Topic 2

Question 1

Intramolecular v Intermolecular bonding

What’s a compound?

Answer 1

Intramolecular – bonding that takes places when atoms join to other atoms (bonding WITHIN a molecule)
[covalent/ionic/metallic]

Intermolecular – bonding BETWEEN molecules – much weaker than covalent/ionic/metallic
[Van der waals forces, permanent dipole-dipole, hydrogen bonding]

Compound - when different elements join/bond together (2 types of bonding in compounds - covalent + ionic)

Question 2

Atoms to atoms bonding types

Ionic bonding?
Cations?
Anions?

Answer 2

• The complete transfer of electrons from one atom to another
• bonding of oppositely charged ions
• Cations = Positive ions = Atoms which have lost electron = metallic
• Anions = Negative ions = Atoms which have gained electron = non-metallic

Question 3

Covalent bonding?

Answer 3

• Electron sharing between non-metallic atoms that are both electron deficient in their outer orbitals
• Only way to achieving full outer shell is by sharing their electrons
• A shared pair of electrons where each atom donates one electron

dot + cross diagrm used

Question 4

Dative covalent bonding / coordinate bonding

Answer 4

• special case of covalent bond where 1 atom donates BOTH electrons that form the shared bond pair
• A shared pair of electrons where one atom donates both electrons

Question 5

Metallic bonding

Answer 5

• bonding in metals, metal atoms lose their outer electron to gain stability+become positive ions (cations)
• +the electrons become delocalised (not fixed in 1 place but are free to move around) + move around this structure of cations, holding it together through electrostatic attraction
• metallic bonding refers to the strong electrostatic forces of attraction between the positively charged metal ions + the “sea” of delocalized electrons that surround them

Question 6

What does electronegativity of an atom mean?

Answer 6

• The electronegativity of an atom is the ability of its nucleus to attract electrons in a bond pair
• EN explans different bondings
• If the EN difference is 0 (the same atoms eg Cl – Cl) there will be a pure covalent bond
• If the EN difference is very large there will be a complete transfer of electrons causing an ionic bond

Question 7

Polar v non-polar covalent bonds

Answer 7

• Polar bond = covalent bond between atoms of different electronegativities = the bonding electrons will be pulled towards the more EN atom =makes bond polar
• In a polar bond, the difference in EN between 2 atoms causes a permanent dipole = difference in charge between 2 atoms caused by a shift in electron density in bond
• Non-polar =covalent bond between 2 atoms of the same element (H2) is non-polar as they have equal electronegativities = e- are equally attracted to both nuclei

Question 8

Intermediate bonds

Polarization of anions

Answer 8

• pure ionic compounds have ions which are perfectly spherical
• If there’s a large difference in charge / density between the cation + anion = the anion (because of its extra electron cloud) becomes distorted by the pull of the cation = polarization of the anion
• Polarization = Distortion of anion’s electron cloud by a nearby cation

Question 9

Fajan’s rules explain effect of ion size + ion charge in this situation

Answer 9

• Either the anion/cation is highly charged (it would make the cations highly polarising + the anion highly polarisable)
• the cation is small (so it will have a high charge density)
• the anion is large (so the e- are far from the nucleus = less under its control)

Question 10

What’s a a polar covalent molecule

Answer 10

• A molecule in which the electrons are shared unequally between 2 atoms due to a difference in their electronegativities
• This unequal sharing creates a dipole moment, where one end of the molecule has a partial positive charge (δ⁺) + the other end has a partial negative charge (δ⁻)

Question 11

Inter-molecular forces [3 types]

1. Permanent dipole

Answer 11

• Dipole attraction = the negative part of one molecule is attracted to the positive part of another, hence there is a bond between the molecules

Question 12

2. Hydrogen bonding?

Answer 12

• occurs when a hydrogen atom [the δ+] covalently bonded to a highly electronegative atom [the δ-] (such as nitrogen, oxygen or fluorine) interacts with another electronegative atom to from H bonds
• The high EN difference results in the N, O or F atom having a much greater “share” of the electrons than the H atom
• The O, N or F atom has lone pair(s), which are attracted strongly to the hydrogen nucleus

Question 13

3. Van der Waals (VdW) Forces
   / Temporary Dipoles

Answer 13

• A group of weak intermolecular forces that occur between molecules, which arise due to temporary / permanent dipoles in molecules
• If you consider an atom to be a central positive nucleus surrounded by e- which are constantly in motion ,there will at any one time be at least one atom whose electrons are on one side or the other
• This causes a temporary dipole within the atom itself

Question 14

Order of strength of the intermolecular forces

Answer 14

H-bonds –> permanent dipole –> temporary dipole (Van der waals)

Question 15

What affects the strength of the Van der Waals (VdW) Forces

Answer 15

1. The strength of the Van der Waals forces increases with the number of e- in the atom / molecule, since the temporary dipoles can be of a larger size if there are more e-
   - –> (noble gases such as helium / neon, which exist as single atoms + have relatively few electrons, the forces are weak = explains their very low boiling point)
2. The strength also depends on the shape of the molecule - long molecules can have induced temporary dipoles all along them
   - –> In general, larger molecules will have larger Van der Waals forces

Question 16

Giant structures

What is diamonds structure?
(C)

Answer 16

• Giant covalent structure
• Each carbon atom is covalently bonded to 4 other carbon atoms
• collectively, these 4 bonds create extremely strong intermolecular forces
• Atoms arrang themselves in a tetrahedral shape

Question 17

Diamond’s physical properties

Answer 17

• very high melting + boiling points
• Insoluble in water + non-aqueous solvents
• Solid at room temperature
• Does not conduct electricity (all outer e- are held in localised bonds)
• Good thermal conductor as vibrations travel easily through stiff lattice
• Crystalline – the hardest known natural material

Question 18

Sodium chloride’s structure
NaCl

Answer 18

• Giant ionic lattice
• ‘giant’ as its made up of the same basic unit repeated over + over again
• The Na+ and Cl- ions are packed together
• lattice is cube shaped

Question 19

Sodium chloride’s physical properties

Answer 19

• Solid at room temperature
• High melting + boiling point
• Soluble in water
• Conducts electricity when molten / in solution
• Crystalline

Question 20

Graphite’s structure
C

Answer 20

• Giant covalent molecule
• Arranged in layers held together by weak Van der Waals forces
• The carbon atoms in the layers are arranged in hexagons (each connected to 3 others, the non-bonded e- from carbon joins with others.)
• These delocalised e- flow along layers but
  not between them

Question 21

Graphite’s physical properties

Answer 21

• Solid at room temperature
• High MPt/BPt
• Insoluble in water + non-aqueous solvents
• Conducts electricity in one direction/plane only
• Feels soft when rubbed (used as a lubricant) because pressure makes the layers move across each other as the weak bonding is broken

Question 22

Iron’s structure
Fe

Answer 22

• Giant structure of cations surrounded by a ‘sea of
  delocalised electrons’
• atoms in iron are held together by metallic bonds

Question 23

Iron’s physical properties

Answer 23

• Solid at room temperature
• High MPt/BPt
• Conducts electricity in all directions
• Insoluble in water and non-polar solvents
• High density

Question 24

Iodine’s structure

Answer 24

• Giant molecular structure
• covalent bonds
• Weak van der Waals forces hold the I2 molecules in a 3-dimensional structure

Question 25

Iodine's physical properties

Answer 25

- Solid at room temperature - Low MPt/BPt (as molecules are attracted to each other only by Van der Waal intermolecular forces, that are weak) - Soft - Does not conduct electricity - Virtually insoluble in water, very soluble in non-polar solvents

Question 26

Carbon dioxide's structure

Answer 26

- Simple molecular structure - strong covalent bonding within molecule, - but only weak van der Waals forces between the molecules - A small light molecule (RMM = 44)

Question 27

Carbon dioxide's physical properties

Answer 27

- Gas at room temperature - Low MPt/BPt

Question 28

# shapes of molecules What are lone pairs? Free radicals? What are bonding pairs?

Answer 28

- **Lone pairs** - 2 electrons that are not shared - on a dot+cross diagram, when there's 2 dots not shared for eg = lone pair - also called unshared e- / non-bonding pair - Free radicals = contain one unpaired e- = very reactive - **Bonding pairs** of e- are shared with another atom in a covalent bond

Question 29

VESPR theory

Answer 29

FC = V - (N+B) FC- formal charge V- number of valence (e- on outer shell) N- number of non-bonding e- B- Number of Bonds calculations of this NOT coming up, but maybe just what the theroy is - **A model used to predict the shapes of molecules based on the idea that electron pairs around a central atom will arrange themselves to minimize repulsion**

Question 30

What are charge clouds?

Answer 30

- Bonding pairs + lone pairs exist as charge clouds - A charge cloud is an area where u have a very big chance off finding an electron pair - The e- don't stay still in them - they whizz around inside the charge cloud

Question 31

When drawing shapes of molecules, what does the thick wedge, and the broken line show? What's a tetrahedral shaped molecule look like

Answer 31

Thick wedge - bond coming out of page Broken line - bond going into page - Tetrahedral - has 4 e- pairs: Bond at top of central atom, and then bottom 3 bonds slightly closer together compared to top one (EG methane CH4) - If top bond replaced by lone pair = bottom 3 get closer together=smaller angles = Trigonal Pyramidal

Question 32

Angles in molecule shape [VESPR theory]

Answer 32

- E- = negative charge = charge clouds will repel eachother as much as they can = e- pairs will orient themselves as far away as possible = predicts the geometry - **Lone-pair charge clouds repel more than bonding-pair charge clouds** - The greatest angle are between lone pairs of e- =bond angles between bonding pairs are reduced as they're pushed together by lone-pair repulsion - **Lone-pair/Lone-pair** angles are biggest --> **Lone-pair-bonding-pair** angles are 2nd biggest --> **Bonding-pair/Bonding-pair** angles are smallest

Question 33

How would u work out the shape of a molecule + the number of lone + e- pairs

Answer 33

1. What's the central atom? [EG: O for H2O] 2. Use periodic table to see how many e- on its outer shell [O = 6] 3. Add the number of atoms that the central atom is bonded to to this number [H2O has 2: 6+2=8] (double bond would count as 2 not 1 eg CO2 has 2 =, so ud do 4 +4) 4. Divide this by 2 to find number of electron pairs on central atom [8/2 = 4 e- pairs] 5. Compare number of e- pairs to number of bonds to find number of lone pairs [H2O =2 bonding-pairs + 2 lone-pairs]

Question 34

QS comin gup in exam

Answer 34

MCQ - Is the compoun polar / non-polar? [halide groups make compound polar] - What's the number of lone pair? - shape? - molarity? - RMM?

Question 35

What is VSEPR + what does it predict?

Answer 35

VSEPR V - valence S - shell E - electron P - Pair R - Repulsion VSEPR predict the arrangment of e- pairs around a central atom

Question 36

Steric effect Steric hindrance?

Answer 36

- When atoms occupy a space close to eachother, this costs energy + can change the shape + reactivity of molecules - Steric hindrance - slows chemical reactions due to presence of steric bulk

Question 37

NEED TO KNOW DIFF SHAPES + NAMES + ANGLES allery chem 3 videos

Answer 37

check sheet i made in black notebook