# Chemistry

### Rationale/Aims

Chemistry is the study of materials and substances, and the transformations they undergo through interactions and the transfer of energy. Chemists can use an understanding of chemical structures and processes to adapt, control and manipulate systems to meet particular economic, environmental and social needs.

### Structure of Chemistry

In Chemistry, students develop their understanding of chemical systems, and how models of matter and energy transfers and transformations can be used to describe, explain and predict chemical structures, properties and reactions.

### Links to Foundation to Year 10

The Chemistry curriculum continues to develop student understanding and skills from across the three strands of the F-10 Australian Curriculum: Science. In the Science Understanding strand, the Chemistry curriculum draws on knowledge and understanding from across the four sub-strands of Biological, Physical, Chemical and Earth and Space Sciences.

### Representation of Cross-curriculum priorities

While the significance of the cross-curriculum priorities for Chemistry varies, there are opportunities for teachers to select contexts that incorporate the key concepts from each priority.

## Unit 1: Chemical fundamentals: structure, properties and reactions

### Unit 1: Chemical fundamentals: structure, properties and reactions Description

Chemists design and produce a vast range of materials for many purposes, including for fuels, cosmetics, building materials and pharmaceuticals. As the science of chemistry has developed over time, there has been an increasing realisation that the properties of a material depend on, and can be explained by, the material’s structure. A range of models at the atomic and molecular scale enable explanation and prediction of the structure of materials and how this structure influences properties and reactions. In this unit, students relate matter and energy in chemical reactions, as they consider the breaking and reforming of bonds as new substances are produced. Students can use materials that they encounter in their lives as a context for investigating the relationships between structure and properties.

Through the investigation of appropriate contexts, students explore how evidence from multiple disciplines and individuals and the development of ICT and other technologies have contributed to developing understanding of atomic structure and chemical bonding. They explore how scientific knowledge is used to offer reliable explanations and predictions, and the ways in which it interacts with social, economic, cultural and ethical factors.

Students use science inquiry skills to develop their understanding of patterns in the properties and composition of materials. They investigate the structure of materials by describing physical and chemical properties at the macroscopic scale, and use models of structure and primary bonding at the atomic and sub-atomic scale to explain these properties. They are introduced to the mole concept as a means of quantifying matter in chemical reactions.

### Unit 1: Chemical fundamentals: structure, properties and reactions Learning Outcomes

By the end of this unit, students:

• understand how the atomic model and models of bonding explain the structure and properties of elements and compounds
• understand the concept of enthalpy, and apply this to qualitatively and quantitatively describe and explain energy changes in chemical reactions
• understand how models and theories have developed based on evidence from a range of sources, and the uses and limitations of chemical knowledge in a range of contexts
• use science inquiry skills to design, conduct, evaluate and communicate investigations into the properties of elements, compounds and mixtures and the energy changes involved in chemical reactions
• evaluate, with reference to empirical evidence, claims about chemical properties, structures and reactions
• communicate, predict and explain chemical phenomena using qualitative and quantitative representations in appropriate modes and genres.

### Unit 1: Chemical fundamentals: structure, properties and reactions Content Descriptions

#### Science Inquiry Skills (Chemistry Unit 1)

Identify, research and refine questions for investigation; propose hypotheses; and predict possible outcomes (ACSCH001)

Design investigations, including the procedure/s to be followed, the materials required, and the type and amount of primary and/or secondary data to be collected; conduct risk assessments; and consider research ethics (ACSCH002)

Conduct investigations, including the use of devices to accurately measure temperature change and mass, safely, competently and methodically for the collection of valid and reliable data (ACSCH003)

Represent data in meaningful and useful ways, including using appropriate graphic representations and correct units and symbols; organise and process data to identify trends, patterns and relationships; identify sources of random and systematic error and estimate their effect on measurement results; and select, synthesise and use evidence to make and justify conclusions (ACSCH004)

Interpret a range of scientific and media texts, and evaluate processes, claims and conclusions by considering the quality of available evidence; and use reasoning to construct scientific arguments (ACSCH005)

Select, construct and use appropriate representations including chemical symbols and formulae, molecular structural formulae, physical and graphical models of structures, chemical equations and thermochemical equations, to communicate conceptual understanding, solve problems and make predictions (ACSCH006)

Select and use appropriate mathematical representations to solve problems and make predictions, including calculating percentage composition from relative atomic masses and using the mole concept to calculate the mass of reactants and products (ACSCH007)

Communicate to specific audiences and for specific purposes using appropriate language, nomenclature, genres and modes, including scientific report (ACSCH008)

#### Science as a Human Endeavour (Units 1 and 2)

Science is a global enterprise that relies on clear communication, international conventions, peer review and reproducibility (ACSCH009)

Development of complex models and/or theories often requires a wide range of evidence from multiple individuals and across disciplines (ACSCH010)

Advances in science understanding in one field can influence other areas of science, technology and engineering (ACSCH011)

The use of scientific knowledge is influenced by social, economic, cultural and ethical considerations (ACSCH012)

The use of scientific knowledge may have beneficial and/or harmful and/or unintended consequences (ACSCH013)

Scientific knowledge can enable scientists to offer valid explanations and make reliable predictions (ACSCH014)

Scientific knowledge can be used to develop and evaluate projected economic, social and environmental impacts and to design action for sustainability (ACSCH015)

#### Properties and structure of atoms

Examples in context

Support materials only that illustrate some possible contexts for exploring Science as a Human Endeavour concepts in relation to Science Understanding content.

## Models of the atom

In the early nineteenth century, Dalton proposed some fundamental properties of atoms that would explain existing laws of chemistry. One century later, a range of experiments provided evidence that enabled scientists to develop models of the structure of the atom. These included using radiation in the form of X-rays and alpha particles, and the passing of particles through a magnetic field to determine their mass (ACSCH010). Evidence from French physicist Becquerel’s discovery of radioactivity suggested the presence of subatomic particles, and this was also a conclusion from gas discharge experiments. British physicist J.J. Thomson was able to detect electrons, and his results, combined with the later work of Millikan, an American experimental physicist, resulted in both the charge and mass of electrons being calculated (ACSCH009). The British chemist Rutherford proposed a model of the atom comprising a heavy nucleus surrounded by space in which electrons were found, and Danish physicist Bohr’s model further described how these electrons existed in distinct energy levels. The last of the main subatomic particles, the neutron, was discovered by the English physicist Chadwick in 1932, by bombarding samples of boron with alpha particles from radioactive polonium (ACSCH010).

Radioisotopes have a wide variety of uses, including Carbon-14 for carbon dating in geology and palaeobiology; radioactive tracers such as Iodine-131 in nuclear medicine; radioimmuno-assays for testing constituents of blood, serum, urine, hormones and antigens; and radiotherapy that destroys damaged cells (ACSCH011). Use of radioisotopes requires careful evaluation and monitoring because of the potential harmful effects to humans and/or the environment if their production, use and disposal are not managed effectively (ACSCH013). Risks include unwanted damage to cells in the body, especially during pregnancy, and ongoing radiation produced from radioactive sources with long half-lives.

## Distribution of elements in the universe

Analysis of the distribution of elements in living things, Earth and the universe has informed a wide range of scientific understandings, including the role of calcium exclusion from bacteria in the evolution of shells and bones; the proliferation of carbon (rather than silicon, which has similar properties and is more abundant in Earth’s crust) in living things; the elemental composition of historical artefacts; and the origin of elements through nuclear fusion in stars (ACSCH011). Analysis of element distribution is informed by data from spectral analysis and other technologies. Evidence from these techniques enables scientists to draw conclusions about a range of phenomena, such as the chemical changes involved in natural processes in both biological and cosmological systems, and the geographic source of historical artefacts (ACSCH014).

Trends in the observable properties of elements are evident in periods and groups in the periodic table (ACSCH016)

The structure of the periodic table is based on the electron configuration of atoms, and shows trends, including in atomic radii and valencies (ACSCH017)

Atoms can be modelled as a nucleus surrounded by electrons in distinct energy levels, held together by electrostatic forces of attraction between the nucleus and electrons; atoms can be represented using electron shell diagrams (all electron shells or valence shell only) or electron charge clouds (ACSCH018)

Flame tests and atomic absorption spectroscopy are analytical techniques that can be used to identify elements; these methods rely on electron transfer between atomic energy levels (ACSCH019)

The properties of atoms, including their ability to form chemical bonds, are explained by the arrangement of electrons in the atom and in particular by the stability of the valence electron shell (ACSCH020)

Isotopes are atoms of an element with the same number of protons but different numbers of neutrons; different isotopes of elements are represented using atomic symbols (for example, $${}_6^{12}C$$, $${}_6^{13}C$$ (ACSCH021)

Isotopes of an element have the same electron configuration and possess similar chemical properties but have different physical properties, including variations in nuclear stability (ACSCH022)

Mass spectrometry involves the ionisation of substances and generates spectra which can be analysed to determine the isotopic composition of elements (ACSCH023)

The relative atomic mass of an element is the ratio of the weighted average mass per atom of the naturally occurring form of the element to $$\frac1{12}$$ the mass of an atom of carbon-12; relative atomic masses reflect the isotopic composition of the element (ACSCH024)

#### Properties and structure of materials

Examples in context

Support materials only that illustrate some possible contexts for exploring Science as a Human Endeavour concepts in relation to Science Understanding content.

## Nanomaterials

Development of organic and inorganic nanomaterials is increasingly important to meet a range of contemporary needs, including consumer products, health care, transportation, energy and agriculture (ACSCH013). Nanomaterials have special physical and chemical properties that make them useful for environmentally friendly products, such as more durable materials, dirt- and water-repellent coatings designed to help reduce cleaning efforts, and insulating materials that improve the energy efficiency of buildings (ACSCH015). Although there are many projected environmental benefits, there are also potential risks associated with the use of nanomaterials due to the size of the particles involved (for example, some are able to cross the human blood-brain or placental barrier) and the unknown effects of these particles on human health and the environment (ACSCH013).

## The importance of purity

There is a large range of situations in chemistry where knowing and communicating the level of purity of substances is extremely important. Impurities can affect the physical and chemical properties of substances, resulting in inefficient or unwanted chemical reactions. Scientists use methods such as mass spectrometry to identify impurities and the level of contamination (ACSCH014). Separation methods which improve the purity of substances are used for food, fuels, cosmetics, medical products and metals used in microelectronic devices. Scientific conventions and international standards are used to represent the purity of materials to ensure consistent applications of standards (ACSCH009).

## Carbon based life and astrobiology

Carbon is far more prevalent in living organisms than silicon, even though silicon is more abundant than carbon in Earth’s crust. This has caused some scientists to question why life on Earth has evolved to be carbon-based. Although carbon and silicon are found in the same group of the periodic table and share similar characteristics, carbon has a range of properties that mean there is more variety in its interactions and the molecules it can form, which is pivotal to biochemical molecules such as carbohydrates, proteins and DNA. These properties of carbon, in addition to analysis of elements found in meteorites, comets and interstellar clouds, cause many astrobiologists to theorise that if life exists elsewhere in the universe, it will be carbon-based as it is on Earth (ACSCH010). Astrobiology, which is concerned with the distribution of life in our own and other solar systems, is a highly interdisciplinary field that draws on the findings of a range of scientists from areas such as geology, molecular biology, astronomy and chemistry (ACSCH011).

Materials are either pure substances with distinct measurable properties (for example, melting and boiling point, reactivity, strength, density) or mixtures with properties dependent on the identity and relative amounts of the substances that make up the mixture (ACSCH025)

Differences in the properties of substances in a mixture, such as particle size, solubility, magnetism, density, electrostatic attraction, melting point and boiling point, can be used to separate them (ACSCH026)

The type of bonding within substances explains their physical properties, including melting and boiling point, conductivity of both electricity and heat, strength and hardness (ACSCH027)

Nanomaterials are substances that contain particles in the size range 1–100 nm and have specific properties relating to the size of these particles (ACSCH028)

Chemical bonds are caused by electrostatic attractions that arise because of the sharing or transfer of electrons between participating atoms; the valency is a measure of the number of bonds that an atom can form (ACSCH029)

Ions are atoms or groups of atoms that are electrically charged due to an imbalance in the number of electrons and protons; ions are represented by formulae which include the number of constituent atoms and the charge of the ion (for example, O2, SO42–) (ACSCH030)

The properties of ionic compounds (for example, high melting point, brittleness, ability to conduct electricity when liquid or in solution) are explained by modelling ionic bonding as ions arranged in a crystalline lattice structure with forces of attraction between oppositely charged ions (ACSCH031)

The characteristic properties of metals (for example, malleability, thermal conductivity, electrical conductivity) are explained by modelling metallic bonding as a regular arrangement of positive ions (cations) made stable by electrostatic forces of attraction between these ions and the electrons that are free to move within the structure (ACSCH032)

Covalent substances are modelled as molecules or covalent networks that comprise atoms which share electrons, resulting in electrostatic forces of attraction between electrons and the nucleus of more than one atom (ACSCH033)

Elemental carbon exists as a range of allotropes, including graphite, diamond and fullerenes, with significantly different structures and physical properties (ACSCH034)

Carbon forms hydrocarbon compounds, including alkanes and alkenes, with different chemical properties that are influenced by the nature of the bonding within the molecules (ACSCH035)

#### Chemical reactions: reactants, products and energy change

Examples in context

Support materials only that illustrate some possible contexts for exploring Science as a Human Endeavour concepts in relation to Science Understanding content.

## Minimising use of energy in industry

Industries are encouraged to reduce their energy requirements in order to save money and reduce greenhouse gas emissions. One of the roles of chemical engineers is to consider the environmental, safety and economic aspects of energy use in the production of chemicals and to design and monitor chemical processes (ACSCH015). Green chemistry principles can be applied to industrial processes to reduce energy requirements; examples of these include recycling heat energy in chemical processes to improve efficiency and reduce cost and environmental impact, and redesigning chemical manufacturing processes to use less energy (ACSCH013).

## Energy in the body

Our bodies rely on the exothermic reaction of respiration to provide us with sufficient energy. Metabolism involves using the energy provided by carbohydrates, proteins and fats in our diet. Typically, food energy is determined based on heats of combustion in a bomb calorimeter, enabling foods to be compared based on the amount of energy they contain (ACSCH011). This information is provided as part of the requirements for processed food labelling in many countries to help consumers control their energy intake. In some instances this information is expressed as a proportion of daily average energy requirements, typically using a value ranging from 7500 to 8700 kJ (ACSCH012). However each individual’s body energy requirements varies depending on their gender, age, mode of activity and the environmental conditions they live in, so an average value may provide limited guidance.

## Use of fuels in society

A significant majority of the energy used for production of electricity, transport and household heating is sourced through the combustion of fuels. Fuels, including fossil fuels and biofuels, can be compared in terms of efficiency and environmental impact, for example by calculating the amount of carbon emissions produced per tonne of fuel used (ACSCH015). Decisions about which fuels to use can reflect social, economic, cultural and political values associated with the source of the fuel. For example, cultural values might inform the use of wood for heating houses; economic and social values might inform the use of crops for biofuel production instead of food production; and economic, social and political values might inform the use of brown coal rather than black coal, despite its being considered a low grade fuel (ACSCH012).

All chemical reactions involve the creation of new substances and associated energy transformations, commonly observable as changes in the temperature of the surroundings and/or the emission of light (ACSCH036)

Endothermic and exothermic reactions can be explained in terms of the Law of Conservation of Energy and the breaking and reforming of bonds; heat energy released or absorbed can be represented in thermochemical equations (ACSCH037)

Fuels, including fossil fuels and biofuels, can be compared in terms of their energy output, suitability for purpose, and the nature of products of combustion (ACSCH038)

A mole is a precisely defined quantity of matter equal to Avogadro’s number of particles; the mole concept and the Law of Conservation of Mass can be used to calculate the mass of reactants and products in a chemical reaction (ACSCH039)