Chapt 4 Chem Bonding

Question 1

Types of chemical bonds

Answer 1

1. STRING Intramoleculer
   1a. Ionic
   1b. Covalent
   1c. Metallic
   __________________ __________________
2. WEAK Intermolecular
   2a. Permanent dipoles—permanent dipoles (PD—PD)
   —
   2b. Instantaneous dipoles—induced dipoles (ID—ID)
   —
   2c. H bonds

Question 2

Define chemical bond

Answer 2

Chem bonds are the
- electrostatic forces of attraction
- between_positive charges_ and negative charges
- in a particle

(atom, molecule, ions)

Question 3

Describe ur Ex bf

Answer 3

Exothermic
Bond form

• heat relased
• Enthalpy H neg
• Energy between + and - charges is lowered
• stability is achieved
• products have lower energy than reactants

Question 4

Property of noble gases

Answer 4

• High IE
• Low affinity for additional electrons (probability of binding/reacting with smth else)
• low resctivity

Question 5

Factors affecting strength of metallic bonds pg 95

Answer 5

1. The number of valence electrons per cation, indicated by the Charge of metal
   - the more Val electrons,
   - The higher the charge, the stronger the metallic bond
2. Size of the cation
   - the smaller the size/ionic radius of the metal cation,
   - the greater the charge density
   - the stronger the electrostatic attraction between the Val electrons and the positive cations
   - the stronger the metallic bond

Question 6

Calculate max number of outer shell electrons a N atom and a Na can hold

(Period 2 and 3 respectively)

Answer 6

N:
2(2)²
= 8

Na:
2(3)²
= 18

Question 7

Why does MgCl₂ exist and not MgCl₃ ?

Answer 7

1. • Too much energy is needed to remove the 3rd electron from Mg to form Mg³⁺
   • because 3rd electron is in the inner shell
     __
     2.
   • Calculate energy needed to form Mg²⁺
     =1st IE Mg+ 2nd IE Mg
     FROM DATA BOOK
     __
     3.
   • Calculate energy needed to form Mg³⁺
     =1st IE Mg+ 2nd IE Mg +3rd IE Mg
     FROM DATA BOOK

Question 8

Define electronegativity

Answer 8

Electrons is the ability of an atom to attract a shared pair of electrons to itself in a covalent bond

Question 9

What does the diff in electronegativity of atoms say about the type of bond formed in a compound

Answer 9

1. Small diff
   - bond is covalent
   - Covalent = 2 non-metals
   - same side of periodic table so similar electroneg

________\_______
2. Big Diff
- Bond is ionic
- Formed between metal & non-metal
- Opposite sides of periodic table
- So electroneg is more different

Question 10

Define ionic bonding

Answer 10

Ionic bonding is the
- electrostatic forces of attraction between 2 oppositely charged ions

• Ions are formed from **complete transfer of electrons from a metal atoms to a non-metal atom
• Possible becuz of large diff in electronegativity

Question 11

Define lattice energy (LE) or enthalpy latt

Answer 11

LE is
- the energy evolved when 1 mole of ionic compound is formed
- from its constituent gaseous ions
- under standard conditions
(1 bar & 25C)
__________________
Ex bf
- Bond forming is exothermic
- so LE is ALWAYS negative

Question 12

Relationship between ionic bonds and LE (lattice energy)

Answer 12

They are directly related
______
- When More heat energy evolved when gaseous ions come tgt to form ionic compounds
- There are Stronger ionic bonds

• so LE is more exothermic or more negative or has larger magnitude

Question 13

Q: Does MgO or MgS have stronger ionic bonds?
5 steps

Answer 13

STRUC
1. Both have giant ionic crystal lattice structures.
__
CHARGE
2. Both O2- and S2- have the same ionic charge of -2
__
IONIC RAD
3. (Check periodic table) O2- has a smaller ionic radius than S2-, so interionic radius between Mg2+ and O2- is smaller than between Mg2+ and S2-
__
4. According to |LE| = k x product of charges (z+z-) over sum of atomic radii (r + r), ionic bonds between MgO are stronger than between MgS
__
ENERGY
5. More energy is needed to overcome the ionic bonds between Mg2+ and O2- than the electrostatic attraction between Mg2+ and S2-
__
Link to Qn
6. So MgO has stronger ionic bonds / higher melting pt

Question 14

LE formula

Answer 14

(Product of charge of anion & cation) / (sum of atomic radii)

Question 15

Explain the Factors affecting covalent bond strengths
IN ORDER OF IMPORTANCE

Answer 15

1. Bond order (number of bonds)
   - More bonds,
   - More orbitals overlap
   - more electrons experience attraction of both nuclei
   - so bond is stronger
   __________________ __________________
2. Atomic radius (ONLY CONSIDER IF BOND ORDER SAME)
   - the Shorter atomic radius, the shorter the bond length,
   - This causes a greater degree of orbital overlap,
   - so the bond is stronger, the higher the bond energy.
   __________________ __________________
3. Bond polarity
   - ONLY CONSIDER BOND POLARITY WHEN BOND ORDER & ATOMIC RADIUS ARE SIMILAR
   - Polar bonds stronger than non-polar
   - bc polar have additional electrostatic attraction from partial charges

Question 16

Octet rule 3 types of exceptions

Answer 16

1. Group 13 metals are e deficient
   - BF3, ALCl3, BeF3
   NOTE: ALF3 is an ionic compound bc F is too electroneg so there is complete transfer of electrons
   - they form 3 covalent bonds & have 6 Val e.
   __________________ __________________
2. Odd electron molecules (FREE RADICALS)
   Eg: NO, NO₂
   - VERY REACTIVE bc Both have double bond w single unpaired electron
   __________________ __________________
3. Period 3 elements onwards can expand octet
   - max number of electrons in outer shell is 2n²

n is the period / principle quantum shell number

Question 17

Dative bonds conditions.
What is a Lewis acidic and Lewis base in dative bonding?

Answer 17

• Donor atom must have line pair of e
• acceptor atom must have energetically accessible orbitals in its valence shell to accept donated e
  __
  only use dative bond when atoms are before period 3 so they cannot expand octet
  __________________ __________________

Lewis acidic: Acceptor
Lewis base: Donator

Question 18

What does VESPR theory state?

Answer 18

1. Bond pairs are positioned as far apart as possible to minimise repulsion
2. Bp-bp repulsion < bp-lp repulsion < lp-lp repulsion

Question 19

Steps to determine shape of using VESPR theory

Answer 19

1. Draw dot & cross
2. Count number of bp & lp of central atom

3.

Question 20

2 bp 0 Lp shape & angle

Answer 20

Shape: Linear
Angle: 180 degrees

Question 21

3 bp, 0 Lp. Total 3 e domains. shape & angle

Answer 21

Shape : trigonal pyramidal
Angle: 120 degrees
The shape is also FLAT

Question 22

2 bp, 1 Lp. Total 3 e domains. shape & angle

Answer 22

Shape : V-shape
Angle: 118
Flat

Question 23

4 bp. 0 Lp. Total 4 e domains. shape & angle?

Answer 23

Shape : tetrahedral
Angle: 109.5
3 D shape

Question 24

3 bp, 1 Lp. Total 4 e domains. shape & angle?

Answer 24

Shape: Trigonal pyramidal
Angle: 107
3D

Question 25

2bp, 2Lp. Total 4 e domains. shape & angle?

Answer 25

Shape: V-shape/bent Angle: 105

Question 26

5bp, 0 Lp. Total 5 e domains. shape & angle?

Answer 26

Shape: trigonal bipyramidal angle: - 90 degrees between axial position & plane - 120 degrees between equatorial positions

Question 27

4 bp, 1 Lp. Total 5 e domains

Answer 27

Shape: see saw Angle: < 90 between axial and equatorial position <120 between axial and equatorial position

Question 28

3bp, 2Lp. Total 5 e domains. shape & angle?

Answer 28

Shape: T shape Angle: <90 between axial & equatorial bps

Question 29

2bp, 3Lp. Total 5 e domains. shape & angle?

Answer 29

Shape: Linear Angle: 180

Question 30

6bp, 0Lp. Total 6 e domains. Shape & angle?

Answer 30

Shape: Octahedral Angle: axial & equatorial position 90 Equatorial position 90

Question 31

Q: Why are AlCl3, AlBr3 and Ali3 covalent?

Answer 31

- Al has **high polarising power** bc Al has **high charge density** - Al polarises the electron cloud of Br / Cl / I to such a large extent - On the other hand, AlF3

Question 32

What is polarisation? What kind of compounds does it occur it? AND What factors affect extent of polarisation?

Answer 32

- Polarisation is the distortion of the e cloud of an anion by a **_cation with high polarising power_** - occurs in ionic compounds with covalent character __________________ __________________ factors that affect extent of polarisation 1. **_Polarising power of cation_** - small ionic radius & high ionic charge - leads to high charge density - 2. **_Polarisability of anion_** - large atomic radius - large e cloud - more easily polarised

Question 33

Electronegativity of central & non-central atom effect on bond angles

Answer 33

**_Central atom_** - more electronegative central atom, draws **electrons closer to itself** - **bond pairs of electrons are nearer to the nucleus of central atom** - AND **exert more repulsion** - causing **_bond angle to be larger_** __________________ __________________ **_non-Central atom_** - More electronegative, draw electrons closer to itself - bond pairs of electrons are **further away from nucleus of central atom** - AND exert **less repulsion** - bond angle is **_smaller_**

Question 34

3 Factors affecting id-id forces

Answer 34

1. **_Size of electron cloud to bo polarised_** - The **_more electrons per molecule_ indicated by a larger Mr**, - the **bigger the size of electron cloud** - so the **electron cloud is more polarisable** - so **id-id forces stronger** __________________ __________________ 2. **_Shape (usually ORGANIC molecules)_** - **More spherical** shape means **less surface area in contact with other molecules**. >> **weaker id-id forces - **More linear shape** >> more surface area in contact w other molecules >> stronger id-id forces __ - Linear shape means more surface area in contact with other molecules __________________ __________________ 3. **_Packing_** - Only when explaining melting points FOR solid molecules - In **solid** state, molecules are **packed closer** together - so **stronger if-I’d forces** in **solids**

Question 35

Factor affecting pd-pd

Answer 35

must compare molecules with similar Mr so id-id forces will be similar __ - the **Greater the diff in electronegativity** between atoms >> the larger the net dipole >> **more polarity of covalent bonds** - **stronger electrostatic attraction between higher dipoles** _ - **pd-pd forces stronger**

Question 36

How pd-pd forces arise?

Answer 36

- when there is **diff in electronegativity** between 2 atoms in a **polar bond** - **electrons** involved in bonding will be **drawn towards more electronegative atom** - this causes an **uneven distribution of charge** in the bond __ - The **partial positive end** of one polar molecule will **_attract the partial negative end of a nearby polar molecule_** __ - pd-pd is the **Weak electrostatic attraction between opposite partial charges in a polar molecule**

Question 37

2 Factors affecting H bonds

Answer 37

1. **_Average number of H bonds per molecule_** Depends on: - Number of H atoms bonded to FON - AND Number of lone pairs on FON **the smaller number will be the no. of H bonds per molecule __________________ __________________ 2. **_Electronegativity diff between H & atom bonded to H_** - Most electroneg diff = H—F >> **strongest H bond bc biggest diff** - Least electronegativity diff = H—N >> **weakest H bond bc smallest diff**