Valence Electrons: the electron(s) in the outer shell of anatom’s electron cloud, which can combine with other atomsto form molecules*The number of valence electrons in an atom of an element determines manyproperties of that element, including the ways in which the atom can bond with otheratoms.
Chemical bonds holdmolecules together .
A chemical bond is a unionbetween atoms formedwhen they give up, gain, orshare 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 for40 cents each and pears for 50 cents each. You have 45cents and want an apple. Your friend also has 45 centsbut wants a pear.
Ions and Ionic Bonds
When an atom loses an electron, it loses a negative chargeand become a positive ion. When an atom gains anelectron, it gains a negative charge and becomes a negativeion.
•An atoms gives upor gains 1 or moreof its electrons toanother.
•The resultingoppositely chargedions attract oneanother, formingan ionic bond.
Ions and Ionic Bonds
For example, in table salt (sodium chloride) the negativechlorine ion attracts the positive sodium ion, forming anionic bond.
Ions and Ionic Bonds
A covalent bond holds together two atoms that shareone or more pair of electrons
Electrons in a covalent bond may be equally orunequally shared between the atoms.
Non-polar covalent bond: atoms share electrons evenly
Polar covalent bond: atoms share electrons unequally
Covalent Bonds
Those atoms with greaterpositive nuclear chargepull more strongly onelectrons in a covalentbond.
Covalent Bonds
.
A carbon dioxide molecule is a nonpolarmolecule because of its straight-line shape. Incontrast, a water molecule is a polar moleculebecause of its bent shape.
H2O is a polar molecule
–The (slightly) positively charged pole is aroundeach hydrogen
–The (slightly) negatively charged pole is aroundthe oxygen
Covalent Bonds
Graphic Organizer
Attractionbetweenoppositelycharged ions
Feature
Ionic Bond
PolarCovalentBond
NonpolarCovalentBond
MetallicBond
How BondForms
Charge onBondedAtoms?
Example
Unequal sharingof electrons
Yes; positive ornegative
Yes; positive
O2 molecule
Equal sharingof electrons
Attractionbetween positiveions andsurroundingelectrons.
Yes, slightlypositive or slightlynegative
No
NaCl crystal (orother ioniccompound)
H2O molecule (orother polarcovalentmolecule)
Calcium (orother metal)