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# Ionization Energy Trends PowerPoint PPT Presentation

4f. 5f. Ionization Energy Trends. Electronegativity. Increasing Electronegativity. Decreasing Electronegativity. Lewis Structure Assumptions. Only valance electrons are involved in bonding. Atoms react to form molecules, so to achieve stable noble gas electron configurations.

Ionization Energy Trends

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4f

5f

### Electronegativity

Increasing Electronegativity

Decreasing Electronegativity

### Lewis Structure Assumptions

• Only valance electrons are involved in bonding.

• Atoms react to form molecules, so to achieve stable noble gas electron configurations.

• Atoms in molecules want eight valance electrons (octet rule) except for hydrogen which wants two electrons (duet rule).

• In covalent compounds atoms share electrons to form bonds in order to achieve stable noble gas electron configurations. In ionic compounds electrons are transferred from one atom to another to achieve stable noble gas electron configurations.

### Rules for Drawing Lewis Structures

Step 1: Count the total number of valance electrons.

Step 2: Identify the central atom (the first atom written unless that atom

is hydrogen). Place all terminal atoms around that atom.

Hydrogen atoms NEVER have more than one bond.

Step 3: Complete the octet for all atoms in the Lewis structure with

lone pairs of electrons (except hydrogen).

Step 4: Check your structure by counting the number of valance

electrons used (they will match step 1 if the structure is

correct). If your valance electrons don’t match you will need

to tweak your structure as follows.

### Tweaking Lewis Structures

Too Many Electrons Initially: Redraw the

Lewis structure from step 2 adding a double

bond. If you still have too many electrons

add another multiple bond and repeat.

Always add double bonds before triple

bonds. Every double bonds effectively

remove two electrons from the structure while

triple bonds effectively remove 4 electrons.

### “Exceptions” to the Octect

Two Few Electrons: If you only have four or

six valance electrons initially you can’t

possibly fill the octet rule (usually BeH2 or

BH3). Just place hydrogens around central

atoms and call it done.

### “Exceptions” to the Octect

Odd number of electrons: One atom will

have to have less than eight electrons.

Draw the Lewis structure as if it had one

more valance electrons than it actually does.

Then subtract one electron from the least

electronegative element (often the central

atom).

### “Exceptions” to the Octect

Exceeding the Octet Rule: If the central atom is in

the third row or below it may be possible to exceed

eight electrons around the central atom. But only if

you absolutely have no choice. If you can give

everything eight and only eight do that first. When

you must break the octet rule draw the structure as

you would in steps 1-4 and the place the extra

electrons around the central atom. Even when

breaking the octet rule no atom will ever have

more than 12 electrons.

### Organic Lewis Structure Rules

• Based on formal charge arguments