1. Introduction to Atoms

2. What are atoms? An atom is the smallest particle into which an element can be divided and still be the same substance.

3. History of the Atom

4. History Democritus – first person to use the word atom, comes from the Greek word atoma, means “indivisible” John Dalton came up with the atomic theory JJ Thomson did experiments using a cathode ray tube, came up with model that included positive and negative charges Ernest Rutherford did the Gold Foil experiment, which changed the model to a positive nucleus surrounded by electrons Niels Bohr determined that electrons move in specific distances from the nucleus based on how much energy they have

5. Atomic theory The atomic theory states 5 things: 1.All matter is made up of atoms 2.Atoms are neither created nor destroyed in chemical reactions (Law of conservation of mass) 3.Atoms of different elements combine in whole-number ratios 4.Each element is made of a different kind of atom 5.The atoms of different elements have different mass and properties

6. Parts of an atom Protons – positively charged particles found in all atoms Neutrons – particles found in all atoms that do NOT have a charge (neutral charge) Electrons – negatively charged particles found in all atoms

8. Nucleus Center of the atom that is extremely dense, positively charged region that contains BOTH protons and neutrons Protons and neutrons = mass number

9. Electron clouds Regions inside the atom, located outside surrounding the nucleus with negatively charged particles (electrons) Bohr proposed that electrons move in paths at certain distances around the nucleus = BOHR MODEL

11. Next time – Atoms and the periodic table

12. Copy the entire figure, drawing and words from page 312, Figure 11

13. Atomic mass unit (amu) The SI unit used to express the masses of the particles of an element Each proton has a mass of 1 amu Each neutron has a mass of 1 amu Electrons are so small that they have a mass unit of almost zero

14. Atomic number How can you tell which elements these atoms represent? Atomic number – number of protons in the nucleus of an atom

15. Isotopes Are all atoms of an element the same? NO Isotopes – atoms that have the same number of protons but different number of neutrons Each element has a limited number of isotopes that occur naturally

16. Mass number Protons + neutrons = mass number Used to determine if an element is an isotope

17. Atomic mass Weighted average of masses of all the naturally occurring isotopes of an element MATH BREAK – pg 316, do in your science journal

18. Physical Property Color, odor, mass, volume Physical PropertiesDefinitionExample Thermal conductivityThe ability to transfer thermal energy from one area to another Plastic foam is a poor conductor, so hot chocolate in a plastic foam cup will not burn your hand. StateThe physical form in which a substance exists, such as a solid, liquid, or gas Ice is water in its solid state. MalleabilityThe ability to be pounded into thin sheets Aluminum can be rolled or pounded into sheets to make foil. DuctilityThe ability to be drawn or pulled in a wire Copper is often used to make wiring. SolubilityThe ability to dissolve in another substance Sugar dissolves in water. DensityMass per unit volumeLead is used to make sinkers for fishing line because lead is more dense than water.

19. Physical vs. Chemical Properties SubstancePhysical propertyChemical property HeliumLess dense than airnonflammable WoodGrainy textureflammable Baking sodaWhite powderReacts with vinegar to produce bubbles Powdered sugarWhite powderDoes not react with vinegar Rubbinmg alcoholClear liquidflammable Red food coloringRed colorReacts with bleach and loses color IronmalleableReacts with oxygen TinmalleableReacts with oxygen