2. CH.3 ELEMENTS, ATOMS AND ISOTOPES

3. Dalton’s Atomic Theory (1808) I.All matter is made of atoms II.Each element has its own kind of atom. Atoms of the same element have the same mass, atoms of different elements have different masses.

4. III.Atoms of different elements combine in simple whole-number ratios to produce compounds (stable groups of atoms.)* IV.Atoms cannot be created or destroyed. H2H2 H2OH2ONH 3 CH 4

5. Abundance of Elements in Earth’s Crust

6. Sub Atomic Particles (smaller than atoms) 1.Protons –Found in nucleus (center part) of atom –Positive charge (+1) –Mass 1 atomic mass unit (a.m.u.) 2.Neutrons –Found in nucleus of atom –Neutral ( 0 charge) –Mass 1 a.m.u. 3.Electrons –Found moving outside the nucleus –Negative charge (-1) –Mass approx 1/1800 a.m.u.

7. Atomic Structure Atoms are electrically neutral, as the number of protons equals the number of electrons.

8. There have been many models of the atom proposed by scienctist over the years. The most recent two are: Bohr Model Protons and neutrons crammed into the center called the nucleus Electrons move in definite orbits around the nucleus Models of the atom:

9. The electron cloud model: - the most accepted model today Almost the same as the Bohr model. Around the nucleus is an electron cloud. Within the cloud there are energy levels that electrons can jump from.

10. Atomic Model The nucleus and electron cloud are separated by vast space, for example: An atom the size of Dodgers Stadium and parking lot would contain a pea sized nucleus containing 95.95% of the atom’s mass!!!!!!

11. Atomic Number mass number (A) - sum of the number of protons and neutrons Mass Number Symbol of the atom atomic number (Z) - the number of protons in the atom

12. Isotopes - atoms of the same element having different masses –contain same number of protons –contain different numbers of neutrons Isotopes of Hydrogen Hydrogen (Hydrogen - 1) Deuterium (Hydrogen - 2) Tritium (Hydrogen - 3)

13. Isotopes of the same element have identical chemical properties Some isotopes are radioactive Atomic Mass and mass number are close, but not exactly the same….atomic mass is the average of all known isotopes and their relative abundance in nature Mass number and atomic mass can help determine how many neutrons there are in an atom (subtract mass number—atomic number)