Topic 1: Materials and their Atoms

© Essentials Education 1

TOPIC 1

1

Topic 1: Materials and their Atoms1.1: Properties and uses of materialsScience understandingThe uses of materials are related to their properties, including solubility, thermal and electrical conductivities, melting point, and boiling point.

© Copyright SACE 2016

Chemistry is the study of matter. Matter is anything that has mass and takes up space. Matter consists of particles including atoms, ions, subatomic particles, and molecules. Materials are anything made from matter.

Materials are described in terms of physical and chemical properties. Chemical properties are determined by transforming the material into another chemical substance. Physical properties are observed and measured without transforming the material into another substance.

ExampleFlammability is a chemical property. Flammable materials ignite when energy and oxygen are supplied. Carbon dioxide (CO2), water vapour (H2O), and other new materials are produced when a material is ignited. Flammability can only be determined by transforming the material into other chemical substances.

The use of a material is dependent on both chemical and physical properties. Flammable materials are not used in applications where materials are combusted. Materials that have low melting points are not used in applications that involve heat transfer. Materials that have good electrical conductivity are used in electric circuits. Common physical properties include melting and boiling point, electrical conductivity and thermal conductivity.

Thermal conductivityHeat is the transfer of energy between two materials due to a temperature difference. Heat flows from higher to lower temperatures. The rate at which energy is transferred (as heat) is dependent on a physical property called thermal conductivity. Materials that have high thermal conductivity transfer heat rapidly. Materials that have low thermal conductivity transfer heat more slowly and store the energy for an extended period.

Metals have excellent thermal conductivity. Metals consist of free moving particles called electrons (Figure 1.01). Free electrons transfer heat rapidly. Metals are used in applications involving rapid heat transfer. Copper is used in the base of cookware to increase the rate at which heat is transferred from stove to food. Nichrome is a mixture of metals (alloy) that is used in heating elements.

Figure 1.01: Thermal conductivity in metals

Materials that have poor thermal conductivity are called thermal insulators. Thermal insulators store energy for an extended period. Thermal insulators are used to reduce the rate of heat transfer between objects. Nylon, cotton, wool, and polyester are materials that are used in clothing. Down feathers are used in quilts, pillows, and blankets. Polystyrene and polyurethane are used in the walls and ceilings of buildings to prevent heat loss.

Chemistry book.indb 1 16/10/2016 13:18

© Essentials Education2

STAGE 1 CHEMISTRY TOPIC 1: MATERIALS AND THEIR ATOMS

Electrical conductivityElectricity is a flow of particles that have an electric charge (positive or negative). Electrical conductors are materials consisting of free-moving electrically charged particles. Charged particles move when the material is connected to a source of electric potential difference. Sources of electric potential difference (called emf) include batteries, power supplies, generators, and wall outlets.

Metals have excellent electrical conductivity. Metals consist of free-moving charged particles called electrons. Electrons have a negative charge. Electrons move in the direction of the positive terminal when connected to an emf (Figure 1.02).

Figure 1.02: Electrical conductivity in metals

Electrolytes have good electrical conductivity. Electrolytes consist of charged particles called ions. Negatively charged ions are called anions. Positively charged ions are called cations. Anions move to the positive electrode, and cations move to the negative electrode when two electrodes are inserted into an electrolyte (Figure 1.03). The movement of ions constitutes an electric current.

Figure 1.03: Electrical conductivity in electrolyte solution

Material that have poor electrical conductivity are called electrical insulators. Electrical insulators consist of charged particles that are not free to move when the material is connected to an emf. Polyvinyl chloride (PVC) is used to insulate electrical wires. Organic oils are used in transformers and capacitors to prevent electric shock. Sulfur hexafluoride is used in operating theatres to prevent ignition of anaesthetic gases due to faulty electrical equipment.



TOPIC 1

1

Melting pointA material transitions from solid to liquid at its melting point. Particles in a solid are held together by strong electrical forces. Energy is added to overcome the electrical forces between particles in a solid material (Figure 1.04). Particles separate and the material transitions to a liquid state when sufficient heat is transferred. Materials that have strong internal forces have higher melting points.

Figure 1.04: Melting point of a material

Metals and continuous compounds have high melting points. Metals and alloys are used in internal combustion engines. Bricks and mortar (continuous compounds) are used in building construction.

Boiling pointA material transitions from liquid to gas at its boiling point. Particles in a liquid are held together by weak electrical forces. Energy is added to separate the particles in a liquid (Figure 1.05).

Figure 1.05: Boiling point of a material

Materials that have low boiling points are used in aerosol sprays. Materials that have high boiling points are used as solvents in chemical industry.

SolubilitySolutes are dissolved by solvents; this forms a solution. A solute is the minority component of a solution. The solvent is the majority component of a solution. A solution consists of a solute that has been dissolved by a solvent. Solubility is a measure of the amount of solute that is dissolved by a given amount of solvent. A solution of sodium chloride is formed by dissolving sodium chloride (solute) in liquid water (solvent). 360 grams (g) of sodium chloride are dissolved in every one litre (L) volume of liquid water. The solubility of sodium chloride is stated as 360 g/L. Solubility depends on the physical and chemical properties of the solute and solvent. Water-soluble solutes dissolve in liquid water. Water-insoluble solutes do not dissolve in liquid water.

Science understandingNanomaterials are substances that contain particles in the size range 1–100 nanometres (nm).


Nanotechnology involves the study and use of extremely small materials called nanoparticles. Nanomaterials consist of particles that are less than 100 nm across. One nanometre is one-billionth of a metre. There are 10 million nanometres in the space between the 0 and 1 cm markings on your ruler (Figure 1.06).

Figure 1.06: Scale of one nanometre




Nanomaterials are present in nature. Spider webs consist of strong nanofibers (proteins). The wings of a butterfly and the skin of a chameleon consist of reflective nanoparticles. Viruses are nanoparticles that spread disease. Lizards and insects use nanomaterials (hairs) on their legs to adhere to surfaces. Chloroplasts are nanostructures that transform light into chemical energy for use in cells.

Scientists and engineers research and manipulate the physical and chemical properties of nanomaterials for use in modern applications. Spider silk is being used to produce bulletproof, waterproof and lightweight clothing. Reflective nanocrystals are used as optical biosensors in the field of materials science. Genetically modified viruses are used to infect humans with healthy genes, providing relief to sufferers of genetic illnesses. Nanomaterials that have adhesive properties are being used to improve adhesion between surfaces.

The physical and chemical properties of nanomaterials differ from those of macroscopic materials. Nanoparticles have a much larger surface area than macroscopic materials (Figure 1.07).

Figure 1.07: Surface area of macroscopic and nanoscopic materials

The rate of a chemical process is increased by using materials that have a larger surface area. Gold nanoparticles reflect red and blue light whereas macroscopic gold particles reflect yellow and red light.

Science understandingSuggest uses of materials, including nanomaterials, given their properties and vice versa.


Nanomaterials have properties that make them useful in modern applications. Medicine, the chemical industry, electronics, and computing are all fields where nanomaterials are used. Zinc oxide and titanium oxide nanoparticles are used in sunscreen, as these particles are effective at reflecting harmful UV radiation. Silver nanoparticles are used in bandages and socks to kill bacteria, to reduce infection and to decrease the frequency at which clothes must be washed. Nanocoatings are hair-like structures that are used in modern fabrics and clothing to prevent stains caused by the absorption of liquids. Titanium dioxide nanoparticles transform dirt into carbon dioxide and water on the surface of glass (self-cleaning windows). The optical properties of gold nanoparticles are used in commercial products (including home pregnancy tests) and as a biosensor in medicine. Fullerenes, such as buckyballs and carbon nanotubes, are used to build lightweight materials that are resistant to chemical attack.

There are many possible medical uses of nanotechnology. Nano-sensors are being used inside the body to perform health checks and deliver appropriate quantities of medicine. Nano-scaffolds are used to support the growth of new skin after fire-damage. Nano-capsules are used in targeted drug therapy to deliver drugs to the site of infection and prevent destruction of the body by the immune system. Nano-coatings are used to coat artificial limbs to prevent rejection by the immune system. Gold nanoparticles are used to shrink tumours in patients suffering from cancer.



TOPIC 1

1

Questions1. Below is a table of properties that you may find useful when comparing materials.

Material Density (g cm−3)

Strength (MPa)

Relative hardness (Units)

high density polyethene 0.96 29 4.0

low density polyethene 0.92 15 2.0

polypropene 0.90 270 10.0

PVC 1.33 20 to 60 20.0

polystyrene 1.05 40 25.0

nylon 1.16 83 10.0

acrylic (Perspex) 1.19 70 34.0

steel 7.70 250 120.0

aluminium 2.70 90 27.0

wood (radiate pine) 0.59 42 3.3

glass 2.49 1500.0

Use the table to explain why:

(a) Polystyrene is used for the casings of computers and not polypropene.

(2 marks) KA2

(b) Instead of steel cans (which were used 50 years ago), polypropene bottles are used to hold cleaning fluids.

(2 marks) KA2

(c) Perspex is used instead of glass in greenhouses.

(2 marks) KA2

(d) Steel, rather than aluminium, is used in the framework of large buildings.

(2 marks) KA2

2. Most tennis racquets are made from a polymer reinforced with carbon fibres.

Nanotechnology is used to make better tennis racquets, as nanoparticles are added to fill gaps in, and therefore reinforce, the polymer.

(a) Explain the meaning of the term ‘nanotechnology’.

(2 marks) KA1

(b) Suggest how these new tennis racquets are better than those that do not contain nanoparticles.

(2 marks) KA2




(c) Explain two properties that are likely to change when an object is nano-sized.

Examples may be used to clarify your explanation.

(2 marks) KA2

3. Nanoparticles are put into beauty products including moisturising face creams.

These creams are easy to apply and are invisible on the skin.

Some scientists are worried about the effects of nanoparticles on the body.

At the moment it is impossible for consumers to tell if the creams contain nanoparticles.

(a) Suggest two reasons why the public is concerned by the use of nanoparticles in consumer products.

(2 marks) KA2

(b) Suggest what action should be taken to reduce the concerns of experts and consumers.

(2 marks) KA2

Science understandingDifferences in the properties of substances in a mixture can be used to separate them.


Materials are categorised into pure substances and mixtures. Pure substances consist of only one type of atom, molecule or formula unit. Elements and compounds are examples of pure substances. Copper consists of copper atoms, and sodium chloride consists of sodium and chloride ions that are combined in a fixed ratio (Figure 1.08).

Figure 1.08: Chemical structures of copper (left), and sodium chloride (right)

Mixtures consist of two or more materials that are not chemically bonded. Crude oil, orange juice, soft drink, smoke, alloys and cleaning products are examples of mixtures.

Mixtures are described as being either homogeneous or heterogeneous. Homogeneous mixtures have a composition that is uniform. Sea water, petroleum and alloys are examples of homogeneous mixtures. Heterogeneous mixtures have a composition that is non-uniform. Gravel, blood and milk are examples of heterogeneous mixtures.



TOPIC 1

1

Science understandingIdentify how the components of a mixture can be separated by methods including filtration, distillation and evaporation.


The components of a mixture are separated using different techniques. The technique used to separate the components of a mixture depends on the physical properties of the materials being separated.

FiltrationFiltration is used to separate an insoluble solid from a solvent. The mixture of insoluble solid and liquid is passed through filter paper. Filter paper consists of small pores that allow liquid to pass through. The liquid that passes through the filter paper is called the filtrate (Figure 1.09). The pores are too small to allow any solid to pass. Solid collects in the filter funnel (Figure 1.09).

Figure 1.09: Simple filtration

EvaporationA solution consists of a solute dissolved in a solvent. A solid solute is separated from a solvent by evaporation. The solution is transferred to an evaporating dish (Figure 1.10). The solution is heated and the solvent evaporates. The evaporated solvent enters the atmosphere and the solid solute remains in the evaporating dish. The solution is heated directly using a burner, hot plate, or steam bath.

Figure 1.10: Evaporation




DistillationMixtures that consist of two or more liquids are separated using simple distillation. The mixture is transferred to a distillation flask (Figure 1.11). The mixture is heated until the boiling point of one component is reached. The first component evaporates and moves into a condenser. The vapours condense into a liquid, which travels into the receiving flask. Distillation is most effective when there is a significant difference in the boiling points of the liquids in the mixture.

Figure 1.11: Simple distillation

Questions4. Use the diagram below concerning the classification of matter to answer the following questions.

(a)

Classification of Matter

X ZHomogeneous Elements

Mixtures Substances

Matter

State the type of mixture represented by X.

(1 mark) KA1

(b) Define the term ‘mixture’.

(2 marks) KA1



TOPIC 1

1

(c) Describe three characteristics of a mixture, and give an example for each characteristic.

(6 marks) KA2

(d) Given a mixture of sand and water, state one process that can be used to separate the water from the sand.

(1 mark) KA1

(e) State the type of substance represented by Z.

(1 mark) KA1

(f) State two differences between Z and mixtures.

(2 marks) KA1

(g) Explain what is meant by the term ‘pure substance’.

(2 marks) KA1

(h) State three characteristics shown by a pure substance.

(3 marks) KA1

(i) Explain, in terms of particle arrangement, why soluble salts form homogeneous mixtures.

(2 marks) KA2

(j) List three points of difference between homogeneous and heterogeneous mixtures. State three examples of each type of mixture.

(6 marks) KA1




5. Mixtures can be separated by a variety of physical techniques. Below is a list of mixtures:

• Crude oil• salt water• insoluble calcium carbonate in water

Use each one as an example to describe the following separation techniques:

(a) Evaporation:

(2 marks) KA2

(b) Filtration:

(2 marks) KA2

(c) Distillation:

(2 marks) KA2


Topic 1: Materials and their Atoms

Documents

Transcript of Topic 1: Materials and their Atoms