Origin of the idea of atom… GREECE Democritus (460 -370 b.c.): matter is made of tiny particles atomos
John Dalton’s Atomic Theory- 1803 Five notions about atoms… 1. All matter is made of atoms 2. All atoms of given element are identical 3. The atoms of one element are different from other elements 4. Atoms combine in whole ratios to make compounds: LAW OF CONSTANT COMPOSITION 5. In chemical reactions atoms are separated, combined, or rearranged. (but cannot be destroyed)
Atomic Structure Atoms are composed of 3 subatomic particles- Electron- J.J. Thompson and Millikan Proton- Goldstein and Rutherford Neutron- Rutherford, Bohr
Electrons: J.J. Thomson- 1856-1940 Using a cathode ray tube he found that atoms emit tiny negative particles “corpuscle” Found that atoms have particles that move AWAY from the negative end, so they must have a negative charge!
Protons- J.J.Thompson-1897 “Plum Pudding” Model Electrons have a negative (-) charge But atoms are neutral (no charge) Therefore there must be a positive (+) charge too!
Protons- Ernest Rutherford - 1911 He shot (+) charged alpha particles at gold foil
Protons- Ernest Rutherford - 1911 Only a few positive particles were repelled This disproved his hypothesis There must be a VERY small positive central core (nucleus) , and the rest of the atom 99.999% is empty space.
Bohr model 1915 Protons and Neutrons are in the nucleus Electrons are outside the nucleus in orbitals Electrons can move from one orbital to another, and release energy as electromagnetic radiation.
Electron cloud Model Electrons are in clouds (Schrodinger)
3 subatomic particles 1.007 1.009 -1 5.486x10-4 Name (symbol) Charge Mass (amu) (atomic mass unit) Actual Mass location Proton (p) +1 1.007 1.673x10-24 g Nucleus Neutron (n) 1.009 1.675x10-24 g Electron (e-) -1 5.486x10-4 (so small that its not counted!) 9.109 x10-28g Outside Nucleus
Activity: As scientists gained more evidence, their THEORIES on atoms changed… Analyze each of the following models with your partner
History of Atomic Theories https://www.youtube.com/watch?v=xazQRcSCR aY
What makes one atom different from another? The number of protons! A difference in number of protons changes the actual element You can change the number of electrons and neutrons and still have the same type of element
Reading the Periodic Table
How do we know how many subatomic particles are in each element? Protons – Look at the atomic number! Electrons – Atoms are neutrally charged, so the number of protons = number of electrons
How do we know how many subatomic particles are in each element? Neutrons – The mass of the atom is made up of protons and neutrons # neutrons = mass number – atomic number Mass number is not the same as atomic mass, it is rounded to a whole number!
Element Coding: