Ions

Ions

Objectives

Determine the number of valence electrons in an atom of a representative element

Explain how the octet rule applies to atoms of metallic and non-metellic elements

Describe how cations and anions form

Valence Electrons

Responsible for the chemical properties of atoms and are those in the outer energy level

Valence electrons – the s and p electrons in the outer energy level› The highest occupied energy level

Core electrons – electrons in the energy levels below highest levels

Keeping Track of Electrons Atoms in the same column...

1) Have the same outer electron configuration.

2) Have the same valence electrons. The number of valence electrons

are easily determined. It is the group number for a representative element

Group 2A: Be, Mg, Ca, etc.› have 2 valence electrons

Valence electrons

Valence Electrons

Usually only electrons used in chemical bonds!!!› This means that only valence

electrons are shown in electron dot structures To us older generations – formerly known as Lewis Dot Diagrams

Electron Dot diagrams are… A way of showing & keeping

track of valence electrons. How to write them? Write the symbol - it

represents the nucleus and inner (core) electrons

Put one dot for each valence electron (8 maximum)

They don’t pair up until they have to

X

The Electron Dot diagram for Nitrogen

Nitrogen has 5 valence electrons to show

First we write the symbol

NThen add 1 electron at a time to each side

Now they are forced to pair up

Practice

Draw the Electron Dot Diagrams of the following:› Carbon› Argon› Calcium› Aluminum

Octet Rule

Octet› 8 valence electrons› Associated with stability of the

noble gases Exception: Helium

› He is stable with 2 valence electrons

Octet Rule

In 1916, Gilbert Lewis used idea of noble gases to explain why atoms form certain kinds of ions and molecules

Octet Rule – in forming compounds, atoms tend to achieve a noble gas configuration – 8 e- in outer level

Cations

Metals LOSE electrons (left side remember!?) to attain a noble gas configuration› When electrons are lost the

resulting ion is POSITIVE Naming – the name of a cation is the

same as element› Example: sodium and sodium

cation

Cation Electron Configuration

Let’s look at configuration of Sodium to explain why metals result in cations:› Na 1s22s22p63s1 1

valence e-

› Na 1s22s22p6 Noble gas configuration Same as what element?Which element is bigger? Why?

Cations

Although names are the same, many chemical differences› Sodium metal reacts explosively

with water› Sodium cation is unreactive

Why?

Electron Dots for Cations

Metals will have few valence electrons (usually 3 or less)› More than 3 electrons lost is rare

but is seen in transition metals Let’s look at calcium – 2 valence

electrons

Ca


Metals will have few valence electrons

Metals will lose their valence electrons

Ca


Metals will have few valence electrons

Metals will lose their valence electrons

Ca2+ No dots are shown for the cation Name: Calcium ion


Try Scandium!

Electron Dots For Cations Let’s do Silver, element #47 Predicted configuration is:

1s22s22p63s23p64s23d104p65s24d9

Actual configuration is: 1s22s22p63s23p64s23d104p65s14d10

Ag = Ag1+ (can’t lose any more, charges of 3+ or greater are uncommon)


Silver cannot lose any more electrons so it does not achieve a true noble gas configuration

Instead it is called “pseudo-noble gas configuration”

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

Electron Dots for Anions

Non-metals gain electrons to attain noble gas configuration› This results in negative charge

(anion) Sulfur – 1s22s22p63s23p4

› 6 valence electrons S2- - 1s22s22p63s23p6

› Noble gas configuration

Naming Anions

Name of an anion is usually the name of the element but you drop last syllable and add “ide”› Chlorine anions – chloride anions› Oxygen anions – oxygen anions

Electron Dots for Anions

Halide ion – ion formed from a halogen element

Non-metals have 5 or more valence electrons› They will GAIN electrons to fill outer

shell

P

3-

Called Phosphide ionSHOW dots!

Stable Electron Configurations

All atoms react to try and achieve a noble gas configuration

Noble gases have 2 s and 6 p electrons› 8 valence electrons = stable

Ionic Bonds and Ionic Compounds

Objectives

Explain the electrical charge of an ionic compound

Describe three properties of ionic compounds

Ionic Bonding

Ionic compounds – compounds composed of cations and anions› Usually metal + non-metal

Ionic bond – electrostatic forces that hold ions together in ionic compounds› Opposite charges are attracted to

each other› Transfer of electrons

Naming Ionic Compounds

Metal cation first then non-metal anion with –ide ending› NaCl› LiF

In these ionic compounds there is one sodium atom for every chlorine atom

Balancing Ionic Compounds

Sometimes an ionic compound will have numbers in addition to symbols› Magnesium chloride = MgCl2

Formula Units

Chemical formula – shows kinds and numbers of atoms in smallest representative unit of a substance› NaCl

Formula unit – the lowest whole-number ratio of ions in an ionic compound› MgCl2

Formula

AlBr3

H2O2

C6H12O6

Ionic Bonding

All the electrons must be accounted for, and each atom will have a noble gas configuration (which is stable).

Ca P

Lets do an example by combining calcium and phosphorus:

Ionic Bonding

Ca P

Ionic Bonding

Ca2+ P

Ionic Bonding

Ca2+ P

Ca

Ionic Bonding

Ca2+ P 3-

Ca

Ionic Bonding

Ca2+ P 3-

Ca P

Ionic Bonding

Ca2+ P 3-

Ca2+ P

Ionic Bonding

Ca2+ P 3-

Ca2+ P

Ca

Ionic Bonding

Ca2+ P 3-

Ca2+ P

Ca

Ionic Bonding

Ca2+ P 3-

Ca2+P

3-

Ca2+

Ionic Bonding

= Ca3P2Formula Unit

This is a chemical formula, which shows the kinds and numbers of atoms in the smallest representative particle of the substance.

For an ionic compound, the smallest representative particle is called a: Formula Unit

Writing a Formula

Write the formula for the ionic compound that will form between Ba2+ and Cl-

Solution:› Balance charge with + and – ions› Write the positive ion first and

negative ion second› Cross charges and write number as

subscripts

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

2. Al3+, Cl-

3. Mg2+, N3-

Learning Check

Naming Compounds

Binary ionic compounds: (what is binary?)› Cation first then anion› Cation = name of the element

Ca2+ = calcium ion› Anion = root + ide

Cl- = chloride› Answer: CaCl2 is calcium chloride

Complete the names of the following binary compounds:Na3N

KBr

Al2O3

MgS

Learning Check

Transition Metals

Transition metals (as seen before) can have more than one possible charge

Roman numeral indicates charge of ion

1+ or 2+ 2+ or 3+

Cu+, Cu2+ Fe2+, Fe3+

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

FeCl3 (Fe3+) iron (III) chloride

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

Names of Variable Ions

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

FeBr2

CuCl

SnO2

Fe2O3

Hg2S

Learning Check

Properties of Ionic Compounds

Most ionic compounds are crystalline solids at room temperature› Crystalline – regular repeating

arrangement of ions in solid Ions strongly bonded together Structure is rigid

Do Ionic Compound Conduct?

What does it mean to conduct electricity??

Do Ionic Compounds Conduct?

Conducting electricity means allowing charges to move

In a solid (such as salt at room temp) ions are locked in place

Ionic salts are insulators› When melted, ions move› ** Melted ionic compounds

conduct electricity

Bonding in Metals

Objectives

Model the valence electron in metal atoms

Describe the arrangement of atoms in a metal

Explain the importance of alloys

Metallic Bonds

Metals are made up of closely packed cations

Metal bonds – consist of attraction of free-floating valence electrons for the positively charged metal ions› Forces of attraction that hold

metals together

Sea of Electrons Model

Metals hold on to their valence electrons very weakly – they want to give them up!

Metallic bonds look like positive ions floating in a “sea of electrons”› Electrons are free to move through

the solid› Metals conduct electricity

Metals

Malleable – hammered into shape (bend)

Ductile – drawn into wires These explain mobility of valence

electrons

- Page 201

1) Ductility

2) Malleability

Due to the mobility of the valence electrons, metals have:

and

Notice that the ionic crystal breaks due to ion repulsion!

Malleable

+ + + ++ + + +

+ + + +

Force

Malleable

+ + + +

+ + + ++ + + +

Mobile electrons allow atoms to slide by

Force

Ionic solids are brittle

+ - + -+- +-

+ - + -+- +-

Force

Ionic solids are brittle

+ - + -

+- +-+ - + -

+- +-

Strong Repulsion breaks a crystal apart, due to similar ions being next to each other.

Force

Crystalline Structure of Metal

If made of one kind of atom, metal atoms are arranged in very compact and orderly patterns

3 arrangements:› Body-centered cubic› Face-centered cubic› Hexagonal close-packed

Body-centered cubic

Every atom has 8 neighbors except for surface atoms

Examples:› Sodium› Potassium› Iron

Face-centered cubic

Every atom has 12 neighbors Examples:

› Copper› Silver› Gold› Aluminum

Hexagonal Close-packed

Every atom has 12 neighbors Different pattern due to hexagonal

shape Examples:

› Magnesium› Zinc› Cadmium

Alloys

Metals are used everyday but most are not pure metals

Alloys – mixture of 2 or more elements (at least 1 is a metal)

Made by melting a mixture of the ingredients then cooling it

Example: Brass – alloy of Cu and Zn Example: Bronze – Cu + Sn

Why Use Alloys?

Properties often better than pure elements› Example: sterling silver is 92.5%

Ag and 7.5% Cu – harder and more durable than pure Ag but still soft enough to make jewelry

Steel – important alloy › Corrosion resistant, ductile,

hardness, cost

List of Common Alloys

Page 203 – Table 7.3 Sterling silver – Ag and CU Cast iron – Fe and C Stainless steel – Fe, Cr, C, and Ni

Types of Alloys

Substitutional alloy – the atoms of the components are about the same size

Interstitial alloy – the atomic sizes are different› Smaller atoms fit into spaces of

larger atoms

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Ions