2a. atoms combine to form molecules by...

2a. Students know atoms combine to form molecules by sharing electrons to form covalent or metallic bonds or by exchanging electrons to form ionic bonds. 2.c. Students know salt crystals, such as NaCl, are repeating patterns of positive and negative ions held together by electrostatic attraction.

• Chemical Bonds hold atoms together.

1. Ionic Bonds

2. Metallic Bonds

3. Covalent

Review…. • Valence electrons are why the families of the

periodic table have similar chemical properties and reactions.

• Valence e- determine the types of chemical bonds an atom will make!

C

• Shows how many valence electrons (ve-) available for bonding and how many of these electrons are paired

• Non-bonding pairs – paired electrons in an electron-dot structure

• Paired electrons are stable and do not form bonds

• Unpaired valence electrons participate in bonds

• By doing so, they become paired with an electron from another atom.

• Valence electrons can be given, taken, or shared!

• Elements with 8 electrons in the valence shell are unreactive and do not form bonds

• Noble gases have a full octet making them stable or unreactive (inert)

• All elements want to be stable

• losing or gaining ve- allow elements to become stable when they achieve a noble gas configuration

• Metals lose electrons (cation +)

• Nonmetals gain electrons (anion -)

• Ionic Bonds form when metals (cations) and nonmetals (anions) bond!

• Held together by electrostatic attraction (+ and – force)

• Electrical force makes a Strong Bond!

• For all ionic bonds…+ and – charges must balance!

• This means that all + charges must equal every – charges

• Charges must also balance in compounds containing ions that carry multiple charges.

• Ex. Calcium ion has a charge of 2+ but the fluoride ion has a 1- charge. Two fluoride ions are needed to balance each calcium ion, the formula for calcium fluoride is CaF2.

• Ionic bonds create crystalline structures (SALTS)!

• Ionic crystals are formed as positive and negative charges attract.

• This repeating pattern creates a crystal lattice or structure.

In an IONIC bond, electrons are lost or gained, resulting in the formation of IONS

in ionic compounds.

F K

F K

F K

F K

F K

F K

F K

F K +

_

F K +

_

The compound potassium fluoride consists of potassium (K+) ions

and fluoride (F-) ions

F K +

_

The ionic bond is the attraction between the positive K+ ion

and the negative F- ion

Ionic Bonding

• All the electrons must be accounted for, and each atom will have a noble gas configuration (which is stable).

Ca P

Lets do an example by combining calcium and phosphorus:

Ionic Bonding

Ca P

Ca2+ P

Ca2+ P

Ca

Ca2+ P 3-

Ca

Ca2+ P 3-

Ca P

Ca2+ P 3-

Ca2+ P

Ca2+ P 3-

Ca2+ P

Ca

Ca2+ P 3-

Ca2+ P

Ca

Ca2+ P 3-

Ca2+ P 3-

Ca2+

= Ca3P2 Formula Unit

• This is a chemical formula, which shows the kinds and numbers of atoms in the smallest representative particle of the substance.

• For an ionic compound, the smallest representative particle is called a: Formula Unit

1. Crystalline solids - a regular repeating arrangement of ions in the solid

2. Ions are strongly bonded together.

– Structure is rigid.

3. High melting points

1. Conducting electricity means allowing charges to move.

2. In a solid, the ions are locked in place.

3. Ionic solids are insulators.

4. When melted, the ions can move around.

5. Melted ionic compounds conduct electricity. 1. NaCl: must get to about 800 ºC.

2. Dissolved in water, they also conduct (free to move in aqueous solutions)

Summary….

• Form from positive and negative ions (Metals and Nonmetals)

• Strongest Bonds! • Creates crystalline structures (Salts) • Conducts electricity when dissolved in water!

• Metal is listed first, followed by nonmetal.

• Change the name of the non-metal to ~ide.

• Examples – nitride, sulfide, fluoride, oxide, bromide, iodide, chloride, phosphide

1. Write the symbols of the 2 elements.

2. Write the charge (oxidation #) of each as superscripts.

3. Drop the positive and negative signs.

4. Crisscross the superscripts so they become subscripts.

5. Reduce when possible.

1. Write the symbols of the 2 elements.

2. Write the charge (oxidation #) for each element.

3. Drop the positive (+) and negative (-) sign.

4. Crisscross the superscripts so they become subscripts.

4. Crisscross the superscripts so they become subscripts.

5. Reduce when possible.

Sr2O2

Al3P3

Pb2O4

Ba3N2

REDUCES TO

REDUCES TO

REDUCES TO

REDUCES TO

SrO

AlP

PbO2

Ba3N2

• Most transition elements have 2 valence electrons (ve-).

• Roman numerals are used in the name of the transition metal in the compound to show the valence on the cation.