Topic 3 Periodic Table The development of the Atomic theory

How did scientists come up with this? Topic 3 The development of the Atomic theory Atoms are made from smaller particles! protons neutrons electrons How did scientists come up with this?

Topic 3 Key questions Who came up with the first theory of atoms? The development of the Atomic theory Key questions Who came up with the first theory of atoms? How did the atomic theory develop? Who discovered the electron? What is the modern atomic theory?

Topic 3 Philosophical idea The development of the Atomic theory Philosophical idea Description of matter began with the Greek philosopher Democritus more than 2000 years ago. He and many other philosophers had puzzled over this question: Could matter be divided into smaller and smaller pieces forever, or was there a limit to the number of times a piece of matter could be divided?

Topic 3 Philosophical idea The development of the Atomic theory Philosophical idea Democritus concluded that matter could not be divided into smaller and smaller pieces forever. Eventually the smallest possible piece would be obtained. Democritus named this small, indivisible piece, an atom; atom comes from the Greek word atomos, which means “not to be cut” or “indivisible.”

Topic 3 Philosophical idea The development of the Atomic theory Philosophical idea Aristotle was part of the generation that succeeded Democritus. Aristotle did not believe in atoms, instead, he thought that all matter was composed of 4 basic elements, water, fire, earth, and air. His opinion was accepted for nearly 2000 years.

The first atomic theory Topic 3 The development of the Atomic theory The first atomic theory In the early 1800’s, the English chemist John Dalton performed a number of experiments that eventually led to the acceptance of the idea of atoms. In 1803, Dalton combined the results of his experiments with other observations about matter and proposed an atomic theory.

Foundations of Atomic Theory Topic 3 The development of the Atomic theory Foundations of Atomic Theory The transformation of a substance or substances into one or more new substances is known as a chemical reaction. Law of conservation of mass: mass is neither created nor destroyed during ordinary chemical reactions or physical changes.

Foundations of Atomic Theory, continued Topic 3 The development of the Atomic theory Foundations of Atomic Theory, continued Law of definite proportions: a chemical compound contains the same elements in exactly the same proportions by mass regardless of the size of the sample or source of the compound. Law of multiple proportions: if two or more different compounds are composed of the same two elements, then the ratio of the masses of the second element combined with a certain mass of the first element is always a ratio of small whole numbers.

Law of Conservation of Mass Topic 3 The development of the Atomic theory Law of Conservation of Mass

Law of Multiple Proportions Topic 3 The development of the Atomic theory Law of Multiple Proportions The ratio of the masses of one element combined with a certain mass of a second element is always a ratio of small whole numbers.

Dalton’s Atomic Theory Topic 3 The development of the Atomic theory Dalton’s Atomic Theory All matter is composed of extremely small particles called atoms. Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties. Atoms cannot be subdivided, created, or destroyed.

Dalton’s Atomic Theory, continued Topic 3 The development of the Atomic theory Dalton’s Atomic Theory, continued Atoms of different elements combine in simple whole-number ratios to form chemical compounds. In chemical reaction, atoms are combined, separated, or rearranged.

Topic 3 Modern Atomic Theory The development of the Atomic theory Modern Atomic Theory Not all aspects of Dalton’s atomic theory have proven to be correct. We now know that: Atoms are divisible into even smaller particles (by a nuclear change) A given element can have atoms with different masses (isotopes)

Topic 3 Modern Atomic Theory The development of the Atomic theory Modern Atomic Theory BUT, Some important concepts remain unchanged. All matter is composed of atoms. Atoms of any one element differ in properties from atoms of another element.