Topic 2 Bonding & Structure Flashcards
What angle is linear?
180
No lone pair, furthest repel
What angle is V shape?
104.5
2 lone pairs
What angle is trigonal planar?
120
No lone pairs
What angle is trigonal pyramidal?
107
1 lone pair
What angle is tetrahedral?
109.5
No lone pairs
What angle is trigonal bypyrimidal?
5 bonds formed
90 in 2
120 in 3
What angle is hexagonal?
90 between every 2 bonds
180 between bottom ones
6 bonds in total
What is an ionic bond?
Strong electrostatic attraction between opposite charged ions
What is the ionic attraction affected by?
Ionic radius (smaller=stronger)
Ionic charge (higher=stronger)
Qualities of ionic bonds
High mp
Soluble in water
Poor electron conductivity when solid but good when molten
Brittle (bcs can slide over each other, same charge repel)
How are ionic bond qualities proven?
Electrolysis
What are covalent bonds? (2 marks)
Strong electrostatic attraction (1)
Between 2 nuclei and the share of pair of electrons (1)
What do σ bonds look like?
Overlap of s orbitals
2 O O overlapping
Or 1 s 1 p (O ∞ overlap)
Or ∞ ∞ overlap
What do π bonds look like?
8 8 overlap
2 p orbital overlapping sideways so 2 areas where electrons are shared
What is the definition of electronegativity?
Ability for an atom to attract bonded pair of electrons from covalent bonds
What is a dative covalent bond?
Empty orbital of one atom overlap with an orbital with lone pair
(Donating a lone pair to an empty orbital)
What are examples of dative covalent bonds? Give 2
NH4+ (N donates to H)
Al2Cl6 (Cl donates to Al)
When u see mp/bp what do u think of?
London forces
PDPD
H bonds
Why can’t S form H bonds?
Not electronegative enough, much less electronegative than O
, doesn’t form very polar bonds like F O N
The structural feature that graphene and graphite have in common is that the carbon atoms are arranged in…
Hexagonal rings within a layer
What is the bond angle in BF3?
120
What are the strongest interactions between molecules in solid boric acid? (H3BO3)
Hydrogen bonds
How to find out the succession ionisation energies and their groups?
Biggest jump
Eg from 2 to 3 then it must be a G2 element
How to determine isoelectronic ion size?
For atoms or ions that are isoelectronic, the number of protons determines the size. The greater the nuclear charge, the smaller the radius in a series of isoelectronic ions and atoms
Ionic bonding is the strong electrostatic attraction between….
Cations and anions
(There are NO delocalised e-s in ionic bonds!)
What does HCl exist at room temperature as?
Giant lattice of oppositely charged ions
(Gas)
What are the bond angles within a layer of graphene and a layer of graphite?
All 120
How is a dative covalent bond formed in NH3BF3?
Lone pair donated from N
BF3 accepts the lone pair and forms a full outer shell
What’s the bond angle and name when there is a lone pair and 3 bonds?
107
Trigonal pyramidal
What’s the bond angle and name when there are 4 bonds?
Tetrahedral
109.5
Why is the mp of silicon(IV) dioxide way higher than iodine when both of them are covalent bonded?
Silicon oxide is a giant structure so contains many strong covalent bonds (1)
Iodine only has weak London forces (1)
More energy is needed to break silicon dioxide
Why do both water and carbon dioxide have polar bonds but only water is a polar molecule? 4 marks
Oxygen is more electronegative than both H and C, so arrow points towards O
So polar bonds are formed, O is delta negative, C and H are delta positive
Water has V-shape, so vectors don’t cancel out
CO2 has linear shape, vectors cancel
In terms of bonding and structure, why is the melting point of silicon way higher than chlorine when both are Period 3 elements?
Silicon: giant molecular, strong covalent bonds, lots of energy needed to break
Chlorine: simple molecular, diatomic and has weak London Forces
Graphite vs graphene
Both hexagonal layer with C joined with 3 other C
London forces hold graphene layers together and make graphite
Unbonded Cs have delocalised electrons that are free to move
Describe structure of diamond
Each C joined with 4 other C by covalent bonds
Regular Tetrahedral structure
No free electrons
Giant covalent lattice structure
Why is lots of energy needed to break CaCO3?
Because of strong bonds within the carbonate ion
Why is more energy required to break AlF than AlCl? (In terms of electronegativity) (6 marks)
- larger electronegativity difference between Al and F than Al and Cl
- AlCl mostly simple covalent
- AlF more polar
- AlCl more weaker London forces/intermolecular
- AlF is giant structure, strong electrostatic attraction between ions
- more energy needed to break stronger bonds
What’s the only covalently bonded compound with a metal in it?
AlCl
What’s the order of strength of intermolecular forces?
H bonds > PDPD > London
Why is methanol and water ‘soluble in all proportions’?
Methanol forms H bonds with water
At least 1 lone pair on oxygen atom at 180 degrees
What are 2 elements with special electronic configurations?
Copper and chromium
What is it mean by hydrogen bonds? 2 marks
Hydrogen atom forming evident bond in the same or different molecule
With another atom (F,O or N) that is more electronegative than H
What is a metallic bond? 2 marks
Electrostatic attraction between metal cation and delocalised electrons (outer shell electrons)
Why is magnesium a better electric conductor than sodium?
Mg is a smaller ion and has 1 extra delocalised electron than Na (group 2 vs group 1)
Why is nitrogen much less reactive than carbon monoxide and hydrogen cyanide? (Given they are isoelectronic) (1 mark)
N has triple bonds with diatomic N, much stronger than C=O, C (triple) N, C-H
N2 also non polar, while the other two are polar
Why is sodium chloride soluble in water? 3 marks
- energy to overcome electrostatic attraction between sodium cation and chloride anion
- lattice breaks down and ions are separated
- energy supplied by hydration of ions by water molecules
What structure is sodium chloride?
Lattice ionic structure
What is it meant by a polar bond? How does polarity arise?
- there is a charge separation between molecules of a bond , one is δ+ and one is δ-
- when bond formation and one molecule is more electronegative than the other
- electron cloud produce higher electron density towards electronegative element
What is a Hydrogen bond like?
Very polarised
high charge density
Why does melting point in G2 decrease down?
Ionic radius increases so metallic bond becomes weaker, making it easier for them to slide past each other
Weaker efoa with e-s so easier to break
Why does electronegativity decrease down G7?
the number of electron shells increases down, so larger atomic radius.
Hence weaker attraction for electrons, making it harder to attract them, hence lower electronegativity.
Predict state of astatine in standard conditions and why.
Solid
Because of increasing London forces down G7 (NOT mp/bp!)
Why is ice less dense than water in terms of hydrogen bonds? (2 marks)
- more space between molecules
- due to 3D lattice structure in ice
- H bonds are stronger than covalent bonds
Which element has the highest bp in Period 3? (1 mark)
Si
What does white phosphorus consist of?
small molecules
What cation would be most polarising?
High charge
small radius
Why is the electrical conductivity of pure silicon very low?
Because there are no free delocalised electrons
all of Si’s free electrons are used to form covalent bonds
Explain the high melting temperature of Silicon in terms of bonding. (2 marks)
Lot of strong covalent bonds (1) needed to be broken by lots of energy to overcome (1)
How to work out if an ion has the largest ionic radius in a MCQ?
least num of proton : electron ratio
so least attraction
How to work out if an ion has the smallest ionic radius in a MCQ?
most num of proton : electron ratio
so most attraction
In terms of orbital overlap, a double bond is
a σ and π bond
What is the C-C-C bond angle in a cycloalkane?
109.5°
Which Intermolecular Force is the strongest?
Hydrogen bonds!!!
Deduce 2 possible reasons why there are 2 widely different values for the compressive strength of graphite. (2.3 and 15.3 GPa) (2 marks)
- due to weaker London forces (between layers)
- strong C-C bonds within layers (in the one with higher GPa)
How do you explain sodium sulfide dissolving in water?
Energy released when sodium ions and sulfide ions are hydrated > energy required to break the attraction between sodium ions and sulfide ions
Why does HCl (g) not conduct but HCl (aq) conduct electricity?
Covalent bond in HCl (g) changes to ionic bond in aqueous solution
What is observed when HCl is added to Na2CO3? (2 marks)
Solid dissolves
Effervescence
Explain why Iron(III) ions form pale green solution but zinc ions form colourless solution. (2 marks)
Zinc ions have full orbitals
So no e-s promoted / move between 3D orbitals
State what it is meant by homologous series. (1)
Series of compounds with same functional group AND same general formula
Why does sulfur not follow the increasing ionisation energy trend across Period 3 fro Al? (2 marks)
- it has 2 electrons in the 3p orbital
- they repel each other and lowers IE
