1. Atomic Structure Part 2

2. History of the Atom   Democritus (Greek 460-370 BC) 1 st to use the word atom Believed that atoms were indivisible & indestructible No scientific support  Aristotle (Greek 384-322 BC) Rejected the theory of atoms Believed in 4 core elements fire, air, water, earth

3. Subatomic Particles  3 types of subatomic particles Protons: Positively charged particle (+) found in the nucleus.Protons: Positively charged particle (+) found in the nucleus. Neutrons: Uncharged particle also found in the nucleus.Neutrons: Uncharged particle also found in the nucleus. Electrons: Negatively charged particle (-) that moves around the outside of the nucleus in the electron cloud.Electrons: Negatively charged particle (-) that moves around the outside of the nucleus in the electron cloud.

4. What makes atoms different from one another?  # of protons  Atomic number = # of protons in the atoms nucleus.  The atomic number determines the identity (what is it) of the atom.

5. How do you determine the # of neutrons?  Atomic mass = total number of # protons and # neutrons in an atom’s nucleus.  Not all atoms of an element have the same atomic mass number. # of neutrons = atomic mass – atomic number

6. What is the atomic mass of helium? What element has an atomic mass of 27? How many protons does this element contain? How many neutrons does this element contain? 4.0026… round to 4 Aluminum 13 27 – 13 = 14

7. Isotopes  Atoms of the same element that have different numbers of neutrons in the nucleus.  The number of protons and electrons are the same.  Symbols: 11 Na 23 or 11 Na 24 6 C 12 or 6 C 13 or 6 C 14

8. Ions  Formed when an atom gains or loses one or more electrons.  Occurs 2 ways: Positive Ion (+)Positive Ion (+) Atom loses one or more electronsAtom loses one or more electrons More protons than electrons, results in a (+) charge More protons than electrons, results in a (+) charge Negative Ion (-)Negative Ion (-) Atom gains one or more electron Atom gains one or more electron More electrons than protons, results in a (-) chargeMore electrons than protons, results in a (-) charge

9. Examples of Ions  H +  Cl -  As 3-  Mg 2+ Lost 1e - Gained 1e - Gained 3e - Lost 2e -