Dalton

1. Dalton • Matter is made up of atoms • Atoms cannot be divided into smaller pieces • All atoms of an element are exactly the same • Different elements are made of different kinds of atoms • “marble” – hardsphere

2. Crookes • Anode – positive charge • Cathode – negative charge • Cathode Ray Tube – CRT • Used for TV/ Computer screens

3. J.J. Tomson • Added a magnet to Crookes cathode ray • Cathode rays are negative charged particles of matter. Now called – Electrons • Particles smaller than an atom exist. • Model – sphere with positive and negative charged particles – “raisin cookie”

4. Rutherford • All of the mass of the atom and all of its positive charge are crammed into a very small space at the center of the atom – nucleus. • Model Nucleus Protons and neutrons Electrons

5. Bohr • Negatively charged particles are attracted to positively charged particles. • Electrons travel in orbits around the nucleus. • Energy levels

6. Rutherford – Bohr Model Protons and neutrons electrons Electron cloud

7. Atoms • Atoms are basic particles from which all matter is made. • An atom is the smallest part of an element. • 3 main parts of an atom • Proton + • Electron – • Neutron O • Atomic mass = protons + neutrons • # of protons = # of electrons

8. Isotopes • Every atom of the same element has the SAME number of PROTONS. • However , the number of NEUTRONS can be different for one element. • These are called ISOTOPES – atoms of the same element that have different number of neutrons. • The atomic mass of each isotope differ, because of the number of neutrons. • How many boys named Jack are there in 8th grade?

9. Periodic Table • Periodic Table classifies elements • Dmitri Medeleev – 1869 • Russian scientist that devised the Periodic Table we use today • Organized by atomic number. • Atomic number = # of protons • Atomic Mass = # of protons + neutrons • Periods • Groups

10. Classification • Metals – shiny, metallic luster, good conductor of heat and electricity • Nonmetals – brittle, dull, poor conductors of heat and electricity, many are gases at room temp. found in human body • Metalloids - have characteristics of both metals and nonmetals, all are solids at room temp. some are good conductors but not as good as metals

11. Molecule • Molecule – a group of atoms that are joined together and act as a single unit. • The force that holds 2 atoms together is called a chemical bond. • From the chemical formula you can tell what elements are present in a molecule of that compound.

12. Element, Compound, Mixture • Elements – made of one substance (Symbol) Ex: Carbon • Compounds – made of 2 or more elements chemically joined (Formula) Ex: Water • Mixture – made of several substances ( no symbol or formula) Ex: Air

13. Mixtures • Homogeneous Mixtures – the same throughout • Heterogeneous Mixtures – has different parts • Solution – a homogeneous mixture that forms when one substance dissolves in another. • Solvent – does the dissolving • Solute – the substance dissolved • Emulsion – mixture of two liquids that will separate after standing. • Colloid – mixture containing solid particles that are small enough to remain suspended in the liquid but will reflect light.

14. Mixtures • Tyndall Effect – particles that are very small (can’t be seen by the naked eye) but can reflect light.