Chapter 7Keefe 1415

Valence electrons

• These are the electrons that are available to participate in reactions: they are always in the OUTSIDE shell of electrons• The number of valence electrons determines the

chemical properties of the element

Valence Electrons• Lithium and sodium each have 1 outer electron, so they have

similar properties. For example, they are soft metals and they corrode easily in air.

Valence Electrons• In forming compounds, atoms tend to achieve the electron

configuration of a noble gas• Octet- a set of 8 valence electrons

Valence electrons

• Exceptions to the OCTET RULE include H, He, and B:• H and He are happy with just TWO electrons• B is happy with SIX electrons

Valence Electrons• Atoms of metals tend to LOSE all of their valence electrons to

leave a complete octet in the next-lower energy level• Atoms of nonmetals tend to GAIN electrons or SHARE

electrons with another nonmetal to achieve an octet

Valence electrons

Anions Versus Cations

Anions versus Cations• Cations want to LOSE electron(s) and therefore have a net

POSITIVE charge:

Anions Versus Cations• Name of a cation is the same as the element name, then add

the word ‘ion’:

ion

Anions Versus Cations• Some transition metals have multiple possible oxidation states

(charges). To name them, you add a ROMAN NUMERAL after the name of the element to indicate the charge:

ion

Anions versus Cations• Anions want to GAIN electron(s) and therefore have a

NEGATIVE charge

Anions Versus Cations• Name of an anion is usually the name of the element, BUT

drop the last syllable and add ‘ide’:• Clorine atoms form chloride anions• Oxygen atoms for oxide anions

Lewis dot structures of atoms• Simply put the symbol of the element and add dots around it

until you have represented all the valence electrons:

Valence Electrons

Compound:

•any substance made up of two or more elements.

Binary Compounds

“Binary” means “two”, as in there are two different elements involved.•There are two types:• Ionic•Covalent

Ionic Compounds • Ionic Compounds are made from a Metal and a Non-metal.

Ionic Compounds

•Naming: metal cation first, then non-metal anion with –ide at the end.• Example: NaCl:

Sodium Chloride• In this Ionic Compound, there is one

Sodium atom for every Chlorine atom.

Balancing Ionic Compounds

•Sometimes an Ionic Compound will have little numbers included in its formula:• Ex. Magnesium Chloride = MgCl2

Balancing Ionic Compounds

• These numbers are called subscripts, and they tell you how many of the previous atoms you have.• One magnesium, two chlorines• Magnesium Chloride = MgCl2

Balancing Ionic Compounds

•Beryllium Fluoride: how do you know whether or not subscripts are needed?

Balancing Ionic Compounds

• There is nothing in their name that indicates that numbers are necessary in the formula• You need the:• Oxidation Number (we call it the

charge)

Balancing Oxidation State Numbers• We’re trying to get these two numbers to add up to zero:

•Be2+ and F-

• BeF2 = Beryllium Fluoride

A visual representationBe2+ F-

We need two “minus ones” to balance out “plus two”

Another Trick:

• How about Aluminum Oxide?• First, find their oxidation numbers:• Al3+ and O-2

• How can we balance out a 3+ and a -2?• Trick: Swap the numbers!• Al2O3 = Aluminum Oxide

Write the formula for the ionic compound that will form between Ba2+ and Cl.Solution:1. Balance charge with + and – ions 2. Write the positive ion of metal first, and the

negative ion Ba2+ Cl

Cl

3. Write the number of ions needed as

subscripts BaCl2

Writing a Formula

Write the correct formula for the compounds containing the following ions:1. Na+, S2-

2. Al3+, Cl-

3. Mg2+, N3-

Learning Check

1. Na+, S2-

Na2S

2. Al3+, Cl-

AlCl3

3. Mg2+, N3-

Mg3N2

Solution

• 1. Cation first, then anion

• 2. Monatomic cation = name of the element• Ca2+ = calcium ion

• 3. Monatomic anion = root + -ide• Cl- = chloride

• CaCl2 = calcium chloride

Naming CompoundsNaming Compounds

Binary Ionic Compounds:

Examples:NaCl

ZnI2

Al2O3

Naming Binary Ionic Compounds

sodium chloride

zinc iodide

aluminum oxide

Complete the names of the following binary compounds:Na3N sodium ________________

KBr potassium ________________

Al2O3 aluminum ________________

MgS _________________________

Learning Check

Complete the names of the following binary compounds:

Na3N

KBr

Al2O3

MgS

Solution

sodium nitride

potassium bromide

aluminum oxide

magnesium sulfide

Elements that can have more than one possible charge

MUST have a Roman Numeral to indicate the charge on

the individual ion.

1+ or 2+ 2+ or 3+Cu+, Cu2+ Fe2+, Fe3+

copper(I) ion iron(II) ion copper (II) ion iron(III) ion

Transition Metals

These elements REQUIRE Roman Numerals because they can have more than one possible charge:anything except Group 1A, 2A, Ag, Zn, Cd, and Al

Names of Variable Transition Ions

Or another way to say it is: Transition metals and the metals in groups 4A and 5A (except Ag, Zn, Cd, and Al) require a Roman Numeral.

FeCl3 (Fe3+) iron (III) chlorideCuCl (Cu+ ) copper (I) chlorideSnF4 (Sn4+) tin (IV) fluoridePbCl2 (Pb2+) lead (II) chlorideFe2S3 (Fe3+) iron (III) sulfide

Names of Variable Ions

Examples of Older Names of Cations formed from Transition Metals(you do not have to memorize these)

Complete the names of the following binary compounds with variable metal ions:

FeBr2 iron (_____) bromide

CuCl copper (_____) chloride

SnO2 ___(_____ ) ______________

Fe2O3 ________________________

Hg2S ________________________

Learning Check

Complete the names of the following binary compounds with variable metal ions:

iron ( II ) bromide

copper ( I ) chloride

tin (IV) oxide

iron (III) oxide

mercury (I) sulfide

Solution

FeBr2

CuCl

SnO2

Hg2S

Fe2O3

Polyatomic ions: MEMORIZE (and I have a trick to help)

Naming polyatomic ions YAS THERE ARE MOAR“ate” anions have one more oxygen then the “ite” ion, but the same charge. If you memorize the “ate” ions, then you should be able to derive the formula for the “ite” ion and vice-versa:

• Examples: • sulfate is SO4 2- , so sulfite has the same charge

but one less oxygen (SO3 2-)

• nitrate is NO3 -, so nitrite has the same charge but one less oxygen (NO2

-)

Naming Polyatomics

• A sulfate ion is SO42- . To get the formula

for hydrogen sulfate ion, you add a hydrogen ion to the front of the formula. Since a hydrogen ion has a 1+ charge, the net charge on the new ion is less negative by one.

Naming polyatomics• Add one more hydrogen to the mix and you get:

Naming polyatomics

• Similarly, adding/subtracting oxygens results in: