Atomic Theory and the Modern Atom

Atomic Theory Each of these scientists helped advance and explore the atom Dalton JJ Thomson Millikan Rutherford Bohr

Dalton Proposed 5 main points of his Atomic theory to All matter is composed of tiny particles called atoms Atoms of a given element are identical in size, mass, and other properties Atoms cannot be subdivided, created or destroyed Atoms of different elements combine in whole numbers In chemical reactions, atoms are combined, separated or rearranged.

Dalton’s Laws The Law of Constant Composition: “Any given compound always consists of the same atoms and the same ratio of atoms. For example, water always consists of oxygen and hydrogen atoms, and it is always 89 percent oxygen by mass and 11 percent hydrogen by mass” The Law of Conservation of Mass: “The total mass of materials before and after a chemical reaction must be the same. For example, if we combine 89 grams of oxygen with 11 grams of hydrogen under the appropriate conditions, 100 grams of water will be produced—no more and no less.”

Dalton’s Laws The Law of Multiple Proportions: “If two elements combine to form more than one compound, the masses of one of the elements that can combine with a given mass of the other element are related by factors of small whole numbers” For example, water has an oxygen-to-hydrogen mass ratio of 7.9:1. Hydrogen peroxide, another compound consisting of oxygen and hydrogen, has an oxygen-to-hydrogen mass ratio of 15.8:1. The ratio of these two ratios gives a small whole number.

Dalton’s Model Billiard Ball Model

JJ Thomson JJ Thomson used a cathode ray tube to discover electrons have a negative charge He found that atoms can be broken into electrons in a positive matrix

JJ Thomson’s Model His model is known as the plum pudding model

Millikan Millikan explored the mass of the electron and confirmed that the electron carries a negative charge by his Oil Drop Experiment

Rutherford Created a more detailed atomic structure Bombarded thin gold fold with alpha particles expecting to have the particles to pass though but what he found was that several particles bounced back towards the source

Rutherford’s Model Thus discovering the nucleus Atoms are mostly empty space with negative electrons orbiting a positive nucleus

Bohr Bohr introduced the idea that electrons move in orbits or “shells” around the nucleus.

Electron Cloud Model Model used today Electrons do not travel in orbits, but rather in an electron cloud.

Chemical Symbols There are about a dozen common elements that have a single capitalized letter for their symbol The rest, that have permanent names have two letters. The first is capitalized and the second is lower case. Some elements have symbols from their Latin names. Ten of the elements have symbols from their Latin or German names.

Subatomic Particles All atoms are composed of the same basic particles Protons Neutrons Electrons The protons and neutrons are located in the nucleus Electrons are located in a cloud around the nucleus

Subatomic Particles The ATOMIC NUMBER of an element is the number of protons in the nucleus and is always whole number The MASS NUMBER is the total number of protons and neutrons in the nucleus and is always whole number The ATOMIC MASS is an average of all naturally occurring isotopes and is usually not a whole number

Two different notations A-Z notation or isotopic notation Hyphen notation Name/Symbol-mass Chromium- 52 Ca2+- 40 Atomic Mass Charge IF PRESENT Symbol Atomic Number

Subatomic Particles If atoms have the same number of electrons as protons, the charges overall charge of the atom is neutral For ions, the electrons can be different. For positive ions- there is a loss of electrons For negative ions- there is a gain of electrons

Subatomic Particles Isotopes are atoms of the same element that have different masses. Isotopes differ in the amount of neutrons

Practice Find the number of protons, electrons and neutrons for the following? 17 electrons 17 protons (35-17=18) 18 neutrons 10 electrons 12 protons (24-12=12) 12 neutrons 29 electrons 29 protons (64-29=35) 35 neutrons

Practice Find the number of protons, electrons and neutrons for the following? 17 electrons 17 protons (35-17=18) 18 neutrons 6 electrons 6 protons (14-6=8) 8 neutrons 47 electrons 47 protons (108-47=61) 61 neutrons

Practice Write the A/Z and Hyphen Notation? 18 electrons 19 protons 21 neutrons 18 electrons 16 protons 18 neutrons