Chemistry - Unit 8 - Covalent Bonding

hydrides

compounds with hydrogen

general rule for boiling point

it increases as we move down the rows of periodic table

what happens if boiling point increases

greater IMF strength

what happens if we move down the periodic table

more principal energy levels thus greater atomic radii

• molecules with greater surface area have greater London forces

What is required for Hydrogen Bonding to occur

molecules contains extreme polar bonds between Hydrogen and nitrogen or oxygen or fluorine

• there needs to be a covalent bonds in the molecule H-F, H-N, or H-O

• once of the molecules bonding needs an H-NOF bond so there can be Hydrogen bonding between CO molecule and H-N molecule

hydrogen bonding

a third IMF which is much stronger than London and Dipole-Dipole forces

• it is an attraction or force not a type of bond

  • can occur within a molecule or between

• Has to be between H-NOF bonds

• it can bond with another molecule, not with H-NOF bond, but has to attract with NOF lone pair from other molecule (non H-NOF)

How are hydrogen bonding drawn

as a dotted line between molecules, never inside the molecule

the hydrogen bonding is always from hydrogen to a lone pair of N/O/F of other molecule

water as hydrogen bonding

water can from max of 4 hydrogen bonds

• they form some hydrogen bonds but not all four, when heating up water the hydrogen bonds break and stay as clumps of water molecules —> why ice floats in liquid water

ice hydrogen bonding

ice has an arrangement with 4 hydrogen bondings forming a tetrahedral structure

• this is why ice is less dense than water as in every ice every water molecule is spread out from neighbouring molecules with the distance of a full hydrogen bond

vapor pressure

increasing volatility increases the vapor pressure

also increases with the temperature

Polarity and IMF strength

polarity influences IMF strength

• only if the size is controlled, more polar means more IMF

• if molecules are small

dipole-dipole forces

between two poles, when we have polar molecules one end is a little more polar while the other is less

electrostatic attraction between opposing charges end of polar molecules

London dispersion

electrostatic attraction between instantaneous dipoles - always present

water solubility

the ability to dissolve in water

• size and polarity influence if it is soluble

  • non-polar molecules are not soluble

  • C6H13NH2 is polar except the size is too big, thus only a small part of the molecule can form hydrogen bonds - thus a -not soluble, big part of its IMF are non-polar London Forces.

  • anything past 4 carbon is unable to mix with water for organic compounds

  • long carbon chains causes less water solubility

• it has to form attractions with water, from hydrogen bonds with water

  • eg, CH3CHO does not have hydrogen bonds but can form hydrogen bonds with water as water has lone pairs

  • this is most relevant for O and N

IMF vs Intramolecula rbonds

covalent, Ionic, and Metallic bonds are stronger than London, Dipole-Dipole Forces, and Hydrogen bonding

hydrogen accepting and donating

this term refers to two molecules of hydrogen bonding, one with and one without H-NOF bonds

ion-dipole reaction

when a molecule is polar it is attracted to the dipole of water creating an ion-dipole reaction

less polar solvents

some solvents are polar but not enough to dissolve in water, they are polar in other solutes such as benzene, ether

other forms of graphite

• Graphene and

  • a single layer of graphite

• C60 Buckmister Fullerene "or Bucky Ball

Graphene

each carbon atom is covalently bonded to 3 other carbon atoms, angle between carbon atoms is trigonal planer 120

electrons delocalised across layers

• thus conductivity very high,

• highest known thermal conductivity,

• very strong and flexible with a high melting point

can be used for voltaic cells and computers, which is very useful

The Bucky Ball

another form of Carbon, found in outer space or hit with lasers in the lab

carbon atoms are bonded together in series of pentagons and hexagons, carbon atoms are always bonded to three other atoms, 6 or 5 rings

• a distorted trigonal planar,

• electrons delocalized around the ball )individual molecule) but electrons can not pass between another molecule next to it

• poor thermal and electrical conductivity

• it is light and strong - non-polar, thus soluble in non-polar solvents

• low melting point - sublimes

• also works as a lubricant as the layers can”roll”past each other

• can act as a cage for smaller atoms

SIlicon

structure is identical to carbon or diamond, except that the atoms are bigger. giant covalent structure

has 4 silicon atoms bonded

• very hard with high melting point, as it has a strong covalent bond in al directions

• it is a semi-conductor s it is a metalloid,

• important to computer and solar energy industry

Silicon Dioxide

a Giant Molecular structure, all covalent bonds

tetrahedral shape every si atom has 4 oxygen atoms and every oxygen atom is bonded to 2 si atoms

the ratio for silicon to oxygen is 1Si: 2O

• extremely hard with high melting points

• can be used in electronics, like watches, unique electrical conductivity properties

• insoluble in water

Graphite

each carbon atoms are covalently bonded to 3 other carbon atoms - it is found in layers, one carbon atom has 1 double bond and 2 single bonds meaning multiple positions = resonance more like 1,5 bonds with delocalised electrons all in the rings and in between each layer

they have London forces in between the layers

trigonal planer

• poor thermal conductivity, because of the space between layers

• high electrical conductivity because of delocalized electrons

• very soft and brittle, acts as a lubricant

• it works on paper, because layers slide past each other, due to weak London forces between layers

diamond

each carbon atom is covalently bonded to 4 other carbon atoms

tetrahedral 109.5

localized electrons, no mobile electrons

• no electrical conductivity

• extremely high thermal conductivity

• very strong because no IMF’s, high melting point with strong bonds

polar and non-polar covalent bonding

non-polar have a small electronegativity between two bonding elements, thus electron pairs are shared more or less evenly

large electronegativity has polar pairs, where electron pairs are shared unevenly between two atoms

metallic bond

electrostatic attraction between a lattice of positive metal cations and delocalized valence electrons moving between them

used for metals and alloys

covalent bond

electrostatic attraction between 2 positive nuclei and the shared electron pairs between them

used for nonmetal elements, all molecules, all organic compounds, giant covalent

covalent bond strength measured via bond enthalpies, the energy required to break 1 mole of a bond in gas phase

ionic bond

electrostatic attraction between oppositely charged ions

used for ionic compounds, salts and minerals

what is the octet rule

the atoms like to have eight electrons only in their full outer shells.

exceptions for the octet rule

beryllium and boron have 2 and 3 valence electrons and, thus, are unable to form molecules with 2 and 3 covalent bonds, leaving them with incomplete octets.

for them to form a complete octet, other species have to donate electron pairs through coordinate covalent bonding

_{coordinate covalent bonding}

a bond between two atoms in which the electron pairs is donated from one atom, H+ and O donates two electrons to form a bond

it can be spotted if one element usually forms 2 bonds but forms three, thus they donated an electron

if it makes more than normal pairs, it is donating electrons, coordinate covalent bond

VSEPR theory

in the valence shell, electron pairs will repel each other as far as possible, due to electron repulsion

electron domain geometries

on electron domain:

• single bond

• double bond

• triple bond

• nonbonding electron pair

if there are non-bonding electron pairs, they repel more than bonding pair of electrons since they do not have an atom pulling it on either side.

bond angles and shapes SL

2 domains:

• linear 180

3 domains:

• no lone pairs, trigonal planar 120

• 1 lone pair; bent 117, remove three for each lone pair

4 domains:

• no lone pairs, tetrahedral 109.5

• 1 lone pair, trigonal pyramidal 106.5

• 2 lone pairs, bent 103.5

how to find the polarity of the molecule

1. are the bonds non-polar, the EN difference less than 0.4

2. what is the molecular geometry, drawn in 3D

3. are the bonds arranged so that they oppose each other? Do they look like they cancel out, or arranges asymmetrically - thus what is the net dipole

rule for polarity in organic molecules

C-H = non-polar

C-N/C=N = slightly polar

C-O/C=O, C-Cl, C-F = polar

N-H = very polar

O-H = very polar

Organic molecules

My - 1 carbon

Elephant - 2 carbon

Poops - 3 carbon

Bananas - 4 carbon

Pentane - 5 carbon

Hexane - 6 carbon

Alkane - C_nH_2n+2

Alkene - C_nH_2n

Alkynes - C_nH_2n-2

Alcohol - C_nH_2n+1OH

In organic molecules, if the chain is long the molecule is not polar

what are the 7 steps for complex lewis structures

1. how many valence electrons do we have to work with, O2 would be 12

2. to satisfy the octet rule each need 8, so how many electrons do we need in total

3. subtract what we need by what we have to see how many electrons are shared

4. divide this number for shared electrons by two to see how many bonds we have in total

5. draw bonds

6. draw lone pairs to give octets

7. check if all available electrons are used

if the number of bonds does not make sense, then an extended octet

polytomic ions

they are held together by covalent bonds, the whole ion makes ionic bonds with other molecules

NH^₄+ = ammonium

NO^₃- = Nitrate

OH^- = Hydroxide

HCO^₃- = hydrogen carbonate

SO₄ ^2- = Sulfate

CO_{3 ^2-} = Carbonate

PO₄^3- = Phospate

resonance

resonance occurs when there is more than one possible location for a pi bond, shows that a double bond can be in multiple places

pi bonds are able to delocalise over multiple bonds when there are multiple parallel p-orbitals in a row. this creates a more stable, resonance hybrid structure where the charge is distributed evenly over the structure, decreasing electron repulsion forces

this creates 1.5 bonds

bond order

a way of describing the actual, net number. of bonds between to atoms. this includes the partial bonds that exist as a result of electron delocalisation - how strong the bond is

single bond = bond order 1

double bond = bond order 2

Bond Order for molecule =

(# of bonds between resonance atoms) / (# of resonance bond locations)

sigma and pi bond

they form when two atomic orbitals overlap head -n. This results in symmetry around the bond axis and electron density between the two bonding nuclei, where electrons spend most time

pi bonds = always p orbitals, form from the sideways overlap of parallel p orbitals and results in electron density above and below the bond axis for each pi bond. , double or triple bonds

sigma bonds = all covalent bonds are sigma bonds, they are the first bond seen, the additional bonds in double bonds are pi bonds

• the head on combination of atomic orbitals where the electron density is concentrated along the bond axis

hybridization

Hybridisation refers to combining of atomic orbitals within an atom to form a new set of hybrid orbitals.

the hybridization of 1 s and 1 p orbital creates 2 equal sp orbitals, which helps to explain linear geometries

the hybridization between 1 s and 2 p orbitals creates 3 equal sp2 orbitals which helps to explain trigonal pyramidal electron domain geometries

number of e domains says the type of hybridization

tetrahedral = 4 orbitals 1s +3p = sp³

trigonal planar = 3 orbitals 1s +2p = sp²

linear = 2 orbitals 1s +1p = sp

melting points

the temperature at which a substance changes from solid to liquid, in order to melt the electrostatic attractions between a substance’s particles must be overcome enough that particles can move past each other

boiling point

the temp at which substance changes from liquid to gas below the surface of a liquid

increasing p = increasing bp

in order for a substance to boil, the attractions between particles must be completley overcome in order to separate into gas phase

volatility

how readily a substance evaporates, changes from liquid to gas at the surface of liquid

in order for particles to evaporate, the attractions between them and the particles beneath them must be completley overcome in order to separate into gas phase

stronger attractions between particles low volatility

vapor pressure

the gas pressure created by a substance’s evaporation at a given temperature, increasing volatility increasing vapor pressure

increasing temp increasing vapor pressure

effect of polarity on physical properties

methods to separate mixtures - 7

evaporating and condensing = separates soluble solids from liquids

magnetism = separates iron and steel from non-magnetic materials

filtering = separates insoluble solids from liquids

sieving = separates different-sized solids

decanting = separating two liquids which have different weights

Solvation - substances with different solubility a non polar substance in water does not dissolve then a non polar solvent above water allows the substance to dissolve in the solvent and then separate two substances

recrystallization - impure solids, separating a mixture of 2 solids, add high temp solvent dissolving both solids, as it cools one solids starts to form crystals - then filter to separate

distillation - evaporating two or more liquids, most volatile liquid evaporates most here it passes through a condenser, where it condenses and can recollect have to do multiple rounds

chromatography

a technique that takes many forms and involves separating components of mixtures mainly for identification purposes

separate components based on different polarities

all involve a stationary phase, where the substance/structure does not move

the mobile phase where the substance/mixture moves along the stationary phase

to find the retention factors: (distance from spot)/ (distance of the solvent front)

ion-dipole interactions

an attractive force that results from the electrostatic attraction between an ion and a neutral molecule that has a dipole.

these forces explain the water solubility of ionic compounds

expanded octets

elements on the 1 and 2 can never have an expanded octet but 3rd and above can, the central atoms has one.

electron energy levels converge at higher energies, beginning in the third energy level the d-orbitals are there. Thus elements from the 3p-block can use empty 3d-blocks to have more than 8 electrons

identify:

• notice a central atoms bonded to more than its normal number of atoms

• try to follow the 7 steps

expanded octet geometries and bond angles

5 bond pairs:

• 5 bond pairs, 0 lone pairs = trigonal bipyramidal 90 and 120 and 180

• 4 bond pairs, 1 lone pairs = seesaw, 117, 97, 183

• 3 bond pairs, 2 lone pairs = T-shaped 183, 87

• 2 bond pais, 3 lone pairs = linear 180

6 bond pairs:

• 6 bond pairs, 0 lone pairs = octahedral 90

• 5 bond pairs 1 lone pair = square pyramidal 87, 183

• 4 bond pairs, 2 lone pairs = square-planar 90, 180

formal charges

it calculates whether an atom within a molecule or ion carries no charge, positive or negative charge

to determine:

1. write the lewis structures

2. count the number of electrons the atom owns

3. if it is resonance structure choose the one with least formal charge and then consider electronegativity thus which atom would attract electrons

intramolecular bonding

covalent, ionic, or metallic

van der waals forces

london and dipole-dipole forces

what influences the amount of force

size or surface area and polarity of molecules

how do bonds effect te wavelengths absorbed

ozone and oxygen in atmosphere absorbs ultraviolet light

oxygen had a bond order of 2 and ozone 1.5 thus O2 stronger and has mroe enrgy which absorbs smaller wavelengths

Benzene

ring of six carbon atoms, each with a hydrogen atom attached and alternating carbon double bonds