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Octet Rule & Ions

Atoms may or may not be stable due to their nuclear composition

They become more stable by undergoing radioactive decay

Atoms may or may not be stable due to their electronic composition

They can become more stable by undergoing ion formation

Ions are electrically charged particles

Nonmetals Gain e-s negative ion

called anions Cl - O2- P3-

Metals Lose e-s positive ion called cations Na+ Mg2+ Fe3+

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The most stable atoms are the Noble gases

Atoms lose or gain e-s to acquire a noble gas electron configuration (8 valence electrons) is called the octet rule.

Exception [He] 2 valence e-s.

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Metals lose electrons due to their low ionization energy.IE = energy required to remove an electron

M + energy → M+ + e-

[Ne] = Stable State 8 valence e-s

Na Na+ + e-

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[Ar] = stable state 8 valence e-s

Nonmetals gain electrons due to their high electron affinity.EA = energy change when an electron is added.X + e− → X− + energy

Cl + e- Cl-

Most common ionic charges

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Transition metalsCharge is always given by means of:

The name Iron (III) chloride

The formula FeCl3

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Ionic Compounds

http://youtu.be/uCwHzTsx5yY

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From charges to chemical formulas

When ionic particles react, they do so in a ratio that cancels their charge. This is what is referred to as “charge balance”.

Na2S

“cross-the-charges”.

Al3+ 02-

2 3

Al203

Always keep the simplest ratio

Mg2+ 02-

2 2

Mg202

Mg0

1. How many e-s will the following elements need to lose or gain to fulfill the octet rule?

N Cl Na Al O Mg

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2. What is the ionic charge developed by the following elements?N Cl Na Al O Mg

3. The symbol for the ion formed by :

N Cl Na Al O

Mg

4. Write the formula of the ionic compound formed by:

a. Calcium and chlorine b. Magnesium and nitrogen c. Barium and oxygen

Practice

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NaCl Sodium chloride FeCl3 Iron (III) chloride

Naming & Writing Ionic Formulas

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Polyatomic Ions

Compounds containing polyatomic ions are named as ionic compounds.

Na+ SO42-

2 1

Na2S04 Sodium sulfate

Al3+ SO42-

2 3

Al2 (S04)3Aluminum sulfate

Note:A polyatomic iontaken more than onceuse parenthesis

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5. Provide the name for the following ionic compounds:

Mg3N2 Fe2O3

Cu2S AuCl3

CaSO4 Cu(NO2)2

6. Provide the formula for the following ionic compounds:

iron(III) chloride chromium(III) oxide

aluminum bicarbonate calcium hydroxide

7. Provide the formula for a compound containing ammonium ion(s) and phosphate ion(s).

8. Draw the electron-dot structure for SO2

Practice

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Has a noble gas electron count Becomes more stable Has lower energy

Covalent bonds form:

• Between two nonmetal atoms. When atoms share valence electrons to complete octets (duet for

hydrogen). Denoted by a line

Gilbert Newton Lewis

Covalent Compounds

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H H

An electron pair being shared is denoted by a line.

Lewis further proposed that by counting valence electrons, it would be possible to predict how many bonds an atom can form:

H O N C1 2 3 4

In his honor, we refer to electron-dot structures as Lewis structures.

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Electron-dot structure = Lewis structure

All valence electrons are shown as dotsor bonding electrons are shown as lines.

C: : :O..

:O..

: : C :O..

O..

:

: : :N:C:H :NCH

Carbon dioxide

Hydrogen cyanide

F2 Fluorine

In a single bond One pair of electrons is

shared.

In a triple bond.Three pairs of electrons are shared.

In a double bond, Two pairs of electrons are shared.

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Guidelines to Writing Lewis Structures Steps

NH3

1. Use the group number to determine the total number of valence e-s

2. Draw a “skeleton” by connecting the atoms with lines.First element of the formula is at the center, the others are surrounding.

3. Provide octets or duets to surrounding atoms & find the remaining e-s.

4. Use the remaining electrons to provide an octet to the central atom.

5. If not enough e-s remain, pull surrounding e-s to form double or triple bonds.

6. Any e-s remaining after all octets are provided, are given to the central atom.

N 5 H 1 x 3 = 3Total = 8

H |H—N—H

8-6=2

H |H—N—H

H |H—N—H

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SO31. Use the group number to determine the total number of valence e-s

2. Draw a “skeleton” by connecting the atoms with lines.First element of the formula is at the center, the others are surrounding.

3. Provide octets or duets to surrounding atoms & find the remaining e-s.

4. Use the remaining electrons to provide an octet to the central atom.

5. If not enough e-s remain, pull surrounding e-s to form double or triple bonds.

6. Any e-s remaining after all octets are provided, are given to the central atom.

S 6 O 6 x 3 = 18Total = 24

O |O—S—O

24-24=0

O |O—S—O

O ||O—S—O

STEP 1 Name the first nonmetal by its element name.

STEP 2 Name the second nonmetal with an --ide ending.

STEP 3 Add prefixes to indicate the number (from subscripts) of atoms of each nonmetal. Mono is always omitted for the first element and usually omitted for the second one.

Exception is CO carbon monoxide

Examples of compounds of N and O:

NO nitrogen oxide nitric oxide nitrogen (I) oxide

NO2 nitrogen dioxide

N2O dinitrogen oxide

N2O3 dinitrogen trioxide

N2O4 dinitrogen tetroxide nitrous oxide nitrogen (II) oxide

N2O5 dinitrogen pentoxide

Naming & Writing Covalent Formulas

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9. Write the electron-dot formula for PCl3, phosphorus trichloride.

10. Write the electron-dot formula for CO2, carbon dioxide.

11. What is the name for P4S3

12. Write the correct formula for each of the following:

A. phosphorus pentachloride B. dinitrogen trioxide

C. sulfur hexafluoride

13. Identify each compound as ionic or covalent and give its correct name.A. SO3 B. BaCl2

C. (NH4)3PO4 D. Cu2CO3

E. N2O4

Practice

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Electronegativity & Bond Polarity

Electrons can be Equally shared Electrons can be Unequally shared

+1 -1= 0

-1 +1= 0

No separation of charge = nonpolar

+1 +17

Yes, separation of charge = polar

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Electronegativity indicates the attraction of an atom for shared electrons.

Linus Pauling

Always on the highest EN valueWhen a separation of charges exists in a bond, it is a polar bond.

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15. Use the electronegativity difference to identify the type of bond between the following:

nonpolar covalent (NP), polar covalent (P), or ionic (I).

A. K-N B. N-O

C. Cl-Cl D. H-Cl

14. Which element is most electronegative? a. N b. F c. O d. C

16. Which compound contains a polar covalent bond?a. HBr b. NaF c. F2 d. H2

17. Which of the following would have the most polar bond? a. Cl – Cl b. F – Cl c. F – I d. I - Br

Practice

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Shapes & Polarity of Molecules

On paper, molecules appear to be flat, two dimensional objects.

Instead, they have a 3-D structure

The valence-shell electron-pair repulsion theory (VSEPR) predicts the shape based on bonding and lone pairs (“electron groups”) around the central atom.

VSPER pronounced V (like in Victor) – and (spr)

4 Electron Groups Four bonding 4 Electron groups Two Bonding and Two Lone Pairs

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Polar bonds can produce a polar molecule or a nonpolar molecule

Based on EN, a bond can be polar.

Based on shape, a bond can be polar, but a molecule nonpolar

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For multiple dipoles, it helps to use “center of (+)” and “center of (-)”

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Example

Solution: Write the electron-dot structure

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Determine the polarity of the H2O molecule.

Determine the shape & bond polarity.

Determine the molecular polarity.

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18. What is the shape of the SO3 molecule. Provide a drawing of the molecule.

a. Trigonal planar b. Bent c. Tetrahedral d. Trigonal Pyramidal

19. What is the shape of the NH3 molecule. Provide a drawing of the molecule.

a. Linear b. Bent c. Tetrahedral d. Trigonal pyramidal

20. Determine the shape of each of the following molecules and whether they are polar or nonpolar. If polar show the direction of the dipole.

A. PBr3 B. HBr

C. Br2 D. SiBr4

Practice