bonding and chemical reactions chapters 6 and 7. compounds and molecules chemical structure: the...

Bonding and Chemical Reactions

Chapters 6 and 7

Compounds and Molecules• Chemical structure: the arrangement of atoms

in a substance

• Chemical Bond: forces that hold atoms together in a compound

Bond Models

• bond length: models distance between nucleus of 2 atoms

• bond angle: models angle the bonds between 3 or more atoms form

• space-filling: shows space that atoms take up

bond angle space-filling

Nature of Bonds

Some bonds are stronger than others, but allbonds can:• bend• stretch• rotate without breaking

Chemical Structure and Properties• compounds with networks are strong solids ex: diamond, quartz, many rocks

• networked compounds have melting and boiling pointsex: salts, rocks, diamonds

Chemical Structure and Properties (cont’d)

• Some compounds are made of bonded ions ex. NaCl (strong attraction between ions)• Some compounds are made of molecules

ex: H2, O2, N2, CO2 (gases with weak attraction for each other)

• Hydrogen bonds are very strong

Bonding

• Atoms bond to gain 8 valence electrons- stable electronic configuration• 2 basic types of bonding: -ionic -covalent

Ionic BondingIonic Bonds: between oppositely charged atoms;usually on opposite sides of the periodic table(metal and nonmetal)• transfer electrons• form networks, not molecules• conduct electricity when dissolved

Lithium Flourine

Covalent BondsCovalent Bonds: share electrons; usually between2 elements close on the periodic table

(nonmetals)• nonpolar covalent bond: e- shared equally• polar covalent bond: e- shared unequally

Metallic Bonding

• “sea of electrons”: electrons can “float” freely between atoms; allows metals to conduct electricity well

Polyatomic Ions

Compounds with both ionic and covalent bonds• acts as a single unit (like ions)• parentheses group polyatomic ion in a compound• most names end in “ite” or “ate” (depending

on # of oxygen atoms)

Compound Names and Formulas

(Compounds have specific names so you cantell how many and what atoms are in thecompound/moleule)

Ionic Naming• Cations: the name of the element • Anions: have “ide” at the end of the element’s

name• Ionic compounds must have a total charge of zero

Sodium ChlorideCation is ALWAYS FIRST

Anion is ALWAYS LAST

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

Transition Metal Naming• Transition metals show their charges as Roman

numerals because they can change charge

FeO = Fe+2 + O-2

Iron (II) OxideFe2O3 = Fe+3 + O-2

Iron (III) Oxide

What is the formula for Lithium oxide?Li- ____O- ____formula: _______________________

What is the name for CuCl2?cation- ___________anion- ___________, ending- __________name- _____________________________

Covalent Naming• To name covalent compounds, put a numerical

prefix in front of the element’s name: 1- mono 6- hexa 2- di 7- hepta 3- tri 8- octa 4- tetra 9- nona 5- penta 10-deca • If only 1 cation is present, no prefix is needed • Atom to the right of the first cation ends in “ide”

What is the name of H2O?_______________________

Formulas• Empirical Formula: smallest whole-number

ratio of atoms in a compound• Molecular Formula: how many atoms are in a

molecule of a compound

GLUCOSE

C6H12O6CH2OEmpirical Formula Molecular Formula

Organic and Biochemical Compounds

• Organic compound: covalently bonded compound that contains carbon

• Polymer: large molecule formed by more than 5 monomers (small units)

ex. DNA

Chemical Reactions1.Result in rearranged atoms2.Involve changes in energy• Exothermic: release energy (heat, fire, fizz, etc)• Endothermic: absorb energy (drop in temp.) -remember, chemical energy is stored in

chemical bonds

Endothermic Reaction Exothermic Reaction

Chemical EquationsDescribing Coefficients:

• individual atom = “atom”

2Mg 2 atoms of magnesium

• covalent substance = “molecule”

3CO2 3 molecules of carbon dioxide

• ionic substance = “unit”

4MgO 4 units of magnesium oxide

Chemical Equations (cont’d)

Balancing Steps

1. Write the unbalanced equation.

2. Count atoms on each side.

3. Add coefficients to make #s equal.Coefficient subscript = # atoms

4. Reduce coefficients to lowest possible ratio, if necessary.

5. Double check atom balance!!!

1 1

1 1

2 3

2 2

3

6 6

3

2 3 3 2 3 2 Al + CuCl2 Cu + AlCl3

Al

Cu

Cl

2 3 2

Balancing Example

Aluminum and copper(II) chloride form copper and aluminum chloride.

Chemical Equations

___ CH4 + ___ O2 ___ CO2 + ___ H2O

methane and oxygen yield carbon dioxide and water

Reactants Products

Balance the Reaction.

___ Mg + ___ O2 ___MgO

Balance the reaction.

___ H2O2 ___H2O + ___ O2

Reaction Types• Synthesis: combines substances A + B AB

• Decomposition: substances are broken apart AB A

• Combustion: ALWAYS has O₂ as a reactant AB + O₂ AO + BO

Reaction Types• Single-Replacement (single-displacement): one element takes the place of another

AX + B A + BX

• Double-Replacement (double-displacement): two compounds appear to exchange ions

AX + BY AY + BX