warmup: think back to the structure of the atom and draw a carbon atom. how many valence electrons...

Warmup:

Think back to the structure of the atom and draw a Carbon atom. How many valence electrons

does carbon have?

Chapter 18 Chemical Bonding

18-1 - Stability in Bonding

• Combined Elements– Elements combine to form compounds– Compounds have properties very different

from original elements– Compounds have chemical formulas to

show the atoms and ratios that make them up.

18-1 - Stability in Bonding

• Chemical Formula Practice

18-1 - Stability in Bonding

• Unfilled & filled energy shells

• Filling Outer energy shells– Valence electrons– Gain/lose electrons– Share electrons

• Forming chemical bonds

An Atomic Model is Needed to Understand How Atoms Bond

• Review shell model of atom (Ch 16)

• Valence electrons –

• Electron Dot Diagrams – – Tells valence electrons– How many (ve) are paired

Electron Shells

K=

L=

M=

N =

O =

P =

Q =

• Atoms are electrically neutral– Why?

• Ions are not electrically neutral– Why?

• Ion –– Can be negative or positive

• Atoms tend to lose or gain electrons so they end up with an outermost occupied shell that is filled to capacity

• The Periodic table can be used to determine the type of ion that an atom tends to form

18-2 - Types of Bonds

Positive Ion (cation)

Negative Ion (anion)

18-2 - Types of Bonds

• Result of transfer of electrons forms a positive ion and a negative ion

• Ionic Bond – • Ionic Compounds – • Characteristics of Ionic Bonds –

– – – –

Ionic Bonds Result from an Transfer of Valence Electrons

18-2 - Types of Bonds

Ionic Bonds: One big greedy thief dog!Ionic bonding can be best imagined as one big greedy dog steeling the other dog's bone.  If the bone represents the electron that is up for grabs, then when the big dog gains an electron he becomes negatively charged and the little dog who lost the electron becomes positively charged.  The two ions (that's where the name ionic comes from) are attracted very strongly to each other as a result of the opposite charges.

18-2 - Types of Bonds

• Covalent bond – • Covalent Compound – • Molecule – • Characteristics of Covalent Bonds –

– – – –

• Can be single, double, or triple

Covalent Bonds Result from a Sharing of Valence Electrons

Covalent Bonds: Dogs of equal strength.Covalent bonds can be thought of as two or more dogs with equal attraction to the bones.  Since the dogs (atoms) are identical, then the dogs share the pairs of available bones evenly.  Since one dog does not have more of the bone than the other dog, the charge is evenly distributed among both dogs.  The molecule is not "polar" meaning one side does not have more charge than the other.

• Dipole – • Electronegativity –

– Difference in electronegativity

• Nonpolar Bond –• Polar Bond -

Polar Covalent Bonds Result from an Uneven Sharing or

Electrons

Polar Covalent Bonds: Unevenly matched but willing to share.These bonds can be thought of as two or more dogs that have different desire for bones.  The bigger dog has more strength to possess a larger portion of the bones.  Sharing still takes place but is an uneven sharing.  In the case of the atoms, the electrons spend more time on the end of the molecule near the atom with the greater electronegativity (desire for the electron) making it seem more negative and the other end of the molecule seem more positive.

• Polar and nonpolar are easy when 2 atoms, more complex when more than 2 atoms are bonded

• End result may be a even distribution or an uneven distribution

• Can make the dipole stronger• Explains why water is “sticky”• May explain other macroscopic

properties

Molecular Polarity Results from an Uneven Distribution of Electrons

This molecular polarity causes water to be a powerful solvent and is responsible for its strong surface tension. The molecular arrangement taken by ice (the solid form of the water molecule) leads to an increase in volume and a decrease in density. Expansion of the water molecule at freezing allows ice to float on top of liquid water.