1. Atomic Structure Spectra of Science Miss Amole By PresenterMedia.com

2. What is an atom? • Simplest unit in an element • Determines the properties of that element • “atom” is derived from a Greek word meaning “unable to be divided” • Contains 3 subatomic particles: protons, neutrons, and electrons

3. Subatomic Particles • PROTON: • Positively charges • Located in nucleus • Have mass

4. Subatomic Particles • NEUTRON: • Neutral = no charge • Located in the nucleus • Have mass

5. Subatomic Particles • ELECTRON: • Negatively charged • No mass (negligible) • Very fast; impossible to pin point exact location, speed, and direction • Located outside nucleus in electron cloud • Electron cloud contains energy levels • Energy levels contain orbitals

6. More About Electrons • The valence electrons an atom has determines reactivity • Valence electrons are those located in the outermost shell or energy level • Each energy level can only hold a certain number of electrons

7. More About Atoms • The number of protons and electrons an atom has is unique to each element • That is to say, every element has a different number of protons in its atom • Coincides with the atomic number • Even though atoms contain charged particles, they are electrically neutral • That is to say an atom has an equal amount of protons and electrons • Atoms contain mostly empty space • If the nucleus of an atom was the size of a marble, the entire element would be the size of a football field

8. Development of Atomic Theory • Democritus • Fourth century BC Greek philosopher • First to suggest the existence of atoms • Believed universe contained these invisible units that caused changes in matter • Believed atoms were indivisible

9. Development of Atomic Theory • John Dalton • 1808 English schoolteacher • Suggested all atoms of a given element were alike • Believed different atoms could join together to form compounds • His theories are considered the foundation for modern atomic theory

10. Development of Atomic Theory • Niels Bohr • 1913 Danish scientist • Suggested electrons move in set paths around nucleus that determine their energy level • Believed electrons would have to gain energy to move to a higher energy level or lose enregy to move down

11. Development of Atomic Theory • By 1925, Bohr’s model no longer explained electron behavior • Current thought suggested electrons are act more like waves on a vibrating string than particles • Impossible to detect an electrons exact location, speed, or direction

12. Other Forms of Atoms • Ions • Cations • Created when an atom loses one or more electrons and becomes positively charged • Anions • Created when an atom gains one or more electrons and becomes negatively charged • Isotopes • Atoms of the same element with a different number of neutrons

13. -Atomic Structure Video-Atom Builder