Patterns on the Periodic Table & Electron Dot Diagrams

1. Patterns on the Periodic Table & Electron Dot Diagrams

2. Some Back Ground Info • Remember that the periodic table is organized by the “Atomic Number” • Atomic Number = the number of protons in the nucleus of an atom • Remember that protons have a charge of “+1” • Also remember that electrons have a charge of “-1”

3. More Background Info • All elements shown on the periodic table have a neutral charge (charge = zero) • Every atom on the periodic table has an atomic number • Therefore, every atom has protons • Therefore, every atom has “positive” charges because protons have a “+1” charge • Therefore, every neutral atom has a number of electrons = to the number of protons so that all the charges “cancel”

4. Structure of an Atom • Think of an Atom like an onion • The core of an onion is similar to the nucleus of an atom • An onion has layers, atoms also have layers that we call energy levels. • Energy levels hold the electrons • Just like in an onion, the out layers are bigger, therefore they can hold more electrons (in the future, electrons will be written as “e-”)

5. Nucleus Energy Levels Electrons and Their Energy Levels • Some Rules to Remember about atoms and their e- • Inner energy levels fill with e- first. • 1st level holds 2 e-, 2nd and 3rd levels hold 8 e-, 4th and 5th hold 18 e- • If there are more e- than an energy level can hold, they “spill” into the next level out

6. Bohr’s Model Diagrams • Traditionally, we used Bohr’s model to show individual atoms. • In Bohr’s model, the nucleus is represented by the symbol of the element. • Each electron is represented by a dot or an “e-” • And all energy levels containing electrons are shown

7. Bohr’s Model Example • Let’s take chlorine: • First, write the symbol for the element to represent the nucleus • Draw in a few energy levels • Use the periodic table to determine how many e- are in the atom. (chlorine has 17) • Start filling in the e-, inner levels first Cl

8. Electron Dot Diagrams • Doing Bohr’s models is a lot of writing, so chemists have come up with a shorter version, called the “Electron Dot Diagram” • The element’s symbol is used to represent the nucleus PLUS all the inner energy levels that are full of electrons. • Therefore, only the outer energy level electrons are used. These electrons are called “Valence Electrons”.

9. Chlorine…Again • First, write the symbol for the element to represent the nucleus PLUS all inner energy levels • Show only the Valence e- by doing the following • Split the molecule in 4 pieces by drawing an “X” • Draw one dot at a time in each empty section • Only have pairs of e- if there are no empty sections Cl

10. Patterns on the Periodic Table • Notice that chlorine is in the 17th column. • How many valence e- does chlorine have? • Yes… 7 • In column 1,2, & 13-18: The “one’s digit” of the column number tells you how many valence e- the atom contains. • How many valence e- do all atoms in the 15th column have? • Yes… 5.

11. Patterns on the Periodic Table • The number of the row tells us how many energy levels in the atom have at least one e- • (remember that rows are also called “Periods”)