Download Atomic Structure/Atomic Theory

Atomic Structure/Atomic Theory
Atomic Structure: Unit 2
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The atom
o The building block of matter
o Each element is a unique type of atom
Areas of the Atom:
o Nucleus
 Center of the atoms
 Contains almost all of the mass but very little of the atoms space
 Contains Protons and Neutrons
o Electron Cloud
 Area around the nucleus
 Contains up to 7 energy levels where electrons can be found
 Each energy level can hold only so many electrons
 1st energy level holds 2 electrons
 2nd energy level holds 8 electrons
 3 rd energy level holds 18 electrons
Particles that make up the atom
o Proton
 Positive charged particle in the nucleus
 Has a mass of 1 atomic mass unit (u)
 The number of protons determines the type of element
o Neutron
 Neutral (no charge) particle in the nucleus
 Has a mass of 1 atomic mass unit (u)
o Electron
 Negative charged particle found in the electron cloud
 Electrons circle the nucleus
 Electrons contain almost no mass. There atomic mass is zero (u)
 In stable atom, the number of electrons will be the same as the
number of protons
 Valence electrons are electrons in an atoms outermost electron
energy level and determine how the atom reacts with other atoms
Elements: The number of protons in an atom determines which type of element the atom
is. The atomic number on the periodic table identifies the number of protons: example H
= atomic number 1 and it has one proton; Carbon is atomic number 6 and it has six
protons.
Atomic Structure/Atomic Theory
Isotopes of an element have different numbers of neutrons
Example Carbon-14 Still has 6 protons, but it has 8 neutrons. Carbon-14 has this
name because its mass is 14
Ions – When an atom loses or gains an electron, then the atom has a positive or negative
charge. Example: if Carbon loses an electron, then it will have 6 protons and only 5
electrons, giving it a positive + 1 charge overall (6 positives protons and 5 negative
electrons)
Development of the Atomic Theory
Democritus (430 BC) Greek Philosopher
 Proposed existence of atoms (atoma) = Greek for indivisible
John
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Dalton (1803) British Chemist
Compounds form from specific amounts of elements
Atoms cannot be created, divided or destroyed
Each atom of the same element is identical, but different from the atoms of other
elements
 Solid Sphere (Bowling ball) model
J.J. Thomson (1897) British Chemist
 Discovered 1st subatomic particle (electrons)
 Plum pudding model – positive sphere with negative particles
Ernest
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Rutherford (1912) New Zealand Physicist
Discovered the nucleus
Nuclear model – small, dense, positive charged particles in the nucleus = protons
Electrons travel around nucleus
Niels Bohr (1913) Danish Physicist
 Discovered energy levels
 Bohr model (planetary model)
 Electrons travel in fixed paths, but can jump from one to another
Erwin Schrodinger (1924) Austrian Physicist
 Developed the electron cloud model
 Exact path of electrons cannot be predicted
James Chadwick (1932) English Physicist
 Discovered neutrons (no charge)
 Mass of neutrons nearly equal to mass of protons (atomic mass unit)