covalent bonding

Question 1

definition of a covalent bond (2m)

Answer 1

electrostatic attraction between a shared pair of electrons and the positively charged nuclei, forming either polar or non - polar bonds

Question 2

Covalent bonding occurs in elements with

Answer 2

non - metals, high electronegativity

Question 3

define lewis formula, lone pairs and the octet rule

Answer 3

Formula that shows all the valence electrons (bonding and lone pairs)
Lone pairs are electrons not involved in the reaction
Octet Rule: Atoms are stable with 8 electrons in their valence shell

Question 4

What are 2 exceptions to the octet rule and why

Answer 4

Berrylium and Boron
because both have fewer than eight valence electrons available for bonding:

Question 5

Chromatography - def

explain how it works

Answer 5

Separates the the components of a mixture based on their relative attractions involving intermolecular forces to mobile and stationary phases

If the substance has stronger intermolecular forces with water in the mobile phase it will travel further up the paper
If the substance has stronger intermolecular forcesd with paper in the stationary phase

Question 6

retardation factor

Answer 6

distance moved by component / distance moved by solvent front

Question 7

order of strength of bonds and length of bonds

what is the relationship and why

Answer 7

triple > double > single
length is vice versa because

Double bonds are shorter because they have two pairs of bonding electrons, while single bonds only have one pair. The two pairs of electrons in double bonds pull the atoms closer together, resulting in shorter and stronger bonds

Question 8

Coordination bond w example

Answer 8

Both the electrons in the covalent/ionic bond come from the same atom

e.g: hydrogen cation + water = hydronium H30+

Question 9

ligand:

Answer 9

ion or molecule that binds to a central metal atom to form a coordination complex
this occurs in transition metals

Question 10

VSEPR 3 principles

Answer 10

1) Electron pairs repel each other and therefore arrange themselves as far apart from each other as possible

2) Lone pairs occupy mmore space than bonding pairs

3) Double and triple bonds occupy more space than single bonds

Question 11

3ED Possibilities

Answer 11

3BP - Trigonal Planar

2BP - Bent

Question 12

2ED + explanation

Answer 12

Linear geometry
Electron pairs repel each other and adopt positions at 180 degrees

Question 13

wedges and dashes

Answer 13

wedges: bonds cmg out of the plane
dashes: going into the plane

Question 14

3ED explanation + angles

Answer 14

Trigonal Planar - electron pairs adopt positions at 120 degrees from each other, the domains form a triangle while the atoms lie flat on the plane

In bent on v shaped (2BP) the angle will be less than 120 degrees because the lone pair exerts a strong repulsion and takes up more space

Question 15

4ED Explanation

Answer 15

Electron pairs adopt positions at 109.5 degrees from each other, the ends of the domains form the corners of teh tetrahedron

Question 16

5ED possibilities

Answer 16

5BP - Trigonal bipyramidal
4BP - Seeasw
3BP - T shaped
2BP - Linear

Question 17

5ED explanation

Answer 17

Trigonal bipyramidal bonding features 5 electron domains with 3 equatorial and 2 axial positions, forming 120° and 90° bond angles

Seesaw bonding arises when 1 lone pair occupies an equatorial position in a trigonal bipyramidal structure,

T-shaped bonding results from 2 lone pairs occupying equatorial positions, leaving 3 bonded atoms in a 90° and 180° arrangement,

Question 18

6ED Possibilities

Answer 18

6BP - Octahedral
5BP - Square pyramidal
4BP - Square Planar
3BP - T shape

Question 19

Formal charge formula

Answer 19

FC = Valance electrons - Non Bonding Pairs - (1/2 x Bonding pairs)

Question 20

Formal charge function
and how we choose

Answer 20

Helps us decide which lewis structure is preferable when there is more than one option
It is preferably when all atoms have a formal charge closest to zero
or the most electronegative atom should have the negative formal charge

Question 21

Sigma and pi bonds
+ electron density

Answer 21

Sigma Bonds: head on overlap of atomic orbitals + electron density conecentrated along the bond axis

Pi bonds: Sideways overlap of atomic orbitals and electron density is concentrated on opposite sides of the bond axis

Question 22

Polarity

Answer 22

How electrons are distributed within bonds, results from the difference of electronegativity of the bonded atoms
One can have a partially positive charge / partially negative charge

Question 23

Pure covalent

Answer 23

Atoms involved in the formation of the bond are identical

the charge is distributed evenly so there is no polarity or dipole moment (dipoles can cancel each other out)

Question 24

2 conditions for polarity

Answer 24

1. Molecules are non - polar when all the bonds are non polar
2. Molecules are polar when their bond dipoles do not cancel each other out and vice versa

Question 25

Covalent networks / Giant covalent definition and 3 properties

Answer 25

Atoms held together by covalent bonds in a continous 3D lattice * High melting and boiling points * Insoluble * Don't conduct electricity

Question 26

Allotropes

Answer 26

Elements with different structural bonds

Question 27

Graphite (5)

Answer 27

1. Layers of carbon sheets bonded in a hexagonal arrangement 2. Trigonal planar geometry around each carbon 3. One delocalised electron per atom - conducts electricity 4. Strong covalent bonds between carbons, Weak LDF between sheets 5. Sheets can be seperated easily making it a good lubricant + soft

Question 28

Graphene (4)

Answer 28

* 2D * One sheet of graphite * Strong, light, flexible and transparent * Conducts electricity just like graphite

Question 29

Fullerenes

Answer 29

C60 Atoms arranged in interlinking 20 hexagonal and 12 pentagonal rings Used in nanotech

Question 30

Silicon Dioxide bonding 2 properties plus crystalline form

Answer 30

3D lattice each silicon bonded to 4 other silicon atoms in a tetrahedral arragement Very strong and semi conductor of electricity Crystalline form of si02: quartz

Question 31

LDF Forces & what affects them | l

Answer 31

Experienced by all molecules from temporary instaneous dipoles. These dipoles occur due to the random movement of electrons around the molecules * Effect increases with increasing number of electrons in the atom as they increase polarizability and hence strength of LDF and molecular shape / size

Question 32

Dipole - induced dipole

Answer 32

Permanent dipole in the polar molecule induces a temporary dipole in the non polar molecule

Question 33

Dipole dipole forces

Answer 33

Permnanent dipoles experienced between polar molecules

Question 34

Hydrocarbon chains (phillic / phobic)

Answer 34

They are non polar and do not form hydrogen bonds with water Long chains are hydrophobic Soap and detergent have a hydrophobic tail and a hydrophillic head: called surface active agents

Question 35

1. Volatility 1. Electrical conductivity 1. Solubility

Answer 35

1. High for molecular substances like CH4, low for covalent network structures like diamond 2. Low because they lack delocalised electrons except graphite 3. Low except compounds that form hydrogen bonds with water molecules like C2H5OH and NH3

Question 36

Resonance structures occurance and properties

Answer 36

1. Occur when there is more than one possible position for a double bond in a molecule or ion 2. They have an identical length and strength as the intermediate between a single and double bond 3. There will always be delocalised electrons present in a resonance structure, as this brings additionally stability 4. Pi electrons of the double bond become delocalised and spread out between the possible bonding positions

Question 37

Benzene property

Answer 37

Pi electrons become delocalised and spread out over all the carbon-carbon bonding positions They form 2 rings above and below the plane of the molecule The bonds have an order of 1.5 The bonds are intermediate in length and strength between single and double bonds

Question 38

Kekule structure & why it was wrong

Answer 38

Shows alternating single and double bonds This is not correct because the bonds would have different length whereas it was proven that the bonds all have the same intermediate length

Question 39

Physical evidence for benzene (2)

Answer 39

Equal carbon carbon bond lengths and strengths with an order of 1.5 Regular hexagonal structure

Question 40

Bond order and relation to length

Answer 40

Stregth of the bond, inversely proportional to length

Question 41

Chemical evidence for benzene (3)

Answer 41

Substitution > Addition – Benzene favors substitution due to delocalized electrons, maintaining aromatic stability. No Bromine Water Reaction – Benzene does not decolorize bromine water as it lacks true double bonds. One Isomer in Substitution – Delocalization ensures all C-C bonds are equivalent, forming only one isomer. Double bonds would result in more than 1 isomer Hydrogenation Less Exothermic – Enthalpy change is less negative than predicted, proving extra stability from aromatic delocalization and lack of 3 double bonds

Question 42

4ED Possibilities & bonding angle trend

Answer 42

4BP - Tetrahedral 3BP- Trigonal Pyramidal 2BP - Bent bonding angle decreases as u go down because lone pairs increase