attraction = shorter bond length

what are coordination bonds? (notation)

a covalent bond in which both shared electrons originate from the same atom - arrow towards atom receiving both electrons

are coordination and covalent bonds different?

once they are formed coordination bonds are no different to covalent bonds

what is the shape of a molecule determined by? why?

repulsions between electron domains around a central atom - bcz electron pairs in the same valence shell have the same charge and repel each other

what are electron domains?

all electron locations in the valence shell: lone pairs, single/double/triple bonds

VSEPR summary

• repulsion applies to electron domains

• total # of electron domains around the central atom determines the geometric arrangement

• the shape of a molecule is determined by the angles between bonded atoms

• lone pairs and multiple bonds cause more repulsion: lone pairs = larger conc. of charge bcz electrons aren’t shared, multiple bonds = larger conc. of charge bcz they have more electrons

difference between electron domain geometry and molecular geometry

electron domain - considers all electron domains (doesn’t consider repulsions)

molecular - position of atoms fixed by the bonding pairs only (considers repulsions)

table of shapes of molecules based on types of electron domains

• 2 electron domains - bonding 2, non 0: (EDG linear 180^o)(MG linear 180^o)

• 3 electron domains - bonding 3, non 0: (EDG planar triangular 120^o)(MG planar triangular 120^o)

• 3 electron domains - bonding 2, non 1: (EDG planar triangular 120^o)(MG v-shaped <120^o)

• 4 electron domains - bonding 4, non 0: (EDG tetrahedral 109.5^o)(MG tetrahedral 109.5^o)

• 4 electron domains - bonding 3, non 1: (EDG tetrahedral 109.5^o)(MG trigonal pyramidal 107^o)

• 4 electron domains - bonding 2, non 2: (EDG tetrahedral 109.5^o)(MG v-shaped 104.5^o)

what is bond polarity?

unequal share of electrons when there is a difference in electronegativity of the bonded atoms: bond dipole

which bonds are non-polar?

pure covalent - F₂, H₂, O₂

how difference in electronegativity affects bond polarity

the larger difference in electronegativity the more ionic:

pure covalent < polar covalent < ionic

what does molecular polarity depend on?

bond polarity and molecular geometry

when are molecules non-polar?

when bonds have equal polarity AND are arranged symmetrically (O=O, O=C=O)

when are molecules polar? (notation)

if bonds don’t have the same polarity or aren’t arranged symmetrically = net dipole

• arrow towards the atom with the most electronegativity

what are covalent network structures?

a single molecules with a regular repeating pattern of covalent bonds

what are allotropes?

different bonding and structural patterns of the same element in the same physical state and so have different chemical and physical properties

properties of the allotropes of carbons

diamond: each C is cov. bonded to 4 others, tetrahedrally with bond angles of 109.5^o

• no electrical conductivity: all electrons are bonded

• very effective thermal conductivity

• transparent crystal, hard

• high MP

graphite: each C is cov. bonded to 3 others, hexagons in parallel layers with bond angles of 120^o - weak LDF layers slide, delocalized valence electrons

• good electrical conductor: delocalized electrons

• no thermal conductivity (unless heat is forced in a parallel direction to layers)

• grey solid, soft, slippery

• high MP

graphene: each C is cov. bonded to 3 others, forms hexagons with bond angles of 120^o - delocalized valence electrons

• very good electrical conductor: delocalized electrons

• very good thermal conductor

• transparent, thin material, strong

• high MP

fullerene: each C is bonded to 3 others in a sphere of 12 pentagons and 20 hexagons

• poor electrical conductor: electrons don’t move much

• very low thermal conductivity

• black powder, light and strong

• low MP

structure and properties of silicon and silicon dioxide

silicon: each Si cov. bonded to 4 others, tetrahedrally

• poor electrical conductor

• grey-white solid

• high MP

silicon dioxide: each Si cov. bonded to 4 O atoms, each O atoms cov. bonded to 2 Si atoms

• no electrical conductivity

• insoluble in water

• strong

• high MP

what are intermolecular forces? (what are they affected by?)

forces that exist between molecules - affected by the polarity and size of the molecules

london dispersion forces (what does strength depend on?)

in non-polar molecules when there is no permanent seperation of charge but electrons are greater over one atom at any moment = induced dipole

• the larger the molecule, the greater the force: bcz more electrons (but still the weakest intermolecular force)

• only force that occurs in non-polar molecules (also on polar but is usually overlooked bcz weak)

dipole-dipole attraction (what does strength depend on?)(high or low MP?)

between opposite dipoles of polar molecules: they have a permanent seperation of charge due to one of the atoms having stronger electronegativity

• strength depends on the distance and orientation of dipoles

• stronger than LDF = causes MP to be higher in polar molecules than non-polar (of similar molecular mass)

dipole-induced dipole attraction (only attraction present?)

when a mixture contains both polar and non-polar molecules the permanent dipole can cause a temporary dipole: acts in addition to LDF and D-D

what is hydrogen bonding?

when a molecule contains hydrogen covalently bonded to a very electronegative atom (fluorine, nitrogen, oxygen): these molecules are attracted to each other by a strong intermolecular force = hydrogen bond

• H is attracted to a lone pair (max. 2) on the electronegative atom of another molecule

• strongest intermolecular force

• high MP: NH₃, HF, H₂O

• hydroxyl group

order of increasing strength of intermolecular forces

LDF < dipole-induced dipole < dipole-dipole < hydrogen bonding

types of molecules involved in each intermolecular force

LDF: non-polar, polar molecules

D-ID: requires a mixture of non-polar and polar

D-D: polar molecules

HB: H-O, H-N, H-F

physical properties of covalent substances

• volatility: strong forces = low

• solubility: non-polar dissolves in non-polar solvent (LDFs) / polar dissoves in polar solvent (dipole interactions and HB) => larger molecules (with a smaller polar molecule) decreases in solubility

• electrical conductivity: do not conduct, but some polar covalent do (they ionize) and some giant covalent molecules do (graphite, graphene)

use of chromatography (paper chromatography?)

to seperate and identify components of a mixture

paper - as water makes H bonds with the water in the paper, it dissolvers the mixtures and carries them at different rate based on polarity

R_f value formula

= distance moved by component / distance moved by solvent

thin paper chromatography?

instead of water in paper → layer of silicon dioxide on glass, metal or plastic

what is the metallic bond?

because metals have small # of valence electrons: in its elemental state, electrons in valence shell of metals are weakly attracted to the nucleus and tend to delocalize and spread across the structure => forms a lattice structure with cations and delocalized electrons

uses of metal related to their properties

• good conductivity (delocalized electrons): electrical circuits

• good thermal conductivity (delocalized electrons): pots and pans for cooking

• malleable & ductile (movement of electrons is non-directional so lattice stay in tact when pressure is applied): moulded for machinery and wires

• high melting point (strong electrostatic attraction): high speed tools

• shiny (delocalized electrons reflect light): jewellry and ornamental strucutres

what is the strength of a metallic bond determined by? (trends on PT)

charge and size of the cation and number of delocalized electrons: more electrons = smaller size (pulled more) = more strong bond

• increases across a period, decreases down a group

what are alloys? (example?)(how is it possible)

produced by adding one metal element to another (or carbon) in liquid state and so the different atoms can mix in solid

• possible because of non-directional nature of delocalized electrons

e.g brass (Cu&Zn), bronze (Cu&Sn), stainless steel (Fe&Ni)

alloys compared to pure metal

different arrangement = different properties

• more chemically stable

• more resistant to corrosion: harder to slip across layers when force is applied

difference between empirical, molecular, structural (full & condensed), stereochemical, skeletal formulas

empirical - simplest whole number ratio

molecular - actual number of atoms in compound

full structural - shows every bond and atom (diagram)

condensed structural - show bonds where they can be assumed and groups atoms together

stereochemical - shows relative positions of atoms around central atom in 3D

skeletal - shows all bond except C-H

what are functional groups?

groups of atoms in an organic compound which determine its physical properties and chemical reactivity

saturated vs unsaturated compounds

saturated - single bonds

unsaturated - double or triple bonds

class, functional group, suffixes

alkanes - … -ane

alkenes - alkenyl (C=C) -ene

alkynes - alkynyl (C=_C) -yne

alcohol - hydroxyl (-OH) -anol

ether - alkoxyl (R-O-R’) -oxyalkane

aldehydes - carbonyl (C=O end) -anal

ketones - carbonyl (C=O middle) -anone

carboxylic acid - carboxyl (COOH) -anoic acid

ester - carboxyl (COOR) -anoate

amide - amido (CO(NH₂)) - anamide

amine - amino (NH₂) -anamine

halogen-alkane - halogeno (F,Cl,Br,I) -fluoro, bromo, chloro, iodo (prefixes)

arene - phenyl (hexagon) -benzene

what are homologous series? (what can this affect?)

family of compounds where members differ by a common structural unit, usually CH₂

• affects physical properties: MP increases with chain length (LDF) and polarity of functional group (D-D&HB)

order of increasing volatility

alkane > halogenalkane > aldehydes > kenote > alcohol > carboxylic acid

london dispersion forces, dipole-dipole, hydrogen bonding

steps for naming compounds

1. identify the longest continuous chain of carbon - root (meth, eth, prop, but, pent, hex)

2. identify the functional group - suffix: number is the carbon FC is attached to

3. identify side chains - prefix: number is carbon attached to (di, tri, tetra if there are multiple of the same side chain)

how to name esters

prefix - chain attached to the O bonded to the C

root - chain attached to the C with =O

[prefix]yl [root]anoate

how to name ethers

prefix - shorter chain

root - longer chain

[prefix]oxy[root]ane

what are structural isomers? (differences?)

molecules with the same molecular formula but different arrangement

differences:

• straight or branched (lower MP bcz less contact) - alkanes

• position of bonds or FC - alkenes

• functional group

difference between primary, secondary and tertiary compounds

primary - C attached to 1 FG, 1 alkyl, 2 hydrogen

secondary - C attached to 1 FG, 2 alkyl, 1 H

tertiary - C attached to 1 FG, 3 alkyl