ATOMIC THEORY

 Which shows a a correct image of what an atom looks like? How do you know? DO NOW:

THE GREEK CONCEPT OF ATOMOS: THE INDIVISIBLE ATOM  Around 440 BC, Leucippus originated the atom concept.  His pupil, Democritus (c BC) extended it  There are five major points to their atomic idea.  All matter is composed of atoms, which are too small to be seen. These atoms CANNOT be further split into smaller portions.  There is a void, which is empty space between atoms.  Atoms are completely solid.  Atoms are homogeneous, with no internal structure.  Atoms can differ in size, shape, and weight

è Spoke openly against the concept — the atom concept diminished è Only a few scholars gave it much thought. è The Catholic Church accepted Aristotle's position — equated atomistic ideas with Godlessness è It was not until 1660 that Pierre Gassendi succeeded in separating the two è not until 1803 that John Dalton put the atom on a solid scientific basis. ARISTOTLE ( BC)

In 1808, John Dalton developed an atomic theory. Dalton believed that a few kinds of atoms made up all matter. According to Dalton, elements are composed of only one kind of atom and compounds are made from two or more kinds of atoms. JOHN DALTON’S ATOMIC THEORY

1.All matter is composed of tiny particles called atoms. 2.All atoms of a given element have identical chemical properties that are characteristic of that element. 3.Atoms form chemical compounds by combining in whole-number ratios. 4.Atoms can change how they are combined, but they are neither created nor destroyed in chemical reactions. 5.Atoms of a given element are identical in their physical and chemical properties. JOHN DALTON MODERN ATOMIC THEORY

John Dalton’s Atomic Theory Almost right. A good start. Structure of the atom after Dalton (ca. 1810) very small

 Atoms are neither created nor destroyed during physical or chemical processes. In a closed system LAW OF CONSERVATION OF ATOMS & MASS Video

LAW OF CONSERVATION OF ATOMS & MASS

 Mass is neither created nor destroyed during physical or chemical processes. LAW OF CONSERVATION OF ATOMS & MASS

 States that two samples of a given compound are made of the same elements in exactly the same proportions by mass regardless of the sizes or sources of the samples.  So for example, every molecule of ethylene glycol is made of the same number and types of atoms. THE LAW OF DEFINITE PROPORTIONS

 A molecule of ethylene glycol has the formula C 2 H 6 O 2, so the law of definite proportions tells you that all other molecules of ethylene glycol have the same formula.  So where we have 1mg or 1000kg of Ethylene glycol the ratio is the same THE LAW OF DEFINITE PROPORTIONS 51.56% oxygen, 38.70% carbon, and 9.74% hydrogen

The law of multiple proportions states that when two elements combine to form two or more compounds, the mass of one element that combines with a given mass of the other is in the ratio of small whole numbers. THE LAW OF DEFINITE PROPORTIONS

Example: Nitrogen Oxides I & II Nitrogen Oxide I : 46.68% Nitrogen and 53.32% Oxygen Nitrogen Oxide II : 30.45% Nitrogen and 69.55% Oxygen in 100 g of each Compound: g O = g & g g N = g & g g O /g N = & Cmpd II Cmpd I = Cmpd I Cmpd II  If elements A and B react to form two compounds, the different masses of B that combine with a fixed mass of A can be expressed as a ratio of small whole numbers: LAW OF MULTIPLE PROPORTIONS

 Proved that an atom can be divided into smaller parts  While experimenting with cathode- ray tubes, discovered corpuscles, which were later called electronsexperimenting  Stated that the atom is neutral  In 1897, proposed the Plum Pudding Model which states that atoms mostly consist of positively charged material with negatively charged particles (electrons) located throughout the positive material  Won a Nobel Prize Image taken from: ayintech_ ayintech_0430 J.J. Thomson (1856 – 1940)

J.J. Thomson (1897): Cathode Rays Atoms subjected to high voltages give off cathode rays.

J.J. Thomson: Cathode Rays Cathode rays can be deflected by a magnetic field. Cathode rays are negatively charged particles (electrons). Electrons are in atoms.

J.J. Thomson – The Electron Structure of the atom after Thomson (ca. 1900) “Plum pudding” model: Negative electrons are embedded in a positively charged mass. Positively charged mass Electrons (-) Unlike electrical charges attract, and that is what holds the atom together.

 In 1909, performed the Gold Foil Experiment and suggested the following characteristics of the atom:Gold Foil Experiment o It consists of a small core, or nucleus, that contains most of the mass of the atom o This nucleus is made up of particles called protons, which have a positive charge o The protons are surrounded by negatively charged electrons, but most of the atom is actually empty space  Did extensive work on radioactivity (alpha & beta particles, gamma rays/waves) and was referred to as the “Father of Nuclear Physics”  Won a Nobel Prize  Was a student of J.J. Thomson  Was on the New Zealand $100 bill Image taken from: web.com/en/Physics/Biographies/Er nestRutherford.html web.com/en/Physics/Biographies/Er nestRutherford.html Ernest Rutherford (1871 – 1937)

Ernest Rutherford (1910) Scattering experiment: firing alpha particles at a gold foil

The Nuclear Atom Some alpha particles bounce off the gold foil. This means the mass of the atom must be concentrated in the center and is positively charged! Thompson’s model could not be correct.

Ernest Rutherford The Nucleus and the Proton Structure of the atom after Rutherford (1910) The mass is not spread evenly throughout the atom, but is concentrated in the center, the nucleus. Electrons (-) are now outside the nucleus. The positively charged particles in the nucleus are protons.

 In 1913, proposed the Bohr Model, which suggests that electrons travel around the nucleus of an atom in orbits or definite paths. Additionally, the electrons can jump from a path in one level to a path in another level (depending on their energy)electrons can jump  Won a Nobel Prize  Worked with Ernest Rutherford Image taken from: commons.wikimedia.org/wiki/File:Ni els_Bohr.jpg commons.wikimedia.org/wiki/File:Ni els_Bohr.jpg Niels Bohr (1885 – 1962)

3 p + 4 n 0 2e – 1e – Li shorthand Bohr - Rutherford diagrams  Putting all this together, we get B-R diagrams  To draw them you must know the # of protons, neutrons, and electrons (2,8,8,2 filling order)  Draw protons (p + ), (n 0 ) in circle (i.e. “ nucleus ” )  Draw electrons around in shells 2 p + 2 n 0 He 3 p + 4 n 0 Li Draw Be, B, Al and shorthand diagrams for O, Na

11 p+ 12 n° 2e – 8e – 1e – Na 8 p+ 8 n° 2e – 6e – O 4 p+ 5 n° Be 5 p+ 6 n° B 13 p+ 14 n° Al

 In 1926, he further explained the nature of electrons in an atom by stating that the exact location of an electron cannot be stated; therefore, it is more accurate to view the electrons in regions called electron clouds; electron clouds are places where the electrons are likely to be found  Did extensive work on the Wave formula  Schrodinger equation  Won a Nobel Prize Image taken from: nobelprize.org/.../1933/schrodinger -bio.html nobelprize.org/.../1933/schrodinger -bio.html Erwin Schrodinger ( )

 Realized that the atomic mass of most elements was double the number of protons  discovery of the neutron in 1932  Worked on the Manhattan Project  Worked with Ernest Rutherford  Won a Nobel Prize Image taken from: ayintech_ ayintech_0227 James Chadwick (1891 – 1974)

James Chadwick – The Neutron Structure of the atom after Chadwick (1932) In the nucleus with the protons are particles of similar mass but no electrical charge called neutrons. Electrons (-) are now outside the nucleus in quantized energy states called orbitals. (From Niels Bohr and quantum mechanics) The positively charged particles in the nucleus are protons. n n +

Structure of the Atom proton (+) neutron nucleus - responsible for the mass of the atom, positively charged electrons - responsible for the volume and size of the atom, negatively charged m m

Subatomic Particles  Protons and electrons are the only particles that have a charge.  Protons and neutrons have essentially the same mass.  The mass of an electron is so small we ignore it.

Atomic Facts FeatureSizeMass 1 amu = 1 atomic mass unit = x g Electrons are outside the nucleus in quantized energy states called orbitals. proton (+) m amu neutron (0) m amu electron (-) m ??? amu + n n