1. Electrons Occupy the space OUTSIDE the nucleus in a region called the Electron Cloud. The diameter of the cloud = the diameter of the atom. The electron cloud takes up the most VOLUME of an atom, whereas the nucleus takes up most of the MASS. EXAMPLE: Think of a Pea in a football field. The pea would be the nucleus, and the electrons would be a large swarm of gnats buzzing around the stadium at an extremely high speed! Electron Cloud Model of Atom

2. Forces inside an atom There are 4 forces working inside an atom: Electromagnetic: Electrons bound to the nucleus by the attractive force between electrons and protons Strong Nuclear Force: The strongest force known in science – Attracts protons and neutrons to each other and only works in small distances in the nucleus Weak force: weaker than both ehe electric and the strong nuclear force Gravity: weaker than the weak force because atom is so small….understanding it is still an unsolved mystery.

3. Bohr first proposed the idea of electrons having energy levels All atoms have energy levels. Each energy level has a certain number of electrons it can hold. Electrons will fill each level before starting to fil the next level. The levels hold 2 – 8 - 8 – 18 Remember: The number of electrons depends on the number of protons (atomic number) 1 st 2 nd 3 rd 4 th

5. Valence electrons valence electrons are the electrons in the very last or outermost energy level the properties of elements depends on how many electrons are in a particular atom’s different levels

6. Beyond Bohr’s Model Quantum Theory states when things get small (like an atom) matter and energy do not obey Newton’s laws or other laws of classical physics Everything is fuzzy in the quantum world. In fact, the Heisenberg Uncertainty Principal states that a particles position, momentum and energy, and time can never be precisely known at the same time. Many orbitals make up an electron level

7. Ions Atoms that have the same number of protons and electrons are said to be electrically neutral. An Ion is an atom has a different number of protons than electrons and thus has a charge. Positively charged ions have more protons than electrons Negatively charged ions have more electrons than protons

9. Read Section 12.2 (pg. 285 – 289) Answer Questions 1-8 on page 290