Electron Dot Diagrams

• The nucleus is represented by the atomic symbol
• For individual elements, you have to determine the number of valence electrons, which are represented by the dots around the atomic symbol
• To find the number of valence electrons is simple, look at the group number the element is in and that shows you the number of valence electrons
• There are four orbitals on each side of the nucleus holding a maximum of two electrons
• Each orbital gets 1 electron before they pair up, making a lone pair

 

Here are some examples of electron dot diagrams for sodium, magnesium and chlorine

Lewis diagrams for compounds and ions

• In covalent compounds, electrons are shared

Follow these two easy steps and learn how to draw a Lewis diagram for compounds and ions

1.       Determine the number of valence electrons for each atom in the molecule, which I explained above

2.       Place atoms so that valence electrons are shared to fill each orbital

This example shows the Lewis diagram for NF3

Double and triple bonds

Helpful Hint: Sometimes the only way covalent compounds can fill all their valence levels is if they share more than one electron

Lewis diagrams: Ionic compounds

• In ionic compounds electron transfer from one element to another
• Determine the number of valence electrons on the cation. Move these to the anion
• Draw [ ] around the metal and the non-metal
• Write the charges outside the brackets

Trends On the Periodic Table

Elements close to each other on the periodic table display similar characteristics.
- There are SEVEN important periodic trends:
1) Reactivity
2) Ion Charge
3) Melting point
4) Atomic Radius
5) Ionization Energy
6) Electronegativity
7) Density
We will only be talking about the first 6, today!

REACTIVITY:

•  metals and non-metals show different trends.
•  the most reactive metal is Francium; the most reactive non-metal is fluorine.

ION CHARGE:

• Elements ion charges depend on their group (column).

MELTING POINT:

• elements in the center of the table of the highest melting point.
• noble gases have the lowest melting points.
• starting from the left to right, melting point increases, until the middle
• carbon is an exception!

ATOMIC RADIUS:

• radius decreases to the up and the right.
• helium has the smallest atomic radius.
• Francium has the largest atomic radius.

IONIZATION ENERGY:

• ionization energy is the energy needed to completely remove an electron from an atom.
• it increases going up and to the right.
• all noble gases have high ionization energy.
• helium has the highest ionization energy.
• francium has the lowest ionization energy.
• opposite trend from atomic radius.

ELECTRONEGATIVITY:

• refers to how much atoms want to gain elections.
• same trend as ionization energy.