Atomic Theory & the Periodic Table A Review

Atomic History Ancient Greeks Alchemists John Dalton Dmitri Mendeleev JJ Thomson Sir William Crookes Ernest Rutherford HGJ Moseley James Chadwick Neils Bohr Erwin Schrödinger

Ancient Greeks (~ 400 B.C.E) Democritus (460 – 370 B.C.E.) All matter is made of tiny, indestructible units called ATOMOS Aristotle (384 – 322 B.C.E) & Plato (428 – 348 B.C.E) Completely disagreed with Democritus. Public opinion sided with these guys that all matter was made of EARTH, AIR, FIRE, & WATER

Alchemists (next 2000 years) People who tried to get rich by turning base metals (like iron or lead) into gold. Some were con artists Some were scientists. Discovered elements like mercury, sulfur, and antimony

John Dalton (1766 – 1844) & Dalton’s Atomic Theory Chemist & Physicist who made a living teaching His theory is backed by many experiments Theory Elements are made of particles called atoms All atoms of an element are identical Atoms of 1 element are diff. from atoms of another element Atoms of elements can combine to form compounds with simple, whole number ratios Atoms can’t be destroyed or created, they’re just rearranged in a chemical reaction

Dmitri Mendeleev: 1834-1907 Dmitri realized that the properties of some elements repeat in a regular pattern so he organized them into the 1st recognized periodic table.

Sir William Crookes: 1832 - 1919 Studied cathode ray tubes and realized that the rays travelled in straight lines. Believed they represented a 4th state of matter: radiant matter.

JJ Thomson (1856 – 1940) & the Cathode Ray Experiment (1890s) Physicist who used a cathode ray tube to show that atoms of any element can be made to give off tiny negative particles (ELECTRONS)

JJ’s Model- The Plum Pudding Model (Chocolate Chip Cookie anyone?)

Ernest Rutherford (1871 – 1937) & Gold Foil Experiment (1911) Expected the positive α (alpha) particles to pass straight through to the back of the detector. He was surprised when they bounced off at strange angles. He surmised that the alpha particles were bouncing off a small + charge in the Gold atoms. He called that part the NUCLEUS!

HGJ Moseley: 1887 - 1915 Realized that atomic numbers are not just arbitrary numbers but represent the number of protons in the nucleus of the atom and that the periodic table is better arranged according to atomic number rather than atomic mass. Father of the modern periodic table

Gold Foil Experiment

Some More Stuff Ernie Did In 1918 – He experimented by bombarding N2(g) with alpha particles. 1 of the results was that a whole lot of H2(g) was created. What’s going on? Ernie figured out that the H atoms must have come from inside the N2. That means that ATOMS ARE DIVISIBLE!!!!!!!! He eventually isolated those H atoms and discovered they were actually PROTONS

Ernie found a friend- James Chadwick (1932). Ernie’s assistant, James Chadwick found the NEUTRON in 1932. He put some Be in a chamber with Po (gives off alpha particles). The alpha particles hit the Be which gave off some particles at high, high speeds. At first he thought they were gamma (γ) rays but they moved too fast for gamma rays. He worked his way thru some calculations and discovered they were not, but some neutral particles that he named (NEUTRONS)

Chadwick- Rutherford Model

Neils Bohr (1885 – 1962) and the Bohr Planetary Model Developed a theory of the H atom, saying that electrons moved in specific ORBITS around the nucleus. Each orbit has a specific amount of energy to it.

Erwin Schrödinger: Modern Model of the Atom (Wave Mechanical Model) States that electrons exist in a state described by an ORBITAL An area where there is a 90% probability of finding an electron

ATOMIC STRUCTURE Physical structure Atomic Number Mass Number Isotopes Atomic Mass Calculating Atomic Mass

Atomic Structure An atom is the defining part of what makes an element, an element. Cannot be broken down chemically. Atoms are mostly empty space! Atoms are very, very small!

Atomic Structure Particle Relative Mass (Actual Mass) Relative Charge Proton 1836 (1.67262158 × 10-27 kg) +1 Neutron 1839 (1.67492729 × 10-27 kg) Electron 1 (9.10938188 × 10-31 kg) -1

Atomic Number & Mass Number Atomic Number = # of protons (p+) = # electrons (e-) Mass Number = # of p+ + # n0

How many p+, n0, and e-? 23 238 U Na 92 11

Isotopes Atoms of an element that have different #’s of neutrons. 11H 21H 31H 63Li 73Li

Atomic Mass Weighted average of all the masses of each isotope of the element. A.M. = (% isotope 1)(Mass isotope 1) + (% isotope 2)(Mass isotope 2) + …

Examples Calculate the average atomic mass of gold 50% of 197Au weighs 197 50% of 198Au weighs 198

Electron Configurations Way of describing which orbitals electrons are within the atom. 7 principal orbitals [n] (energy levels) 4 sublevels (s, p, d, f) Valence e- - electrons in the highest orbital (energy level)

Orbital Sub Levels s p d f

Orbital Filling Diagram s sublevels can hold 2 e- p sublevels can hold 6 e- d sublevels can hold 10 e- F sublevels can hold 14 e-

Electrons and Light Valence electrons Electromagnetic Spectrum Light characteristics Electrons and Light

Valence e- Fe – 1s22s22p63s23p64s23d6 {2 valence e-} Rb – [Kr]5s1 {1 valence e-} Cl – [Ne]3s23p5 {7 valence e-} These are the electrons that are involved in bonding and chemical reactions!!!!!!!

Valence Electrons and the Periodic Table

What do e- have to do with light? When you add energy to an element (perhaps by heating it up), the valence e- get “excited”. In other words they jump up to a higher energy level or orbital. BUT… they are unstable up there. So they release that added energy in the form of colored light! Huh?

Electromagnetic Spectrum

Light Characteristics Light moves in wave from the light source to you eye or other detector! Waves have several characteristics!

Wave Characteristics c = λ× ν c = speed of light = 3.00 × 108 m/s λ = wavelength ν = frequency c = λ× ν

Light can also act as particles, we call them PHOTONS!!!!!! Moving along those waves, there are little packets of energy called photons. Photons have specific amounts of energy as determined by the frequency of the light. E = h × ν The higher the frequency of the light, the more energy the light has.

So how does light tie into excited electrons? When you add energy to an element, it’s valence e- absorb that packet of energy & become unstable. In order to return to stability (lower their energy) they “spit out” that energy in the form of a photon that has a frequency in the visible light part of the electromagnetic spectrum that we can see.