Rev 6/7/ BC Atomic Model Development

Early Philosophers

Democritus ( BC) Defined an Atom as the smallest unit of a material that can not be split up Greek word “atom” means invisible

Democritus’s Theory Matter is made up of empty space through which atoms move. There is an indestructible and indivisible particle called the atom. Different atoms have different sizes and shapes. Different properties are related to the size and shape of the atoms.

John Dalton (1766 – 1844) Revised Democritus’s theory of the atom making Dalton’s atomic theory. Atom: smallest particle of an element that still retains the properties of that element.

Dalton’s Postulates All matter is made of atoms Atoms of same element are the same. If it is a different element, the atoms are different Atoms can not be created or destroyed but can be combined, rearranged, or separated. Atoms form in simple whole number ratios to form compounds. Example: H 2 O water is always found in a 2:1 ratio

The History of Subatomic Particles William Crookes – Invented cathode-ray tube

JJ Thomson – ( ) Used cathode ray tube to perform experiments using magnets and observing what effect the magnets had on the ray within the tube

Thomson’s Atom Discovered electrons are smaller than a Hydrogen atom Plum Pudding model of atom Electrons - charge + charge “pudding”

Robert Millikan (1868 – 1909) Oil Drop Experiment: Determined Charge of Electron (-1) Determined Mass of Electron 1/1840 th that of Hydrogen

The Nuclear Atom Rutherford ( ) –

Rutherford’s Gold Foil Experiment Performed and discovered by YOU!!! End Conclusions: 1) 2)

James Chadwick Additional mass of nucleus must be made up by a neutral particle known as the neutron

Nucleus © responsible for most of the mass of the atom © protons (+ charge) © neutrons (no charge)

(-) charge responsible for most of the volume of the atom negligible mass (0)

Determining P, N, and E Atomic Number – The number of protons in an atom. In a neutral atom: Number of protons = number of electrons Mass Number= # protons + #neutrons # of Neutrons = atomic mass – protons

Isotopes Kind of like twins…alike, but different Isotopes -Same element, but with different mass due to different # of neutrons Same number of protons

Isotopes can be written 2 ways:

1. Nuclear Notation mass #--> < -- element Symbol atomic #--> K neutrons + protons-->

2. Hyphen Notation Hyphen notation looks like this: C-12 & C-14 The number after the hyphen = mass number (atomic mass) Carbon So what does that mean?

Practice (Neutral Atoms) ProtonsElectronsNeutrons Silicon O He

Average Atomic Mass Average Atomic Mass – The average of all naturally occurring isotopes.

Uranium has three common isotopes. If the abundance of 234 U is 0.01%, the abundance of 235 U is 0.71%, and the abundance of 238 U is 99.28%, what is the average atomic mass of uranium?

Titanium has five common isotopes: 46 Ti (8.0%), 47 Ti (7.8%), 48 Ti (73.4%), 49 Ti (5.5%), 50 Ti (5.3%). What is the average atomic mass of titanium?

Isotopic Abundance Nitrogen is made up of two isotopes, N-14 ( ) and N-15 ( ). Given nitrogen's atomic weight of , what is the percent abundance of each isotope?

Copper is made up of two isotopes, Cu-63 ( amu) and Cu-65 ( amu). Given copper's atomic weight of , what is the percent abundance of each isotope?

Lithium has 2 natural isotopes, Li6 and Li7. they have atomic masses of amu and amu respectively, which isotope would be found in greater abundance?

Bohr and Lewis Bohr Model – A planetary model of the atom with electrons orbiting the nucleus Lewis Dot Structure – model representing the valence electron pattern across the periodic table Valence Electron – electron in the outermost shell/energy level

p+p+ Bohr’s atom

Drawing Bohr Models Electrons are arranged in Energy Levels or Shells around the nucleus of an atom. - first shell a maximum of 2 electrons - second shell a maximum of 8 electrons - third shell a maximum of 8 electrons - fourth shell a maximum of 2 electrons