Bonding

What are the three types of Bonding?

Ionic, Covalent, Metallic

What are the two types of structures that these bonds can form?

Giant structures and simple molecules

What is Ionic Bonding?

A transfer of electrons from the less electronegative element to the more electronegative element, forming positive and negative ions

Definition of an ionic bond (SEFABOCI)

The Strong Electrostatic Force of Attraction Between Oppositly Charged Ions

Describe how the ions in an ionic compound are held together

They are held together by non-directional electrostatic forces that are constantly repeatting patterns in a giant lattice structure in which the electron density falls to zero

What are the typical physical properties of Ionic Compounds

High Melting/Boiling points
Cannot conduct electricity when solid
Can conduct when Molten or in Solution
Can dissolve in Polar Solvents

Formula for Sulfate ions

SO₄^2-

formula for Nitrate ions

NO₃^1-

Formula for phosphate ions

PO₄^3-

Formula for Carbonate ions

CO₃^2-

Formula for Hydrogen Carbonate ions

HCO₃^1-

Formula for Hydroxide ions

OH^-

Formula for ammonium ions

NH₃¹⁺

How is the periodic table arranged?

In order of increasing Atomic Number, in periods showing repeating trends in physical and chemical properties

What is the general trend in Ionisation energy across a period?

Ionisation energy increases across a period

What happens to ionisation energy between group 2 and group 13?

It decreases because the group 13 e- goes into a 2p orbital which is slightly higher energy than the 2s orbital

What happens to ionisation energy as period number and group number increase?

Ionisation energy decreases for elements in each Group as Period number increases (higher energy orbital)

What happens to Atomic radius across a period. 

It decreases across a period:
Increase in number of protons
Similar Shielding
Increase in Effective Nuclear Charge + Nuclear attraction

What is Electronegativity

The ability of an atom to attract the shared pair of e- in a covalent bond to itself

What is a dative covalent bond?

A shared pair of electrons in which both electrons are donated by one atom

What is the Octet rule

Each atom shares electrons with neighbouring atoms to achieve a total of 8 valence electrons

Some molecules can expand the octet rule give an example of this

Sulphur

What is Bond Order?

the bond order is the number of bonds between 2 atoms, It is used to predict the properties of a molecule.

What are the properties of simple covalent molecules

Low boiling point
non conductors/insulators
insoluble in water

Properties of Giant Covalent structures

Extremely high melting points
Hard
Chemically unreactive

How does electronegativty change across the periodic table?

Electronegtaivity increases across the period and up the group

What is a Polar molecule?

A molecule that has a charge on one side of the molecule that is not cancelled out

Polarisation in Covalent compounds:

"

As

bond polarisation increases the electron cloud is progressively distorted and

attracted towards the atom at the negative end of the molecule.

 The

electron density between the atoms decreases and the bond has some ionic

character.

 A

very large difference in electronegativity gives rise to ionic bonding. "

Polarisation in Ionic Compounds:

"

In

a purely ionic bond there is no electron density between the ions.

 But

small positively charge cations (e.g., Be2+)

can distort the electron cloud of a neighbouring anion, particularly if it is

large.

 This

concentrates electron density between the ions so the bond now has some

covalent character. "

What are Fajan's rules

"

 A set of empirical rules that describe the

influence of polarizability on the nature of chemical bonding in ionic compound"

When does Covalent character increase in an Ionic Compound?

• Positive Ion is small - high ionisation energy
• Positive ion has multiple charges
• Negative ion is Large - Increase in e- shells
• Negative ion has multiple charges

Which atoms, when in compound, can form an incomplete octet

Be and B 

Why do Compounds form expanded octets?

Elements from the third period onward can accomodate more than eight electrons in their outermost energy levels due to availability of d orbitals. It is energetically favourable to do so as energy is released when a covalent bond is made

What are the rules for shapes

"Electron pairs repel

(negative charges - like charges repel)
Lone pairs (non bonding pair

of electrons) repel more than bonded pairs
Shape is found to minimise

electron pair repulsion (pairs of electrons get as far away from each

other as possible"

What is a dipole moment?

dipole moments are vectors that have magnitude and direction

What do the magnitude and direction of dipole moments depend on?

Number of polarised covalent bonds
Shape of molecule

What are van de Waals Forces?

weak forces acting between all atoms and molecules. These are the only forces that are acting between atoms of Noble Gas elements

What causes London Forces

• Uneven distribution of electron
• which then causes an instantaneous dipole
• which induces a dipole on a neighbouring molecule
• which results in overall cohesive force results

What are factors affecting van der Waals forces

Increasing number of electrons increases the strength of the forces
Molecular shape and increased contact area increases strength of van der waals forces

Attraction in permenant dipole-dipoles

Molecules with permenant dipoles are attracted together more strongly than those with just van der waals forces

What is Hydrogen Bonding?

 A type of attractive dipole-dipole interaction in which a hydrogen atom bridges two elctronegative atoms

What are the conditions for Hydrogen Bonding?

One molecule must have a hydrogen atom attached to a highly electronegative atom, so it is highly positively polarised
the other molecule must have a small highly electronegatice atom, one of N,O,F, and this atom must have a lone pair of electrons

What is the evidence for Hydrogen Bonding?

"Boiling points increase going down the group because of increasing van der Waals forces as the electron number increases

100

50

? —50

-100

-150

-200

H 20

CH4

Group 1 7

Group 16

Group 1 5

SbH

snH4

HCI

SiH

H2Se

ASH *

HBr

GeH4

Period "" src=""paste-c65cd572ce8a5827393d3dc3c027ae3bd18c2245.png"" width=""226"">

"

Solubility of Covalent Molecules in Water:

When a solute disolves in water the permenant dipole-dipole Interactions between water molecules must be broken
new intermolecular forces are made between the solute and water
The energy balance between forces broken and new forces made determines solubility

What does the phrase likes dissolve likes mean?

Substances with similar polarities mix well and those with different polarities do not mix well

How does Hydrogen Bonding affect Biochemistry

Hydrogen bonds hold protein secondary structures in place and contribute to the tertiary structure including the active site shape of enzymes.
Hydrogen bonds also hold complementary bases together

What are the rules for solubility? (5 Marks)

All sodium, potassium and ammonium compounds are soluble
All nitrates are soluble
Most chlorides are soluble except Lead and Silver chlorides
Most sulfates are soluble except lead and barium sulfates
Most oxides,hydroxides and carbonates are insoluble except sodium, potassium and ammonium

What is a precipitation reaction?

When two or more soluble salts react to form an insoluble product

What is a Redox reaction?

When both oxidation and reduction occurs at the same time

What is an Oxidation Number?

The oxidation number can be regarded as the charge that an atom would have if the more electronegative atom in the bond aquired both of  the electrons in the bond

What are the rules for assigning oxidation states?

The sum of the oxidation number of all the atoms in the species is equal to its charge
For atoms in their elemental form it is equal to 0

What is dispropotionation?

When an element has been simultaneously both oxidised and reduced

What are Redox Couples?

Metal/Metal ion systems. (reduced form on the right and oxidised form on the left of the solid aqueous boundary

What is the Standard electrode potential?

A measure of the reducing potential of the metal in a redox couple in volts

What does the negativity of the standard electrode potential mean?

The more negative the standard electrode potential, the stronger the reducing power of the couple

What is the most negative element?

Sodium is the most negative, so has the strongest tendency to lose an electron, which makes it the most reactive of the metals on the list