Atoms

Slide 3-8 Atomic Theory Slide 3-8 Atomic Theory Slide 9 Distinguishing Between Atoms Slide 9 Distinguishing Between Atoms Slide 10 Isotopes Slide 10 Isotopes

Democritus of Abdera, was a teacher who lived in Greece before Christ. Democritus of Abdera, was a teacher who lived in Greece before Christ. He suggested the existence of these particles called atoms. He suggested the existence of these particles called atoms. He said they were indivisible and indestructible. He said they were indivisible and indestructible. The real nature of atoms and the connection between observable changes and events at the atomic level were not established for more than 2000 years. The real nature of atoms and the connection between observable changes and events at the atomic level were not established for more than 2000 years.

 2000 years later, an English school teacher performed experiments to test and correct his atomic theory.  Dalton studied ratios in which elements combine in a chemical reactions. This led to the development of his atomic theory.

 All elements are composed of tiny indivisible particles called atoms.  Atoms of the same element are identical. Atoms of any one element are different from those of any other elements.  Atoms of different elements can physically mix together or can chemically combine with another in simple or whole number ratios to form compounds.  Chemical reactions occur when atoms are separated, joined or rearranged. Atoms of one element, however, are never changed into atoms of another element as a result of a chemical reaction.

Rutherford theorized that atoms have their positive charge concentrated in a very small nucleus, [5] and thereby pioneered the Rutherford model or planetary model of the atom, through his discovery and interpretation of Rutherford scattering in his gold foil experiment. (wikipedia) Rutherford theorized that atoms have their positive charge concentrated in a very small nucleus, [5] and thereby pioneered the Rutherford model or planetary model of the atom, through his discovery and interpretation of Rutherford scattering in his gold foil experiment. (wikipedia)nucleus [5]Rutherford model atom Rutherford scatteringgold foil experimentnucleus [5]Rutherford model atom Rutherford scatteringgold foil experiment

Niels Bohr profited by following the experimental work going on in the Cavendish Laboratory under Sir J.J. Thomson's guidance, at the same time as he pursued own theoretical studies. In the spring of 1912 he was at work in Professor Rutherford's laboratory in Manchester, where just in those years such an intensive scientific life and activity prevailed as a consequence of that investigator's fundamental inquiries into the radioactive phenomena. Niels Bohr profited by following the experimental work going on in the Cavendish Laboratory under Sir J.J. Thomson's guidance, at the same time as he pursued own theoretical studies. In the spring of 1912 he was at work in Professor Rutherford's laboratory in Manchester, where just in those years such an intensive scientific life and activity prevailed as a consequence of that investigator's fundamental inquiries into the radioactive phenomena.Sir J.J. Thomson'sProfessor Rutherford'sSir J.J. Thomson'sProfessor Rutherford's Contributions to Physics and Chemistry Contributions to Physics and Chemistry The Bohr model of the atom, the theory that electrons travel in discrete orbits around the atom's nucleus. The Bohr model of the atom, the theory that electrons travel in discrete orbits around the atom's nucleus.Bohr modelelectronsorbitsnucleusBohr modelelectronsorbitsnucleus The shell model of the atom, where the chemical properties of an element are determined by the electrons in the outermost orbit. The shell model of the atom, where the chemical properties of an element are determined by the electrons in the outermost orbit.shell modelshell model

Discovery of the Electron Discovery of the Electron In 1897, Thomson was the first to suggest that the fundamental unit of the atom was over 1000 times smaller than an atom, suggesting the sub-atomic particles now known as electrons. In 1897, Thomson was the first to suggest that the fundamental unit of the atom was over 1000 times smaller than an atom, suggesting the sub-atomic particles now known as electrons. Thomson discovered this through his explorations on the properties of cathode rays. Thomson made his suggestion on the 30 th of April 1897 following his discovery that Lenard rays could travel much further through air than expected for an atomic- sized particle. [4 Thomson discovered this through his explorations on the properties of cathode rays. Thomson made his suggestion on the 30 th of April 1897 following his discovery that Lenard rays could travel much further through air than expected for an atomic- sized particle. [4cathode raysLenard rays [4cathode raysLenard rays [4 Other work Other work In 1905 Thomson discovered the natural radioactivity of potassium. [7] In 1905 Thomson discovered the natural radioactivity of potassium. [7] radioactivitypotassium [7] radioactivitypotassium [7] In 1906 Thomson demonstrated that hydrogen had only a single electron per atom. Previous theories allowed various numbers of electrons. [8][9] In 1906 Thomson demonstrated that hydrogen had only a single electron per atom. Previous theories allowed various numbers of electrons. [8][9] hydrogenelectron [8][9] hydrogenelectron [8][9] (wikipedia) (wikipedia)

The atomic number of an element=the number of protons and the number of electrons. The atomic number of an element=the number of protons and the number of electrons. Mass number is the total number of protons and neutrons in an atom. Mass number is the total number of protons and neutrons in an atom. To get the number of neutron do this: To get the number of neutron do this: Mass number – Atomic number = # of Neutrons.

 Isotopes are atoms that have the same number of protons but different numbers of neutrons.  Because isotopes of an element have different numbers of neutrons, they also have different mass numbers.  Isotopes are chemically alike because they have identical numbers of p+ and e-.

Since the 1920’s, it has been possible to determine these tiny masses (atom’s mass) by using a mass spectrometer. Since the 1920’s, it has been possible to determine these tiny masses (atom’s mass) by using a mass spectrometer. The atomic mass of an element is a weighted average mass of the atoms in a naturally occurring sample of the element. The atomic mass of an element is a weighted average mass of the atoms in a naturally occurring sample of the element.

Ions- atom or group of atoms that have a positive or negative charge. Ions- atom or group of atoms that have a positive or negative charge. Charge is due to the loss or gain of electrons Charge is due to the loss or gain of electrons – Cation – ion with a positive charge Ex: Al 3+ Ex: Al 3+ -Anion – ion with a negative charge Ex: O 2-

Atomic mass- weighted average mass of the atoms in a naturally occurring sample of the element. Atomic mass- weighted average mass of the atoms in a naturally occurring sample of the element. Atomic mass unit (amu)- standard unit used for indicating atomic mass. Atomic mass unit (amu)- standard unit used for indicating atomic mass. – One -twelth the mass of a carbon-12 atom.

-Involves the relative abundance of naturally occurring isotopes of an element. -Involves the relative abundance of naturally occurring isotopes of an element. -Relative abundance is calculated by dividing the number of atoms of each isotope by the total # of atoms in the sample. -Relative abundance is calculated by dividing the number of atoms of each isotope by the total # of atoms in the sample. – Relative abundance can also be given as a %. If you are given a percentage you must divide by The Relative abundance of each isotope is then multiplied by the mass of that isotope. This is the relative mass. -The Relative abundance of each isotope is then multiplied by the mass of that isotope. This is the relative mass. -The relative masses are added together and that equals the average atomic mass. -The relative masses are added together and that equals the average atomic mass.

Ex: Neon has two naturally occurring isotopes. The mass and # of atoms of each isotope are shown below. What is the average atomic mass of neon? Ex: Neon has two naturally occurring isotopes. The mass and # of atoms of each isotope are shown below. What is the average atomic mass of neon? Isotope# of atoms in sample Mass Neon Neon