Writing Formulas for Binary Ionic

Compounds

The first thing we need is a couple of definitions:

The first thing we need is a couple of definitions:1. When a metal combines with a non-

metal, an ionic compound is formed.

The first thing we need is a couple of definitions:1. When a metal combines with a non-

metal, an ionic compound is formed.2. A binary compound consists of only

two elements.

In Science 10, you’ll be given this Periodic Table:

In Science 10, you’ll be given this Periodic Table:

In Science 10, you’ll be given this Periodic Table:

See the staircase!

In Science 10, you’ll be given this Periodic Table:

METALS

In Science 10, you’ll be given this Periodic Table:

METALS NON-METALS

A binary ionic compound forms when:

A binary ionic compound forms when: a positively charged metal ion combines with

A binary ionic compound forms when: a positively charged metal ion combines with a negatively charged non-metal ion.

What the formula for an ionic

compound means.

The formula for the ionic compound sodium chloride is NaCl.

The formula for the ionic compound sodium chloride is NaCl.This does NOT mean that sodium chloride consists of individual NaCl “molecules” like this:

The formula for the ionic compound sodium chloride is NaCl.This does NOT mean that sodium chloride consists of individual NaCl “molecules” like this:

Na Cl

The formula for the ionic compound sodium chloride is NaCl.This does NOT mean that sodium chloride consists of individual NaCl “molecules” like this:

Na Cl

Na+ ion

Cl– ion

Na+ ion

Cl– ion

Crystal lattice of NaCl

For every Na+ ion, there is one Cl–

ion

Na+ ion

Cl– ion

Na+ ion

Cl– ion

The formula for an ionic compound gives the smallest whole number ratio of ions.

For every Na+ ion, there is one Cl–

ion

Na+ ion

Cl– ion

The formula for sodium chloride is

Na1Cl1= NaCl

For every Na+ ion, there is one Cl–

ion

Na+ ion

Cl– ion

The formula for sodium chloride is

Na1Cl1= NaCl

The formula for calcium fluoride is CaF2

This means that calcium fluoride consists of a huge pile of Ca2+ and F–

ions.

CaF2

The formula for calcium fluoride is CaF2

This means that calcium fluoride consists of a huge pile of Ca2+ and F–

ions.

CaF2

The formula for calcium fluoride is CaF2

This means that calcium fluoride consists of a huge pile of Ca2+ and F–

ions.

CaF2For every Ca2+ ion, there are 2 F– ions

Finding the formula for an

ionic compound

There are two methods that we will show you for finding formulas.

There are two methods that we will show you for finding formulas. Then you can decide which method works best for you.

There are two methods that we will show you for finding formulas. Then you can decide which method works best for you. The two methods are:

There are two methods that we will show you for finding formulas. Then you can decide which method works best for you. The two methods are:1. Equalizing + and – charges

There are two methods that we will show you for finding formulas. Then you can decide which method works best for you. The two methods are:1. Equalizing + and – charges2. Crossing down charges

Finding a formula by equalizing + and – charges

Finding a formula by equalizing + and – charges

What is the formula for aluminum bromide?

Finding a formula by equalizing + and – charges

What is the formula for aluminum bromide?

Ion Name aluminum bromide

Ions Al3+ Br1–

Br1–

Br1–

Total Charges

Formula

Finding a formula by equalizing + and – charges

What is the formula for aluminum bromide?

Ion Name aluminum bromide

Ions Al3+ Br1–

Br1–

Br1–

Total Charges

Formula

Finding a formula by equalizing + and – charges

What is the formula for aluminum bromide?

Finding a formula by equalizing + and – charges

What is the formula for aluminum bromide?

Ion Name aluminum bromide

Ions Al3+ Br1–

Br1–

Br1–

Total Charges

Formula

Finding a formula by equalizing + and – charges

What is the formula for aluminum bromide?

Ion Name aluminum bromide

Ions Al3+ Br1–

Br1–

Br1–

Total Charges +3 –1

Formula

Finding a formula by equalizing + and – charges

What is the formula for aluminum bromide?

Ion Name aluminum bromide

Ions Al3+ Br1–

Br1–

Br1–

Total Charges +3

Formula

Finding a formula by equalizing + and – charges

What is the formula for aluminum bromide?

Ion Name aluminum bromide

Ions Al3+ Br1–

Br1–

Br1–

Total Charges +3 –3

Formula

Finding a formula by equalizing + and – charges

What is the formula for aluminum bromide?

Ion Name aluminum bromide

Ions Al3+ Br1–

Br1–

Br1–

Total Charges +3 –3

Formula

Add up to 0

Finding a formula by equalizing + and – charges

What is the formula for aluminum bromide?

Ion Name aluminum bromide

Ions Al3+ Br1–

Br1–

Br1–

Total Charges +3 –3

Formula AlBr3

Finding a formula by equalizing + and – charges

What is the formula for calcium phosphide?

Ion Name calcium phosphide

Ions Ca2+

Ca2+

Ca2+

P3–

P3–

Total Charges +2 –3

Formula Ca3P2

Finding a formula by equalizing + and – charges

What is the formula for calcium phosphide?

Ion Name calcium phosphide

Ions Ca2+

Ca2+

Ca2+

P3–

P3–

Total Charges +2 –3

Formula Ca3P2

Finding a formula by equalizing + and – charges

What is the formula for calcium phosphide?

Finding a formula by equalizing + and – charges

What is the formula for calcium phosphide?

Ion Name calcium phosphide

Ions Ca2+

Ca2+

Ca2+

P3–

P3–

Total Charges +2 –3

Formula Ca3P2

Finding a formula by equalizing + and – charges

What is the formula for calcium phosphide?

Ion Name calcium phosphide

Ions Ca2+

Ca2+

Ca2+

P3–

P3–

Total Charges +2 –3

Formula Ca3P2

Finding a formula by equalizing + and – charges

What is the formula for calcium phosphide?

Ion Name calcium phosphide

Ions Ca2+

Ca2+

Ca2+

P3–

P3–

Total Charges +6 –6

Formula Ca3P2

Finding a formula by equalizing + and – charges

What is the formula for calcium phosphide?

Ion Name calcium phosphide

Ions Ca2+

Ca2+

Ca2+

P3–

P3–

Total Charges +6 –6

Formula Ca3P2

Finding a formula by equalizing + and – charges

What is the formula for calcium phosphide?

Ion Name calcium phosphide

Ions Ca2+

Ca2+

Ca2+

P3–

P3–

Total Charges +6 –6

Formula Ca3P2

Finding a formula by equalizing + and – charges

What is the formula for calcium phosphide?

Ion Name calcium phosphide

Ions Ca2+

Ca2+

Ca2+

P3–

P3–

Total Charges +6 –6

Formula Ca3P2

Add up to 0

Finding a formula by equalizing + and – charges

What is the formula for calcium phosphide?

Ion Name calcium phosphide

Ions Ca2+

Ca2+

Ca2+

P3–

P3–

Total Charges +6 –6

Formula Ca3P2

Finding a formula by crossing down charges

Finding a formula by crossing down charges

What is the formula for rubidium sulphide?

Finding a formula by crossing down charges

What is the formula for rubidium sulphide?

Finding a formula by crossing down charges

What is the formula for rubidium sulphide?

Rb1+ S2–

Rb2S

Finding a formula by crossing down charges

What is the formula for rubidium sulphide?

Rb1+ S2–

Rb2S

Finding a formula by crossing down charges

What is the formula for rubidium sulphide?

Rb1+ S2–

Rb2S

Finding a formula by crossing down charges

What is the formula for rubidium sulphide?

Rb1+ S2–

Rb2S

Finding a formula by crossing down charges

What is the formula for rubidium sulphide?

Rb1+ S2–

Rb2S

Finding a formula by crossing down charges

What is the formula for rubidium sulphide?

Rb1+ S2–

Rb2S Formula

Finding a formula by crossing down charges

What is the formula for vanadium(IV) oxide?

Finding a formula by crossing down charges

What is the formula for vanadium(IV) oxide?

Finding a formula by crossing down charges

What is the formula for vanadium(IV) oxide?

Mulitvalent

metal

Finding a formula by crossing down charges

What is the formula for vanadium(IV) oxide?

Mulitvalent

metal

Finding a formula by crossing down charges

What is the formula for vanadium(IV) oxide? Tells us what the

ion charge is

Finding a formula by crossing down charges

What is the formula for vanadium(IV) oxide?

Finding a formula by crossing down charges

What is the formula for vanadium(IV) oxide?

V4+ O2–

V2O4

Finding a formula by crossing down charges

What is the formula for vanadium(IV) oxide?

V4+ O2–

V2O4

Finding a formula by crossing down charges

What is the formula for vanadium(IV) oxide?

V4+ O2–

V2O4

Finding a formula by crossing down charges

What is the formula for vanadium(IV) oxide?

V4+ O2–

V2O4

Finding a formula by crossing down charges

What is the formula for vanadium(IV) oxide?

V4+ O2–

V2O4

Finding a formula by crossing down charges

What is the formula for vanadium(IV) oxide?

V4+ O2–

V2O4

Finding a formula by crossing down charges

What is the formula for vanadium(IV) oxide?

V4+ O2–

V2O4Both of these numbers are multiples of 2

Finding a formula by crossing down charges

What is the formula for vanadium(IV) oxide?

V4+ O2–

V2O4Divide both

of these numbers by 2

Finding a formula by crossing down charges

What is the formula for vanadium(IV) oxide?

V4+ O2–

V2O4

VO2

÷2

Finding a formula by crossing down charges

What is the formula for vanadium(IV) oxide?

V4+ O2–

V2O4

VO2Formula