Year 11 ATAR Chemistry - History of Atomic Structure Research PDF

History of Atomic Structure Research Year 11 ATAR Chemistry Learning Objective CFU To outline the developments in research relevant to our What are we learning? understanding of atomic structure. Success Criteria I will be able to:...

History of Atomic Structure Research Year 11 ATAR Chemistry Learning Objective CFU To outline the developments in research relevant to our What are we learning? understanding of atomic structure. Success Criteria I will be able to: Identify the chemists involved in developing models of the atom. Explain their contributions to research in this area. Concept Development CFU Early theories of atomic structure Who postulated the first theory regarding Discussions relevant to elemental forms of matter occurred in particulate matter? 300-600 B.C. by philosophers Plato, Aristotle and Anaximander of Miletus. CFU Democritus was thought to be the first to postulate that matter Where does the word wasn’t infinitely divisible and that it consisted of tiny particles ‘atom’ come from? that could not be divided. He called the particles atomos, with this Greek word meaning ‘indivisible’. Concept Development CFU Dalton’s atomic theory What ideas did John Dalton come up with English teacher & scientist John Dalton (1766 – 1844) is thought relating to atoms? of to be the origin of our current understanding of the atom. His theory was based on the following postulates: Elements are made up of tiny particles called atoms. All atoms of an element are identical with the same physical and chemical properties. Atoms cannot be created, destroyed or transformed into different atoms. A chemical reaction involves the rearrangement of atoms. Compounds are formed when certain collections of atoms come together in specific ratios. Concept Development CFU Thomson’s contributions What did J.J. Thomson discover? J.J. Thomson (1856 – 1940) is generally accepted as the person who discovered the concept of an electron. CFU He used a cathode ray tube to pass a narrow beam between metal plates How did he make this under a magnetic field. discovery? The rays moved in a curved path. By adjusting charge, he was able to estimate the charge and mass of the particles flowing. Work with Chicago chemist Robert Millikan helped to determine the mass to charge ratio of the particles which identified the mass of an electron as 9.11 x 10-31kg. His model of an atom was the ‘plum pudding’ model. Concept Development CFU Rutherford’s contributions What was Ernest Rutherford known for? Ernest Rutherford (1871-1937) was credited as the person who discovered that an atom has a nucleus. CFU Ernest Rutherford’s gold foil experiment, conducted in 1909, involved firing What was the ‘gold foil alpha particles at a thin sheet of gold foil and observing their scattering experiment’? patterns. The surprising result showed that while many passed through, a small fraction were deflected at a large angle. This led to the conclusion that atoms have a dense, positively charged nucleus at their centre. Also discovered the “proton” by bombarding nitrogen nuclei with alpha particle as it ejected a hydrogen atom (+1 charge) Concept Development CFU Chadwick’s contributions What was James Chadwick credited with discovering? James Chadwick is responsible for developing our understanding of the neutron. CFU He identified neutrons as a product of bombarding beryllium with alpha How did he do this? particles. He then postulated that there were neutral particles that existed within an atom. Concept Development CFU Bohr’s contributions. What is the basis for Niels Bohr’s model of the atom? Niels Bohr (1885 – 1962) proposed the Bohr model in 1913, which introduced the idea that electrons orbit the nucleus in fixed paths or energy levels. He suggested that these orbits correspond to specific energy states, and that electrons can jump between these levels by absorbing or emitting energy in the form of photons. Bohr’s model successfully explained the spectral lines of hydrogen, providing a clearer understanding of atomic behaviour. Lesson Closure 1. What was Democritus’ contributions to atomic theory? 2. What was John Dalton’s contributions to atomic theory? 3. What was J.J. Thomsons contributions to atomic theory? 4. What was Ernest Rutherford’s contributions to atomic theory? 5. What was James Chadwick’s contributions to atomic theory? 6. What was Niels Bohr’s contributions to atomic theory? Lesson Closure Identify the chemists involved in developing models of the atom. Explain their contributions to research in this area. Questions Set 3 Questions 1,5,6,7,8,9.