Matter and atoms the beginnings

Compounds

Most of the materials we come into contact with are compounds, substances formed by the chemical combination of two or more atoms of the elements. A single "particle" of a compound is called a molecule. Water, for example, is always made up of two parts hydrogen and one part oxygen. The chemical formula of a compound is written by listing the symbols of the elements together, without any spaces between them. If a molecule contains more than one atom of an element, a number is subscripted after the symbol to show the number of atoms of that element in the molecule. Thus the formula for water is H2O, never HO or H2O2.

Law of Definite Proportions

The idea that compounds have defined chemical formulas was first proposed in the late 1700s by the French chemist Joseph Proust. Proust performed a number of experiments and observed that no matter how he caused different elements to react with oxygen, they always reacted in defined proportions. For example, two parts of hydrogen always reacts with one part oxygen when forming water; one part mercury always reacts with one part oxygen when forming mercury calx.

Atoms

A single unit of an element is called an atom. The atom is the most basic unit of matter, which makes up everything in the world around us. Each atom retains all of the chemical and physical properties of its parent element. At the end of the nineteenth century, scientists would show that atoms were actually made up of smaller, "subatomic" pieces, which smashed the billiard-ball concept of the atom

Boyle, Robert

English chemist and theologian, born at Lismore Castle, Munster, Ireland (1627-1691). Boyle published on a broad array of topics, including chemistry, physics, medicine, and theology. He is best known for Boyle's Law, from which the ideal gas law is derived. In 1661, Boyle published The Sceptical Schymist or Chymico-Physical Doubts and paradoxes, which is considered a conerstone in the field of modern chemistry. Boyle was also one of the founding members of the Royal Society of London.

Dalton's theory concepts 4

When elements react to form compounds, they react in defined, whole-number ratios. The experiments that Dalton and others performed showed that reactions are not random events; they proceed according to precise and well-defined formulas.

Dalton's theory 2

All atoms of a given element are identical; atoms of different elements have different properties. Dalton's theory suggested that every single atom of an element such as oxygen is identical to every other oxygen atom; furthermore, atoms of different elements, such as oxygen and mercury, are different from each other. Dalton characterized elements according to their atomic weight; however, when isotopes of elements were discovered in the late 1800s, this concept changed.

Dalton's theory concepts 1

All matter is composed of indivisible particles called atoms. Bernoulli, Dalton, and others pictured atoms as tiny billiard-ball-like particles in various states of motion. While this concept is useful to help us understand atoms, it is not totally correct.

Elements require more explanation.

As early as 1660, Robert Boyle recognized that the Greek definition of element (earth, fire, air, and water) was not correct. Boyle proposed a new definition of an element as a fundamental substance, and we now define elements as fundamental substances that cannot be broken down further by chemical means. Elements are the building blocks of the universe. They are pure substances that form the basis of all of the materials around us.

Dalton's theory 3

Chemical reactions involve the combination of atoms, not the destruction of atoms. Atoms are indestructible and unchangeable, so compounds, such as water and mercury calx, are formed when one atom chemically combines with other atoms. This was an extremely advanced concept for its time; while Dalton's theory implied that atoms bonded together, it would be more than 100 years before scientists began to explain the concept of chemical bonding.

Early ideas about matter

Did you know that some ancient Greeks believed that all matter was made up of four substances: fire, air, water, and earth? They believed that rabbits were soft because they had more water than earth. Although this idea seems silly now, it contains a fundamental principle of atomic theory: that matter is made up of a small number of fundamental elements.

Priestley, Joseph

English chemist, natural philosopher and theologian, born in Yorkshire (1733-1804). He is most frequently noted for discovering oxygen. Priestly also isolated and characterized 7 additional gases, and his work furthered the scientific understanding of photosynthesis and respiration.

Dalton, John

English physicist, chemist and meteorologist born in Eaglesfield, Cumberland (1766-1844). Dalton published Experimental Essays on the Constitution of Mixed Gases; on the Force of Steam or Vapour from water and other liquids in different temperatures, both in a Torricellian vacuum and in air; on Evaporation; and on the Expansion of Gasses by Heat, in which he details his theory of partial pressures in gas mixtures. He is most famous for his investigation of relative atomic weights, and for founding atomic theory.

Empedocles's theory was quite popular, but it had a number of problems.

For example, regardless of how many times you break a stone in half, the pieces never resemble any of the core elements of fire, air, water, or earth. Despite these problems, Empedocles's theory was an important development in scientific thinking because it was among the first to suggest that some substances that looked like pure materials, like stone, were actually made up of a combination of different "elements."

Proust, Joseph

French chemist, born in Angers (1754-1826). Proust proposed that the proportions of substances that combine in a given reaction are always the same. This is now known as the Law of Definite Proportions or Proust's Law.

Lavoisier, Antoine

French chemist, born in Paris (1743-1794). He is famous for proving that air is composed of several gases. He also experimentally established the Law of Conservation of Mass, devised the system of chemical nomenclature that is currently in use, and authored the first modern chemistry textbook, Traité Élémenaire de Chimie (Elementary Treatise of Chemistry).

Democritus

Greek natural philosopher born in Thrace (ca. 460-370 BCE). With his teacher, Leucippus, Democritus developed the atomist concept of the cosmos, which held that the world is composed of invisible, minute particles suspended in a void. Democritus called these infinitesimally small pieces of matter atomos, meaning 'indivisible'. We use the term "atom" today.

Empedocles

Greek philosopher born in Acragas (490-430 BCE). He is credited (by Aristotle) with inventing rhetoric, and by the philosopher Galen with founding the science of medicine. Empedocles is remembered for his belief that all matter was composed of four elements: earth, air, fire, and water. He also proved experimentally that air was a substance, rather than empty space, and deduced that light travels at a finite velocity.

Elements

Some elements can be seen in pure form, such as mercury in a thermometer; some we see mainly in chemical combination with others, such as oxygen and hydrogen in water. We now know of approximately 116 different elements. Each of the elements is given a name and a one- or two-letter abbreviation. Often this abbreviation is simply the first letter of the element; for example, hydrogen is abbreviated as H, and oxygen as O. Sometimes an element is given a two-letter abbreviation; for example, helium is He. When writing the abbreviation for an element, the first letter is always capitalized and the second letter (if there is one) is always lowercase.

The way science grows

The story of the development of modern atomic theory is one in which scientists built upon the work of others to produce a more accurate explanation of the world around them. This process is common in science, and even incorrect theories can contribute to important scientific discoveries. Dalton, Priestley, and others laid the foundation of atomic theory, and many of their hypotheses are still useful. However, in the decades after their work, other scientists would show that atoms are not solid billiard balls, but complex systems of particles. Thus they would smash apart a bit of Dalton's atomic theory in an effort to build a more complete view of the world around us.

element

a pure chemical substance that is made of only one kind of atom

matter

physical substances