What do I need to know for the test?

460 BC-created the 1 st Atomic Theory of Matter (not modern atomic theory however) HIS THEORY Matter is composed of empty space through which atoms move Atoms are solid, homogeneous, indestructible, and indivisible Different kinds of atoms have different sizes and shapes The differing properties of matter are due to the size, shape, and movement of atoms Changes in matter result from changes in groupings of atoms and NOT from changes in the atoms themselves

Dalton revived Democritus’s ideas in the 19 th century. Much time has passed.

Dalton’s Model

Father of the Modern Atomic Theory 5 parts Each element is composed of tiny, indestructible particles called atoms All atoms for a given element have the same mass and properties Atoms cannot be created, divided into smaller particles, or destroyed Atoms combine in whole number ratios to form compounds In a reaction, atoms are separated, combined, and rearranged

He used a cathode ray tube experiment to discover electrons. He measured both magnetic and electric fields on the cathode rays and observed that there was a teeny tiny particle, much smaller than the Hydrogen atom  Electron Plum Pudding Model Negatively charged electrons are distributed throughout a uniform positive charge

Plum Pudding ModelCathode Ray

Discovered the charge (-1) of an electron by doing the oil drop experiment experiment-a experiment-a124624

Oil Drop

He was interested in studying how alpha particles (+ charge ) interact with atoms Rutherford thought that, in his experiments, only a few positively charged alpha particles would slightly deflect and the rest would go straight through. Using the Gold Foil Experiment he discovered that some of those particles deflected at large angles and even bounced straight back at him.

That means that the plumb pudding model was wrong and there was a small dense center to an atom called a NUCLEUS! Which means that the electrons floated around in empty space….so he also discovered the orbital theory of electrons, in other words, electrons orbit the nucleus (small charge) in circular paths

Gold Foil Experiment

Mendeleev was the first to put all the known elements into some sort of arrangement. His periodic table is NOT the periodic table we know today. He arranged the table in order of atomic mass, NOT number.

Arranged the periodic table according to atomic number NOT atomic mass (Mendeleev) This is our periodic table that we use today Periodic Law-Elements close to one another have similar properties.

Bohr’s Model is based on the light emission spectrum of Hydrogen… He proposed that a hydrogen atom has only certain allowable energy levels. (energy is quantized) Lowest energy level is ground state When an electron is excited it moves up to an excited state He proposed that electrons can only orbit in certain circular paths (like planets) Each path is a different energy level

Bohr’s Energy Levels

When an electron falls from an excited state to the ground state, light is emitted…. His model explained Hydrogen’s spectrum, but not any other element

Louis went one step further than Bohr… Theorized that all moving particles have wave like characteristics, even electrons!

Went further with the wave/particle theory Discovered electron clouds (s, p, d, f) Explains that electrons move like waves and not in a fixed patterns

At any given time, an electron can be found somewhere within its electron cloud. (90% of the time)

Essentially discovered neutrons (no charge) and how it pairs with protons in a mass called a nucleus