Ch. 7 and 8 Outline Answers

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Chemistry
Ch. 7 and 8 Key Concepts and Outline
Name
I Can Statements….
1. I can determine the number of valence electrons a representative element has by its position on the periodic table, whether it
will gain or lose electrons in a bond, what its expected charge is, and whether it will be a cation or an anion.
2. I can draw electron dot structures for any single atom of a representative element, and a dot structure of a simple compound
using bond lines or shared electron dots.
3. I can answer a multiple choice question based on the definition of any of the bold terms in this outline or in Ch. 7 and 8.
4. I can identify the properties of an ionic compound, a metallic compound, a covalent compound and a polar compound.
5. I can determine what kind of bond (mentioned above) two atoms would form (when they react) using their position on the
periodic table, and/or the electronegativities chart on page 177.
6. Based on a data table containing the properties of a compound (melting point, boiling point, phase etc…) I can determine what
kind of bond it contains.
7. I can determine the molecular shape of a compound by drawing its electron dot structure and using the VSEPR theory.
8. I can identify isomers of the same molecular formula.
9. I can use bond dissociation energies to determine the relative stabilities of a compound.
10. I can name the various intermolecular attractions and apply their forces to common biological principles like the structure of
DNA and surface tension of water.
Homework
Outline
Ch. Rvw
Labs/Activities
Ionic vs Covalent Lab
Galvanic Cells Lab
Section 7.1
What is a valence electron?
Electron found in the last/outer occupied shell/Energy Level of an atom. Determines reactivity/properties
KC 3 How can you determine the number of valence electrons in an atom of a representative element?
It is the same as its group number
What are (Lewis) Electron Dot Structures?
Shorthand representations of the chemical symbol and the number of valence electrons
Give an example of an electron dot structure for an element from each of the representative groups.
KC 4 Atoms of which elements tend to gain electrons? Atoms of which elements tend to lose electrons?
Metals tend to lose, and non-metals tend to gain
KC 5 How do cations form?
Losing electrons, usually a metal
Write an equation for a sodium atom losing an electron.
Na  Na+ + eWhat is a pseudo noble gas configuration?
When an atom gains or loses electrons until they have a stable octet. “Behave” like a noble gas, but do not become one
KC 6 How do anions form?
Gaining electrons, usually a non-metal
Write an equation for a chlorine atom losing an electron.
Cl + e-  ClWhat is a halide ion?
An atom from the halogen group that has gained an electron and become an ion
Section 7.2
What is an ionic compound?
A compound formed from the bonding of an cation and an anion
KC 14 How can you describe the electrical charge of an ionic compound?
Electrically neutral, the positive cation and the negative anion cancel each other out
What is an ionic bond?
The electrostatic (like magnetic positive and negative) bond that holds ions together
Write an equation that describes the exchange of a valence electron between Sodium and Chlorine.
Na + Cl  Na+ + ClWhat is a chemical formula?
Shows the kinds and numbers of atoms in the smallest representative unit of that substance
What is a formula unit?
Lowest whole number ratio of ions in an ionic compound
What happens to the charges of the individual ions when a bond is formed?
They cancel out
What is the chemical formula for the compound formed from Magnesium and Chlorine? Aluminum and Bromine?
MgCl2 AlBr3
KC 15 What properties characterize ionic compounds?
crystalline solids, high melting points, conduct electricity in liquid or dissolve solution forms,
Why are ionic compounds stable?
Large attractive forces between positive and negative ions
What is the coordination number?
Number of ions of opposite charge that surround an ion in a crystal
What is the coordination number for Cesium with Chlorine?
8
Why do you think Cesium’s coordination number is higher than Sodium’s with Chlorine?
Cesium is a large atom and more chlorine’s can fit around it compared to the smaller sodium atom
What is a crystal lattice?
The orderly repeating pattern of 3 dimensional atoms in a crystal
Section 7.3
KC 23 How do chemists model the valence electrons in metal atoms?
The valence electrons of metal atoms can be modeled as a sea of electrons
What is a metallic bond?
The attraction of the free-floating valence electrons for the positively charged metal ions
How do the properties of a metal relate to the sea-of-electrons model?
Moving electrons result in shiny light, the lack of consistent bonds results in malleable and ductile
Why does an ionic compound shatter when struck with a hammer?
By changing the location of atoms in the crystal pattern you move like charged ions near each other and they repel apart
KC 24 How can you describe the arrangements of atoms in metals?
Very compact and orderly pattern, similar to a crystal
Give 3 examples of arrangements of metal atoms in a crystal.
Body centered, face centered, hexagonal close
What is an alloy?
Mixture of 2 or more elements (at least one of which is a metal)
KC 25 Why are alloys more useful than pure metals?
Properties are often superior to those of their component elements
Give 3 examples of alloys and their constituent elements.
Sterling silver (Ag and Cu)
Cast Iron (Fe C) Brass (Cu Zn)
Bronze (Cu Sn)
What is an electrochemical cell?
An electrochemical cell is a device capable of either deriving electrical energy from chemical reactions, or facilitating
chemical reactions through the introduction of electrical energy.
How does it relate to a battery?
A battery is an electrochemical cell. It separates two types of metal immersed within a strong ionic solution (electrolyte).
How does it generate electricity?
The property for the tendency of metals to exchange electrons is enhanced when immersed in a strong ionic solution, that
allows the electrons to flow between the two different metals. This flow of charge is electricity.
Chapter 8.1
What is a covalent bond?
An equal sharing of valence electrons, usually between two or more nonmetals (electronegative atoms).
What is a molecule?
A group of atoms joined by covalent bonds, with no net charge.
What is a diatomic molecule?
Consists of two atoms covalently bonded together (usually the same kind of atom)
What is a molecular compound?
A Compound composed of molecules
What is the difference between a molecule and a formula unit?
A molecule can exist as a single entity, like water or carbon dioxide. Table salt (ionic compounds) cannot. They are
networks solids.
KC 1 How are melting points and boiling points of molecular compounds usually different from those of ionic componds?
Relatively low melting points and boiling points (gases and liquids)
What is a molecular formula?
The chemical formula of a molecular compound
KC 2 What information does a molecular formula provide?
How many atoms of each element a molecule contains
What does a molecular formula not tell you?
The structure and order of the atoms
For example, what is glucose, l-fructose and d-fructose?
Each are “generic” forms of sugar with the molecular formula of C6H12O6. Yet they are very different compounds
What is a structural formula?
The formula that shows you the specific arrangement of the atoms found in a molecule
What are the other common models for structural formulas on page 215?
Structural, space filling, ball and stick, perspective
What is an isomer?
Compounds that have the same molecular formula (numbers and types of atoms) but different structures
Section 8.2
KC 13 What electron configurations do atoms usually achieve by sharing electrons to form covalent bonds?
Noble gases
Which groups of elements are commonly found in covalent bonds?
The greedy nonmetals, 4A, 5A, 6A, 7A (Halogens)
What is a single covalent bond?
Two atoms held together by the sharing of a pain of electrons
KC 14 How is an electron dot structure used to represent a covalent bond?
The shared pair of electrons are dotted in between
How does a structural formula show a covalent bond?
By dashes
What is an unshared pair?
A pair of valence electrons that isn’t shared between two atoms
Draw an electron dot structure for water, carbon dioxide, methane and ammonia.
KC 15 When are two atoms likely to form a double bond between them? A triple bond?
If they can attain a noble gas structure by sharing two or more pairs of electrons
What is a double covalent bond?
A Bond from two shared pairs (4 total electrons)
What is a triple covalent bond?
A bond from three shared pairs (6 total electrons)
What is the simplified (not what actually occurs) electron dot structure of an oxygen molecule? A nitrogen molecule?
Consider the chart on page 222
What is a coordinate covalent bond?
One atoms contributes both shared electrons (its less greedy than the one it is bonding to)
Give an example of a coordinate covalent bond.
Carbon Monoxide
KC 16 How is a coordinate covalent bond different from other covalent bonds?
The shared pair of electrons comes from one atom, not one from each
What is a polyatomic ion?
A tightly bound group of atoms that has a charge, and yet behaves as a unit (package)
Draw the steps of generating the structural formula for the Sulfite ion.
What is bond dissociation energy?
Energy required to break a covalent bond between two atoms (Ex: H2 molecule = 435kJ/mol)
KC 17 How is the strength of a covalent bond related to its bond dissociation energy?
A large bond dissociation energy corresponds to a strong covalent bond.
Explain this idea in terms of carbon compounds, like methane and coal, and their relative stability.
Carbon and Hydrogen are equally strong in their pull, and therefore hard to separate = stable
KC 18 Draw the electron dot structure resonance structures of ozone and explain how they describe its bonding.
Ozone is a hybrid, or mixture of the extremes of the resonance forms
What are resonance structures?
A structure that occurs when it is possible to draw two or more valid electron dot structures
KC 19 List three ways in which the octet rule can sometimes fail to be obeyed.
Cannot be satisfied in molecules whose total number of valence electrons is an odd number, there are also molecules in
which an atoms has fewer, or more, than a complete octet (like NO2 page 228)
Draw the electron dot structure for sulfur hexafluoride. What is the unique application of sulfur hexafluoride.
Page 229
Section 8.3
What is a molecular orbital?
Orbitals formed when individual sublevels overlap in a molecular/covalent bond to form one larger orbital
KC 23 How are atomic and molecular orbitals related?
Just as an atomic orbital (s and p) belong to one atom, a molecular orbital belongs to the molecule as a whole
What is a bonding orbital?
A molecular orbital that can be occupied by two electrons of a covalent bond
What is a sigma bond?
Two atomic orbitals form a molecular orbital that is symmetrical around the connecting axis
What is a pi bond?
Electrons are most likely found in a sausage shaped region above and below the bond axis
What is VSEPR theory?
Valence Shell Electron Pair Repulsion Theory
KC 24 Explain how the VSEPR Theory can be sued to predict he shapes of molecules.
Repulsion between e- pairs causes molecular shapes to adjust so the valence-electron pairs stay as far apart as possible
Name some of the common molecular shapes.
Page 233
What shape is methane? What shape is water? Methane? Carbon dioxide?
Tetrahedral, bent triatomic, linear triatomic
KC 25 How is orbital hybridization useful in describing molecules?
Section 8.4
What is a nonpolar covalent bond?
Bonding electrons are shared equally
What is a polar covalent bond or polar bond?
Bonding electrons are shared unequally
KC 32 How do electronegativity values determine the charge distribution in a polar covalent bond?
The more electronegative atom attracts electrons more strongly and gains a slightly negative charge, the less
electronegative atom has a slight positive charge.
Use the chart on page 238 and the chart on page 177 to determine the bond between F and O, O and Cl, N and H, H and O.
What is a polar molecule?
One end of the molecule is slightly negative, and the other end is slightly positive
What is a dipole?
A molecules that has two poles (opposite charges on each end)
KC 33 What happens when polar molecules are between oppositely charged metal plates?
They orient themselves with respect to their poles and the charges of the plates
KC 34 Compare the strengths of intermolecular attractions to the strengths of ionic bonds and covalent bonds.
Weaker than ionic or covalent bonds
What are van der Waals forces?
Two weakest molecular attractions caused by dipole interactions and dispersions
What are dipole interactions?
Polar molecules attracted to one another
What are dispersion forces?
The weakest force caused by the motion of electrons in a non-polar molecule from one side of the molecule to the other
creating temporary dipole charges
What are hydrogen bonds?
A specific type of dipole interaction when attractive forces in which a hydrogen covalently bonded to a very
electronegative atom is also weakly bonded to an unshared pair of another electronegative atom
How does hydrogen bonding affect water?
Surface tension
How does hydrogen bonding affect the structure of DNA?
Attraction across the 2 different helixes, or base pairing is due to Hydrogen bonding
What is a network solid?
Solids in which all the atoms are covalent bonded to each other
KC 35 Explain why network solids have high melting points.
Requires breaking covalent bonds through the entire solid
Use the chart on page 244 to compare and contrast ionic and covalent compounds, but also include polar and metallic compounds.
Property
Melting Points
Metallic
Ionic
Polar
Boiling Points
Solid, Liquid Or Gas
Conductivity
Malleable Ductile
***What facet of atomic structure and bonding accounts for this wide array of properties?
Covalent
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