Reading Atoms From Democritus to Dalton Empedocles – argued that all matter was composed of four elements: fire, air, water, and earth. Democritus – infinitesimally small pieces of matter atomos, meaning "indivisible." He suggested that atomos were eternal and could not be destroyed. Torricelli & Bernoulli – showed that air had weight and was capable of pushing down on a column of liquid mercury, pictured air and other gases as loose collections of tiny billiard-ball-like particles that are continuously moving around and bouncing off one another. Priestley – substances could combine together or break apart to form new substances with different properties. Lavoisier – Law of Conservation of Mass Goal of reading: Understand key hypotheses that allow us to get out of the particle model.

Dalton's atomic theory had four main concepts: All matter is composed of indivisible particles called atoms. All atoms of a given element are identical; atoms of different elements have different properties. Chemical reactions involve the combination of atoms, not the destruction of atoms. When elements react to form compounds, they react in defined, whole-number ratios. Dalton Lightly educated English Quaker Born 1766 He was bright and at the age of 12 he was put in charge of the school, and in his spare time reading Newtons work in Latin. At 15 he moved to Mancheaster and began writing books ranging in subjects, Meteorology to grammar But it was a rather plump (900 pages) book called A New system of Chemical Philosophy, published in 1808 that established his reputation. Short chapter, he purposed that the root of all matter are exceedingly, tiny, irreducible particles called atoms. For a century it remained hypothetical, until Rutherford.

Dalton’s atomic theory vs. Atomic Theory Atomic Theory – states that matter is composed of discrete units called atoms Dalton’s ideas about what matter looks like at the simplest level. But, there are parts of his ideas that have changed…. Today, we have the Atomic Theory- which states nature of matter, which states that matter is composed of discrete units called atoms. Explaining that matter is make of atoms, that explain the why…for a lot of different situations. In the decades after their work, other scientists would show that atoms are not solid billiard balls, but complex systems of particles

Worksheet #2 Hydrogen Oxygen Water Hydrogen Chlorine Product

Worksheet #2 Nitrogen Hydrogen Ammonia

Reactions of Gases Gay-Lussac noted that gases appear to react in simple integer ratios Example: Two volumes of hydrogen reacted with one volume of oxygen to produce two volumes of water These findings appeared to contradict the idea that equal volumes of gases have equal numbers of particles

Avogadro’s Key Contribution: The molecules of some gaseous elements must contain two atoms. Hydrogen Chlorine Hyrdrogen Chloride

Avogadro’s Hypothesis assumed: Equal volumes of gases have equal numbers of molecules. These particle can be split into half-particle during chemical reactions (particles of some gaseous elements must contain two atoms.) That particles of elemental gases could contain more than a single atom. Dalton Lightly educated English Quaker Born 1766 He was bright and at the age of 12 he was put in charge of the school, and in his spare time reading Newtons work in Latin. At 15 he moved to Mancheaster and began writing books ranging in subjects, Meteorology to grammar But it was a rather plump (900 pages) book called A New system of Chemical Philosophy, published in 1808 that established his reputation. Short chapter, he purposed that the root of all matter are exceedingly, tiny, irreducible particles called atoms. For a century it remained hypothetical, until Rutherford.

Worksheet #2 Hydrogen Oxygen Water

Avogadro’s Hypothesis Two volumes of hydrogen react with one volume of oxygen to produce two volumes of water when hydrogen and oxygen can be split into half-molecules!

A diatomic is made of two of the same element bonded together (7 + 1).

Is everything a simple particle? One of the greatest challenges early chemists faced was trying to find a way to connect the mass of a substance to the number of particles in the sample.

Avogadro’s Hypothesis If we accept Avogadro’s Hypothesis, we can compare the mass of various gases and deduce the relative mass of the molecules. To do this, we pick a weighable amount of the lightest element (how about 1.0) then use mass ratios to assign atomic masses to the other elements.

Relative Mass To assign relative masses to elements it is necessary to know that the samples being compared have the same number of particles If particles are all the same size, the same size sample would have the same number of particles If particles are different sizes, the same size sample would have different numbers of particles

Relative Mass At the time, chemists did not know which was true and tended to think the second one was more likely Example: A bucket of baseballs has fewer balls than an identical bucket of golf balls If this is true in the macroscopic world, why wouldn’t it be true in the microscopic one?

Relative Mass Consider earlier this year when we studied density: was iron more dense than the stopper because iron had more particles per given volume than the stopper or because iron’s individual particles were more massive than the stopper’s? Could it be some combination of both?

We did not know earlier this year, neither did Dalton. Relative Mass We did not know earlier this year, neither did Dalton.

Percent Composition Law of conservation of mass 100 gram of carbon that react with 100 grams of oxygen. After the compound is made there is left 43g O and 58g C. How much does compound weight? How many grams of oxygen and carbon are in the products?

Law of Definite Proportions Law of Definite Proportions – A compound is always composed of the same elements in the same proportion by mass Use percent mass to calculate proportion of each element.

Percent Composition Mass of element * 100 = % element mass of compound A 20.00 g sample of table sugar was analyzed by mass. Carbon was 8.44g, hydrogen was 1.30g, and the rest was oxygen. Determine its percent composition of each element.

Percent Composition Since the Law of Definite Proportions states that a compound is always composed of the same elements in the same proportion by mass: This table sugar compound is always 42.20% carbon, 6.50 % hydrogen, and 51.30% oxygen, regardless of the sample size.

Law of Multiple Proportions The masses of one element which combine with a fixed mass of the second element are in a ratio of simple whole numbers.

Dalton’s Atomic Theory Dalton's Atomic Theory had four main concepts: All matter is composed of indivisible particles called atoms. All atoms of a given element are identical; atoms of different elements have different properties. Chemical reactions involve the combination of atoms, not the destruction of atoms. When elements react to form compounds, they react in defined, whole-number ratios. Dalton Lightly educated English Quaker Born 1766 He was bright and at the age of 12 he was put in charge of the school, and in his spare time reading Newtons work in Latin. At 15 he moved to Mancheaster and began writing books ranging in subjects, Meteorology to grammar But it was a rather plump (900 pages) book called A New system of Chemical Philosophy, published in 1808 that established his reputation. Short chapter, he purposed that the root of all matter are exceedingly, tiny, irreducible particles called atoms. For a century it remained hypothetical, until Rutherford. Dalton’s Law: Law of Multiple Proportions

ANSWER The best way is….. If it is a gas (same number of particle per unit volume) If it is a liquid or gas (different number of particle per unit volume)