Last chapter - atoms:smallest unit of an element

-properties determined by electron configuration

-combine together to form compounds

compound - substances made up of

combinations of elements

compounds formed or broken down in

chemical reactions - changes in

matter

when different chemical substances are

created by forming or breaking

“chemical bonds”-bind atoms together

H2 and O2 (diatomic) form H20

new properties due to

changes in e- configuration

Remember noble gases (stable)-never combine

monatomic molecules - gases

molecules - special bonding arrangements

acting as independent units - neutral groups of atoms

chemical bonding between electron orbitals

cause substances to change their properties

Chapter 9 - Chemical Bonds

Compounds absorb energy to increase chemical energy

-release energy to lower chemical energy

Example:PHOTOSYNTHESIS

sunlight+carbon dioxide+water

plant material+oxygen

{CHEMICAL EQUATIOMN- blueprint for reaction

-read: reactants yield products}

plants increase chemical energy - store radiant energy

can also release energy - burning of wood

plant + oxygen

carbon dioxide+water+energy

Chemical bonding involves changes in the internal potential energy - chemical energy

releases all of the sunlight energy stored

-energy stored by forming bond -energy released by breaking bond

The energy exchanges are achieved through changes in the electronic structure of the atoms

- highest n value

- usually s & p orbitals (1 to 8 electrons)

- “fingers of atom”

- determine chemical properties of an element

- valence = group number

Representative (A group) elements attempt to

acquire an outer orbital with

eight electrons octet rule

(except H - s2 orbital stable)

rule of thumb: metals lose electrons (+)

non-metals gain electrons (-)

want noble gas configuration

closed “fingers”

Valence electrons - outer shell electrons of an atom

Example: how sodium form stable configuration?

Na Group IA - 1 valence electron (metal-lose e-)

electron dot: Na. + energy Na+ + electron

What are the charges for the following ions:

Ca, Br, Al, O, P

Types of Chemical bonds

chemical bond - attractive force that holds atoms

together in a compound

-atoms gain or lose electrons to

achieve lower energy

-most stable arrangement “octet”

Three types of bonding:

ionic bond- atoms transfer electrons

-Coulombic attraction between ions

-generally between metals & non-metals

covalent bond- atoms share electrons

-share valence electrons to form octet

-generally bonding between non-metals

metallic bond- all of the metal atoms

share electron sea

-gives metallic properties

- we will not consider this bonding

IONIC BOND - transfer of electronschemical bond of electrostatic attraction - Coulomb’s Law

valence electrons are lost or gained to achieve

stable noble gas configuration - octet

form solids-water soluble as ions

BOND BETWEEN METALS AND NON-METALS

metals lose electrons positive ions

non-metals gain electrons negative ions

opposite charged ions attract

energy is released when bond forms

lower chemical energy

heat of formation - energy released when an

ionic bond is formed

-same energy required to break bond

energy conserved in decomposition

Illustration:

Na + Cl Na+ Cl- + energy

Na+ formation requires energy

Cl- formation releases energy

net energy released

forms crystalline solid - each ion surrounded

by opposite ion in one giant unit made of charged ions

. ..... ..Cubic crystal

Ionic Bonds continued

remember electrons transferred to form octet:

isolated atoms with extra or less charge

-electroneutrality -

electrons gained by one atom

equals electrons lost by other

Describing IONIC COMPOUNDS: held by ionic bonds

chemical formula - describes what elements

are present and in what proportions

-uses element symbols

-and subscripts for number

of atoms in compound

-no subscript if only one atom

NaCl understood 1Na & 1Cl

must know charge on atoms:

Group IA and IIA- positive charge = family

Group VI & VII-negavive charge=8-family

Transition metals - form positive ions

variable charge - several possible

charge values

i.e., copper Cu+ and Cu+2

Ionic chemical formula determined by electroneutrality

Charge on positive ion(s) must balance charge on negative ions

Example: what is the chemical formula forthe ionic compound containing calcium and fluorine?

Ca:Group IIA - positive ion (metal)loses 2 e- to form octet (Ar config)

Ca+2

F: Group VIIA - negative ion (non-metal)gains 1 e- to form octet (Ar again)

F-

NEED 2F- to cancel 1Ca+2

alternatively, 2 e- from Ca tranferred to 2F

chemical formula : CaF2

Transition metals- Table 9.2 different charges possible-form colored solids-multiple chemical formulae with

same elements

Cobalt with Chlorine (Cl-)

Co+2 Co+3

CoCl2 CoCl3form different compounds with different properties

Polyatomic Ions

Groups of two or more elements (poly) that form charges

bond together covalently - share electrons

separate unit with net charge

that act like single ions

HAVE SPECIFIC NAMES AND CHARGES

Table 9.3

sulfate (SO4-2) nitrate (NO3

-)

typically bond with metals like Ca:

CaSO4 Ca(NO3)2

( ) needed if more than

one needed fo rbondCovalent Bond - chemical bond formed by the

sharing of an electron pair

-tightly bound in a molecule - smallest unit of

covalent compound

-electrons move throughout entire molecular orbital

-both elements count the electron pair

to achieve octet

-bonding between NON-METALS

Halogens GroupVII (non-metals)

reactive elements that often form diatomic molecules

Example of covalent bond: fluorine

Halogen gas F F both electrons counts as octetnonmetals F-F for each atom - shared

represents covalent bond - dash is bonding pair - shared

-keeps molecule together

orbital pairs: - two electrons (s=+/-1/2) in orbitallone pairs that are not shared in bond

WATER H2O

O O H H H HO -- octet H -- He config

..... .x

x x

xxx

x.

.

...... .

SINGLE COVALENT BOND - single electron pair shared by each atom

DOUBLE COVALENT BOND - two electron pairs shared by each atom

each element must have 2 unpaired e-: C, N, O, S

Example: ehtylene (gas from ripening fruit) C2H4

H H H H double dash-C C C C double bond

H H H HTRIPLE BOND - 3 pairs of electrons shared (C,N) H C C H

ACETYLENE

.

..... xx

xx ..

Ionic versus Covalent

General rule:ionic - opposite sides of periodic table

(metal & non-metal

covalent- bonding between non-metals

Depends on how tightly elements can hold ontotheir outer electrons

compounds can have ionic and covalent properties

Electronegativity - comparative ability of atoms to attract bonding electrons FIG. 9.10

- higher number, attracts electrons well-will pull off e;ectrons better to form ionic-about same number share electrons

covalent

ABSOLUTE ELECTRONEGATIVITY DIFFERENCE subtract electronegativity of two elements-predict bond type

difference>1.7 steals electrons - ionicdifference <0.5 shares electrons - covalent

Polar molecule between 0.5 and 1.7- unequal sharing

one side of molecule more (+)other side more (-)

Electronegativity Table 9.10

F holds onto electrons best - largest electronegativity

Fr has smallest electronegativity - easily gives up electrons

mixed polar molecules not charged-just unequal sharing

Examples: HF difference=

ionicseparate charges

N2 difference=

covalentshare equally - diatomic

HCl difference=polar covalent

+ -

+ -

Electronegativity difference describes percentage ionichow close it is to removing electrons

How to name compoundsHistorically: name based on usage

“soda” sodium carbonate (from sodium)baking soda-sodium bicarbonatecaustic soda (burns)-sodium hydroxidepot ash – potassium carbonate

washing soda, etc.

STANDARDIZE: so everyone knows what compound systematic rules -can determine compositionRULE: if two elements, ends in –ide (unless

polyatomic ion)Naming different for ionic and covalent

IONIC COMPOUND NAMESRepresentative Elements (A groups) metal first, then non-metal with –ide ending

NaCl sodium chloride

MgF2 magnesium fluoride

definite charge – only one compound possible

Transition Metals (B groups) variable charges – different compounds possible

need to indicate charge-balance charges to get formula

old way- latin root: -ic higher charge state -ous lower charge state

oxidation number -charge on ion

Ionic compound names – transition metalsoxidation numbers: Table 9.6

Modern way to indicate oxidation state – Roman numerals

Roman numeral in parenthesis- (II) means +2

Fe+3 iron (III)

Fe+2 iron (II)

(Fe2)+6(S3)

-6 iron(III) sulfide

Name these: What is the formula?

CuCl lead(II)sulfide

SnO

chromium(III)bromide

Fe2S3 lead(II)oxideIonic compounds with polyatomic ions:

two or more elements-act like single ion

-have specific names Table 9.3

hydroxide (OH)-

sulfate (SO4) -2

nitrate (NO3)-

-ate: one more O than –ite

-per: one more Othan –ate

-hypo: one less Othan -ite

Name the following: write formula:

Na2SO4 rubidium chlorate

Ca(NO3)2 lead(II) sulfate

Fe(NO3)2 barium permanganate

Summary: Method for writing ionic formula

1. Write positive element first (metal) then least metallic

2. Balance number of ions (polyatomics) by making neutral

cross-over technique: decide numbers of each ion

in compound by using charge number of

the other element (or polyatomic)

Ca+2 & Cl-1 CaCl2

Sn+2 & F-1 SnF2

Mg+2 & O-2 MgO

iron(III) oxide :

lead(II) phosphate :

zinc carbonate :

magnesium hydroxide :

Covalent Compound Names

Molecules – made of non-metals

Problems:

-no metal to put first!

-possibility of multiple bonds

two elements form various

compounds

Name must indicate compound better!!!

RULES: for two element covalent compounds

1. Least metallic (to the left) element first with prefix

if number more than one atom

2. Stem name of 2nd element (with –ide ending)

adding prefix only if elements form more

than one compound

Examples: CO carbon monoxide

CO2 carbon dioxide

N2O2 dinitrogen dioxide

N2O3 dinitrogen trioxide

Formula tells you how to write name

-only one C

-multiple compounds possible

Name: CS2 N2O CCl4

laughing gas

Covalent name tells you how to write formula

EXAMPLES: write chemical formula for the following:

manganese dioxide

dinitrogen pentoxide

dihydrogen dioxide

this very specific naming necessary

because you need to know how they bond

in order to get the chemical formula

O=C=O CO2 can form double bonds

-but C will always form same

number of covalent bonds

-combinations of single,

double and triple

same number of bonding pairs

VALENCE – number of covalent bonds an atom can form

Carbon C 4 bonding electrons

valence of 4 – can form 4 covalent bonds

H valence of 1 4 single, 2 double,

O valence of 2 1 double - 2 single, etc.

N valence of 3

.. ..