The Building Blocks of Matter

Objectives Recognize that science is a progressive endeavor that reevaluates and extends what is already known. (SPI Inq.1) Compare and contrast historical models of the atom. (SPI ) Explain the relationship between Dalton’s atomic theory and the law of conservation of mass, the law of definite proportions, and law of multiple proportions.

Democritus(400B.C.) called nature’s basic particle an atom, based on the Greek word meaning indivisible. He felt that matter was noncontinuous(this means you can’t divide matter). He had interesting theories about what held these atoms together—he thought things such as hooks.

Aristotle did not believe in atoms. He thought that all matter was continuous– that it was infinitely smaller and what you see with the eye would be no different than what you could see with the microscope. His opinion was accepted for nearly 2000 years.

There was no experimental evidence to support either Democritus or Aristotle’s ideas, so they remained speculations until the 18 th century. It was then that scientists started gathering evidence for the atomic theory of matter.

Law- observation that is repeated without fail Theory- attempt to explain why a law exists. Theories may be completely correct, partially correct, or totally wrong. But they help get the ball rolling in order to help us understand what we observe.

Three Fundamental Laws of Chemistry Law of Conservation of Mass (1789): In ordinary chemical reactions, mass is neither created nor destroyed. Mass of the reactants equals the mass of the products. Law of Definite Proportions (1797): A chemical compound contains the same elements in exactly the same proportions regardless of the size of the sample or source of the compound. Example: water – hydrogen to oxygen ratio is always 2 to 1.

Law of Multiple Proportions (1803): if two or more different compounds are composed of the same two elements, then the proportions can be expressed as simple, whole-number ratios. Example: Carbon and Oxygen Carbon monoxide - CO Carbon dioxide – CO 2

In 1808, an English schoolteacher named John Dalton proposed an explanation for the law of conservation of mass, the law of definite proportions, and the law of multiple proportions. His model was called 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. Atoms of different elements combine in simple whole- number ratios to form chemical compounds. In chemical reactions, atoms are combined, separated, or rearranged.

Incorrect Parts of Dalton’s Theory Atoms have no subatomic particles. We now know that atoms are made of protons, neutrons, and electrons. Atoms of a given element are not all identical. We will learn later in this unit that a given element can have atoms with different masses.

What We Know About Matter We can’t create or destroy matter. Matter can be changed. Matter had recognizable properties. Matter exists in different states.