4.1 Atomic Theory and Bonding
Atomic Theory
• An atom is the smallest particle of an element that still
has the properties of that element
• Atoms are made up of smaller particles called subatomic particles.
Š 50 million atoms, lined up end to end = 1 cm
Š An atom = proton(s) + neutron(s) + electron(s)
• Atoms join together to form compounds.
Š A compound is a pure substance that is composed of two or more atoms
combined in a specific way.
Š Oxygen and hydrogen are atoms/elements; H2O is a compound.
• The nucleus is at the centre of an atom.
Š
Š
Š
Š
Š
• A chemical change occurs when the arrangement of atoms in
compounds changes to form new compounds.
See pages 168 - 169
The nucleus is composed of protons and neutrons.
Electrons exist in the space surrounding the nucleus.
# of protons = # of electrons in every atom
Nuclear charge = charge on the nucleus = # of protons
Atomic number = # of protons = # of electrons
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Organization of the Periodic Table
See page 170
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The Periodic Table
• In the periodic table elements are listed in order by
their atomic number.
Where are the
following?
• Atomic
number
INCREASING REACTIVITY
Š Metals are on the left (the transition metals range from group 3 to group 12),
non-metals are on the right, and the metalloids form a “staircase” toward the
right side.
Š Rows of elements (across) are called periods.
ƒ All elements in a period have their electrons in the same general area
around their nucleus.
Š Columns of elements are called groups, or families.
ƒ All elements in a family have similar properties and bond with other
elements in similar ways.
ƒ Group 1 = alkali metals
ƒ Group 2 = alkaline earth metals
ƒ Group 17 = the halogens
ƒ Group 18 = noble gases
• Period
• Group/Family
• Metals
• Non-metals
• Transition
metals
• Metalloids
• Alkali metals
• Alkaline earth
metals
• Halogens
• Noble gases
See page 171
See page 172
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Periodic Table and Ion Formation
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Bohr Diagrams
• Atoms gain and lose electrons to form bonds.
Š The atoms become electrically charged particles called ions.
Š Metals lose electrons and become positive ions (cations).
ƒ Some metals (multivalent) lose electrons in different ways.
ƒ For example, iron, Fe, loses either two (Fe2+) or three (Fe3+) electrons
Š Non-metals gain electrons and become negative ions (anions).
Š Atoms gain and lose electrons in an attempt to have the same number of
valence electrons (electrons farthest from the nucleus) as the nearest noble
gas in the periodic table.
• Bohr diagrams show how many electrons appear in each
electron shell around an atom.
Š Electrons in the outermost shell are called valence electrons.
Š Think of the shells as being 3-D like spheres, not 2-D like circles.
• It has 2 + 8 + 8 = 18
electrons, and
therefore, 18 protons.
What element is this?
~
~
• It has three electron
shells, so it is in
period 3.
• It has eight electrons
in the outer (valence)
shell.
See page 173
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18 p
22 n
argon
See page 174
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1
Patterns of Electron Arrangement
in Periods and Groups
Forming Compounds
• Electrons appear in shells in a very predictable manner.
• There is a maximum of two electrons in the first shell, eight in the
2nd shell, and eight in the 3rd shell.
• When two atoms get close together, their valence electrons interact.
Š If the valence electrons can combine to form a low-energy bond, a compound is
formed.
Š Each atom in the compound attempts to have the stable number of valence
electrons as the nearest noble gas.
Š Metals may lose electrons and non-metals may gain electrons (ionic bond), or
atoms may share electrons (covalent bond).
Š The period number = the number of shells in the atom.
Š Except for the transition elements, the last digit of the group number = the
number of electrons in the valence shell.
• Ionic bonds form when electrons are transferred from positive ions to
negative ions.
• Covalent bonds form when electrons are shared between two
non-metals.
Š The noble gas
elements have full
electron shells
and are very
stable.
Š Electrons stay with their atom but overlap with other shells.
See page 175
See pages 176 - 177
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Forming Compounds (continued)
Lewis Diagrams
• Lewis diagrams illustrate chemical bonding by showing only an
atom’s valence electrons and the chemical symbol.
• Ionic bonds are formed between positive ions and negative ions.
Š Generally, this is a metal (+) and a non-metal (-) ion.
Š For example, lithium and oxygen form an ionic bond in the compound Li2O.
Š Dots representing electrons are placed around the element symbols at the
points of the compass (north, east, south, and west).
Š Electron dots are placed singly until the fifth electron is reached then they
are paired.
+
lithium
oxygen
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Li+
Electrons are transferred from the positive
ions to negative ions
O2Li+
lithium oxide, Li2O
• Covalent bonds are formed between two or more non-metals.
Š Electrons are shared between atoms.
+
Hydrogen fluoride
See pages 176 - 177
hydrogen
electrons are shared
fluorine
Lewis Diagrams of Ions
• Lewis diagrams can also represent covalent bonds.
Š For positive ions, one electron dot is removed from the valence shell for
each positive charge.
Š For negative ions, one electron dot is added to each valence shell for each
negative charge.
Š Square brackets are placed around each ion to indicate transfer of electrons.
••
•
••
•
•
Cl
••
•
•
••
Each beryllium has two
electrons to transfer away,
and each chlorine can
receive one more electron.
•
•
Cl
••
••
• •
• •
••
• •
•
Be •
Cl
••
••
••
•
•
Since Be2+ can donate two
electrons and each Cl– can
accept only one, two Cl– ions
are necessary.
•
•
Cl
••
••
• •
• •
Be
••
Š Like Bohr diagrams, valence electrons are drawn to show
sharing of electrons.
Š The shared pairs of electrons are usually drawn as a straight
line.
–
2+
–
••
Be •
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Lewis Diagrams of Covalent Bonds
• Lewis diagrams can be used to represent ions and ionic bonds.
•
•
See page 178
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••
••
••
Cl
•
•
••
beryllium chloride
See page 179
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See page 179
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2
Lewis Diagrams of Diatomic Molecules
4.2 Names and Formulas of Compounds
• Diatomic molecules, like O2, are also easy to draw as Lewis diagrams.
••
••
•
•
O
••
•
•
•
•
O
••
•
•
•
•
••
O
••
Several non-metals join to
form diatomic molecules.
••
••
••
O
••
•
•
•
•
••
Valence electrons are
shared, here in two
pairs.
O
••
••
••
••
O
•
•
••
This is drawn as a
double bond.
• Ionic compounds are made up of positive and negative ions.
Š All of the positive and negative ions organize in a pattern.
ƒ Negative-positive attract.
ƒ Negative-negative and positive-positive repel.
Š Ionic compounds form from the inside out as solid crystals.
Š Ionic compounds are like a solid stack of bricks.
ƒ A salt shaker contains thousands of small pieces of NaCl.
Salt, NaCl
• Covalent molecules share electrons.
Š There is generally no order to the formation of covalent molecules.
Š These molecules clump together as solids, liquids or gases.
Š Covalent molecules are like a play-pit full of plastic balls.
ƒ Each plastic ball = 1 covalent molecule of H2O
Take the Section 4.1
Quiz
See page 180
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The Chemical Name and Formula
of an Ionic Compound
See pages 184 - 185
Water, H2O
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The Chemical Name and Formula
of an Ionic Compound (continued)
• Ionic compounds are composed of positive ions and negative ions.
Š The name of an ionic compound = positive ion + negative ion-ide.
Š For example, an ionic compound forms between magnesium and oxygen.
ƒ The positive ion is the first part of the name, magnesium.
ƒ The negative ion forms part of the ending of the name, oxygen.
ƒ Add -ide to the end of the name to form magnesium oxide.
• Ionic formulas are based on the ions of the atoms involved.
Š Remember the naming principles above.
Š For example, what is the name of Ca3N2?
ƒ Ca, the positive ion, is calcium.
ƒ N, the negative ion, is nitrogen.
ƒ Drop the end of the anion and add -ide.
ƒ Calcium nitride
Magnesium
oxide is used
as a drying
agent.
See pages 186 - 187
• Writing formulas for ionic compounds:
Š In an ionic compound, the positive charges balance out the negative charges.
Š The ratio of positive:negative charges gives the proper formula.
Calcium oxide, also
ƒ The ratio is always written in reduced form.
known as
“quicklime” was
Š For example, what is the formula for magnesium phosphide?
ƒ
ƒ
ƒ
ƒ
once produced by
cooking limestone
in ancient kilns.
magnesium is Mg2+
phosphorous is P3–
Lowest common multiple of 2 and 3 is 6
3 Mg2+ ions and 2 P3– ions
Mg3P2
Š Try the formula for calcium oxide.
oxygen is O2–
ƒ calcium is Ca2+
ƒ 1 Ca2+ ion and 1 O2– ions
ƒ Ca2O2, which is simplified and written as CaO
See page 188
(c) McGraw Hill Ryerson 2007
Formula of an Ionic Compound
with a Multivalent Metal
Polyatomic Ions
• Some transitional metals are multivalent, meaning they
have more than one ion form.
Š On the periodic table, the most common form of the ion is listed on top.
Š In the name of the compound, Roman numerals are used following the
positive ion to indicate which ion was used.
Š For example, what is the formula manganese (III) sulphide?
ƒ
ƒ
ƒ
ƒ
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• Some ions, called polyatomic ions, are made up of several
atoms joined together with covalent bonds.
Š The whole group has a + or – charge, not the individual atoms.
Š What is the formula of sodium sulphate?
Na+ and SO42–
Š What is the name of the compound KClO? K+ = potassium
This manganese is Mn3+.
sulfur is S2–
Lowest common multiple of 3 and 2 is 6
2 Mn3+ ions and 3 S2– ions
Mn2S3
Na2SO4
ClO– = hypochlorite
potassium hypochlorite
Š Try the name for TiF4
ƒ titanium is Ti4+ or Ti3+
ƒ 1 Ti4+ ion and 4 F– ions
ƒ titanium (IV) fluoride
fluorine is F–
See pages 189 - 191
See pages 192 - 193
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3
Names and Formulas of
Covalent Compounds
Naming Binary Covalent Compounds
• Covalent compounds, also called molecules, rely on the
chemical formula to reveal the components of the molecule.
Š Covalent compounds are made up of two or more non-metals.
Š Names may reveal the components, but often they do not.
Š Subscripts mean something different in covalent compounds
ƒ Ionic compounds subscripts show the smallest
whole-number ratio between the ions in the compound.
ƒ Covalent molecules have subscripts that show the actual number of
atoms in the molecule.
Š What is the chemical formula for the molecule ethanol?
ƒ C2H6O, a name that must be memorized or looked up when needed.
Š What is the name of the molecule C12O22H11?
ƒ Sucrose, also called table sugar.
See page 193
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Comparing Ionic and Covalent Compounds
•
To determine whether a compound is ionic or covalent:
See pages 196 - 197
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Conservation of Mass in Chemical Change
• Chemical change means new compounds are created.
Š What is the chemical formula for the molecule trinitrogen tetrachloride?
ƒ N3Cl4
Š What is the name of the molecule Si3P6?
ƒ Trisilicon hexaphosphide
See pages 194 - 195
(c) McGraw Hill Ryerson 2007
• Chemical reactions result in chemical changes.
Š Chemical changes occur when new substances are created.
Š The original substance(s), called reactants, change into new
substance(s) called products.
• Chemical reactions can be written in different ways.
Š A word equation:
ƒ Nitrogen monoxide + oxygen → nitrogen dioxide
Š A symbolic equation:
State of matter
ƒ 2NO(g) + O2(g) → 2NO2(g)
- Letters indicate the state of each
compound.
Coefficients
(aq) = aqueous/dissolved in water
- Indicate the ratio of compounds
in the reaction.
(s) = solid
- Here, there is twice as much
NO and NO2 than as is O2.
(g) = gas
( ) = liquid
See pages 202 - 203
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Writing and Balancing Chemical
Equations
• The simplest form of chemical equation is a word equation.
Š No new matter is created or destroyed; atoms are just rearranged.
Š All of the matter in the reactants = all of the matter in the products.
Š John Dalton, 200 years ago, realized that atoms simply rearrange
themselves during chemical reactions.
Š Number of each atom in reactants = number of each atom in products.
• The law of conservation of mass:
Š In chemical reactions, atoms are neither created nor destroyed.
Š This law was developed by Antoine and Marie-Anne Lavoisier in the 1700s.
Š Mass of reactants = mass of products
If you could collect and measure all of
the exhaust from this car, you would
find that mass of reactants (gas + O2)
= mass of products (exhaust).
Š Covalent compounds may have many or few atoms sharing
electrons.
ƒ CH4 = methane and C25H52 = candle wax
Š Prefixes are often used before the atom name to indicate the
number of atoms in the molecule.
ƒ CO = carbon monoxide, CO2 = carbon dioxide
Š Write the most metallic atom (farthest left) first
ƒ Add -ide to theend of the second atom’s name
4.3 Balancing Chemical Equations
1. Examine the formula.
• Ionic compounds start with a metal or the ammonium ion.
• Covalent compounds start with a non-metal.
2. If the compound is covalent:
• Use the prefix system of naming if the compound is binary and does not
start with hydrogen.
• If there are more than two different elements, or it starts with H, there is
probably a different, simpler name for the covalent molecule.
3. If the compound is ionic:
• Check the metal to see if it is multivalent (add a Roman numeral if it is
multivalent). Naming starts with the name of the metal atom.
• If it ends with a single non-metal, naming will just end in -ide.
• If it ends in a polyatomic ion, look up the name/formula.
Take the Section 4.2
Q i
• Binary covalent compounds (two non-metal atoms)
use a system of prefixes.
See pages 204 - 205
(c) McGraw Hill Ryerson 2007
Š Potassium metal + oxygen gas → potassium oxide
• A skeleton equation shows the formulas of the elements/compounds.
Š A skeleton equation shows atoms, but not quantities of atoms.
ƒ K + O2 → K2O
• A balanced chemical equation shows all atoms and their quantities
Š Balancing ensures that the number of each atom is the same on both sides of
the reaction arrow.
Š Always use the smallest whole-number ratio.
ƒ 4K + O2 → 2K2O
See page 206
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4
Counting Atoms to Balance an Equation
Hints for Writing Word Equations
• Using the law of conservation of mass, we can count
atoms to balance the number of atoms in chemical equations.
Š Word equation:
methane + oxygen → water + carbon dioxide
→ H2O + CO2
Š Skeleton equation: CH4 + O2
ƒ To balance the compounds, take note of how many
atoms of each element occur on each side of the
reaction arrow.
The same number
of atoms must be
CH4 + O2 → H2O + CO2
on each side.
1 carbon, 4 hydrogen, 2 oxygen → 1 carbon, 2 hydrogen, 3 oxygen
Š To balance, attempt to find values that equate atoms on both sides
Š Balanced equation: CH4 + 2O2 → 2H2O + CO2
1 carbon, 4 hydrogen, (2×2) oxygen → 1 carbon, (2×2) hydrogen, (2×1)+2 oxygen
Š Skeleton equation:
See Page 207
(c) McGraw Hill Ryerson 2007
• Word equations require careful examination to be written correctly.
Š The chemical symbol is used for most elements not in a compound.
ƒ Be careful of diatomic and polyatomic elements
such as O2, P4 and S8 .
ƒ The “special seven” are all diatomic elements
• H2, N2, O2, F2, Cl2, Br2, I2
Š Several common covalent molecules containing
hydrogen have common names that you should know.
ƒ For example, methane = CH4, glucose = C6H12O6,
ethane = C2H6, ammonia = NH3
See page 208
(c) McGraw Hill Ryerson 2007
Strategies for Balancing Equations
• Balance chemical equations by following these steps:
Š
Š
Š
Š
Š
Š
Š
Trial and error will work but can be very inefficient.
Balance compounds first and elements last.
Balance one compound at a time.
Only add coefficients; NEVER change subscripts.
If H and O appear in more than one place, attempt to balance them LAST.
Polyatomic ions (such as SO42–) can often be balanced as a whole group.
Always double-check after you think you are finished.
• Balance the following:
Š Fe + Br2 → FeBr3
Š Sn(NO2)4 + K3PO4 → KNO2 + Sn3 (PO4)4
Š C2H6 + O2 → CO2 + H2O
See pages 209 - 211
Take the Section 4.3
Quiz
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5