Unit 1: Topic 2 Bonding and properties

Question 1

Q: What are the three main types of chemical bonding?

Answer 1

Ionic bonding – Transfer of electrons between metal and non-metal atoms, forming charged ions.
Covalent bonding – Sharing of electron pairs between non-metal atoms.
Metallic bonding – A ‘sea of delocalized electrons’ shared among metal atoms.

Question 2

Q: List the key properties of ionic compounds and explain why they occur.

Answer 2

High melting and boiling points – Strong electrostatic forces between oppositely charged ions require large amounts of energy to break.
Hard but brittle – Rigid crystalline lattice structure makes them strong, but shifting layers of ions cause repulsion and shattering.
Electrical conductivity (only in liquid or dissolved state) – Ions are mobile in molten or aqueous state but fixed in a solid lattice.
Solubility in water – Water’s polarity weakens ionic attractions, allowing dissolution.

Question 3

Q: Why do metals have high melting and boiling points?

Answer 3

A: Strong electrostatic attraction between delocalized electrons and metal cations requires a lot of energy to break.

Question 4

Q: Why are metals good electrical and thermal conductors?

Answer 4

A: Free-moving delocalized electrons carry electrical current and transfer heat efficiently.

Question 5

Q: Why are metals malleable and ductile?

Answer 5

A: The metallic lattice allows layers of atoms to slide over each other without breaking the bonds.

Question 5

Q: What are the properties of simple covalent molecular substances?

Answer 5

Low melting and boiling points – Weak intermolecular forces require little energy to break.
Poor electrical conductivity – No free electrons or ions to carry charge.
Variable solubility – Some dissolve in polar solvents (e.g., sugar in water), others in non-polar solvents (e.g., oil in benzene).
Soluble in hexane if nonpolar – “Like dissolves like.” Nonpolar covalent molecules dissolve in nonpolar solvents like hexane.
Insoluble or slightly soluble if polar – Polar covalent molecules (e.g., H₂O, NH₃) do not mix well with nonpolar hexane.

Question 6

Q: How do giant covalent networks differ from molecular covalent substances?

Answer 6

High Melting Points – Strong covalent bonds require lots of energy to break (e.g., diamond, SiO₂).
Usually Hard – Rigid structure due to strong bonds, except graphite, which has weak layers that slide.
Poor Conductors – No free electrons, except graphite, which has delocalized electrons.

Question 6

Q: What are the three main types of hydrocarbons and how do they differ?

Answer 6

Alkanes (saturated) – Only single C-C bonds (e.g., methane, ethane).
Alkenes (unsaturated) – At least one C=C double bond (e.g., ethene, propene).
Alkynes (unsaturated) – At least one C≡C triple bond (e.g., ethyne, propyne).

Question 6

Q: What are hydrocarbons?

Answer 6

A: Organic compounds composed only of carbon and hydrogen atoms.

Question 7

Alkanes

Answer 7

Alkanes are saturated hydrocarbons, meaning they consist only of carbon (C) and hydrogen (H) atoms with single covalent bonds between the carbon atoms.

They follow the general formula CₙH₂ₙ₊₂ and are generally unreactive but undergo combustion and substitution reactions.

e.g methane, ethane

Question 8

Alkynes

Answer 8

Unsaturated At least one C≡C triple bond (e.g., ethyne, propyne).

Question 9

Alkenes

Answer 9

Unsaturated At least one C=C double bond (e.g., ethene, propene).

Question 10

Q: Why is benzene (C₆H₆) unusually stable?

Answer 10

A: Delocalized electrons create a resonance structure, making benzene less reactive than typical alkenes.

Question 11

What does saturated vs unsaturated mean?

Answer 11

Saturated compounds have only single bonds, while unsaturated compounds have double or triple bonds that can react and add more atoms.

Question 12

Q: How do the structures of diamond and graphite differ?

Answer 12

Diamond – Each carbon forms 4 strong covalent bonds in a 3D lattice, making it extremely hard with a high melting point.
Graphite – Each carbon bonds to 3 others in layered hexagonal sheets with weak forces between layers, making it slippery and able to conduct electricity.

Question 13

What are bonds?

Answer 13

Bonds are electrostatic forces (attractions between positive and negative charges) which hold atoms together.

Question 14

Structure of ionic compounds

Answer 14

Ionic substances appear as giant lattice structures in which the ions are held together by electrostatic force between oppositely charged ions.

Question 15

Properties of Metals

Answer 15

High Melting & Boiling Points – Strong metallic bonds require a lot of energy to break.
Insoluble – No ions or polar regions to attract water; metallic bonding is too strong.
Malleable & Ductile – Layers of atoms can slide over each other without breaking bonds.
Good Conductors – Delocalized electrons move freely, allowing heat and electricity to pass through.
Reactivity with Water – Some metals (e.g., Na) react; Group 1 metals have weak bonding, so electrons are easily removed.
Lustrous (Shiny) – Delocalized electrons reflect light.
High Density – Metals have a closely packed lattice structure.

Question 16

Alloy

Answer 16

mixture of metals (or small amounts of a non-metal)
Addition of other element/s alters the properties of the original metal
EG steel (Fe + C)harder and less malleable than iron
stainless steel (+ Cr)resistant to corrosion

Question 17

What are allotropes

Answer 17

Different structural forms of the same element – may have different physical and chemical properties
e.g. oxygen (O2) and ozone (O3)
diamond (3D lattice) and graphite (2D lattice)

Question 18

What is a lattice?

Answer 18

A lattice is a regular, repeating arrangement of particles (atoms, ions, or molecules) in a solid structure.

Question 19

What are the types of lattice

Answer 19

Ionic Lattice – Found in ionic compounds like NaCl, where oppositely charged ions are held together by strong electrostatic forces.
🔹 Metallic Lattice – Found in metals, where positive metal ions are surrounded by a sea of delocalized electrons.
🔹 Covalent Lattice – Found in giant covalent structures like diamond and graphite, where atoms are bonded by strong covalent bonds.

Question 20

What type of chemical reaction do alkanes generally undergo?

Answer 20

Alkanes mostly undergo substitution reactions. This is because they are relatively unreactive as a result of their single carbon-carbon bonds.

Question 21

What type of chemical reaction do alkenes generally undergo?

Answer 21

Alkenes mostly undergo addition reactions. This is because their double carbon-carbon bond is reactive and can easily break to form new single bonds with other atoms.

Question 22

What type of chemical reaction do Alkynes generally undergo?

Answer 22

Alkynes mostly undergo addition reactions. This is because their triple carbon-carbon bond is highly reactive and can break to form new single or double bonds with other atoms.

Question 23

What is the general formula for alkenes?

Answer 23

Cₙ H₂ₙ

Question 24

What is the general formula for alkanes?

Answer 24

CnH2n+2

Question 25

What is the general formula for alkynes?

Answer 25

CnH2n–2

Question 26

What does Polar vs non-polar mean

Answer 26

Polar molecules have an uneven charge distribution due to a difference in electronegativity between atoms, creating partial positive and negative charges (e.g., H₂O). Non-polar molecules have an even charge distribution, either because the atoms share electrons equally or because their dipoles cancel out (e.g., O₂, CO₂).

Question 27

Delocalized electrons

Answer 27

Electrons that are not bound to a single atom or bond but move freely within a structure, such as in metals or conjugated systems.

Question 28

Electrostatic attraction

Answer 28

The force that pulls oppositely charged particles toward each other due to their electric charges.

Question 29

If something is polar what is it's solubility in water?

Answer 29

A polar substance is generally soluble in water because water is also polar, following the principle "like dissolves like."

Question 30

What is ENC? and it's trend

Answer 30

Effective Nuclear Charge (ENC) is the net positive charge experienced by an electron in an atom. It accounts for the attraction of the nucleus and the repulsion from inner electrons. ENC increases across a period (more protons, minimal increase in shielding). ENC remains relatively constant down a group (more shielding offsets increased nuclear charge). Higher ENC leads to stronger attraction on outer electrons, increasing ionization energy and electronegativity.

Question 31

How does ENC affect ionization energy?

Answer 31

Higher ENC → Higher Ionization Energy (Electrons held tighter) Lower ENC → Lower Ionization Energy (Electrons easier to remove) Trends: Across a Period: ENC increases → Ionization Energy increases Down a Group: Shielding increases → Ionization Energy decreases

Question 32

Why Does ENC Increase Across a Period?

Answer 32

Protons (Z) increase, strengthening nuclear attraction. Electrons increase but stay in the same energy level. Shielding remains nearly constant (no new inner shells). Result: ENC increases, pulling electrons closer and increasing ionization energy.

Question 33

How do water molecules affect the solubility of ionic compounds?

Answer 33

Solubility in Water – Water’s polarity allows it to weaken ionic bonds. The negative ion is attracted to water’s positive hydrogen, and the positive ion to water’s negative oxygen. This pulls ions apart, breaking the lattice and allowing them to disperse in solution.

Question 34

Q: List the key properties of metallic bonds and explain why they occur.

Answer 34

High melting and boiling points – Strong electrostatic attraction between delocalized electrons and metal cations requires large amounts of energy to break. Malleable and ductile – Layers of metal atoms can slide over each other without breaking metallic bonds. Good electrical and thermal conductivity – Free-moving delocalized electrons allow easy flow of electricity and transfer of heat. Luster (shiny appearance) – Delocalized electrons reflect light effectively. Insoluble in water and most solvents – The strong metallic bonds between metal atoms are not broken by interaction with water or common solvents. Insoluble in hexane – Metals do not interact with nonpolar solvents like hexane. Their metallic bonds remain intact.

Question 35

Q: List the key properties of covelant molecular bonds and explain why they occur.

Answer 35

Low melting and boiling points – Weak intermolecular forces (such as Van der Waals forces, dipole-dipole, or hydrogen bonding) require little energy to overcome. Soft and flexible – Weak intermolecular forces allow molecules to move more freely. Poor electrical conductivity – No free-moving charged particles to conduct electricity. Solubility varies – Polar molecules dissolve in polar solvents (e.g., water), while nonpolar molecules dissolve in nonpolar solvents (e.g., oil).

Question 36

Q: List the key properties of covelant network and explain why they occur.

Answer 36

Very high melting and boiling points – Strong covalent bonds throughout the structure require a large amount of energy to break. Extremely hard – Atoms are held in a rigid, three-dimensional network, making them very strong. Poor electrical conductivity – No free electrons or ions (generally not conductive in any state) (except graphite, which has delocalized electrons allowing conductivity). Insoluble in most solvents – Strong covalent bonds prevent dissolution in common solvents. Insoluble in hexane – Strong covalent bonds throughout the structure cannot be broken by hexane.

Question 37

Can metals be polar?

Answer 37

In metals, electrons are delocalized in a "sea of electrons," meaning there are no fixed regions of partial positive or negative charge. Polarity arises from differences in electronegativity between bonded atoms, but in metals, atoms share electrons collectively rather than in directional bonds, preventing polarity.

Question 38

How come if something is soluble in water it is polar?

Answer 38

Substances that are soluble in water are typically polar because their charged regions interact with the polar water molecules, allowing them to dissolve.