Bonding

Why do atoms form a chemical bond?

Why do atoms form a chemical bond?

• 1. The positive nucleus of one atom and the negative electrons of another are attracted

• 2. there is attraction between positive and negative ions.

• What two things are in the nucleus of an atom?

Valence electrons

• Lewis dot diagrams show how many electrons there are on the outermost energy level

• You can identify this number quickly by counting the groups on the PTE.

• For example, Lithium is in Group 1 so how many valence electrons does it have?

• Nitrogen is in group 15 does it have 15 electrons?

Positive ion formation

• A positive ion is formed when an atom loses an electron. In a neutral atom it has equal parts positive and negative charges. When it loses the electron it has more positives left. Therefore, it is called a cation.

• If a neutral atom of Na lost 1 electron it would be positively charged by 1 positive. Na1+

• Do you think metals or nonmetals are more likely to lose electrons?

Negative Ion formation

• Non-metals gain electrons because they are closer to being full and stable

• When they gain an electron they have a negative charge and are called anions

• If a neutral atom of S gained 2 electrons it would have a negative charge by 2. S2-

How do you write the charge for an ion?

• You can tell how many an atom gains or loses by how far it is from having a full outer energy shell.

• If a neutral atom of S gained 2 electrons it would have a negative charge by 2. S2-

• If a neutral atom of Na lost 1 electron it would be positively charged by 1 positive. Na1+

• Write this, • metals lose e- =positive charges. • Nonmetals gain e- =neg. charge

PracticeWrite the charge for each and the lewis dot diagram as a neutral atom and as an

ion. Use a separate piece of paper

• Li= Li1+

• Be• B• C• N• O• F• Ne

Ionic bonds

• Metal + nonmetal• Identify at least 3 possible ionic compounds.• 1. • 2.• 3.

Ionic bonding, compound formation

• We know that each ion has a charge. But how do ions bond to make the atom neutral?

• For example, Oxygen has a 2- charge. It’s longing for 2 electrons. How could it become a happy ion?

Answer

• There are several answers. It could bond with 2 ions with a 1- charge or one atom with a 2- charge.

Lattice Energy

• The energy needed to break the bond between two atoms.

• Is directly related to atomic radius. Which is related to melting point and boiling point, and electronegativity

• What do we know about atomic radius?

Atomic radius

• The smaller the radius of the two elements:• the stronger the attraction to each other.• Higher the Lattice Energy• Higher the melting and boiling point

Decreasing

Increasing

Examples

• LiBr has a larger lattice energy than LiCl• True or False• Pay attention to the elements that are different.

In this case, BR and Cl.• Where are they on the PTE?• Cl is higher on the PTE than Br. Therefore, has a

smaller radius, therefore, stronger attraction, higher melting point, higher boiling point.