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 bondsIonic

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 or gains 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)