Warm-up• Determine the number of valence electrons and the

charge of an atom of these elements:• Example: Chlorine: 7 valence electrons and -1 chargeBeryllium Be: 2 valence and Be+2

SulfurS: 6 valence and S-2

FluorineF: 7 valence and F-1

OxygenO: 6 valence and O-2

CHEMISTRYUnit Four, Day OneKimrey26 September 2012

CHEMICAL BONDING Its what happens when elements fall in love!

3 Types of Bonds• Covalent bonding• Ionic bonding• Metallic Bonding

Covalent Bonding-The perfect relationship

• Bond is formed by the sharing of electrons between two nonmetals.

• Two types of covalent bond polar and nonpolar.• Polar covalent bond- unequal sharing of electrons. • Nonpolar covalent bond- equal sharing of electrons.

Ionic bonding-The stage five clinger

• One element steals all the electrons from another. -or more technically

• A transfer of valence electrons between a cation (+) and an anion (-).

• Typically between a metal and nonmetal or a metal and polyatomic ion.

ex. NaCl, LiF, CaF2

• Polyatomic ion- a group of bonded atoms that have a charge.

ex. OH-, SO42-, etc.

Metallic Bonding-when two people merge into one.

• Between two metals and forms a sea of electrons.• Attraction between the positive nucleus and surrounding

electrons. • Forms a sea of electrons.• This is why metals are malleable and ductile.

• Electrons don’t belong to either element – instead just float around the nuclei

Answer these questions:

An atom that gains one or more electrons will have a ____________________ charge.

An atom that loses one or more electrons will have a ____________________ charge.

An atom that gains or loses one or more electrons is called an ____________.

A positive ion is called a ______________ and a negative ion is called an _______________.

POSITIVE

NEGATIVE

ION

CATIONANION

What is an ionic bond?

Atoms will transfer one or more ________________ to another to form the bond.

Each atom is left with a ________________ outer shell.

An ionic bond forms between a ___________ ion with a positive charge and a ________________ ion with a negative charge.

Example B1: Sodium + Chlorine Example B2: Magnesium + Iodine

ELECTRONS

COMPLETE

METALNONMETAL

What is a covalent bond?

Atoms ___________ one or more electrons with each other to form the bond.

Each atom is left with a ________________ outer shell.

A covalent bond forms between two _________________.

Example C1: Hydrogen + Hydrogen Example C2: 2 Hydrogen + Oxygen

SHARE

COMPLETE

NONMETAL

Electronegativity • The ability of an atom in a compound to attract valence

electrons to itself. • Scale of 0-4• Differences in electronegativity is used to determine the

type of bond. 0-0.4 = Nonpolar covalent0.4-1.7 = Polar Covalent1.7-4.0 = Ionic

• Example:Sodium bonded to bromine

Practice

• Identify the following bonds as polar or non-polar covalent:

• H bonded to O• H bonded to C• C bonded to F• C bonded to N

Formulas for Ionic Compounds• Ionic compounds will bond in a ratio that cancels their ion

charge • ALL compounds no matter what are neutral

Steps for Writing Formulas 1. Find the charges of the elements.2. Find the simplest ratio needed to cancel out the

charges.3. Write the ratio numbers as subscripts (ones do not get

written!)4. Write the positive ion first followed by the negative ion.

Make sure not to write the charges of the ions in the formula.

Examples• Sodium and Chlorine

NaCl• Potassium and Iodine

KI• Calcium and Bromine

CaBr2

• Barium and Oxygen BaO

Those pesky polyatomics. • Polyatomic is a group of bonded atoms that still has a

charge. • Same steps as binary compounds plus…5. If a subscript is added to a polyatomic ion place the entire polyatomic in ().

REMEMBER! Never ever change the subscripts in a poly-atomic ion.

Examples• Sodium and Hydroxide (OH-1)

NaOH• Lithium and sulfate (SO4

-2)Li2SO4

• Calcium and phosphate (PO4-3)

Ca3(PO4)2

• Ammonium and fluorine (NH4+1)

NH4F

What does all this mean?• The chemical formula tells you the number of each

element in that compound.

1. Complete the chart using your knowledge of atoms.

Vocab Review

1 – What do we call the electrons in the outermost energy level?

2 – What term refers to an atom that has lost or gained electrons?

3 – What is a cation?

4 – What is an anion?

Valence ElectronsIons

A positively charged ion

A negatively charged ion

2. Ionic Bonds - Draw the Lewis structures for each atom, draw arrows to show the transfer of electrons, write the charge for each ion, and then write the chemical formula.

(A) Potassium + Iodine (B) Magnesium + Oxygen

(C) Lithium + Nitrogen

3. Covalent Bonds – Draw the Lewis structures for each atom, draw circles to show the electrons that are shared, and then write the bond structure and chemical formula.

(A) Fluorine + Fluorine (B) 3 Hydrogen + 1 Phosphorus

(C) 2 Hydrogen + 1 Sulfur

Potassium + Iodine Sodium + Oxygen

Calcium + Chlorine Aluminum + Chlorine

Chlorine + Chlorine Oxygen + Oxygen

Carbon + 2 Oxygen Carbon + 4 Hydrogen

What about other metals?• Other metals charges will always be given in roman

numerals. e.g. I,II, IV

• These charges are always positive. • What is the charge of Iron (II)?

2+