1. Structure of Matter Structure of Matter Structure of Matter History of the Atom

2. The Greek Model The Greek Model Greek scholar: Democritus developed the idea that matter is made of particles that are indivisible (atomos). Greek scholar: Democritus developed the idea that matter is made of particles that are indivisible (atomos).

3. The Dalton Model John Dalton- English chemist who proposed the first atomic theory.

4. Dalton’s Atomic Theory All elements are composed of indivisible particles called atoms. All atoms of the same element are identical. Atoms of different elements are different. When a chemical reaction occurs, the atoms are simply rearranged in a fixed whole-number ratio. All elements are composed of indivisible particles called atoms. All atoms of the same element are identical. Atoms of different elements are different. When a chemical reaction occurs, the atoms are simply rearranged in a fixed whole-number ratio.

5. Thomson’s Experiment Voltage source +- Vacuum tube Metal Disks

6. Thomson discovered the first component part of the atom: the electron, a particle with a _____ electric charge. Thomson discovered the first component part of the atom: the electron, a particle with a _____ electric charge. DISCOVERY OF THE ELECTRON

7. J.J. Thomson’s Model or the “plum pudding” Model  He proposed that an atom was made of ________ portion(pudding).  Spread throughout these positive charges were the negative charges called ________ (plums).  He proposed that an atom was made of ________ portion(pudding).  Spread throughout these positive charges were the negative charges called ________ (plums).

8. The Rutherford Gold Foil Experiment

10. 1. The atom contains a tiny BUT dense center called the nucleus. 1. The atom contains a tiny BUT dense center called the nucleus. 2. The nucleus is positively charged. 2. The nucleus is positively charged. 3. The electrons move around in the empty space of the atom surrounding the nucleus. 3. The electrons move around in the empty space of the atom surrounding the nucleus. 1. The atom contains a tiny BUT dense center called the nucleus. 2. The nucleus is positively positively charged. 3. The electrons electrons move around in the empty space of the atom surrounding the nucleus. Rutherford's Nuclear Model These concepts appear in the finals always – so they are very, very, very IMPORTANT!!! The atom is made mostly of empty space with a dense and positively- charged nucleus called the nucleus !!!

11. Hypothesis : Rutherford expected the a- particles to pass undeflected through the atoms. Results: Rutherford observed that a small fraction of the a-particles were ______; to explain the observation, he proposed the ________ model of the atom. Explanation: To deflect the energetic a- particles, the ________ must be dense, with ________ charge. For the fraction deflected to be small, the nucleus must be (small,big), the atom must be mostly empty space.

12. James Chadwick – discovered the neutrons Neutrons are neutral particles James Chadwick – discovered the neutrons Neutrons are neutral particles

13. Bohr’s Model Electrons in atoms could exist only at certain energy levels around the nucleus in regions of space shaped like the surface of a ball. Electrons can jump from the lowest energy level (ground state) to a higher energy level (excited state). As electrons return to the lowest energy level again, the same amount of energy the atom absorbed will be released in the form of light. Electrons in atoms could exist only at certain energy levels levels around the nucleus in regions of space shaped like the surface of a ball. Electrons can jump from the lowest energy level (ground state) to a higher energy level (excited state). As electrons return to the lowest energy level again, the same amount of energy the atom absorbed will be released released in the form of light. Absorb energy Energy released

14. Spectrum of hydrogen Spectrum of neon

15. Planetary Model 3-D orbits

17. The Charge-Cloud Model Scientists now describe the possible positions of electrons in terms of __________ Scientists now describe the possible positions of electrons in terms of __________

18. Wave-Mechanical (charge-cloud) Model An__________ is the distribution of probabilities: probabilities: it is thickest in the regions where we are most likely to find the electron electron (orbital) (orbital) at any given moment. Orbital Orbital – 3-dimensional, cloudlike space Electrons have dual characteristics: wave wave and particle

19. Atomic Structure Atomic Structure

21. Periodic Table of Elements Periodic Table of Elements

23. Symbol / Representation: Symbol / Representation: Symbol / Representation:  A – the mass no.  Z – the atomic no.  X – the symbol of the atom Mass No. Atomic No. Subtract !!! Neutrons

24. Atomic Representation Atomic Representation

25. Outside the nucleus: Outside the nucleus:  Shell or energy level – main area where the electrons are found  Sublevel or Subshell – subdivision of the main shell  Orbital – a three-dimensional space where the electron is found with greatest probability or chance. SSSShell or energy level – main area where the electrons are found SSSSublevel or Subshell – subdivision of the main shell OOOOrbital – a three-dimensional space where the electron is found with greatest probability or chance.