bonding

Why do atoms form chemical bonds?

Atoms form chemical bonds to achieve a stable noble gas configuration by obtaining a full outer electron shell. This lowers their potential energy and increases stability.

What is meant by a noble gas configuration?

A noble gas configuration is a complete valence shell. Atoms are more stable when their outer shell is full, which is why they lose, gain or share electrons during bonding.

What fundamental force is responsible for all chemical bonding?

Electrostatic attraction between positive and negative charges. The specific particles involved differ depending on whether the bond is ionic, metallic or covalent.

Explain how ionic bonding forms.

Ionic bonding forms when electrons are transferred from a metal atom to a non-metal atom. The metal becomes a positive ion, the non-metal becomes a negative ion, and the resulting electrostatic attraction between oppositely charged ions forms the ionic bond.

Why do metals tend to form positive ions?

Metals have relatively low ionisation energies because their valence electrons are further from the nucleus and experience weaker attraction. As a result, they lose electrons easily and form cations.

Why do non-metals tend to form negative ions?

Non-metals have high electronegativity and a strong attraction for electrons. They readily gain electrons to achieve a stable full valence shell.

Why is an ionic lattice formed rather than individual ion pairs?

Electrostatic attractions are non-directional and act equally in all directions. Each ion attracts multiple oppositely charged ions, producing a giant three-dimensional lattice.

Describe the bonding in sodium chloride.

Sodium transfers one electron to chlorine. Sodium forms Na⁺ with configuration 2.8, chlorine forms Cl⁻ with configuration 2.8.8, and strong electrostatic attraction between the ions creates an ionic lattice.

Why do ionic compounds have high melting points?

Large numbers of strong electrostatic attractions exist throughout the giant ionic lattice. Significant energy is needed to overcome these attractions and separate the ions.

Why do ionic compounds have high boiling points?

Substantial energy is required to completely separate ions held together by powerful electrostatic attractions throughout the lattice.

Explain why solid ionic compounds do not conduct electricity.

In the solid state the ions are locked into fixed positions within the lattice. Since no charged particles can move, electrical current cannot be carried.

Explain why molten ionic compounds conduct electricity.

Melting breaks some of the electrostatic attractions, allowing ions to move freely. These mobile ions act as charge carriers.

Explain why ionic compounds conduct electricity in aqueous solution.

Water separates the ions from the lattice and allows them to move independently through the solution. These mobile ions carry electrical charge.

Explain why ionic compounds are brittle.

When force shifts layers of ions, ions with the same charge may become aligned. The strong repulsion between like charges causes the crystal lattice to fracture.

Why are ionic compounds hard?

Ions are held in fixed positions by strong electrostatic attractions that resist deformation.

Explain metallic bonding.

Metallic bonding is the electrostatic attraction between a lattice of positive metal ions and a sea of delocalised electrons.

What are delocalised electrons?

Electrons that are not attached to one particular atom and are free to move throughout the entire metallic lattice.

How does metallic bonding form?

Metal atoms lose their valence electrons. These electrons become delocalised while the atoms become positive ions. Electrostatic attraction between the ions and electrons holds the structure together.

Why do metals conduct electricity?

Delocalised electrons are free to move through the metallic lattice and act as mobile charge carriers when a voltage is applied.

Why do metals conduct heat well?

Delocalised electrons rapidly transfer thermal energy throughout the structure, and vibrations are passed efficiently between closely packed metal ions.

Explain why metals are malleable.

Metal ions can slide past one another while remaining attracted to the sea of delocalised electrons. Metallic bonds are maintained despite changes in shape.

Explain why metals are ductile.

The non-directional nature of metallic bonding allows the lattice to stretch and deform without breaking the bonding network.

Explain why metals usually have high melting and boiling points.

Large numbers of strong metallic bonds must be overcome before metal particles can separate.

How does cation charge affect the melting point of a metal?

Higher cation charge creates stronger attraction to delocalised electrons, resulting in stronger metallic bonding and higher melting points.

How does packing density affect metallic bond strength?

More closely packed ions increase electrostatic attractions and strengthen metallic bonding, leading to higher melting and boiling points.

Explain covalent bonding.

Covalent bonding occurs when two non-metal atoms share one or more pairs of electrons. The bond is the electrostatic attraction between both nuclei and the shared electron pair.

Why do non-metals form covalent bonds?

Sharing electrons allows each atom to achieve a stable noble gas configuration without completely losing or gaining electrons.

What particles are involved in a covalent bond?

Two positively charged nuclei and a shared pair of electrons.

Why are covalent bonds described as directional?

Shared electrons are localised between specific atoms, causing bonds to exist along particular directions and produce fixed molecular shapes.

Why are ionic and metallic bonds non-directional?

Electrostatic attractions extend equally in all directions, resulting in giant lattice structures.

What is a covalent molecular substance?

A substance consisting of discrete molecules containing a small number of covalently bonded atoms.

What is a covalent network substance?

A giant three-dimensional structure where atoms are connected by covalent bonds throughout the entire lattice.

Why do covalent molecular substances usually have low melting points?

Only weak intermolecular forces need to be overcome to separate the molecules.

Why do covalent molecular substances usually have low boiling points?

Weak intermolecular attractions require relatively little energy to overcome.

Why are covalent molecular substances poor conductors of electricity?

Their electrons are localised within covalent bonds and cannot move freely to carry charge.

Why are covalent molecular substances generally soft?

Molecules are held together by weak intermolecular forces that are easily overcome.

Explain why covalent network substances have very high melting points.

A large number of strong covalent bonds must be broken to disrupt the giant network structure.

Explain why covalent network substances are hard.

Atoms are joined by strong covalent bonds throughout a giant three-dimensional structure that resists deformation.

Why are most covalent network substances electrical insulators?

Their electrons are localised within strong covalent bonds and cannot move freely.

What is an allotrope?

A different structural form of the same element in the same physical state.

Why are diamond and graphite allotropes of carbon?

Both consist only of carbon atoms but have different bonding arrangements and structures.

Describe the structure of diamond.

Each carbon atom forms four covalent bonds in a giant three-dimensional tetrahedral network.

Explain why diamond is extremely hard.

Every carbon atom is bonded strongly to four others, creating a rigid three-dimensional covalent network.

Why does diamond not conduct electricity?

All four valence electrons of each carbon atom are involved in covalent bonds and no mobile charge carriers exist.

Why does diamond have a very high melting point?

Many strong covalent bonds throughout the giant lattice must be broken.

Describe the structure of graphite.

Each carbon atom forms three covalent bonds within layers. The fourth electron becomes delocalised.

Why does graphite conduct electricity?

Delocalised electrons can move through the layers and carry electrical charge.

Why is graphite soft despite being a covalent network substance?

Layers are held together by weak attractions and can slide over one another easily.

Why does graphite still have a very high melting point?

Strong covalent bonds within each layer must be broken to melt the structure.

Compare diamond and graphite conductivity.

Diamond is a non-conductor because it has no mobile electrons, whereas graphite conducts because it contains delocalised electrons.

Compare diamond and graphite hardness.

Diamond is extremely hard due to its three-dimensional network, while graphite is soft because its layers can slide over one another.

What are carbon nanotubes?

Cylindrical structures formed by rolling graphene sheets into tubes.

Why are carbon nanotubes useful in electronics?

Depending on their structure they can behave as conductors or semiconductors.

What are nanoparticles?

Particles with dimensions between 1 and 100 nanometres.

Why do nanoparticles often have different properties from bulk materials?

Their extremely small size produces quantum effects that alter physical and chemical behaviour.

Why are ZnO and TiO₂ nanoparticles used in sunscreen?

They remain almost transparent on the skin while still providing protection from UV radiation.

What are quantum dots?

Semiconductor nanoparticles whose colour depends on their size.

Why do quantum dots display different colours?

Changes in particle size alter their electronic structure and therefore the wavelength of light emitted.

What advantages does nanosilver have over bulk silver?

Nanosilver displays antibacterial and antifungal properties that make it useful in medical and consumer products.