Chapter 6 The Structure of Matter
6.1 Compounds and Molecules
((A compound is a substance that is made of atoms of two or more different elements joined by
chemical bonds.))
The ((properties of compounds are very different than the properties of the elements
that make it.))
Chemical Bonds
A chemical bond is the force of attraction that holds two atoms together.
((Chemical bonds are the attractive force that holds atoms or ions together.
Three Types- Ionic Bonding, Covalent Bonding, and Metallic Bonding))
((Bonds can bend, stretch, and rotate without breaking
Chemist use solid bars to represent bonds, however they are more like flexible springs .))
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Chemical structures
((Chemical structure tells you how a compound’s atoms or ions are connected.))
((Models of Compounds))
((Ball and Stick model – the atoms are balls
and the bonds are sticks. Shows bond angles and bond
lengths))
((Structural formulas can also show the structures of
compounds. Only chemical symbols are used to
represent the atoms.))
((Space-filling models show the space occupied by
atoms))
HOW DOES STRUCTURE AFFECT PROPERTIES?
((Compounds with network structures are strong solids))
Substances such as quartz and sand have very strong, rigid structures. ((Network structures are solids,
hard and inflexible, and have very high melting points and boiling points.))
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((Ionic Bonding forms network structure))
Table salt is made of a repeating network connected by strong bonds.
This network is a network of ions, not of atoms, connected by strong bonds.
((Covalent bonding usually forms individual molecules))
Sugar, an individual molecule; made of carbon, hydrogen, and oxygen atoms.
((The strength of attraction between molecules varies (S-L-G)))
((In Covalent Bonding, the attractions between molecules are much weaker than the attractions
that hold the atoms that make up a single molecule.))
The attractions of sugar molecules to form sugar crystals are much weaker than the attractions that hold the
carbon, hydrogen, and oxygen together to make a single sugar molecule.
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((The strength of attraction between molecules of a solid, liquid and gas determines its state at
room temperature.))
((High attraction
medium
Low attraction for one another))
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((6.2 Ionic, Covalent Bonding, and Metallic))
((Why do chemical bonds form?
Atoms join to form bonds so that each atom has a stable electron configuration. Recall that
atoms join to form bonds so that each atom has a full outermost energy level)), which will
resemble a noble gas.
((Ionic Bonding))
Ionic bonding is a type of ((chemical bonding that results from the electrical attraction between
oppositely charged ions.))
((Ionic bonds are formed by the transfer of electrons))
In ionic bonding, electrons are completely transferred from one atom to another.
In the process of either losing or gaining negatively charged electrons, the reacting atoms form ions, which
usually have filled outermost shells.
((The oppositely charged ions are attracted to each other by electrostatic forces which are the
basis of the ionic bond.))
For example, during the reaction of sodium with chlorine:
sodium (on the left) loses its one
valence electron to chlorine (on
the right),
resulting in
Sodium Cation + Chloride Anion
a positively charged sodium ion
(left) and a negatively charged
chlorine ion (right).
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((Ionic compounds are in the form of networks, not molecules))
((Ionic bonds form between metals and non-metals, ))
Ionic compounds tend to ((form network solids)) with high melting temperatures. (strong bonds)
((Ionic crystals exist as one, continuous system.))
Therefore, the ((smallest unit of an ionic compound is a formula unit,)) Ex: the ((formula unit for
table salt is NaCl)) even though the network structure could be made from millions of cations and anions.
Cl-1 Na+1 Cl-1 Na+1 Cl-1
Na+1 Cl-1 Na+1 Cl-1 Na+1
Cl-1 Na+1 Cl-1 Na+1 Cl-1
Na+1 Cl-1 Na+1 Cl-1 Na+1
Sodium Chloride Crystal NaCl Crystal Schematic
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((When melted or dissolved in water, ionic compounds conduct electricity))
Ionic compounds ((dissolve easily in water and other polar solvents))
((Metallic Bonding))
Metallic bonding is chemical bonding that result from the ((attraction between metal atoms and all the
surrounding electrons. Metals do retain most of their individual properties when combined
(Alloys) ))
((Electrons move freely between metal atoms.))
Metal atoms are closely packed due to the ((attraction between one atom’s nucleus and the electrons
of the neighboring atoms. “Sea of Electrons” ))
This proximity allows the ((electrons of the outermost energy level to overlap and travel freely from
atom to atom. (electrical conductivity) and allows atoms to slide past each other without
breaking (flexibility). ))
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((Covalent Bonding ))
Covalent molecules exist as true molecules.
((Covalent bonding occurs between non metal atoms.))
Because both of the non-metals will want to gain electrons, the ((elements involved will share electrons
in an effort to fill their valence shells.))
Because electrons are shared in covalent molecules, no full ionic charges are formed. Thus ((covalent
molecules are not strongly attracted to each another.))
As a result, covalent molecules move about freely and ((tend to exist as liquids or gases at room
temperature. ))
((Covalently-bonded substances are easy to melt, usually have low melting points,
Do not conduct electricity when melted or dissolved))
((Atoms may share more than one pair of electrons))
((Multiple Bonds: For every pair of electrons shared between two atoms, a single covalent bond
is formed.
Some atoms can share multiple pairs of electrons, forming multiple covalent bonds.)) For
example, oxygen (which has six valence electrons) needs two electrons to complete its valence shell. When two
oxygen atoms form the compound O2, they share two pairs of electrons, forming two covalent bonds.
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((Triple bonds are stronger than double bonds, which are stronger than single bonds.))
Triple and double bonds are shorter than single bonds.
((A non polar covalent bond is formed when electrons are shared equally between identical
atoms.))
If they share them equally, the covalent bond is nonpolar, like we saw above.
However, if the electrons are more strongly attracted to one of the atoms, the covalent bond is polar.
Polar covalent bonding occurs because one atom has a stronger affinity for electrons than the other (yet not
enough to pull the electrons away completely and form an ion). ((In a polar covalent bond, the bonding
electrons will spend a greater amount of time around the atom that has the stronger affinity for
electrons.))
A good example of a polar covalent bond is the hydrogen-oxygen bond in the water molecule.
Because the valence electrons in the water molecule spend more time around the oxygen atom than the
hydrogen atoms, the oxygen end of the molecule develops a partial negative charge (because of the
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negative charge on the electrons). For the same reason, the hydrogen end of the molecule develops a partial
positive charge.
((A polar bond is formed when electrons are unequally shared between two atoms. ))
The primary difference between the H-O bond in water and the H-H bond is the degree of electron sharing.
The large oxygen atom has a stronger affinity for electrons than the small hydrogen atoms.
Because oxygen has a stronger pull on the bonding electrons, it preoccupies their time, and this leads to unequal
sharing and the formation of a polar covalent bond.
((Table: Comparing Ionic and Molecular (covalent) compounds. ))
Molecular compounds
Ionic compounds
smallest particles
molecules
Formula unit
elements present
close on the periodic table widely separated on the periodic table
electrical conductivity
poor
good, when melted or dissolved
state at room temperature solid, liquid, or gas
solid
other names
salts
covalent compounds
((Polyatomic Ions))
Polyatomic compounds are ((groups of covalently bonded atoms that have either lost or gained
electrons.))
Polyatomic ions usually ((have a charge)) because the collection of atoms has either gained or lost an extra
electron.
((Most of the polyatomic ions have negative charges.)) This means the ion has more electrons than the
neutral atoms that are in the ion.
A polyatomic ion like phosphate, [PO4] 3- has three extra electrons beyond the electrons on the P and O atoms.
If you count up the valence electrons in the phosphate ion you will see there are 32 electrons. The neutral P and
O atoms originally had only 29 valence electrons.
The negative charge is due to the extra three electrons that came from some outside source like metal atoms that
formed cations.
The ((charge is written outside the brackets)) to indicate the charge is spread on the ion as a whole.
Common polyatomic ions include:





ammonia, (NH4)+1
nitrate, (NO3)-1
carbonate, (CO3)-2
sulfate, (SO4)-2
and phosphate, (PO4)-3
When naming these compounds, write the name of the cation followed by the name of the anion.
There are many polyatomic ions
((Parentheses group the atoms of a polyatomic ion))
Parentheses group the atoms of a polyatomic ion to remind you that it acts like a single ion.
((Some polyatomic anion names relate to their oxygen content, ate’s have more Oxygen
than ite’s))
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((6.3 Compounds Names and Formulas))
((Naming Ionic Compounds))
The naming system of ionic compounds involves combining the names of the compound's positive and negative
ions.
Steps for naming ionic compounds made up of two elements:


((Write the name of the cation.))
((Write the name of the anion.))
You’ll know that a compound is ionic because the formula will begin with a metal cation. Formulas can end
with a polyatomic anion or a single anion. If only two elements are present, they are usually from opposite sides
of the periodic table, like in KCl.
An ((ion formed from a single atom)) is known as a ((monatomic ion.))
((To name a monatomic cation, write the name of the element, followed by "cation.")) In the case
of metals, use stock nomenclature as needed. Al+3 is the aluminum cation
((To name a monatomic anion)), write the ((name of the element, dropping the ending and adding
"–ide")) to the root, then write "anion." O-2 is the oxide ion
Polyatomic anion: you must memorize the polyatomic ion’s name. NO2-is the nitrite ion.
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((Some cation names must show their charge))
((Transition metals may form several cations)), each with a different charge. In cases like this, the cation
name must be ((followed by a Roman numeral in parentheses)). The Roman numeral shows the cation's
charge.
Steps for naming compounds made up of two elements using the stock system:
1. ((Write the name of the cation.
2. In parentheses, write the cation's charge.
3. Write the name of the anion ending with –ide.))
((Writing Formulas of Ionic Compounds))
1. ((write the cation formulas, including charge))
2. ((write the anion formulas, including charge))
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3. ((combine enough cations with enough anions to give a total charge of zero))
 trick: swap charges as subscripts (Criss-Cross Method)
 don't write charges when the ions are combined
4. ((use the simplest (lowest) cation-to-anion ratio possible))
5. ((list cations first, anions last))
Potassium ions (K+) and chloride ions (Cl-) combine to give potassium chloride, KCl
Calcium ions (Ca2+) and bromide ions (Br-) combine to give calcium bromide, CaBr2
Aluminum ions (Al3+) and sulfide ions (S2-) combine to give aluminum sulfide, Al2S3
((Naming Covalent Compounds))
The naming system of covalently-bonded compounds involves ((combining the names of the compound's
elements.))
((Numerical prefixes are used to name covalent compounds of two elements))
Some compounds can be named using the prefix system. The prefix indicates the number of atoms of the
element to which the prefix is attached.
Common numerical prefixes include:
1.
2.
3.
4.
5.
mono–
di–
tri–
tetra–
penta–
((If there is only one atom of the first element, it does not get a prefix.
Whichever element is farther to the right on the periodic table is named second and ends in ide.))
If the ((second element’s name begins with a vowel, the a at the end of the prefix is usually
dropped. N2O5 is dinitrogen pentoxide, not dinitrogen pentaoxide. PCl5 is phosphorous
pentachloride, not phosphorous pentchloride.))
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((Chemical Formulas for Covalent Compounds))
A ((molecular formula)) is a chemical formula that ((shows the exact number and kinds of atoms))
in a molecule of a compound.
A compound’s ((simplest formula is its empirical formula)), which gives the ((smallest wholenumber ratio)) of atoms in the compound.
Molecular formulas are determined from empirical formulas. Molecular formula is a chemical formula that
reports the actual numbers of atoms in one molecule of a compound.
((Different compounds can have the same empirical formula))
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