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89 Cards in this Set

  • Front
  • Back

What are covalent bonds?

Arise from the sharing of electrons between two atoms

What are coordinate bonds?

Where bothe electrons come from one atom

How do electrons reach the configuration of the nearest noble gas?

Through bonding - filling all the available orbitals in the outer shell

What is the octet rule?

When the atom is in the main group, this means that it has eight electrons around it (1xs + 3xp orbitals)

What is the 18-electron rule?

When the atom is a transition metal, it has 18 electrons around it (1xs + 3xp +5xd orbitals)

What is meant by paramagnetic?

Where molecules with unpaired electrons are attracted to the poles of a magnet

What is meant by diamagnet?

Molecules with no unpaired electrons are repelled from the poles of a magnet

What is the issue with the Lewis theory?

Not a complete story


Evident by the presence of unpaired electrons in bonded molecules

What is the first step general strategy for Lewis structure?

Calculated the total number of electrons for the molecule by adding up the valence electrons

What is the second step general strategy for Lewis structure?

Draw out the skeletal structure

What is the third step general strategy for Lewis structure?

Distribute electrons to atoms surrounding

What is the fourth step general strategy for Lewis structure?

Place remaining electrons on central atom

What is the five step general strategy for Lewis structure?

If there are less than 8 on the central atom, redistribute one or more from external atoms to form new bonds

What is resonance?

The property of having a molecular structure which cannot adequately be represented by a single structural formula but is a composite of two or more structures of higher energy

What is the first exception to the octet rule?

If the total number of valence electrons is odd then one atom cannot satisfy the octet rule (e.g. NO)

What is the second exception to the octet rule?

In electron deficient molecules, the central atom can have fewer than 8 electrons

What is the third exception to the octet rule?

Elements in the 3rd period can have more than 8 electrons - expanding their octet

What is the formula for formal charge?

Formal charge = V - L - 1/2B


V= number of valence electrons is a free atom


L= the number of lone pair electrons


B= the number of electrons in bonds

How to choose the right Lewis Structure?

If more than one structure is possible, choose the one with the lowest formal charges

What is the Valence Shell Electron Pair Repulsion Theory?

VSEPR


Based on the idea that pairs of electron will repel each other


The optimal geometry about the central atom depends on the number of electron pairs surrounding it

How can we calculate the number of bonding electrons around a central atom?

By looking at the lewis structure of the molecule

What is the method to count electrons for VSEPR predictions?

Identify central atom + peripheral atoms


Count no. of valence electrons of central atom


Count no. of electrons donated to central atom by ligands


Determine total no. of electron pairs around central atom


This gives VSEPR predicted geometry for electron distribution


Distinguish lps + bbs


Distribute the lp + bp to obtain a molecular geometry

What is the shape with 4 pairs - all bonding?

Tetrahedral

What is the shape for four pairs - 3 bp?

Trigonal pyramidal

What is the shape for four pairs = 2 bp?

bent

What is the order of repulsion strength?

lp-lp > lp-bp > bp-bp

What causes subtle changes to bond angles?

lps occupy more space than bps


Double/triple bond occupy more space than a single bond

What's the shape for 5 bonds?

trigonal bipyramindal

What's the shape of 5 pairs - 4 bps?

seesaw

What are all transitions accompanied by?

A change in energy (enthalpy)

What is enthalpy related to in reactions?

Changes in bonding

What is homolytic bond cleavage (fission)?

When a bond breaks, bond electrons are shared equally between bonding atoms

What is heterolytic bond cleavage (fission)?

When a bond breaks, bond electrons are not shared equally between bonding atoms, resulting in ion formation

What are bond energies?

Average enthalpy for breaking a bond in the gas phase

What causes bond energies to increase?

Increase in no. of bonds (double > single)


Increases across a period



What causes bond energies to decrease?

Decrease down a column

What can bond energies be used for?

Estimating enthalpies of a reaction

What do ionic compounds contain?

Cations (pos) + Anions (neg)

What are some simple ionic compounds?

Na+ + Cl- -> NaCl


Mg^2+ + 2Cl- -> MgCl2


2Al^3+ + 3O^2- -> Al2O3

What are some complex ionic compounds?

Ca^2+ + CO3^2- -> CaCO3


Ho^3+ + PO4^3- -> HoPO4

What is meant by isoelectronic?

Having the same number of electrons or same electron structure

Name two ions that are isoelectronic with Li+

Be^2+


B^3+

What is ionisation energy?

The energy required to remove one electron from an atom

Where on the periodic table has the highest affinity for electrons?

The right-hand side

What is Delta-Hf?

Enthalpy of formation


Energy required to form a compound from its constituent elements in their natural state (under stable conditions)

What is lattice energy?

Change in energy when an ionic solid is changed into isolated ions in the gas phase


This is very difficult to directly measure

What is Coulomb's law?

Ions are held together by electrostatic forces

What can be used to determine lattice energies?

Born-Haber cycle

Using the Born-Haber cycle for NaCl, determine the lattice energy

1. Enthalpy of atomization of Na = +108 kJ mol^-1


2. 1/2 bond dissociation enthalpy of Cl2 +240/2 = +120kJmol-1


3. Ionisation enthalpy of Na = +496 kJ mol-1


4. Electron affinity of Cl = -349kJmol-1


5.Minus lattice energy of NaCl

When do electrostatic interactions increase?

If Q+ or Q- increases


If radius of cation or anion gets smaller


This means lattice energies are largest for small, highly charges ions

What happens with energy in a covalent bond?

On formation, Delta-H is positive, energy is required


In dissociation, Delta-H is negative, energy os released

What holds ionic compounds together?

Electrostatic interactions

What is lattice energy related to?

Charge on the ions + their radii

How is lattice energy measured?

Using Born-Haber cycles

Where is ion size the largest on the periodic table?

Left on the period


Down the column

What is the solubility of a salt dependent on?

Lattice energy


Energy of hydration

How are ions attracted to water molecules?

Via an ion-dipole force

What do ionic solids experience?

Strong attractive forcesAlso strong attractions between ions + water molecules

When does hydration energy increase?

When Q increases


Radius decreases

Why is solubility often difficult to predict?

Factors that give large lattice energies also give large hydration energies

What substances are soluble?

Compounds of group 1are soluble


Compounds of group 2 are less soluble


Compounds of group 17(e.g. Cl-) are soluble


Nitrates (NO3-) + most sulfates (e.g. SO4^3-) are soluble





What substances are insoluble?

Most sulfides (S^2-)


Most Carbonates (CO3^2-)


Most Hydroxides (OH-)


Oxides (O^2-)

What general rules govern solubility?

Salts where ions are similar of size are less soluble than those where ions have different sizes

Why does this rule govern solubility?

Lattice energy remains unchanged by hydration energy increases so, solubility increases

What are oxidation states?

A way of keeping track of the valence electrons in a compound


Essential in balancing oxidation-reduction

What is the oxidation state of an atom in its elemental form?

Zero

What is the oxidation sate of a monoatomic ion? (e.g. Na+)

The same value as the charge


(+1 for Na+)

What are the rules for assigning oxidation states?

1. F is always -1 (except F2, which is 0)


2. Oxidation state of other halogens is always -1, unless bonded to a halide above it


3. O is -2, unless bound to F or itself


4. H is +1, but -1 when bound to metals


5. Os of Group 1 is +1 in most cases


Os of Group 2 is +2 in most cases

What is nomenclature?

Choosing names for things

What are the alternate nomenclautres of Cr^6+

Cr^VI+


Cr^+VI


Cr^VI


Cr(VI)

Why do oxidation states need to be determined?

Some elements have multiple possible oxidation states

What are the rules for assigning oxidation states based on?

The principle that electrons in bonds between 2 atoms should be assigned to the more electronegative atom, so that both achieve closed shell electron configurations

What happens to electrons in partners that are equally electronegative?

Electrons are shared equally

What if the number of bonded electrons is more than the valence electrons?

Negative oxidation number

What if the number of bonded electrons is less than the valence electrons?

Positive oxidation number

What are reduction reactions?

The transfer of electrons from another species to the reduced species

What are oxidation reactions?

The transfer of electrons from the oxidised substance to reduced

What are spectator ions?

A species that remains the same on both side of an equation

Why are spectator ions cancelled out of an equation?

To get a net ionic equation

What happens to the oxidation states in redox reaction?

Os of the reducing agent will increase


Os of the oxidising agent will decrease

What is OIL RIG?

Oxidation is loss of electrons


Reduction is gain of electrons

What are reducing agents?

Donates electrons


Is oxidised itself

What are oxidising agents?

Accepts electrons


is reduced itself

What are the metallic trends in the periodic table?

Left is metallic


Right is not metallic


Metallic nature increases down a column

What is a trend in the first row of the periodic table?

The first row of the periodic table is often very different from the other rows

What are traits of group 1 + 2 of the periodic table?

Low ionisation energies


Low electronegativities


Large radii


All metallic



What gives elements metallic propeties?

Delocalised electrons to form sea because the ionisation energy is low - easy to remove electrons

What is a difference between group 1 + 2 elements?

Group 2 elements are generally harder + less reactive than their group 1 counterpart




This is due to the extra electron in the sea for group 2, so there is more glue sticking the metal atoms together

what is amphoterism?

Ability to react with both acids + bases


Evident in group 1 + 2