1.1-1.2 Nature of Chemistry and Atomic Structure

1. 1.1-1.2 Nature of Chemistry and Atomic Structure Unit 1

2. What is Chemistry? • -study of matter and its interactions. • -involves experimenting in the macroscopic world and theorizing about the microscopic world

3. Types of Knowledge Empirical knowledge- knowledge that comes from investigation and observation Theoretical knowledge - knowledge that explains scientific observation. -based on ideas created to explain observation

4. Theory vs.Law Theory - an explanation or model based on observation, experimentation and reasoning. -best understanding of why something happens -allows us to predict future events -evolve and change over time as new information is collected Law – a generalized rule to explain a body of observations either as a statement or mathematical equation -has been proven over and over (has stood the test of time)

5. The International Union of Pure and Applied Chemistry (IUPAC) a council that was established in 1919 to regulate standards and procedures in chemistry so that information in the field can be understood worldwide

6. 1.2 Atomic Structure What is an ATOM? -smallest possible particle of an element

7. Atomic Models Model - an attempt to use familiar ideas to describe things in a visual way. There have been several models of the atom. TIMELINE OF ATOMIC MODELS Greek Philosophers -matter can be subdivided into tiny particles called atomos (cannot be cut or indivisible)

8. Democritus -atoms have different sizes, are in constant motion, and are separated by empty spaces -simply a round sphere with no electrons, protons, or neutrons Aristotle -all matter is composed of four essential substances: earth , air, water, and fire

9. Dalton -atoms are solid spheres like billiard balls He said: a. all matter is made up of tiny, indivisible particles called atoms b. all atoms of an element are identical c. atoms of different elements are different d. atoms are rearranged to form new substances in chemical reactions but they are never created or destroyed (Law of conservation of mass) *doesn't explain how things acquire electrical charge

10. Thomson -used the cathode ray tube to discover the electron -plum pudding model: electrons are small negative particles evenly spaced in a positive sphere

11. Rutherford -aimed tiny positive alpha particles at gold foil and measured how many alpha particles deflected off the foil on a fluorescent screen and found most were absorbed by the foil and only a few were deflected -nuclear model: an atom contains a small, dense positive central nucleus. -The positive particles are protons. -The nucleus is surrounded by mostly empty space occupied by electrons. -predicted the existence of the neutron (same mass as the proton but has no charge)

12. Chadwick -confirmed the existence of the neutron Bohr -observed that hydrogen emitted light when excited by energy -realized hydrogen has a unique spectrum -planetary model: electrons orbit the nucleus in definite energy levels and can jump between energy levels. Each energy level holds a specific number of electrons. -The outer orbit of electrons is called the valence shell.

13. Bohr’s Model

14. Summary of Subatomic Particles The mass of atomic particles is so tiny that IUPAC has decided to measure the mass of atoms in atomic mass units (U). The atomic mass unit is 1/12 the mass of a carbon -12 atom PARTICLELOCATIONCHARGEMASS Electron Orbit -1 0 Proton Nucleus +1 1U Neutron Nucleus 0 1U

15. Bohr -Rutherfold Diagrams #of protons = atomic number(Z) # of electrons = # of protons= atomic number #of neutrons = mass(A)-atomic number Rule to fill orbits for elements #1-18: level 1 -2 electrons maximum level 2 - 8 electrons maximum level 3 - 8 electrons maximum

16. TRY THIS: Draw a Bohr diagram for Calcium Atomic Mass 40 20 P= 20 N= 20 E= 20 Ca Standard Atomic Notation Atomic Number

17. Homework: P. 10 #4,6 P.16 #1-2,5,10