Atomic Structure and Timeline Objectives: Describe the process why which the atomic structure was discovered Describe what an atom is an what makes it up. Identify differences in protons, neutrons and electrons

Democritus 400 BC Proposed that matter was composed of tiny indivisible particles Not based on experimental data

John Dalton 1807 British schoolteacher that based his theory on other’s data Billiard Ball Model Atom is uniform, solid sphere

Dalton’s 4 Postulates Elements are composed of small indivisible particles called atoms Atoms of the same element are identical. Atoms of different elements are different. Atoms of different elements combine together in simple proportions to create a compound. In a chemical reaction, atoms are rearranged, but not changed

Henri Becquerel 1896 Discovered radioactivity Spontaneous emission of radiation from the nucleus Alpha, beta and gamma (p, neg, neu)

J.J. Thomson Cathode Ray Tube Experiments Discovered electrons Beam of negative particles Discovered electrons Negative particles within an atom Plum-pudding Model

Plum-Pudding Model

Ernest Rutherford 1911 Gold Foil Experiment Discovered the nucleus Dense, positive charge in center of atom Nuclear Model

Niels Bohr 1913 Energy Levels Electrons can only exist in specific energy states

Erwin Schrodinger 1926 Quantum mechanics Electron Cloud Model E- can only exist in specified energy states Electron Cloud Model Orbital-region around nucleus were electrons are likely to be found

James Chadwick 1932 Discovered neutrons Neutral particles in the nucleus of an atom

Atomic Structure An element is composed of one type of atom Atom—smallest piece of matter that sill retains the properties of the element Composed of: protons, neutrons and electrons

Atomic Components Protons (+1)and neutrons (neutral) found in nucleus Nucleus--Positively charged Surrounded by electrons(-1) Nucleus—center core of atom

Most of the atom’s mass. Atomic Number equals the # of...

Atomic Components Protons and neutrons are made up of quarks So far, only 6 uniquely different quarks Scientist theorize that 3 quarks held together with strong nuclear force produces a proton A different arrangement of 3 other quarks produces a neutron

Electron Cloud Model Electron cloud—area around the nucleus of an atom where electrons are most likely found 100,000 times larger than the diameter of the nucleus Electrons in the cloud are a lot smaller than a proton Electrons are so small and moves so quickly, it is impossible to describe its exact location Bohr Model: Electrons can only exist at certain energy levels Low levels—close to nucleus Each level can hold 2n2 Level 1—2 Level 2—8 Level 3—18 Level 4--32

Atomic Mass Nucleus contains most of the mass b/c protons and neutrons are so large Mass of proton and neutron are about equal

Atomic Mass Unit of measurement—atomic mass unit (amu) Mass of a proton and neutron is about 1 amu

Protons The number of protons defines the atom Ex. Every carbon atom has six protons; all atoms with six protons are carbon atoms # protons=atomic number

Mass Number Sum of protons and neutrons in the nucleus of an atom Always a whole number

Neutrons Number of neutrons=mass number-atomic number Not all atoms of an element have the same number of neutrons Isotopes—atoms of same element with different number o f neutrons Mass Number Atomic Number

Isotopes

Identifying Isotopes Models of two isotopes of boron are shown below. Neutrons are different, so the mass numbers are different You use the name of the element followed by the mass number of the isotope to identify each Boron-10 and boron-11

Identifying Isotopes Average atomic mass—weighted-average mass of the mixture of isotopes 4 out of 5 atoms of boron are boron-11 and one out of five are boron-10

Practice Using the periodic table of elements in the back of your text book: Identify the number of protons, neutrons and electrons in each of the following elements Ca, B, C, O, N, F, Na, K, Mg, Mn, Si, As, He, H Draw an Electron Cloud Model (Bohr Model) for each of the following elements Cl, Br, N, O, C, Mg

Project Pick an element on the Periodic Table Construct a 3D Bohr Model of that element Make a brochure using the same element Include: Atomic mass Atomic number Who discovered it When was it discovered How was it named What is its natural state Melting/boiling point Group Characteristics Interesting facts Pictures Bohr model Due Friday