H2O

Valence Electrons: the electron(s) in the outer shell of an atom’s electron cloud, which can combine with other atoms to form molecules

*The number of valence electrons in an atom of an element determines many properties of that element, including the ways in which the atom can bond with other atoms.

Chemical bonds hold molecules together .

A chemical bond is a union between atoms formed when they give up, gain, or share electrons .

3 types of bonds

Ionic

Covalent –Non-polar –Polar

Hydrogen

Ions and Ionic Bonds

You and a friend walk past a market that sells apples for 40 cents each and pears for 50 cents each. You have 45 cents and want an apple. Your friend also has 45 cents but wants a pear.

Ions and Ionic BondsWhen an atom loses an electron, it loses a negative charge and become a positive ion. When an atom gains an electron, it gains a negative charge and becomes a negative ion.

•An atoms gives up 1 or more of its electrons to another.

•The resulting oppositely charged ions attract one another, forming an ionic bond.

Ions and Ionic Bonds

For example, in table salt (sodium chloride) the negative chlorine ion attracts the positive sodium ion, forming an ionic bond.

Ions and Ionic Bonds

A covalent bond holds together two atoms that share one or more pair of electrons

Electrons in a covalent bond may be equally or unequally shared between the atoms.

Non-polar covalent bond: atoms share electrons evenly

Polar covalent bond: atoms share electrons unequally

Covalent Bonds

Those atoms with greater positive nuclear charge pull more strongly on electrons in a covalent bond.

Covalent Bonds

.A carbon dioxide molecule is a nonpolar molecule because of its straight-line shape. In contrast, a water molecule is a polar molecule because of its bent shape.

H2O is a polar molecule –The (slightly) positively charged pole is

around each hydrogen –The (slightly) negatively charged pole is

around the oxygen

Covalent Bonds

Graphic Organizer

Attraction between oppositely charged ions

Feature Ionic BondPolar Covalent Bond

Nonpolar Covalent Bond

Metallic Bond

How Bond Forms

Charge on Bonded Atoms?

Example

Unequal sharing of electrons

Yes; positive or negative Yes; positive

O2 molecule

Equal sharing of electrons

Attraction between positive ions and surrounding electrons.

Yes, slightly positive or slightly negative

No

NaCl crystal (or other ionic compound)

H2O molecule (or other polar covalent molecule)

Calcium (or other metal)

Hydrogen Bonds Polar molecules have partially charged atoms at their ends.

Hydrogen bonds form when partial opposite charges in different polar molecules attract each other.

Individual hydrogen bonds are rather weak, but collectively they are quite strong

Self QuizDo atoms always have an equal number of protons, neutrons and electrons? 1.Yes. 2.No.

A chemical bond is formed through: 1.The gaining, losing, or sharing of protons. 2.The gaining, losing, or sharing of neutrons. 3.The gaining, losing, or sharing of electrons. 4.The gaining, losing, or sharing of isotopes. 5.The gaining, losing, or sharing of ions.

After sodium loses an electron, it is: 1.A positive ion. 2.A negative ion. 3.A neutral ion. 4.An isotope. 5.A compound.

After chlorine gains an electron, it is: 1.A positive ion. 2.A negative ion. 3.A neutral ion. 4.An isotope. 5.A compound.

Self Quiz

What is the difference between a nonpolar covalent bond and a polar covalent bond? 1.A polar covalent bond results when there is unequal sharing of electrons in a molecule, whereas electrons are shared equally in a nonpolar covalent bond. 2.A polar covalent bond has two equal sides and a nonpolar covalent bond has two different sides. 3.A nonpolar covalent bond is positively charged and a polar covalent bond is negatively charged. 4.A polar covalent bond is positively charged and a nonpolar covalent bond is negatively charged.

Self Quiz