Ionic Bonding and structure

What is ionic bonding

Transfer of electrons from a metal to a non-metal

To from an ion with full outer shell (electron configuration similar to a noble gas)

Describe how cations are formed:

Metals lose electrons on their outer shell, forming positively charged cations

Describe how anions are formed

Non - metals gain electrons in their shell, forming negatively charged anions

What are giant ionic lattices?

Formed by ionic compounds

3D networks of oppositely charged ions held together by strong electrostatic attractions between ions in all directions

Regular repeating pattern of alternating cations and anions

Melting / boiling point of ionic compounds

Solid at room temp

Strong electrostatic forces of attraction between opposites charged ions, so large amount of energy needed to overcome

The strength of the ionic bonding increases with..

Ionic charge

More highly charged ions have stronger attractions

Solubility of ionic compounds

Dissolve in polar solvents (Water)

Depends on balance between ionic bonding and attraction between ions and polar solvent molecules

Greater ionic charge. Less soluble it is

What are two main factors solubility is dependant on for ionic compounds?

Breaking down the ionic lattice

Polar molecules attracting and surrounding the ions

Describe how water react with ionic compound (solubility)

Polar molecules (water) break down ionic lattice

And surround each ion in a solution

δ+ Surrounds negative ion, and the δ- surrounds the positive ion

Electrical conductivity of ionic compounds

Don’t conduct electricity when solid, no free electrons

Can conduct when they are molten / aqueous as the lattice is broken down and ions are free

What is covalent bonding?

Between 2 non-metals, is the electrostatic attraction between the nuclei and shared pair of electrons (outer shell)

What is bond energy?

Energy required to break one mol of covalent bonds in gaseous state

Larger bond energy = stronger covalent bond

Average bond enthalpy:

Average energy needed to break a specific bond type

Describe how stronger covalent bonds are shorter:

Triple bonds are stronger than double bonds ,and single bonds and are shorter

Due to increased electron density pulling bonded atoms closer

Electron deficient

Accommodating less than 8 electrons in outer shell

Lone pairs

Pair of electron not used for covalent bonding

What is the expansion of octet:

Only happens in electron after period 3, as they dont have a d su shell, can make 10 pairs

How is dative covalent bonding done?

Lone pair of electrons are used to make covalent bond with another atom

How to draw a dative bond?

Arrow point away from element providing lone pair

Shapes of molecule: finding 3D shape of molecule, signs and meaning

Normal solid lines = lie on plane of page

Wedge = bond coming out of plane of page

Dotted wedge = bond cprojecting back behind the plane of the page

Electron Pair repulsion theory:

Used to find a shape of a molecule

Determined by electron pairs surrounding the central atom (outer shell)

Based on fact pairs of electrons repel others, so they move far apart to minimise this

Shapes of molecules: linear

Two regions of electrons density around central atom

Repel equally to minimise repulsion

Bond angle - 180

Shares of molecules: Trigonal Planar

Three bonding pairs and no lone pairs

Bond angle - 120

Shapes of molecules; Pyramidal

Three bonding pairs and one lone pair

Lone pair repels bonding pairs more strongly, pushing them closer together

Bond angle - 107

Shape of Molecules: non - linear (bent)

2 bonding pairs and 2 lone pairs

Line pairs enter strong repulsive forces, compressing bond angle

Bond angle - 104.5

Shapes of molecules: Trigonal bipyramidal

Five bonding pairs, no lone pairs

Three lie 120, 2 are 90 degrees to minimise repulsion

Shapes of molecules: octahedral

Six bonding pairs and no lone pairs

Bond angle - 90

Shapes of molecules: Tetrahedral Molecule

Four pairs of bonded electrons and no lone pairs (109.5)

What is electronegativity?

The ability of an atom to attract the pair of electrons in a covalent bind

What happens if chlorine is more electronegative than hydrogen

Electron pair in covalent bond are closer to the chlorine nucleus

Why are the pairs of electrons equally attracted to the hydrogen nuclei in hydrogen?

Because hydrogen has the same electrongeativity

Electronegativity scale

Group 4 is most electronegative, it increases at top right of table

What 3 factors does the electronegativity scale depend on?

Size of positive charge on nucleus = increased positive charge increases attraction between nucleus and pair of electrons

Atomic radius: smaller atomic radius means bonding electrons are closer to nucleus

Shielding of nucleus by electrons on inner shell: greater number of shells, lower electronegativity,

As electrons on inner shell screen outer electrons from positive charge of nucleus

What type of bond is hydrogen chloride?

Polar covalent bond = hydrogen chloride has a dipole moment

How to show if a bond is polar

Use delta positive and negative charge

delta means charge is small, as electron pair has only shifted towards more electronegative atom

Delta

Why is carbon dioxide have no overall polarity

The polar bonds point in opposite direction so dipoles cancel eachother

Arrow point towards more electronegative atom

Why is water a polar molecule?

Bonds act in opposite directions but don’t point in a straight line si they don’t cancel out

What is the Pauling scale?

Assigns a value of electro negativity for each atom Fluorine is the most electronegative atom on periodic table (4)

Why does electronegativity decrease down the group?

Nuclear charge increases, more protons are being added to nucleus

However, each element has extra filled electron shell, so increases shielding

Extra shells increase the distance between the nucleus and outer electron , resulting in larger atomic radius

Decrease in attraction between the nuecleus and outer electrons

Why does electronegativity increase across a period?

The nuclear charge increases with the addition of protons to nucleus

Shielding remains constant as no new shells are added

Nucleus has increasing string attraction for bonding electrons across periodic table

Results in smaller atomic radii

How does a covalent bond become non-polar

When 2 atoms have the same electronegativity

When does the covalent bond become polar?

When two atoms have different electro negativities

Electron is drawn to most electronegative atom

What is the result of a polar bond?

Negative and positive charge centre dont coincide together

Electron distribution is asymmetric

Less electronegative atom = delta positive

More electronegative atom = delta negative

A bond becomes more polar because

There is a greater difference in electrongeatity

What is a dipole moment

Measure of bond polarity

How is a dipole moment shown?

Direction of dipole moment

Arrow points to delta negative end of dipole

Intermolecular forces

Forces within a molecule

Describe London forces

Exists between all atoms

1. Electron charge cloud constantly moves

2. Electron charge cloud is more on one side of atom than the other, causing a temporary dipole

3. This induced a dipole on neighbouring atoms

4. The delta positive charge on one atom is attracted to the delta negative end on the neighbouring atom, so they are attracted to eachother

How would you make London forces (induced dipole dipole) stronger?

Greater number of electrons

Describe a permanent dipole bond?

Polar molecules have permanent dipoles

Molecule will always have positive and and negative charged end

These oppositely charged ends with neighbouring atoms are attracted to eachother

What is stronger, permanent dipoles forces or London forces?

Permanent dipole forces

Relative ti number of electrons

What s hydrogen bonding?

Strongest form of intermolecular forces

Type of permanent dipole dipole bonding

What is needed for hydrogen bonding to take place? And describe

Compound with O, N or F (very electronegative atom) Bonded to a hydrogen, becomes very polarised

H becomes very delta positive charged that it’s forms a lone pair in another molecule

What are the properties of water?

High melting and boiling point caused by strong intermolecular forces of hydrogen bonding between molecules

The molecules are tightly held together by hydrogen bonds

A lot of energy required to break them

Properties of ice

Water molecules are packed in 3D hydrogen bonded network in a rigid lattice

This network and the relatively long bond lengths means that the water molecules are slightly further apart

So has lower density than water

Describe properties of iodine due to its structure:

Molecular lattice of iodine —> neat arrangement of molecules held together by weak intermolecular forces

Non polar molecule, so bonding is due to instantaneous dipole - induced dipole interactions

Principal of solubility

Non - polar dissolved in non- polar solvents

Polar covalent substances dissolve in polar solvents as a result of dipole dipole interactions, formation of hydrogen bonds between solute and solvent

What happens to solubility as covalent molecules become bigger?

Their solubility decreases as polar part of molecules is smaller part of overall structure

Why can’t polar covalent substance dissolve in non - polar solvents?

As their dipole dipole attractions are unable to interact with the solvent

Why can’t giant covalent substances dissolve in solvents?

As the energy needed to overcome the strong covalent bonds in the lattice structures is too great

Why arent covalent substances conductive?

Don’t contain free moving charged particles so they are unable

Under some conditions, polar covalent molecules can ionise and wiki conduct electricity

What is electronic configuration?

The arrangement of electron in an atom

They are arranged around the nucleus in principal energy levels

Name the number of electrons found in each principal quantum energy level:

N = 1 (2 electrons)

N = 2 (8 electrons)

N = 3 (18 electrons)

N = 4 (32 electrons)

N = 5 (50 electrons)

Name the subshells that principal energy levels are split tino:

S

P

D

F (elements with more than 57 electrons)

What are atomic orbitals:

Exists at special energy levels, electron can not be found at these specific levels

Each orbital can be occupied by a maximum of two electrons with opposite spins

Descubre the number of orbitáis in each subshell

S = one orbital = 2 electrons

P = 3 orb = 6 electrons

D = 5 orbitals = 10 electrons

F = 7 orbitals = 14 electrons

Describe the s orbital shape:

Spherical

Size of s orbital increases with increasing shell number

Describe the p orbital shape:

Dumbbell shape

Occupy the x, y and z axed at right angles

Lobes become larger and longer with increasing shell number

Filling orbitals:

Electrons are spinning charges that rotate around their axis in a clockwise or anti-clockwise direction

The spin creates a tiny magnetic field, with N-S pole pointing up or down

What is the spin pair repulsion for electrons?

Electrons with the same spin repel eachother

So electron occupy separate orbitals to minimise repulsion

Then they pair up with another electron that spins in the opposite direction

Why do negatively charged electrons occupy the same region of space in orbitals

Because moving an electron to higher energy empty orbital requires more energy Than is saved by reducing repulsion

So they pair up

What is the ground state?

Most stable electronic configuration of an atom which has the lowest amount of energy

Achieved by filling the lowest energy subshell first

How to use the shorthand version to write electron configuration?

Symbol of the nearest noble gas, followed by the rest of the electron configuration

What elemts fill in the 4s subshell before the 3D subshell

Transition metals

They also lose electrons from 4s first rather than the 3D subshell

What is the aufbau principal:

Rule in chemistry that states electrons fill atomic orbitals in order of increasing energy

Exceptions to the aufbau principle

Cr and Cu

Because the other configuration is energetically favourable

Promoting an electron from 4s to 3D, the atoms reach half full or full d - subshell