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H 2 o

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
3 types of bonds

  • Ionic

  • Covalent

    –Non-polar

    –Polar

  • Hydrogen


Ions and ionic bonds
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 bonds1
Ions and Ionic Bonds

When 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.


Ions and ionic bonds2
Ions and Ionic Bonds

•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.


Covalent 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.


.

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.


Covalent Bonds

H2O is a polar molecule

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

–The (slightly) negatively charged pole is around the oxygen


Graphic organizer
Graphic Organizer

Polar Covalent Bond

Nonpolar Covalent Bond

Metallic Bond

Feature

Ionic Bond

Attraction between positive ions and surrounding electrons.

Attraction between oppositely charged ions

How Bond Forms

Equal sharing of electrons

Unequal sharing of electrons

Charge on Bonded Atoms?

Yes, slightly positive or slightly negative

Yes; positive or negative

No

Yes; positive

H2O molecule (or other polar covalent molecule)

NaCl crystal (or other ionic compound)

Example

Calcium (or other metal)

O2 molecule


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