1. When scientists wanted to find out what an atom was, they were not able to look directly at what the atom was made of. They had to make inferences from the results of many different experiments. It was like trying to describe a picture, such as the one below, with only small portions visible. 2. What information or parts of the picture would make your descriptions more accurate without revealing the entire picture? 1.Write two sentences describing what you can see of the above picture. Bellringer/Section 1 Notes

2. I. What are Atoms? A.Atoms – smallest part of an element that still contains the element’s properties. B. Atoms are made up of: 1.Protons – 3. Electrons – 2. Neutrons –Have no charge Have a positive (+) charge a.Orbit around the nucleus in the electron cloud a.Both found in the nucleus Have a negative (-) charge C. The number of protons & neutrons each atom has is unique for that element

3. D. The number of protons and electrons an atom has determines its overall charge Example: Neon has 10 Protons(+) and 10 Electrons(-). +10 + (-10) = 0

4. II. Models of the Atom A.Niels Bohr (1913) – electrons travel in orbits around the nucleus 1.Electrons with more energy are farther away from the nucleus B. Later theories state that electrons do not necessarily orbit the nucleus in an orbital path

5. C. An electron’s exact location cannot be determined, only estimated 1.Areas of electron location are shaded a darker color

6. D. Electrons exist in energy levels 1.NOTE: even though an energy level can hold 8 electrons it will not always have 8 electrons

7. E. The outermost (last) energy level holds valence electron(s) 1.Valence electrons determine how an atom will react with other atoms 2. Valence electrons can vary in number: a.The 1 st energy level will contain up to two valence electrons b. The 2nd energy level will have up to eight valence electrons