History of the ATOM AP Chemistry. History of the Atomic Theory Democritus (460- 370 BC) thought that matter must be made up of tiny particle called “atomos”

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History of the ATOM AP Chemistry

History of the Atomic Theory Democritus ( BC) thought that matter must be made up of tiny particle called “atomos” which means invisible in Greek.

History of the Atomic Theory Plato ( BC) and later Aristotle ( BC) believed there could be no “ultimate particle”. This view was preferred by most until the late 1700s.

Fundamental Chemical Laws Law of Conservation of Mass-proved through Lavoisier’s careful measurements of masses of reactants and products that mass is neither created nor destroyed. Law of Definite Proportions-Proust showed that a given compound always contains exactly the same proportion of elements by mass.

Fundamental Chemical Laws Law of Multiple Proportions-Dalton found that when two elements form a series of compounds, the ratios of the masses of the second element that combine with 1 gram of the first element can always be reduced to small whole numbers. These laws led to….

Dalton’s Atomic Theory In the early 1800s John Dalton revived the “atoms” concept. “Everything is made of atoms.” His theory proposed that atoms were invisible and indestructible.

Dalton’s Theory Cont’d He also stated that atoms of one element are all the same and different from those of other elements Atoms combine in small whole number ratios to form compounds. In chemical reactions atoms are just rearranged.

Gay-Lussac and Avogadro Gay-Lussac first determined the formula for water by measuring the volumes of gases that combined to form a given volume of water. Avogadro’s hypothesis-based on this work stated that equal volumes of gases at standard temperature and pressure contain equal numbers of particles.

J.J. Thomson and e - Using cathode ray tubes, Englishman J.J. Thomson found the ratio between charge and mass for subatomic particles that we know as electrons. This proved part of Dalton’s theory wrong.

Robert Millikan finds the mass of the electron. Plum-pudding Using Thomson’s experiments and his own data he determined the mass of the electron and found it to be very small, about 9.1 x g. With this information, Thomson proposed a model of the atom that had positive and negative charges in the atoms like plums in a pudding. (“plum pudding” model)

Rutherford’s Gold Foil Experiment. A look inside. Ernest Rutherford tried to determine the internal arrangement of atoms by shooting  particles at VERY thin gold foil. If the charges inside the atom were evenly spaced the particles would pass through unchanged. That wasn’t the case, a few were deflected at large angles.

Rutherford’s Nuclear Atom The results of the gold foil experiment led Rutherford to realize that there was a small positive mass in the center of atoms that contained most of the mass of the atoms, called the nucleus, and electrons must orbit the nucleus. He called the positive particles that made up the nucleus “protons”.

3 Subatomic Particles Protons are found in the nucleus. They have a positive charge. They have a mass 1840 x that of the electron. Neutrons are found in the nucleus. They have no charge. They have a mass about 1840 x that of the electron. Electrons are found in the orbital and have a negative charge. Table 2-1

Atomic Number All atoms of the same element have the same number of protons, this is their atomic number. For neutral atoms, the number of protons is the same as the number of electrons. Atomic number (Z) = # of protons= # electrons

Isotopes Some atoms of an element have different numbers of neutrons. There weight is different from other atoms of the same element. These are called isotopes. Mass number (A) is the number of protons and the number of neutrons.

Covalent Bonds form molecules. Covalent bonds occur between atoms that result in the sharing of electrons between two nonmetallic atoms so that each achieves a noble gas configuration. e - e-e-e-e- e-e- Nonmetallic Atom e - e-e- e-e-e-e- e-e-e-e- e-e- Molecule e - e-e- e-e-e-e- e-e-

Forming covalent molecules Only nonmetals are bound. Enough electrons are shared so that each atom “thinks” that it has a full outer shell. A molecule is formed that has an overall charge of zero.

Representations of Molecules Ball-and-Stick ModelSpace-filling model

Ionic Bonds form ions. Ionic Bonds are formed when electrons are given by metallic atoms to nonmetallic atoms so that each achieves noble gas configuration. e - e-e-e-e- e-e- e-e- Metallic Atom Nonmetallic Atom e - e-e-e-e- e-e- e- e- Metallic Atom Nonmetallic Atom e - e-e-e-e- e-e-e-e- Metallic Ion +1 Cation Nonmetallic Ion -1 Anion

Forming ionic compounds The metal gives electrons to the nonmetal. The number of electrons given and received must be equal, the sum of the charges = 0. Sometimes more than one ion of each is necessary to equal zero

The Periodic Table

PT Organization To the left of the staircase are the metals. To the right are the nonmetals. Metalloids are touched on two sides by the staircase (except boron and aluminum). Groups or families are the columns (they are alike) Periods are the rows.

PT by Group Alkali metals – group 1, most reactive metals, form ions with a +1 charge Alkaline earth metals – group 2, still pretty reactive, form ions with a +2 charge Halogens- group 17, most reactive nonmetals, form ions with a -1 charge Noble Gases- group 18, very stable