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