Chemical Bonds

Chapter 5 2

Ions

• Ions have different numbers of electrons and protons

• Cations have lost electrons and have net positive charge

• Anions have gained electrons and have net negative charge

Chapter 5 3

Chemical Bonds

• Force of Attraction between any two atoms in a compound

• Involve VALENCE electrons

• Related to shape of molecule

• Related to chemical and physical properties of materials

Chapter 5 4

Types of Bonds

• Ionic BondElectrostatic attraction between positive and negative ions.

Involves transfer of electrons from one atom to another

• Covalent bond

Two atoms share a pair of electrons.

Chapter 5 5

Definitions

• Valence electrons – outermost level with electrons

• Core electrons – all other electrons in an atom

• Isoelectronic – same number of electrons

Chapter 5 6

Octet Rule

• Most stable situation is full octet of electrons in outermost energy level – Exception: H and He need only 2 electrons

• Atoms gain, lose or share electrons to achieve this octet (noble gas arrangement)

• This changing of electrons involves a reaction

Chapter 5 7

Lewis Symbols

• Also called Lewis Dot or Electron Dot

• Way of depicting Valence Electrons around an atom (s and p electrons in highest energy level)

• Show valence electrons as “dots”

Chapter 5 8

Lewis Single Atom

The number of dots is equal to the number of: – valence electrons– outermost energy level electrons – outermost shell electrons– Group number (main groups only)

Chapter 5 9

Lewis Symbol for single atom

• Show atomic symbol

• Show valence electrons as “dots”

Li• •Mg•

Chapter 5 10

Lewis Symbols

Chapter 5 11

Electron-Dot Structures

Chapter 5 12

Write the Lewis structure for:

Mg

C

Ar

I

Rb

P

Chapter 5 13

.

Chapter 5 14

Lewis Dot Symbol for Ions

Electrons are gained or lost to form full octet

Chapter 5 15

Cations (Positive Ions)

Groups IA, IIA, IIIA form ions by removing the electrons in the outermost shell

This is generally the group number of electrons

Ca group IIA lose 2 e- Ca2+

Na group IA lose 1 e- Na+

Chapter 5 16

Chapter 5 17

Anions (Negative Ions)

Groups VA, VIA, VIIA form ions by adding electrons to the outermost shell to make full octet

This is the number of electrons that when added to the group number give eight

N group VA add 3 e- N3-

Cl group VIIA add 1 e- Cl-

Chapter 5 18

Chapter 5 19

What ion is formed from:

FMgOCsBaPAr

Chapter 5 20

.

Chapter 5 21

• Generally, metals in groups IA, IIA and IIIA react with nonmetals in groups VA, VIA and VIIA to form ionic compounds

Chapter 5 22

1. Form positive ion by removing electrons from a group A metal

2. Form negative ion by adding electrons to form a full octet

3. Write the formula for the ionic compound formed

(smallest ratio of ions to give neutral compound)

Chapter 5 23

Reaction of Sodium with Chlorine

Sodium—Soft grayish metal

Chlorine—pale yellow-green gas (poisonous)

Sodium Chloride—White crystalline solid (Table salt)

Chapter 5 24

Reaction of Sodium with Chlorine

Chlorine gains electron from sodium

Chapter 5 25

Ionic Bonding in NaCl

• Form Na+ and Cl- ions

• Opposite charges attract each other

• Organize themselves in orderly arrangement (crystal)

Chapter 5 26

Chapter 5 27

• Do not have “pairs” of Na+ and Cl- ions paired up with each other

• Each Cl- is “associated” with 6 Na+ ions

• Each Na+ is “associated with 6 Cl- ions

• Formula unit: lowest ratio of ions that form compound

Chapter 5 28

Ionic Compounds

Writing Formula

Naming Compound

(Nomenclature)

Chapter 5 29

Combining Ions to Make Compounds

Compound must be neutral

positive charges = negative charges

net charge = 0

Chapter 5 30

To write formula: Need correct number of each ion to give neutral compound

Na+ and Cl- (+1) + (-1) = 0 NaCl

Na+ and S2- (+1) + (-2) =

2Na+ and S2- 2(+1) + (-2) = 0

Na2S (indicate 2 Na+ with subscript)

Chapter 5 31

The formulas of ionic compounds are determined from the charges on the ions.

atoms ions –Na + F : Na+ : F : NaF

sodium fluorine sodium fluoride

The overall charge of NaF is zero (0).

(1+ ) + (1-) = 0

Ionic Formulas: Sodium Fluoride

Chapter 5 32

Sodium Chloride

Chapter 5 33

MgCl2 Ions with 2+ and -1 charges

Chapter 5 34

More Ionic Compounds

Chapter 5 35

Binary Ionic Compounds• Only two elements in compound

Chapter 5 36

Write formula for compound made from :

Mg2+ and S2-

Al3+ and Cl-

Mg2+ and P3-

Chapter 5 37

Write formula for compound made from :

Mg2+ and S2- MgS

Al3+ and Cl- AlCl3

Mg2+ and P3- Mg3P2

Chapter 5 38

Naming Ionic Compounds

Name of positive ion first

Name of negative ion second

Do not need to indicate how many of each ion is in compound

Need to know how to name ions first

Chapter 5 39

Naming Ions

• For cations, simple positive ions– Add the word ion to element name– Examples: Na+ – sodium ion

Al3+ – aluminum ion

• For anions, simple negative ions– Change the usual element ending to -ide– Examples: Cl– – chloride

S2– – sulfide

Chapter 5 40

Common Ions (from single atoms)

Chapter 5 41

Chapter 5 42

Polyatomic Ions

Groups of atoms that combine and have an overall charge

NH4+ ammonium ion

OH- hydroxide ion

Chapter 5 43

Table 4.3

Chapter 5 44

Naming Ionic Compounds

1. Name positive ion first

2. Name negative ion second

Note: Do not need to show how many ions are in formula

Chapter 5 45

Naming Ionic compounds

MgS

AlCl3

Mg3P2

Chapter 5 46

Naming Ionic compounds

MgS Magnesium Sulfide

AlCl3 Aluminum Chloride

Mg3P2 Magnesium Phosphide

Note: Number of ions not in name

Chapter 5 47

Compounds with Polyatomic Ion

Mg2+ NO3-

Mg(NO3)2 magnesium nitrate

Use parentheses to show that there are two nitrate ions

Chapter 5 48

Octet Rule

Atoms tend to gain or lose electrons to reach more stable octet arrangement

Octet has eight valence electrons

(H has only two)

Full octet same as noble gas valence shell

Chapter 5 49

Ionic vs Covalent Compounds

• Ionic:– held together by charges on ions– Contain a metal and a nonmetal

• Covalent:– held together by shared electrons– Contain two non-metals

Chapter 5 50

Covalent Compounds

Contain only covalent bonds

(share electron pairs to complete octet)

Rules for naming covalent (molecular) compounds DIFFERENT than rules for naming ionic compounds

Chapter 5 51

What kind of compound is it?Ionic or Covalent

For compounds with only TWO elements:

An ionic compound contains one metal and one non-metal

A covalent compound contains two non-metals

Chapter 5 52

Ionic or Covalent?

• CaO N2O

• H2S H2O

• MgCl2 IF3

• CS2 Na2O

Chapter 5 53

Naming covalent compounds

• Name each element in order it appears in compound

• For second element, use stem + “ide”

• Use prefix to indicate number of atoms of each element

(mono if only one atom is present)

• Final vowel in prefix may be dropped if element begins with a vowel

Chapter 5 54

Naming Covalent Compounds

Use prefixes to show number of each type of atom

Chapter 5 55

Example

NO2 ( ) nitrogen ( ) oxide

2 O’s nitrogen dioxide

1 N Mononitrogen dioxide

often omit “mono”

Nitrogen dioxide

Chapter 5 56

Name the following:

CCl4

N2O3

SiS2

Chapter 5 57

Name the following:

CCl4 carbon tetrachloride

N2O3dinitrogen trioxide

SiS2 silicon disulfide

Chapter 5 58

Write the formula for

dihydrogen monoxide

Silicon tetrafluoride

dinitrogentetroxide

Chapter 5 59

Write the formula for

dihydrogen monoxide H2O

Silicon tetrafluoride SiF4

dinitrogentetroxide N2O4

Chapter 5 60

Covalent Compounds

Contain only covalent bonds

(share electron pairs to complete octet)

Rules for naming covalent (molecular) compounds DIFFERENT than rules for naming ionic compounds

Chapter 5 61

Naming covalent compounds

• Name each element in order it appears in compound

• For second element, use stem + “ide”

• Use prefix to indicate number of atoms of each element

(mono if only one atom is present)

• Final vowel in prefix may be dropped if element begins with a vowel

Chapter 5 62

Table 4.4