Listen to the Atom Song http://www.youtube.com/watch?v=vUzTQWn-wfE Test #5 Atomic Theory Listen to the Atom Song http://www.youtube.com/watch?v=vUzTQWn-wfE

Models of the Atom 1. Our model or picture of the atom has changed over a long period of time (hundreds of years) through the work of many scientists.

Democritus 2. Democritus (a Greek philosopher) said matter is made many tiny hard rigid spheres called ‘atomos’.

John Dalton (1808) 3. Dalton’s Atomic Theory stated that atoms are not created or destroyed during chemical reactions, instead, they rearrange to form new compounds. http://www.teachertube.com/viewVideo.php?video_id=228303

J J Thompson (1897) 4. JJ Thompson’s Plum Pudding Model describes the atom as a positive sphere with negative electrons spread throughout it.

Background Into – Don’t Copy Three types of radiation:  particles (positively charged) = Alpha  particles (negatively charged) = Beta rays (not a particle – no charge) = Gamma http://www.youtube.com/watch?v=vuGvQjCOdr0&feature=related Figure 2.8 © 2009, Prentice-Hall, Inc.

Ernest Rutherford (1911) http://www.youtube.com/watch?v=5pZj0u_XMbc Rutherford discovers the nucleus of the atom!

Ernest Rutherford (1911) 5. Ernest Rutherford’s Gold Foil Alpha Scattering Experiment suggested that atoms have a small, positive center called the nucleus that contains most of the mass of the atom. They rest of the atom is mostly empty space with negative electrons are swirling around outside the nucleus.

Discovery of the Nucleus Ernest Rutherford shot positively charged alpha () particles at a thin sheet of gold foil and observed some particles were deflected. Figure 2.10 © 2009, Prentice-Hall, Inc.

The Nuclear Atom Since most of the alpha particles passed straight through the gold foil, Thompson’s model could not be correct. The positive alpha particles were ‘deflected’ or repelled only when they hit the positive nucleus. Later, Rutherford discovered the nucleus contained positive protons. Figure 2.11 © 2009, Prentice-Hall, Inc.

Niels Bohr’s Model of the Atom http://www.youtube.com/watch?v=wCCz20JOXXk

Niels Bohr (1913) 6. Niels Bohr’s experiments studying light given off by excited atoms led to the proposal that each electron has a distinct amount of energy and moves around the nucleus in a specific energy level or shell.

James Chadwick James Chadwick (1932) – He discovered neutrons were also in the nucleus of the atom

Most Modern Model of the Atom 7. The Modern Model is called the Orbital Model or Electron Cloud Model or Wave Mechanical Model. It states electrons are in regions of space called orbitals. Orbitals are not rings! They are regions where the electrons probably are located 90% of the time. 1.5 Minute Video Showing Orbital Models http://www.youtube.com/watch?v=K-jNgq16jEY&feature=mfu_in_order&list=UL

Atoms Are Neutral 7.Atoms are neutral in charge because the # of positive protons in the nucleus always is equal to the # of negative electrons surrounding it.

Subatomic Particles Protons – Positively Charged (+1), p+ Mass = 1 amu, Located inside the nucleus of the atom Neutrons – No Charge (Neutral), no Electrons – Negatively Charged (-1), e- Mass = 1/1836 amu, Located in energy shells surrounding the nucleus of the atom

Calculating # P+,E-,No for Neutral Atoms # Protons = Atomic Number (27) # Electrons = Atomic Number (27) Mass number = Atomic Mass rounded-off to nearest whole number (59) # Neutrons = Mass Number – Atomic Number (59 – 27 = 32)

3 Ways to Notation The ATOMIC MASS or AVERAGE ATOMIC MASS of an element is calculated from the relative abundances and atomic masses of that element’s naturally occurring isotopes. 2. The MASS SPECTROMETER can accurately measure atomic weights (masses). 5927Co Cobalt-59 C-59

Electron Configuration Electron configuration tells the number of electrons in each energy level of an atom 2 – 8 – 15 – 2 *Note: Elements 72 and above

Valence Electrons Valence electrons: 1. Are really important in determined the chemical properties of an atom 2. They are the electrons in the outermost energy level of an atom 3. It’s the last number of the electron configuration 2 – 8 – 15 – 2  4. Example: Cobalt has 2 valence electrons An intro: http://www.youtube.com/watch?v=rSwnODMNULI&feature=related

Lewis Structures Lewis Electron Dot Structure – dots drawn around the symbol of the atom to represent its # of valence electrons Co The pattern X 3 6 4 7 1 2 5 8

Lewis Electron Dot Structures Groups 1 2 13 14 15 16 17 18

Drawing Bohr Models Steps Draw a circle to represent the nucleus and put the #p and #n in it. Draw concentric circles to represent the electron energy levels. Draw dots or use #’s to represent the electrons 3. This example is for 2311Na whose electron configuration is 2-8-1. *What is its nuclear charge? *How many valence electrons does it have? *Can you write its Lewis electron dot structure? Answers: +11, 1, and Li. http://www.chemicalelements.com/ Really cool interactive Periodic Table

Nuclear Charge Nuclear charge is : the charge on the nucleus of an atom. It is always a positive number. equal to the total number of protons in the nucleus of the atom. equal to the atomic number of the atom. *Atoms, overall, are neutral!!! Why? *What is the nuclear charge of a cobalt atom? Ans = +27

The Periodic Table The Periodic Table arranges the elements by increasing ATOMIC NUMBER (not mass). GROUPS (vertical columns) contain atoms having the same # of valence electrons & similar chemical properties. PERIODS (horizontal rows) contain atoms having the same # of occupied electron shells. Their properties vary from metal to metalloid to nonmetal.

Special Group Names Group 1 = Alkali metals (Li, Na, K, Rb, Cs, Fr) Group 2 = Alkaline earth metals (Be, Mg, Ca, Sr, Ba, Ra) Groups 3 to 11 = Transition metals (have colored solutions!) Group 17 = Halogens (F, Cl, Br, I, At) Group 18 = Noble gases (He, Ne, Ar, Kr, Xe, Rn)

Special Group Names

Classes of Elements METALS – have luster (shiny), malleable (pliable), ductile (wire), good conductors of heat & electricity. METALLOIDS – have properties of both metals & nonmetals. NONMETALS – if solid, they are brittle, poor conductors. NOBLE GASES – inert (don’t react) gases

Location METALS – left of ‘staircase’ *Except hydrogen (symbol H) which is a nonmetal NONMETALS – right of ‘staircase’ and hydrogen METALLOIDS – on staircase (B, Si, Ge, As, Sb, Te) (Boron, Silicon, Germanium, Arsenic, Antimony, Tellurium) NOBLE GASES – in Group 18

Atomic Mass The mass of an atom is measured in a unit called the amu. One ATOMIC MASS UNIT (amu) = 1/12 the mass of a carbon-12 atom or 1.66 x 10-24g. The ATOMIC MASS or AVERAGE ATOMIC MASS of an element is calculated from the relative abundances and atomic masses of that element’s naturally occurring isotopes.

Isotopes ISOTOPES are atoms of the same element with different masses due to differences in # of neutrons. Notation: 31H 3 = mass number 1 = atomic number 3. Another way: H-3

When I say Isotope, You say Sedman! Isotopes are atoms of the: S = same E = element that D = differ in M = mass A = and number of N = neutrons!

Figure of the # of p, e, n in each isotope of Lithium Isotopes Figure of the # of p, e, n in each isotope of Lithium

Calculating Avg. Atomic Mass (also called atomic weight – AW) There are 3 steps: For each isotope, multiply its atomic mass times it percent abundance. Add each of these values together. Divide by 100 to obtain the avg atomic mass if you didn’t use the % sign. AM = [(atomic mass)(%)] + [(atomic mass)(%)] Then, ask yourself if your answer for the average makes sense? © 2009, Prentice-Hall, Inc.

Calculate its atomic weight using: Example Rubidium has 2 naturally occurring isotopes. Rb-85 (atomic mass = 84.9118 amu, abundance 72.15%) and Rb-87 (atomic mass = 86.9092 amu, abundance 27.85%) Calculate its atomic weight using: AW = [(atomic mass)(%)] + [(atomic mass)(%)] 2. Set-up: AW = [(84.9118)(72.15%)] + [(86.9092)(27.85%) 3. Answer: AW = (61.26) + (24.20) = 85.46 amu* *If you got 8546 amu for the answer, you need to divide by 100