Chapter 4 - 2 Warm - Up 1. Describe the different parts of an atom. 2. What did Bohr’s model of an atoms resemble? 3. How many electrons does the 2nd energy level hold? 4. What does a p orbital look like?

Chapter 4 – 2 Atoms and the Periodic Table A Guided Tour of the Periodic Table

Organizing the Table Groups similar elements together Elements represented by symbols Order based the number of protons

Periodic Law Periodic Law – Repeating chemical and physical properties of elements change periodically with the atomic number of the elements.

Electron Arrangement Periods – horizontal row of elements # of protons and electrons increase from left to right

Electron Arrangement

Organizing into Groups Group – vertical column of elements Same # of valence electrons Determines chemical properties

Ions Group 1 elements Ionization – atoms with outer shell not filled Reactive because outermost energy level has 1 e- Ionization – atoms with outer shell not filled Gain or lose e- No longer has the same # of p+ and e-

Ion Ion – atom that has lost or gained one or more electrons Has a charge

Lithium Reaction Lithium – Group 1 Reacts with air or water vapor Single valence e- Reacts with air or water vapor Cation – positive ion Li+

Lithium Cation

Fluorine Reaction Fluorine – Group 17 Needs 1 e- to have a complete energy level Anion – gains an electron to become a negative ion F-

Atomic Number Atomic Number – number of protons in nucleus

Atomic Mass Nucleus - contains most of the mass of the atom Protons and neutrons - far more massive than electrons. 1,836 times larger than an electron. Proton mass = Neutron mass

Atomic Mass Mass number – sum of the # of protons and neutrons in the nucleus Atomic mass unit (amu).

Mass Number Mass number = # of protons in atom + # of neutrons in atom.

Calculating the # of Neutrons Neutrons = Mass # - Atomic #

Isotopes Isotopes - Atoms of the same element that have different numbers of neutrons Name of the element followed by the mass number of the isotope to identify each isotope Example: Hydrogen-2 and Hydrogen-3.

Identifying Isotopes Average atomic mass – weighted average mass of the mixture of its isotopes.