1. ATOMIC STRUCTURE More Clues about the Nature of Elements

2. More famous guys in the history of chemistry Avogadro – equal volumes of gases, at the same temperature and pressure, contain the same number of molecules. AND AND The number of molecules in one gram molecular weight of an element is 6.023 x 10 23 which he called a “mole.”

3. More famous guys in the history of chemistry 1. Cathode rays have electrical charge 2. Cathode rays can be bent by a magnetic field 3. Electric charge is very light compared to its strength He concluded that: atoms contain sub-particles with electrical charge. He called these particles electrons JJ Thompson – observed that:

4. More famous guys in the history of chemistry Elements emit positive particles and negative particles. When alpha particles are aimed at gold foil, most will go through, but some will bounce back. He concluded that: An element’s atoms are mostly space, they have a positively charged nucleus and orbiting electrons (like the solar system) Ernest Rutherford observed:

5. More famous guys in the history of chemistry Why don’t electrons get pulled into the positive nucleus (since opposites attract)? He found a relationship between the energy in electrons and the frequency of their orbits Bohr wondered:

6. More famous guys in the history of chemistry Electrons travel in set orbits that have specific energies and specific distances from the nucleus. Electrons can move to higher levels if they are fed energy. They give off light when they return to their normal energy level. Bohr concluded that:

7. What is an atom? the smallest part of an element that is still that element The atom’s nucleus contains positively charged protons (+) and neutral neutrons. Electrons (-) have negative charge and orbit the nucleus in energy levels, or orbitals. The number of electrons matches the number of protons, giving the atom a neutral charge.

8. What’s the scale of an atom? If an atom were the size of a football field, the nucleus would be the size of a football. Although it only occupies a speck of space in the atom, the nucleus contains almost all the atom’s mass

9. What’s the Mass of an atom? Compare one gram of the element to one gram of carbon12. It’s also expressed as the total protons and neutrons in an atom’s nucleus.

10. What is ATOMIC MASS? Determined by the mass of protons and neutrons in the atom. Since they are calculated relative to a carbon12 atom, they are relative to each other. ELEMENT Relative Atomic Mass Aluminum26.98 Copper63.55 Iodine126.90 Iron55.85 Magnesium24.31 Silicon28.09 Sulfur32.06 Zinc65.38

11. Test yourself 1. The guy who experimented with cathode ray tube and came up with the idea of electrons was: A) Rutherford B) Bohr C) JJ Thompson D) Crick C) JJ Thompson

12. Test yourself 2. The guy who experimented with gold foil and came up with the idea that atoms are shaped like the solar system: A) JJ Thompson B) Rutherford C) Bohr D) Democritus B. Rutherford When most particles went through the foil and some particles bounced back, he knew there was lots of space inside a gold atom.

13. Test yourself 3. The number 6.023 x 623 is: A) Dalton’s folly B) Rutherford’s rabbit C) Avogadro’s mole D) Bohr’s bear C. Avogadro’s Mole 1 mole of Cu has 6.022 x 10 23 atoms and weighs about 63.54 grams.

14. Test yourself 4. If an atom was the size of a football field, the nucleus would be the size of a: A) basketball B) snowball C) tennis ball D) football D) football

15. Imagine… 6. The atomic number of Sulfur is 16. The atomic mass is 32. It therefore has A) 16 protons B) 16 electrons C) 16 neutrons D) all of the above D) All of the above. Atomic mass is the total number of particles in the nucleus. If there are 16 protons (atomic number) there must also be 16 neutrons. (32 – 16 = 16)

16. Test yourself 5. The guy who came up with the energy level theory to explain why elements each have a particular spectrum of light was: A) Einstein B) Bohr C) Rutherford D) JJ Thompson B) Bohr He is known as the father of quantum mechanics.