4.2 Bonding, structure and the properties of matter

Define compound

A substance formed when two or more different elements are chemically bonded together in fixed proportions

Name the three types of strong chemical bonds and describe their bonding

• Ionic

  • the particles are oppositely charged ions

  • occurs in compounds formed from metals and non-metals (metals lose electrons to form positive ions, non-metals gain electrons to form negative ions)

• Metallic

  • the particles are atoms which share delocalised electrons

  • occurs in metallic elements and alloys

• Covalent

  • the particles are atoms which share pairs of electrons

  • occurs in most non-metallic elements and in compounds of non-metals

What is meant by the empirical formula and molecular formula?

Give both formulas for carbon dioxide and glucose

The empirical formula is the simplest whole number ratio of atoms of elements present in a compound

Molecular formula is the actual whole number ratio of elements present in a compound

Carbon dioxide:

• Empirical: CO₂

• Molecular: CO₂

Glucose:

• CH₂O

• C₆H₁₂O₆

Describe what happens when a metal reacts with a non-metal

• Metal atoms lose electrons to become positively charged ions

• Non-metal atoms gain the electrons to become negatively charged ions

• These oppositely charged ions are strongly attracted to one another by electrostatic forces; this attraction is an ionic chemical bond

Draw the dot and cross diagram to show the formation of sodium chloride

Sodium (metal) and chlorine (non-metal) react to form an ionic compound

Describe the structure of an ionic compound

Ionic compounds form giant ionic lattices:

• An ionic compound is a giant structure of ions that form a closely packed regular lattice arrangement

• Ionic compounds are held together by strong electrostatic forces of attraction between oppositely charged ions

• These forces act in all directions in the lattice

The electrostatic force of attraction is the ionic bond

Describe the limitations of using these diagrams to represent a giant ionic structure:

• Dot and cross diagram

• Ball and stick diagram

• 2D diagrams

• 3D diagrams

Dot and cross diagram:

• Don’t show the 3D lattice structure of the ions

• Do not show us the ionic bonds between the ions

Ball and stick diagram:

• Large gaps between balls suggest that ions are far apart, when they are actually tightly packed

• Doesn’t show the electrostatic forces between ions that make up the bonds, and instead shows the bonds as physical ‘sticks’

• Does not show how ions were formed

2D diagrams:

• Shows only a flat layer, not the full 3D lattice structure

• Does not show how ions were formed

3D diagrams:

• Usually shows large gaps between ions, when they are actually tightly packed together

• Only shows a small part of the lattice, so may be misleading by showing the structure to be much smaller than it actually is

Describe the bonding between non-metal atoms

• They share pairs of electrons to form covalent bonds

• The positively charged nuclei of the bonded atoms are attracted to the shared pair of electrons by electrostatic forces, making covalent bonds very strong

What are simple molecular substances?

Simple molecular substances are made up of small molecules (molecules containing only a few atoms jointed together by covalent bonds)

Name the types of substances formed from covalent bonding

• Simple molecular substances

• Polymers

• Giant covalent structures

Give examples of giant covalent structures

• Diamond

• Silicon dioxide

Draw the polymer polyethene

Describe the limitations of using these diagrams to represent a covalent structures:

• Dot and cross diagram

• Ball and stick diagram

• 2D diagrams

• 3D diagrams

Dot and cross diagram:

• Don’t tell us about the shape of the molecule

• For giant covalent structures, they only show a small section, not the full repeating network

Ball and stick diagram:

• Don’t accurately show the shape of the molecule

• Cannot tell which electron in the covalent bond came from which atom

• Shows the bonds as ‘sticks’ and not shared pairs of electrons

• Shows large spaces between the atoms when actually they are very close together

2D diagrams:

• Cannot show the full repeating structure of giant covalent structures

• Cannot tell which electron in the covalent bond came from which atom

• Does not show the covalent bonds

3D diagrams:

• Cannot show the full repeating structure of giant covalent molecules

• Can show large spaces between the atoms when they are actually very close together

Describe metallic bonding

• Metals consist of giant structures of atoms arranged in a regular pattern

• The electrons in the outer shell of the atoms are delocalised and so are free to move through the whole structure

• The sharing of delocalised electrons gives rise to strong metallic bonds

What temperature does freezing take place?

Below the substance’s melting point

Where does condensation take place?

Below the substance’s boiling point

Draw simple models of the three states of matter

• Give the limitations of the models

Limitations:

• It does not show the intermolecular forces between particles

• Represents the particles as spheres

• Represents the particles as solid and inelastic (which is not accurate as atoms are mostly empty space)

What does the amount of energy needed to change state from solid to liquid depend on?

The amount of energy needed to change state from solid to liquid depends on the strength of the intermolecular forces between the particles of the substance; the nature of the particles involved depends on the bonding and structure of the substance

• The stronger the intermolecular forces between the particles, the higher the melting and boiling point of the substance

When does a change of state occur?

When energy is transferred to overcome the intermolecular forces holding particles of a substance together

Describe how a substance changes from solid to gas in terms of its particles

• Within a solid, particles are closely packed together in a regular arrangement

• As a solid is heated, the particles gain more energy and begin to vibrate

• As the temperature increases the particles gain even more kinetic energy and at a certain temperature (melting point) the particles have enough energy to overcome some of the strong forces of attraction to melt to form a liquid

• When a liquid is heated, the particles gain even more energy

• This energy makes the particles move faster, and eventually the particles gain enough energy to completely overcome the forces of attraction between particles/ break the bonds holding them together - this is called the boiling point

• The particles evaporate to become a gas

Describe how a substance changes from a gas to a liquid in terms of particles

• As a gas cools, particles no longer have enough energy to overcome the forces of attraction between them

• Bonds form between the particles

• At the boiling point, so many bonds have formed between the gas particles that the gas becomes a liquid through condensation

• When a liquid cools, the particles have less energy, so move around less

• There’s not enough energy to overcome the attraction between particles, so more bonds form between them

• At the melting point, so many bonds have formed between the particles that they’re held in place; the liquid freezes to become a solid

True or false: atoms themselves have the bulk properties of materials

FALSE: atoms do not have the bulk properties of materials

• Bulk properties: the physical characteristics of a substance that emerge from the collective behaviour of millions of particles/ atoms interacting together

What is the particle theory model used for?

Particle theory is a model that considers each particle as a small, solid inelastic sphere; can be used to explain how the particles in a material behave in each of the three states of matter

Use particle theory to describe the behaviour of particles in solids, liquids and gases

• Solids:

  • Strong forces of attraction between particles

  • These strong forces of attraction hold them very close together in fixed positions, forming a regular lattice arrangement

  • Particles don’t move from their fixed positions so keep a definite shape and volume; they do not flow

  • Particles vibrate about their fixed positions

• Liquids:

  • Weak forces of attraction between particles

  • Randomly arranged and are free to move past each other

  • Have a definite volume (cannot be compressed as particles are too close together) but do not have a definite shape (as particles can slide over each other), so can flow

  • Particles are constantly moving with random motion

• Gases:

  • Very weak forces of attraction between particles

  • Particles are free to move and far apart

  • Gases don’t keep a definite shape or volume and fill their container (as particles can spread out)

  • Particles are constantly moving with random motion

Explain the limitations of the particle theory model

• Particles are represented as solid and inelastic

• Represents the particles as spheres

• Does not show the forces between the particles

Describe and explain the physical properties of solids, liquids and gases

• Solids

  • Has a fixed shape and cannot flow, because the particles are held together by very strong bonds/ forces

  • Cannot be compressed, because the particles are held very close together and have no space

• Liquids

  • Flow and take the shape of the container as the particles can move around each other due to weaker forces/ bonds

  • Cannot be compressed as particles are held too close together

• Gases

  • Flow and completely fill their container because the particles can move quickly in all directions

  • Can be compressed as the particles are very far apart so have space to move into

Give all of the state symbols for chemical equations

• Solids (s)

• Liquids (s)

• Gases (g)

• The substance is dissolved in water (aq)

Describe and explain the properties of ionic compounds

• High melting and boiling points

  • Large amounts of energy needed to break the many strong bonds

• When melted or dissolved in water they conduct electricity

  • As when ionic compounds are melted or dissolved in water, the ions are free to move and carry charge

Describe and explain the properties of small molecules

• Usually gases or liquids at room temperature as they have relatively low melting and boiling points

  • Due to weak intermolecular forces between the molecules (it is these intermolecular forces that are overcome when the substance melts/ boils, not the strong covalent bonds)

• Substances do not conduct electricity because they do not have an overall electric charge (and have no delocalised electrons)

As the size of the molecules increases, the intermolecular forces between molecules increases (as there are a greater number of electrons), so the melting and boiling points increase

Describe and explain the properties of polymers

• Polymers are very large molecules; the atoms in the molecules are linked to other molecules by very strong covalent bonds

  • They are composed of long chains of smaller, repeating units (monomers)

• The intermolecular forces between polymer molecules are relatively strong (as polymer molecules are very large) so these substances are solids at room temperature

Describe the structure of giant covalent structures

• Give examples of these structures

• All of the atoms in the structure are bonded to other atoms by strong covalent bonds

• They have very high melting and boiling points as these many strong bonds must be overcome for the substance to melt or boil

Eg. Diamond, graphite, silica (silicon dioxide)

Describe and explain the properties of all metals

All metals:

• Metals are often solids at room temperature as they have high melting and boiling points

  • This is because they are made up of giant structures of atoms with strong metallic bonding

• Metals are good conductors of electricity

  • As the delocalised electrons in the metal are free to move to carry charge

• Metals are good conductors of thermal energy

  • Thermal energy can be transferred to the delocalised electrons, which are free to move and carry this energy throughout the metals

Describe and explain the differences in the properties of pure metals and alloys

Pure metals:

• In pure metals, atoms are arranged in regular layers as all atoms are of the same element and so are of the same size; this means that the layers can slide over each other more easily

  • This makes them softer and more malleable

Alloys:

• In alloys there are different elements, so the different atoms of different elements have different sizes. This distorts the layers of atoms, making it more difficult for them to slide over eachother

  • This makes them harder and less malleable

Name the different allotropes of carbon

• Diamond

• Graphite

• Graphine

Describe and explain the structure and properties of diamond

• Diamond has a giant covalent structure

• Made up of carbon atoms that each form four covalent bonds with other carbon atoms

  • Makes it very hard

  • These strong covalent bonds require a lot of energy to break, giving diamond a very high melting point

  • It has no delocalised electrons and has no overall electric change so cannot conduct electricity

Describe and explain the structure and properties of graphite

• Graphite is an allotrope of carbon

• Each carbon atom forms three covalent bonds with three other carbon atoms, forming layers of hexagonal rings which have no covalent bonds between layers

  • As there are no covalent bonds between layers, they are held together weakly so are free to move over each other, making graphite soft and slippy and ideal for use as a lubricating material

• In graphite, one electron from each carbon atom is delocalised

  • Allows graphite to conduct electricity and thermal energy

• The covalent bonds in the layers require large amounts of energy to break, giving graphite a high melting point

Describe and explain the structure and properties of graphene

• Graphene is an allotrope of carbon

• It is a single layer of graphite (one atom thick)

• It is a layer of carbon atoms that form three covalent bonds with three other carbon atoms; each carbon atoms has one delocalised electron

  • This means that it can conduct electricity throughout the whole structure (giving it uses in electronics)

  • The network of covalent bonds also makes it very strong

  • As it is only one layer, it is very light

Explain the uses of graphene

Graphene is an allotrope of carbon; it is a single layer of graphite

• Useful in electronics

  • As each carbon atom has one delocalised electron

• Useful in composite materials (combination of two materials with different chemical and physical properties; graphene can improve the strength of materials without adding much weight)

  • The network of covalent bonds makes it very strong and as it is only one atom thick, it is very light

What are fullerenes?

• Fullerenes are molecules of carbon atoms with hollow shapes

• They are nanoparticles

  • They are mainly made up of hexagonal rings of carbon atoms, but may also contain rings of 5 (pentagon rings) or 7 (heptagon rings) atoms

What was the first fullerene to be discovered? What is its shape?

• Buckminsterfullerene (C₆₀)

• Spherical shape; forms a hollow sphere

Name the two types of fullerenes (at GCSE level) and give their shapes

• Buckminsterfullerene (C₆₀), hollow spherical shape

• Carbon nanotubes, cylindrical shape

What are carbon nanotubes?

• Carbon nanotubes are cylindrical fullerenes with very high length to diameter ratios

Describe the properties and uses of carbon nanotubes

• High length to diameter ratio

• Have delocalised electrons, allowing them to conduct both electricity and heat

• High tensile strength (the resistance of a material to breaking under tension; stretched, bent)

Uses in:

• Nanotechnology

• Used in electronics

• Specialised sports equipment (strengthen the materials without adding weight)

• Can be used to reinforce materials by adding strength without adding weight to composite materials

Give uses of fullerenes

• Targeted drug delivery

  • As fullerenes can be used to ‘cage’ other molecules

• Lubricants (spherical)

  • Due to spherical shape and weak intermolecular forces between molecules

• Catalysts

• Strengthening materials (cylinderical fullerenes)

State the three categories of particle and their diameters

• Coarse particles

  • Diameter of particles: 2,500nm - 10,000nm

• Fine particles

  • Diameter of particles: 100nm - 2,500nm

• Nanoparticles

  • Diameter of particles: 1nm - 100nm

What does nanoscience refer to?

The science of structures that are 1nm - 100nm in side

What is the relationship between the side of a cube and its surface area to volume ratio

• As the side of a cube decreases by a factor of 10

• The surface area to volume ratio increases by a factor of 10

What is the defining property of nanoparticles?

Their high surface area to volume ratio

Why may nanoparticles have properties different from those for the same materials in bulk?

• Due to their high surface area to volume ratio

What does the high surface area to volume ratio of nanoparticles cause?

• Nanoparticles tend to have properties different from those for the same materials in bulk

• May mean that smaller quantities are needed to be effective than materials with normal sizr particles

What type of particles are fullerenes?

Nanoparticles

Describe some of the uses of nanoparticles

• Uses in medicine

  • May be more easily absorbed by the body, fullerenes for ‘caged’ drug delivery

• Uses in electronics

  • Carbon nanotubes have one delocalised electron, allowing them to conduct electricity

• Sun creams

• Deodorants

• Catalysts

  • Due to high surface area to volume ratio

Describe the disadvantages of nanoparticles

• Nanoscience technology is still new, so the way that they affect the body is not fully understood (eg. the long term effects on human health are unknown)

• As they are so small, they are easily to breathe in and enter the body - they might catalyse reactions that are harmful

• Toxic substances could bind to them due to their high surface area to volume ratios, harming health if nanoparticles enter the body

• Harmful effects on the environment

Why is it incorrect to say that one molecule of water has a boiling point of 100 degrees?

• Boiling point is a bulk property

• Referring to the relationships between many particles/ molecules

Describe why electrons can conduct heat

• Metals have a sea of delocalised electrons

• Which are free to move and transfer heat throughout

Explain why fullerenes are used in catalyst systems

• Very high surface area to volume ratio

• Many catalyst molecules can be attached to the surface of nanotubes

• Providing a large surface area on which reactants can collide

Give benefits of the particle model

Allows the

• Arrangement

• Movement

of particles to be compared between different states of matter