IB DP1 ChemistryBonding

What makes atoms join together to make compounds?

Topic 4: Bonding (12.5 hours)

4.1 Ionic bonding4.1.1 Describe the ionic bond as the electrostatic attraction between oppositely charged ions.4.1.2 Describe how ions can be formed as a result of electron transfer.4.1.3 Deduce which ions will be formed when elements in groups 1, 2 and 3 lose electrons.4.1.4 Deduce which ions will be formed when elements in groups 5, 6 and 7 gain electrons.4.1.5 State that transition elements can form more than one ion.4.1.6 Predict whether a compound of two elements would be ionic from the position of the elements in the periodic table or from their electronegativity values.4.1.7 State the formula of common polyatomic ions formed by non- metals in periods 2 and 3.4.1.8 Describe the lattice structure of ionic compounds.4.2 Covalent bonding4.2.1 Describe the covalent bond as the electrostatic attraction between a pair of electrons and positively charged nuclei.4.2.2 Describe how the covalent bond is formed as a result of electron sharing.4.2.3 Deduce the Lewis (electron dot) structures of molecules and ions for up to four electron pairs on each atom.4.2.4 State and explain the relationship between the number of bonds, bond length and bond strength.4.2.5 Predict whether a compound of two elements would be covalent from the position of the elements in the periodic table or

from their electronegativity values.4.2.6 Predict the relative polarity of bonds from electronegativity values4.2.7 Predict the shape and bond angles for species with four, three and two negative charge centres on the central atom using the valence shell electron pair repulsion theory (VSEPR).4.2.8 Predict whether or not a molecule is polar from its molecular shape and bond polarities.4.2.9 Describe and compare the structure and bonding in the three allotropes of carbon (diamond, graphite and C60 fullerene).4.2.10 Describe the structure of and bonding in silicon and silicon dioxide.4.3 Intermolecular forces4.3.1 Describe the types of intermolecular forces (attractions between molecules that have temporary dipoles, permanent dipoles or hydrogen bonding) and explain how theyarise from the structural features of molecules.4.3.2 Describe and explain how intermolecular forces affect the boiling points of substances.4.4 Metallic bonding4.4.1 Describe the metallic bond as the electrostatic attraction between a lattice of positive ions and delocalized electrons.4.4.2 Explain the electrical conductivity and malleability of metals.4.5 Physical properties4.5.1 Compare and explain the properties of substances resulting from different types of bonding.

Ionic Bonding

Crystals: 7 ‘perfect’ crystal shapes

Halite- rock salt- sodium chloride

Sodium chloride is an ionic compound with ions arranged in a lattice

Ionscharged particles with electrostatic attraction between them

Na+ Cl-

Sodium and chloride ions formed when electrons transfer

Na + Cl Na+ + Cl-

2,8,1   2,8,7   2,8   2,8,8

Ions Group 1: H+, Li+, Na+, K+, Rb+, Cs+, Fr+

Group 2: Be2+, Mg2+, Ca2+, Sr2+, Ba2+

Group 3?/13: B3+, Al3+, Ga3+

Group 6?/16: O2-, S2-, Group 7?/17: F-, Cl-, Br-, I-

Which is the smallest ion?

Na+

Al+3

Cl-P3-

Two or more electrons can be transferred

Different sized atoms give different mineral structures as they pack in a different way

Hexagonal Beryl crystal; Image Wikipedia

What is the formula of iron (III) oxide?

Fe2OFeOFe3O2Fe2O3

Polyatomic ions: charge distributed over more than one atom

For example phosphate, PO4-

3

can be found in products of reactions of phosphoric acid

Some common polyatomic ions Nitrate NO3

-

Hydroxide OH- Sulphate SO4

2-

Carbonate CO32-

Hydrogen carbonate HCO3-

(Bicarbonate)

Phosphate PO43-

Ammonium NH4+

Common Anions Common Name Formula Alternative

name Simple Anions Chloride Cl− Fluoride F− Bromide Br− Oxide O2− Polyatomic anions Carbonate CO3

2- Hydrogen carbonate

HCO3− bicarbonate

Hydroxide OH− Nitrate NO3

2- Phosphate PO4

3- Sulfate SO4

2- Anions from Organic Acids Ethanoate CH3COO− acetate Methanoate HCOO− formate Ethandioate C2O4

−2 oxalate Cyanide CN-

Common Cations Common Name Formula Alternative

name Simple Cations Aluminium Al3+ Calcium Ca2+ Copper(II) Cu2+ cupric Hydrogen H+ Iron(II) Fe2+ ferrous Iron(III) Fe3+ ferric Magnesium Mg2+ Mercury(II) Hg2+ mercuric Potassium K+ kalic Silver Ag+ Sodium Na+ natric Polyatomic Cations Ammonium NH4

+ Hydronium H3O+

Careful with... name of atom can change when ion is formed

chlorine atom (Cl) chloride ion (Cl-)

-ate is often a polyatomic ion with oxygen eg sulphate, phosphate, etc.

different ions often have similar names... nitrate NO3

-

nitrite NO2-

nitride N-3

What is the formula of ammonium sulphate? NH4SO4 (NH4)2SO4 NH4(SO4)2 SO4(NH4)2

d-block (transition elements) can have variable valencies

Mn2+ manganese(II)Mn3+ manganese(III)Mn4+ manganese(IV)Ni2+ nickel(II)/nickelousNi3+ nickel(III)/nickelicPb2+ lead(II)/plumbousPb4+ lead(IV)/plumbic

Cr2+ chromium(II)/chromousCr3+ chromium(III)/chromicCu1+ copper(I)/cuprousCu2+ copper(II)/cupricFe2+ iron(II)/ferrousFe3+ iron(III)/ferricHg2+ mercury(I)/mercurous

Covalent bonding

Define electronegativity

Electronegativity is the tendency of an atom to attract electrons towards itself. The atoms with higher values attract electrons more strongly.

Highest flourine (and rest of groups 7,6,5)FONClBrISCHWikipedia table

How ionic is an ionic compound? bigger difference in electronegativity more ionic (‘ionic’ usually De-neg> 1.8 difference) usually metal + non-metal

Which aluminium compounds will be ionic?atom Al F O Cl Brelectronegativity

1.5 4.0 3.5 3.0 2.8

Formula of aluminium compound

De-neg ‘Ionic’ or ‘covalent’?

‘Sharing’ electrons De-neg < 1,7covalent bonding forms molecules

Often between non-metals

Covalent bond formation- valence electrons

2, 4 or 6 electrons? Single bond: the two atoms share two electrons

(1 pair) Double bond: the two atoms share four

electrons (2 pairs) Triple bond: the two atoms share six electrons (3

pairs)

Lewis structures (dot structures) show valence electrons in pairs as dots, crosses or lines

skeletal formula for complex organic molecules

Condensed formulapropanol CH3CH2CH2OH

Coordinate covalent bond (dative bond)

both electrons in the bond from the same atomonce formed, is the same as any other covalent bond

Bond lengths and Bond strengths

As the number of shared electrons increases (single to triple) the bond lengths shortens and the bond energy increase

Bond Bond type Lengths (pm) Energy (kJ/mol)

CC Single 154 347

CC Double 134 614

CC Triple 120 839

Which bond has the highest bond polarity, δ

H-HCl-ClAl-FAl-Br

Non-polar covalent bond

In, H2 the two electrons in the bond are shared equally between the two hydrogen atoms. H-H De-neg =0. The electron distribution is symmetrical.

Polar covalent bond If two different atoms form a covalent bond there

will be a difference in De-neg.

The atom with highest electronegativity will have the electrons closer; they don’t share equally.

Unsymmetrical electron distribution.

Bonds100% Covalent bond Polar covalent bond Ionic bond % ionic character of a bond: 0-90%

(there are no 100% ionic compounds)

Molecular shapes

What shape are molecules? VSEPR theory (Valence shell electron pair

repulsion) pairs of electrons repel and sit as far away as

possible from each other double and triple bonds count as a pair

VSEPR: electron repulsion molecular shape

Structure of molecule given by pairs of electrons arranging around an atom to be as far apart as possible

non-bonded pairs repel more than bonded pairs double and triple bonds count as one

Build molecules from plasticine and straws bond: 3cm length of straw atom: 1cm diameter plasticine ball unbonded pair of electrons 1cm straw length

Number of charge centres

Name of shape Bond angles (s)

Example

2 linear 180 BeCl23 trigonal planar 120 BF3

4 tetrahedral 109.5 CH4

5 trigonal bipyramidal

90, 120, 180

6 octahedral 90, 180

Shapes of simple molecules

http://en.wikipedia.org/wiki/Phosphorus_pentafluoridehttp://en.wikipedia.org/wiki/Sulphur_hexafluoridehttp://en.wikipedia.org/wiki/Boron_triflouride

Methane, Water and Ammonia

greater repulsion between non-bonding pairssmaller bond angles than predicted

Intermolecular forcesWhy do molecules stick together to form liquids and solids?

Intermolecular forces hold molecules together, affecting physical properties

Melting and boiling points Strength Flexibility Viscosity Deflection in electric field Volatility (how easy a compound will convert to gas) Electrical conductivity Solubility

Intermolecular forcesHydrogen bond strongDipole-dipole weakervan der Waal’s forces weakest

Why do molecules attract each other to make liquids and gases?

Intermolecular forces: electrostatic attraction between permanent dipoles (polar molecules) permanent dipole and a temporary dipole

(induced polarity) temporary diploes (induced polarity)A dipole is a overall charge imbalance in a molecule.

Induced dipoles in all molecules (van der Waal’s forces)

Image: http://www.uwec.edu/boulteje/Boulter103Notes/11December.htm

Movements in electron cloud Temporary dipoles.

Temporary dipole in one molecule can induce a temporary dipole in another.

van der Waals forces The strength increases with molar mass of the

molecule. He b.p 4KXe b.p. 165K.

Only effective over short range so the molecule “area” is also important.

Pentane, C5H12, b.p. 309K

Dimethylpropane, (CH3)4C b.p. 283K

Trends in physical properties

melting point /C boiling point /CFlourine -220 -188Chlorine -102 -34Bromine -7 59Iodine 114 184Astatine 302 337

Plot one graph showing melting point and boiling point (in Kelvin) against molar mass for the halogensDescribe the pattern (2 sentences)Explain the pattern (2 sentences)

Data: http://en.wikipedia.org/wiki/Halogen

Is a molecule polar?A polar molecule has polar covalent bonds.

Is there a difference in electronegativity? (FONClBrISCH)

AND has an asymmetric shape according to charge

distribution.

Otherwise it is a non-polar molecule.

Molecular polarity

Images: http://en.wikipedia.org/wiki/Molecular_polarity

HF

H2O

NH3

http://phet.colorado.edu/en/simulation/molecule-polarity

Molecular polarity http://phet.colorado.edu

/en/simulation/molecule-polarity

Dipole-dipole

Electrostatic attraction between molecules with permanent dipoles.Stronger than vdW.Hydrogen chloride M= 36,5 g/mol b.p. 188 KFluorine M= 38 g/mol b.p. 85K

Induced dipole

Image: http://www.uwec.edu/boulteje/Boulter103Notes/11December.htm

Hydrogen bonding H bonded to a highly electronegative element- F,

O or N proton unbonded pair important in water

Image: http://en.wikipedia.org/wiki/Induced_dipole#Debye_.28induced_dipole.29_force

ExamplesH2O b.p. 373K H2S b.p 212K

NH3 b.p. 240K PH3 b.p 185K

C3H8 bp20 oC

CH3CHO bp42 oC

C2H5OH bp78 oC

Ice

Image: http://en.wikipedia.org/wiki/Ice

Polar and non-polar liquids are immiscible

Image: http://en.wikipedia.org/wiki/Petroleum

Allotropes

Allotropes: different structural forms of the same element

http://catalog.flatworldknowledge.com/bookhub/4309?e=averill_1.0-ch18_s04

OxygenO2 diatomic oxygenO3 ozone

Allotropes of Carbon

C allotropes: Diamond Hard, colourless, insulator Tetrahedral, giant structure Covalent bonds sp3

orbitals.

Image: http://en.wikipedia.org/wiki/Diamond

C allotropes: Graphite Slippery, black conductor Layers of fused six-

membered rings Each carbon surrounded by 3

others in a trigonal planar arrangement sp2 + p-orbital

p-orbital perpendicular to layers and gives close-packed p-orbitals

Delocalized electrons electrical conductor

Image: http://en.wikipedia.org/wiki/Diamond

C: Allotropes: Fullerene, C60

Spherical molecule 12 pentagons and 20

hexagons.

Image:http://en.wikipedia.org/wiki/Fullerine

C allotropes: Carbon nanotubes

Image:http://en.wikipedia.org/wiki/Fullerine

Silicon solid at room temperature high melting and boiling points of 1414 and 3265

°C conducts heat well grey color and a metallic luster strong, very brittle crystallizes in a diamond cubic crystal structure

Images: http://en.wikipedia.org/wiki/Silicon

Silicon dioxide SO2 Silica giant structure

similar to diamond silicates, SiO4,

tetrahedral, silicon-oxygen single bond

Image: http://www.green-planet-solar-energy.com/silicon-element-facts.html

Metals

Metallic bond Metals have low

electronegativity. Atoms packed into a lattice. Calence electrons

delocalised valence electrons have no

“home” atoms positive ions in a sea

of electrons that keep them together.

Image: http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_gateway/periodic_table/metalsrev2.shtml

Metallic properties Electrical conductivity: electrons float around. Put

one in, one is pushed out.

Malleability and Ductility: if the atom moves, the electron follows. Bond is between ion and electrons, not between ions.

Patterns in bonding and properties

How strong are the forces between molecules?

Bond type Dissociation energy (kJ/mol)

Covalent 1600Hydrogen bonds 50–70Permanent dipoles 2–8Induced dipoles <4

Data: http://en.wikipedia.org/wiki/Induced_dipole#Debye_.28induced_dipole.29_force

Ionic salts Hard, brittle, Conduct electricity in solution or melted. High melting points and boilign points Ions hydrated in aqueous solution

Covalent compounds low mp and bp poor conductors of electricty and heat

Summary of properties Structure typeProperty

GiantMetallic

GiantIonic

GiantCovalent

MolecularCovalent

Hardness and malleability

Variable hard-ness, malleable rather than brittle

Hard and brittle Hard and brittle Usually soft and malleable unless hydrogen bonded

Melting and boiling points

Variable dep. On No of valence e-

High Very High Low

Electrical and thermal conductivity

Good in all states

Not as solids, conduct in (aq) or (l)

No No

Solubility 

Insoluble, except as alloys

In Water mostly Insoluble Often more soluble in other than water except if H-bonded

Examples Iron, copper NaCl, Na2SO4 Diamond,SiO2 (Sand)

CO2, Cl2, ethanol, sugar

Investigation

Investigate a physical property of a mixture related to intermolecular forces

Quantitative independent variable (cause)

Quantitative dependent variable (effect) viscosity, deflection by charged object, or other physical property

Links Ionic bonding

http://www.teachersdomain.org/asset/lsps07_int_ionicbonding/

Covalent bonding http://www.teachersdomain.org/asset/lsps07_int_covalentbond/

Polarity links

http://phet.colorado.edu/en/simulation/molecule-polarity

Viscosity http://www.youtube.com/watch?v=3KU_skfdZVQ

States of matter http://phet.colorado.edu/en/simulation/states-of-matter

Polarity links http://phet.colorado.edu/en/simulation/molecule-polarity http

://antoine.frostburg.edu/chem/senese/101/liquids/faq/h-bonding-vs-london-forces.shtml

States of matter http://phet.colorado.edu/en/simulation/states-of-matter http://employees.oneonta.edu/viningwj/modules/

CI_dipoleinduced_dipole_forces_13_5a.html Notes: http://www.uwec.edu/boulteje/Boulter103Notes/11December.htm Snowflakes: http://www.its.caltech.edu/~atomic/snowcrystals/class/

class.htm Ice crystals http://www.edinformatics.com/interactive_molecules/

ice.htm

Links http://phet.colorado.edu/en/simulation/molecule-

shapes http://en.wikipedia.org/wiki/

Phosphorus_pentafluoride http://en.wikipedia.org/wiki/Sulphur_hexafluoride http://en.wikipedia.org/wiki/Boron_triflouride

Teaching notes