1. Topic 3
Periodic Table
The development of the Atomic theory

2. 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?

3. 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?

4. 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?

5. 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.”

6. 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.

7. 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.

8. 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.

9. 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.

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

11. 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.

12. 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.

13. 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.

14. 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)

15. 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.