Chemical bonding and structure

• The tendency of atoms to achieve the electronic arrangement of the nearest noble gas in the periodic table (octet rule)

• Chemical species: atom, ion, and molecule

• Ionic bonding and structure exemplified by sodium chloride

• Covalent bonding and simple molecular structure exemplified by water, oxygen and carbon dioxide

• Giant covalent structure exemplified by diamond and graphite

• Draw electronic diagrams to represent atoms, ions and molecules

• Predict the formation of ionic and covalent substances and write their chemical formulae

• Draw electronic diagrams of ionic and simple molecular substances

• Build models of ionic and simple molecular substances

• Explain the properties of ionic substances by their structures

• Explain the properties of simple molecular substances by their structures

• Predict structures and properties of substances

• Write balanced equations for the formation of simple ionic and covalent substances

Module highlights

In this module, students have opportunities to:

• appreciate that people at different times and in different cultures have always been seeking ways to make sense of the vast variety of matter existing around them (e.g.

people in the East and the West proposed different frameworks for the ‘basic elements’

making up the world)

• recognise the periodic table as an organiser resulting from pattern seeking and logical thinking to organise our understanding of elements

• appreciate that scientists make use of patterns and trends to make predictions (e.g.

predicting the chemical properties of unfamiliar elements based on trends revealed in the periodic table)

• develop skills in risk assessment in conducting experiments

• realise that discrepancies from patterns and trends (e.g. some elements did not fit into their expected positions in the periodic table constructed then) led scientists to further investigations and refinements of the periodic table

• appreciate that the atomic model (a conceptual model) is developed through systematic observations and much imagination (e.g. Rutherford’s experiment)

• recognise the contribution of the atomic model to the development of the modern periodic table, to appreciate that scientific knowledge is a product of the collective wisdom of different scientists

• value the curiosity of scientists which drives them to scientific investigations (e.g.

inference of the existence of ions through electrolysis, which shed light on the understanding of the structure of ionic compounds)

• recognise that scientists make generalisations (e.g. the octet rule) from observations to describe the behaviour of entities in a system

• appreciate that scientists developed symbols (e.g. chemical symbols), formulae and equations as concise languages to communicate in science

• recognise that matter is conserved and charges are balanced (constancy) in all chemical changes

C 5 Electrical Enlightenment

Overview Introduction

Scientists of different nationalities contributed to the study of electricity and magnetism during the period 1800 – 1840. It started with a continuous and steady supply of current electricity from a chemical cell invented by the Italian scientist Volta in 1800. Two decades later, Oersted, a Danish scientist, serendipitously discovered that current could produce a magnetic effect. Ampere, a Frenchman, formulated and explained the relationship among current, magnetic field and force. This was an attempt by scientists to operationally define something that could not be seen and used simple mathematical equations to represent the interrelationships, making predictions of cause-effect relationships between electricity and magnetism possible. In 1831, the great British experimenter, Faraday, discovered electromagnetic induction, which led to large-scale generation of electricity from mechanical energy.

From then onwards, we moved from the age of discovery to invention as we were able to harness electricity and magnetism. Students should find the stories of inventions, such as that of Bell, Edison and Marconi, stimulating. In the new millennium scientists are still working hard with the quest for superconductors that are viable for commercial uses.

In this module, a historical approach is adopted to lead students to revisit the work of pioneers in electricity and magnetism. By repeating their experiments, students will come to appreciate the importance of experimentation in the advancement of science. Students are expected to learn electricity and magnetism from a perspective which relates the significance of the discoveries and the state-of-the-art applications.

Focusing Questions

• What is the basic principle of chemical cells? What drives charges to circulate in a circuit?

• How is the interaction between electricity and magnetism utilised to generate mechanical energy?

• What determines the magnitude of the current in an electric circuit?

• What is electromagnetic induction, and how do we generate electrical energy from mechanical work?

• How do we harness electrical energy to other forms? How can electricity be used safely at home?

• What is the significance of experimentation in the study of electricity and magnetism and the subsequent development from discoveries to inventions?

Module Organisation

Timeline Pioneer Major discovery Significance Implications & applications 1800 Volta

Italian

y Electricity from chemical reaction

y Stable supply of current that allows a leap from electrostatics to current electricity y Electrolysis

y Chemical cell y Fuel cell

1820 Oersted Danish

y Magnetic effect of a current y The first time in history that we knew magnetism can be produced from electricity

Ampere French

y Solenoid

y Force on current-carrying conductor in a magnetic field

y The birth of electromagnetism y EM waves

y Telecommunication 1821 Faraday

British

y Electromagnetic rotation y Electricity can be harnessed to drive machines, i.e. from electrical energy to mechanical energy

y Motor

1827 Ohm German

y Ohm’s Law

y Heating effect of current

y The relationship between current and voltage in a circuit

y Fuse

y Quest for superconductor

1831 Faraday British

y Electromagnetic induction y Conversion of mechanical energy to electrical energy

y a.c. electricity

y Generator

y Long distance transmission of electricity

y EM waves

y Telecommunication 1840 Joule

British

y Conservation of electrical energy

y Quantifying electrical energy y Electricity consumption

y Domestic electricity

C 5: Electrical Enlightenment

Students should learn Suggested learning and teaching activities 5.1 Volta and the chemical cell

• Volta’s discovery of producing electric current from chemical reactions in 1800

• Basic structure of a simple chemical cell

• Reactions that occur at the electrodes in simple chemical cells

• Redox reaction as the basic principle of chemical cells

• Working principles and implications of fuel cells

• Repeat Volta’s experiment to make a voltaic cell

• Make simple chemical cells and compare their voltages

• Write ionic half equations for reactions that occur at the electrodes in simple chemical cells

• Examine different types of batteries (e.g. alkaline, mercury, Li-ion, Ni-Cd batteries, lead acid accumulator)

• Search and present information on the prospect of fuel cells