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Atomic Theory
All matter is made of atoms
Law of definite proportions Water is 88.8 % oxygen and 11.2 %
hydrogen Law of conservation of mass
Mass cannot be created or destroyed Law of multiple proportions
CO , CO2 / C6H12O6 , C12H22O11 / H2O , H2O2
Dalton’s Atomic Theory
1. All matter is made of extremely small particles called atoms.
2. Atoms of a given element are identical in their properties.
3. Atoms cannot be created, destroyed, or subdivided.
4. Atoms of different elements combine in simple whole-number ratios to form compounds.
5. In chemical reactions, atoms are combined, separated, or rearranged.
Discovery of the electron
Electrons were discovered in a Cathode Ray Tube
Electrons are very small particles that have a negative charge
Original model of an atom
“Plum pudding” model
Electrons were embedded in a positively charged ball of matter
Discovery of the nucleus
Rutherford shot a stream of positive particles at a piece of gold foil and expectedthe particles to go right through the atoms of gold.
Rutherford’s gold foil experiment
He expected most of the particles to go straight through but some ofthe particles bounced straight back. Something very dense and positivelycharged had to be the reason it bounced back.
New model of the atom
Old model
New and improved model
The atom is very large compared to the size of the nucleus
Counting Subatomic Particles
Atomic number = number of protons
Protons = electrons
Atomic mass = protons + neutrons
Isotope – atoms of a certain element that have a different mass because it has a different number of neutrons.
Where are the electrons
Electrons are found in 3-dimensional spaces around the nucleus called orbitals.
We use 4 quantum numbers to tell:1. The distance from the nucleus2. The shape of the orbital3. The relationship of the orbitals with the
x,y,z axes4. The spin of the electrons
Principal Quantum Number
Indicates the main energy level Values = 1 – 7
This shows how far the orbital is from the nucleus.
Magnetic Quantum Number
Indicates the orientation of the orbitals on the x, y, and z axes.
How many orbitals there are s – 1 p – 3 d – 5 f – 7
Spin Quantum Number
Electrons spin in opposite direction (+1/2, -1/2)
2 electrons can fit in each orbital
Electron Configuration
Oxygen – 8 electrons 1s22s22p4
Sodium – 11 electrons 1s22s22p63s1
Argon – 18 electrons 1s22s22p63s23p6
Arsenic – 33 electrons 1s22s22p63s23p64s23d104p3