Using the Periodic Table Atomic number- always a whole number, increases in order, represents the number of protons in each atom Atomic name, often in Latin, sometimes uses a common name, sometimes there are disagreements Atomic symbol – often, but not always, matches the name; Always capitalize the first (only the first ) letter Atomic mass- the mass of the atoms based on the average of all the most common isotopes 6 Carbon C 12.011 amu

Chapter 6 Atoms

Aristotle, the famous Greek philosopher and scientist, argued that a substance could be divided again and again, forever getting smaller and smaller pieces During his time people believed the universe was made of four elements; fire, water, earth and air.

The idea of “uncuttable” particles was first suggested by Democritus around 440 B.C. “Atomos” means indivisible

Section 1 Atomic Theory Atomic Theory (by John Dalton) published in 1803 All substances are made from atoms. Atoms cannot be created, divided or destroyed. Atoms of the same element are exactly alike. Atoms can join together to form new substances.

JJ Thomson discovered the negatively charged electrons inside the atom. Ernest Rutherford discovered that the atom is mostly empty space with a tiny positive nucleus and orbiting electrons. Neils Bohr determined that electrons traveled along paths or energy levels. Schrodinger & Heisenberg

Pictures of Atoms

Atomic Size Atoms are extremely small… Aluminum foil is 100,000 atoms thick. A Penny has 20,000,000,000,000,000,000,000 atoms!

What’s Inside an Atom? Protons (+): Neutrons (0): Electrons (-): Positively Charged Particles Mass=1amu Location: Nucleus Neutrons (0): Particles with No Charge Mass=1amu Location: Nucleus Electrons (-): Negatively Charged Particles Mass= almost zero Location: Electron Clouds

Outside the nucleus, orbiting at nearly the speed of light Parts of the Atom Particle Charge Location Size Proton Positive In the nucleus 1 a.m.u. Neutron No charge (neutral) Almost 1 a.m.u. Electron Negative Outside the nucleus, orbiting at nearly the speed of light Very tiny, 1/1000th a.m.u.

Structure of the Atom + Protons Positively charged Found in the nucleus of the atom (center) Mass of 1 amu (atomic mass unit) Gives the element its atomic number on the periodic table #1 (hydrogen) has 1 proton #4 (beryllium) has 4 protons Protrons were discovered by Ernest Rutherford in 1911 and he discovered the empty space within an atom in 1909

N Neutrons Neutral charge ( no charge) Found in the nucleus (center) Mass slightly smaller than a proton, still considered 1 amu Protons + Neutrons @ atomic mass (rounded to the nearest whole number) N

Isotope Atoms can often be found with different numbers of neutrons Hydrogen (H-1), most common 99.9% Isotope Atoms can often be found with different numbers of neutrons Some atoms have only one stable isotope, others have several Averaging the masses of the isotopes in their correct percentages gives the exact atomic mass for each element Unstable isotopes break down (radioactive decay) deuterium (H-2), tritium (H-3), least common, radioactive

Electrons Negatively charged particles Found outside the nucleus, moving at nearly the speed of light, in specific levels Most commonly atoms are neutral particles having equal numbers of protons and electrons Very small ( about 1/1000th of a proton) Proton Neutron Electrons were discovered by J.J. Thompson in 1897

* In 1913 Niels Bohr suggested that electrons travel in specific paths called Electron Shells 32 18 Each level can only contain a certain number of electrons before it is full Each level will fill completely before electrons go to the next level Lower levels fill first 18 8 8 2