A chemical symbol is a short or abbreviated way to write the name of an element. Where do element’s symbols come from? Elements are named to honor scientists, for places, or for their properties. Do you know any of the element’s symbols? Which ones?

 Nucleus  Protons  Neutrons  Electrons  Positively charged, center of the atom  Particles found in the nucleus with a positive charge  Particles found in the nucleus that are neutral  Particles that are in orbit around the nucleus with a negative charge

The electrons are moving in orbit around the nucleus. The nucleus is found at the center and is made up of protons and neutrons! nucleus electrons protons neutrons

Using your textbook (pg.510) and colored paper and pencils from the side counter, create a timeline of the changing atomic model!

1. Democritus' Uncuttable Atom 2. Thomson Model 3. Rutherford Model 4. Bohr Model 5. Electron Cloud Model 6. DATES 7. Descriptions of each model 8. Any other interesting information

 Most of the mass of an atom is found in the nucleus! › This is because proton’s and neutron’s masses are much greater than electron’s mass and the protons and neutrons make up the nucleus. › When massing an atom, electrons aren’t even considered as part of the mass because they are so light!

 The unit of measurement used for atomic particles is the atomic mass unit (amu). › The mass of a proton or a neutron is almost equal to 1 amu-this is not a coincidence-the unit was set up that way! › Much easier to work with than the mass of particles in grams.

 Elements are different because they have different numbers of protons. › Elements are defined by how many protons they have!! So, the number of protons tells you what type of atom you have.  The number of protons (and electrons for our purposes) in an atom is equal to a number called the atomic number (number at the top of the squares).

 What is the atomic number for aluminum?  How many protons does aluminum have?  How many protons does magnesium have?  How many electrons will a neutral atom of magnesium have?

 The mass number of an atom is the sum of the number of protons and neutrons in the nucleus of an atom.  So, you can apply the following equation to solve for the number of neutrons for any element: › Number of neutrons = mass number - atomic number

 Beryllium, which has 4 protons and 4 neutrons?  Nitrogen, which has 7 protons, 7 electrons, and 8 neutrons?  Boron, which has 6 electrons and 5 neutrons?

 Isotopes: Not all atoms of an element have the same number of neutrons. › Atoms of the same element that have different numbers of neutrons are called isotopes!  Example: C-12 and C-14 › The numbers represent the mass number and you can use this mass number to calculate number of neutrons using the formula from above, so C-12 has 6 neutrons and C-14 has 8 neutrons.

 Because most elements have more than one isotope, each element has an average atomic mass. The average atomic mass of an element is the weighted average mass of the mixture of its isotopes.

 Groups › AKA Families › Vertical Columns › Numbered 1-18 › Elements in each group have similar properties  Periods › Horizontal Rows › Numbered 1-7 × Metals, Nonmetals, Metalloids

 Element symbol  Number of protons for each atom › Electron number is the same in a neutral atom  Number of valence electrons for the representative elements  Solid, liquid, or gas  Average atomic mass  Metal, metalloid, or nonmetal

 Scientists have found that electrons within the electron cloud have different amounts of energy.  This is shown using “energy levels”  Energy levels nearer the nucleus have lower energy than those levels that are farther away.  Electrons fill these energy levels from the inner levels to the outer levels.

 Refer to page 520  Energy level one: Max of 2 electrons  Energy level two: Max of 8 electrons  Energy level three: Max of 18 electrons  Energy level four: Max of 32 electrons › Very important: A stable outer energy level will contain 8 electrons, when the number exceeds 8, the electrons fill in the lower levels again, so you really never have more than 8 electrons in the outer level!