Daltons Atomic Theory Dalton stated that elements consisted of tiny particles called atoms He also called the elements pure substances because all atoms of an element were identical and that in particular they had the same mass.

Dalton’s atomic theory is essentially correct, with four minor modifications: 1. Not all atoms of an element must have precisely the same mass. 2. Atoms of one element can be transformed into another through nuclear reactions. 3. The composition of many solid compounds are somewhat variable. 4. Under certain circumstances, some atoms can be divided (split into smaller particles: i.e. nuclear fission). The Atomic Theory of Matter Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

Dalton’s Atomic Theory 1.All matter consists of tiny particles. Dalton, like the Greeks, called these particles “atoms”. 2.Atoms of one element can neither be subdivided nor changed into atoms of any other element. 3.Atoms can neither be created nor destroyed. 4. All atoms of the same element are identical in mass, size, and other properties. 6.In compounds, atoms of different elements combine in simple, whole number ratios. 5.Atoms of one element differ in mass and other properties from atoms of other elements.

Dalton’s Atomic Theory 1. All matter is made of tiny indivisible particles called atoms. 2. Atoms of the same element are identical, those of different atoms are different. 3. Atoms of different elements combine in whole number ratios to form compounds 4. Chemical reactions involve the rearrangement of atoms. No new atoms are created or destroyed. California WEB

In 1803, Dalton proposed that elements consist of individual particles called atoms. His atomic theory of matter contains four hypotheses: 1. All matter is composed of tiny particles called atoms. 2. All atoms of an element are identical in mass and fundamental chemical properties. 3. A chemical compound is a substance that always contains the same atoms in the same ratio. 4. In chemical reactions, atoms from one or more compounds or elements redistribute or rearrange in relation to other atoms to form one or more new compounds. Atoms themselves do not undergo a change of identity in chemical reactions. The Atomic Theory of Matter Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

Thomson Model of the Atom J.J. Thomson discovered the electron and knew that electrons could be emitted from matter (1897). William Thomson proposed that atoms consist of small, negative electrons embedded in a massive, positive sphere. The electrons were like currants in a plum pudding. This is called the ‘plum pudding’ model of the atom. - electrons

J.J. Thomson He proved that atoms of any element can be made to emit tiny negative particles. From this he concluded that ALL atoms must contain these negative particles. He knew that atoms did not have a net negative charge and so there must be balancing the negative charge. J.J. Thomson

William Thomson (Lord Kelvin) In 1910 proposed the Plum Pudding model –Negative electrons were embedded into a positively charged spherical cloud. Zumdahl, Zumdahl, DeCoste, World of Chemistry  2002, page 56 Spherical cloud of Positive charge Electrons

Plum-Pudding Model Zumdahl, Zumdahl, DeCoste, World of Chemistry  2002, page 56

Thomson Model of the Atom J. J. Thomson - English physicist Made a piece of equipment called a cathode ray tube. It is a vacuum tube - all the air has been pumped out. 07_01_archive.htmlhttp://spcpchemroom6.blogspot.com/2010_ 07_01_archive.html (video)

Other pieces Proton - positively charged pieces –1840 times heavier than the electron Neutron - no charge but the same mass as a proton. How were these pieces discovered? Where are the pieces?

httphttp: %b3micos%20.NET/Modelos/Experiencias /ExperienciaRutherford.aspx

Rutherford Experiment.

Structure of the Atom 3: The Rutherford Model Rutherford mkMY8http:// mkMY8 /cchschem atomic-structure- entertainment-ppt-powerpoint/ /cchschem atomic-structure- entertainment-ppt-powerpoint/

Particles in the Atom Each element is chemically unique. To understand why they are unique, you need to know the structure of the atom (the smallest particle of an element) and the characteristics of its components.

Electrons (-) charge no mass located outside the nucleus Protons (+) charge 1 amulocated inside the nucleus Neutrons no charge 1 amulocated inside the nucleus Particles in the Atom

Los electrones (-) coste no masa situado fuera del núcleo Protones (+) coste 1 amuSituado en el interior del núcleo Neutrones sin cargo 1 amuSituado en el interior del núcleo Partículas en el átomo

electronsprotonsneutrons Atoms consist of electrons, protons, and neutrons. 1. Electrons and protons have electrical charges that are identical in magnitude but opposite in sign. Relative charges of  1 and +1 are assigned to the electron and proton, respectively. 2. Neutrons have approximately the same mass as protons but no charge—they are electrically neutral. 3. The mass of a proton or a neutron is about 1836 times greater than the mass of an electron. Protons and neutrons constitute the bulk of the mass of the atom. Particles in the Atom Copyright 2007 Pearson Benjamin Cummings. All rights reserved.

Discovery of the Neutron James Chadwick bombarded beryllium-9 with alpha particles, carbon-12 atoms were formed, and neutrons were emitted. + + Dorin, Demmin, Gabel, Chemistry The Study of Matter 3rd Edition, page 764 *Walter Boethe

Humor Two atoms are walking down the street. One atom says to the other, “Hey! I think I lost an electron!” The other says, “Are you sure??” “Yes, I’m positive!” A neutron walks into a restaurant and orders a couple of drinks. As she is about to leave, she asks the waiter how much she owes. The waiter replies, “For you, No Charge!!!”

Subatomic particles Electron Proton Neutron NameSymbolCharge Relative mass Actual mass (g) e-e- p+p+ nono / x x

Structure of the Atom There are two regions The nucleus With protons and neutrons –Positive charge –Almost all the mass Electron cloud –Most of the volume of an atom –The region where the electron can be found

Subatomic Particles Most of the atom’s mass. NUCLEUS ELECTRONS PROTONS NEUTRONS Negative Charge Positive Charge Neutral Charge ATOM QUARKS Atomic Number equals the # of... equal in a neutral atom Courtesy Christy Johannesson

Subatomic Particles Most of the atom’s mass. NUCLEUS ELECTRONS PROTONS NEUTRONS Negative Charge Positive Charge Neutral Charge ATOM QUARKS Atomic Number equals the # of... equal in a neutral atom Courtesy Christy Johannesson

Subatomic Particles Quarks –component of protons & neutrons –6 types –3 quarks = 1 proton or 1 neutron He Courtesy Christy Johannesson

Size of an atom Atoms are incredibly tiny. Measured in picometers ( meters) –Hydrogen atom, 32 pm radius Nucleus tiny compared to atom –Radius of the nucleus near m. –Density near g/cm 3 IF the atom was the size of a stadium, the nucleus would be the size of a marble. California WEB

Counting the Pieces Atomic Number = number of protons # of protons determines kind of atom Atomic Number = number of electrons in a neutral atom Mass Number = the number of protons + neutrons California WEB 12 6 C 14 6 C 12 6 C Mass Number = A Atomic Number = Z