Atomic Theory and Structure Unit 2

Atomic Theory Based on experimental data Elements are made of only one kind of particle. This basic particle is called an atom

Dalton’s Atomic Theory All matter is composed of very small particles called atoms. Atoms of a given element are identical; atoms of different elements are different. Atoms cannot be subdivided, created or destroyed. [LAW OF CONSERVATION OF MATTER] Atoms of different elements combine in simple whole-number ratios (1:1, 1:2, 3:5, etc.) to form chemical compounds. [Law of Definite Proportions] In chemical reactions, atoms are combined, separated, or rearranged.

Modern Atomic Theory Atoms of the same element may have different masses (isotopes), but will always have the same atomic #. Atoms are made of smaller particles.

Changing Models of the Atom

Dalton’s Model 1830 Major change: particle model Physical model: solid spheres, billiard balls Could not be created, divided into smaller particles, or destroyed

J.J. Thomson Model 1898 Major change: protons and electrons Physical model: plum pudding Negatively charged electrons were distributed throughout a uniform positive charge

Rutherford’s Model 1911 Major change: nucleus Physical model: solar system model Electrons orbit around the nucleus which contains proton and neutrons

Bohr’s Model 1931 Major change: energy levels Physical model: energy level model Protons and neutrons located within the nucleus but electrons are located on orbitals with different energy levels

Quantum, Wave mechanical, Schrodinger Late 1930’s Major change: uncertainty principle Physical model: cloud model Atom consist of cloud of electrons around a very small nucleus of protons and neutrons

Evolution of the Atom

Properties of Particles That Make-Up the Atom Particle Mass Rel. Mass Charge Rel. Charge Location Electron x x e - cloud Proton x x Nucleus Neutron x zero0 Nucleus

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Atomic Structure Continued…

Facts About The Atom All atoms are electrically neutral; therefore an atom must have equal numbers of protons and electrons. Any atom of a given element contains the same number of protons as any other atom of that element. (this also applies to electrons.) For a given element, two different atoms of that element may contain differing numbers of neutrons. (definition of an isotope)

Characteristics of Atoms Atomic number- The number of protons in the nucleus of the atom. In a neutral atom, this is also the number of electrons. Mass number- The total number of particles in the nucleus of the atom. # protons + # neutrons A Z X A: mass number & z: atomic number Isotopes- Atoms with the same atomic numbers but different mass numbers. That is, with the same number of electrons and protons, but different numbers of neutrons. Nucleus- Very small and very positive. Contains most of the mass of the atom. Made up of protons and neutrons. Nuclear forces- Hold the protons and neutrons together in the nucleus.

Isotopes atoms of the same element with different numbers of neutrons and therefore different atomic mass. Example: carbon-12 and carbon-14 Isotopes of Hydrogen Protium Hydrogen-1 Protons___ Electrons___ Neutrons___ DeuteriumHydrogen-2 Protons___ Electrons___ Neutrons___ Tritium Hydrogen-3 Protons___ Electrons___ Neutrons___

Law of Multiple Proportions A compound consists of molecules of integral numbers of atoms. In a series in which one element forms more than one compound with a second element, the atoms must combine in small integral numbers. Hence, the weights of the second element combining with a fixed weight of the first element will be in the ratio of small integral numbers.

Compound g of oxygen combining with 1g of nitrogen Ratio of weights Atomic grouping Nitrous oxide NO Nitric oxide 1.142NO 2 Nitrogen trioxide 1.713NO 3 Nitrogen tetroxide 2.284NO 4 Nitrogen pentoxide 2.855NO 5