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Explore the evolution of elemental understanding from ancient Greek philosophy to modern atomic theory, including key figures and groundbreaking discoveries such as Dalton's Atomic Theory and the development of scientific models. Delve into the concepts of compounds, elemental composition, and the evolution of scientific laws and theories. Discover the significance of the Law of Definite Composition and explore the innovative models proposed by scientists like Thomson, Rutherford, Bohr, de Broglie, and Schrödinger. Witness the transformation of scientific ideas through observations and experiments, shedding light on the intricate nature of matter and elements.
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Science 9 Unit 2 Topic 3: What are Elements?
Ancient Greek philosophers thought that all matter was made out of fire, water, earth and air • Were referred to as “elements” • Everything were a combination of 4 elements and had varying properties of dryness, hotness, coldness, and wetness
The current view of the elements began to develop several; hundred years ago • Sir Francis bacon (1561-1626) • Published book • Argued that science should be built on experimental evidence rather than on thought • Robert Boyle (1627-1691) • Recognized that elements could be combined to form compounds
Taking Matter Apart • Scientists learned to take matter part by ordinary chemical means until it would not break down any further • They were able to determine if a substance was a pure substance or a mixture
Taking Matter Apart • Antoine Lavoisier (1743- 1794) • Defined elements as pure substances that cannot be decomposed into simpler substances by means of a chemical change • Identified 23 pure substances as elements • Successful techniques as an experimenter was his careful measurements of mass • He measured the mass of all the substances involved in a chemical change • Created the law of conservation of mass • States “in a chemical change, the total mass of the new substances is always the same as the total mass of the original substances”
The Law of Definite Composition • Compounds are pure substances that contain 2 or more elements combined together in fixed (or definite) portions • Ex. water
New Discoveries • 19th Century • Voltaic pile • A device we now call a battery • Scientist began using voltaic pikes to pass electricity through water • Discovered hydrogen and oxygen gasses were produced, and that the water had been decomposed into hydrogen and oxygen • Electrolysis • The process of decomposing a chemical compound by passing an electric current through it • Used electrolysis to isolate • Potassium, sodium, magnesium, calcium, strontium, barium
Dalton’s Atomic Theory • The particle model of matter cannot account for particles of different substances combining or decomposing • John Dalton (1766-1844) • Introduced a new way of explaining chemical facts and laws in his atomic theory • All matter is made up of small particles called atoms • Atoms cannot be created, destroyed, or divided into smaller particles • All atoms of the same elements are identical in mass and size • Compounds are created when atoms of different elements link together in definite proportions.
Element • A pure substance made of one type of particle or atom • Compounds • Pure substances that are made up of 2 or more elements chemically combined together
Laws, Theories, Models, and Observations • Laws • Describe and summarize what happens • Theories • Imaginative ways to explain why something happens • Thousands of observations and hundreds of experiments are often made before a theory is accepted by scientists
Scientific ideas may change over time as more evidence is gathered • Scientific models help to picture structures or processes that cannot directly be seen
A brief history of atomic Models • J.J Thomsen • Developed the “plum pudding” or “raisin bun” model • Thought that negatively charged electrons were stuck in a positively charged mass
A brief history of atomic Models • Ernest Rutherford • Hypothesized the atomic nucleus • Almost all the mass of an atom is at the centre • Was made from protons (positively charged particles) and another particle (later named neutron- uncharged particles) • The rest of the area was mostly empty except for orbiting electrons (negatively charged particles)
A brief history of atomic Models • Niels Bohr • Both Bohr and Rutherford pictured the atom like a solar system • Rutherford’s system did not explain many of the atom’s properties • Bohr suggested that electrons move around the nucleus in fixed pathways called electron shells
A brief history of atomic Models • Louis de Broglie and Erwin Schrodinger • Concluded that atoms due in fact have electron levels • Suggested that there was an area around the nucleus where electrons were most likely found • This region was called the electron cloud
(-) negative (+) positive Neutral- no charge Very light Heavy Slightly greater than protons In Nucleus In nucleus Around nucleus, in electron cloud
