Download Chapter 4 Notes - Atomic Theory

4.1 Atomic Theory & Bonding
ATOM: smallest particle of an element, has a neutral
charge.
PEN = proton(s) + electron(s) + neutron(s)
ELEMENT: made up of 1 type of atom (eg.oxygen O)
IONS: atoms with charges (eg. oxygen is O2-)
MOLECULES: groups of covalently bonded atoms
(eg. oxygen molecules are O2)
COMPOUNDS: are made up of at least 2 atoms
bonded together.
 Hydrogen and oxygen are atoms/elements
 H2O is a compound
Numbers to Remember :
Protons = Atomic Number
Neutrons = Mass number – Atomic number (Mass
# - proton #).
Electrons in an atom = atomic number (also
proton #)
Electrons in an ion = atomic number – ion charge
Structure of an Atom:
Name
Symbol
Charg
e
Location
Atomic
Mass
Proton
p
1+
nucleus
1 AMU
Neutron
n
0
nucleus
1 AMU
Electron
e
1–
area surrounding
the nucleus
1/1836 (0)
Families of the Periodic Table:
 Columns of elements are called groups, or families
 All elements in a family have…
 similar properties
 bond with other elements in similar ways
 have the same number of valence electrons
 Family names (on the periodic table!):
 Group 1 = alkali metals (1+, highly reactive)
 Group 2 = alkaline earth metals (2+, reactive)
 Group 17 = the halogens (1-, very reactive)
 Group 18 = noble gases (0, unreactive)
 Periods are horizontal rows on the periodic table.
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Periodic Table of
the Elements
Periodic Table & Ion Formation:
Where are the
following?
INCREASING REACTIVITY
• Atomic
Number
• Period
• Group/Family
• Metals
• Non-metals
• Transition
metals
• Metalloids
• Alkali metals
• Alkaline earth
metals
• Halogens
 Ions: Atoms that gain and lose electrons to become
stable (full valence shells).
 1. Cations: metals that lose electrons & form
positive ions (Na+)
 Multivalent: Some metals can have more than
one charge (Fe2+ or Fe3+).
 2. Anions: Non-metals gain electrons & form
negative ions (O-2)
• Noble gases
Bohr Diagrams:
Bohr Diagrams
 Bohr diagrams show how many electrons
appear in each electron shell around an
atom. (2, 8, 8, 18, 18)
 Valence electrons: electrons in the outermost
shell ONLY.
 If the valence shell is full = stable
 If the valence shell is not full = reactive
What element is this?
•It has 2 + 8 + 8 = 18
electrons, and therefore
18 protons
18 p
22 n
•It has 8 electrons in the
outer (valence) shell
Argon!
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Covalent Bonds:
Ionic Bonds:
 Formed between cations (metal or NH4+) &
anions (non-metal or polyatomic ions).
 Valence electrons are transferred to create
the cation and anion.
 Eg. Li2O
 Formed between two or more non-metals
 Valence electrons are shared between
atoms (so NO CHARGES are formed)
 Eg. HF
+
Lithium
+
Oxygen
Electrons are transferred from
the cations to the anion
Li+
O2Li+
Lithium oxide,
Li2O
Lewis Diagrams:
Lewis Diagrams for Ions:
Ex. Nitrogen ion
 Remove or add electron dots to
make full valence shells.
 Square brackets and the charge
are placed around each ion
 Dots representing valence electrons are placed
around the element symbols (on 4 sides,
imagine a box around the symbol)
Ex: Nitrogen
atom
Electrons are shared
Fluorine
Hydrogen
 Only valence electrons are shown
 Electron dots are placed singularly,
then they are paired.
Hydrogen fluoride
••
•
•
•
••
Be
••
••
•
•
Cl
•
•
••
Each beryllium has two
electrons to transfer
away, and each chlorine
wants one more electron
•
•
Cl
••
••
••
•
•
•
•
Be
•
•
••
•
•
Cl
•
•
• •
Since Be2+ wants to
donate 2 electrons and
each Cl– wants to
accept only one, two Cl–
ions are necessary
•
•
•• –
•
•
••
Cl
2+
••
•
•
•
•
••
Be
•
•
–
••
•
Cl •
••
The ionic compound
Beryllium chloride is
formed
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Lewis Diagrams For Covalent Compounds:
Lewis Diagrams for Ionic Compounds:
••
•
•
•
••
Be
••
••
•
•
Cl
•
•
••
Each beryllium has two
electrons to transfer
away, and each chlorine
wants one more electron
•
•
Cl
••
•
Be
•
•
••
•• –
••
••
•
•
•
•
•
Cl
•
•
• •
Since Be2+ wants to
donate 2 electrons and
each Cl– wants to
accept only one, two Cl–
ions are necessary
•
•
Cl ••
••
2+
••
•
•
•
•
••
Be
•
•
–
••
Cl
•
•
••
The ionic compound
Beryllium chloride is
formed
4.2 – Ionic and Covalent Compound Naming
Ionic Compounds:
- are made up of positive and
negative ions arranged in a
crystal structure.
Salt, NaCl
Covalent Molecules:
- are made up of atoms
sharing electrons.
 valence electrons are drawn to show sharing of
electrons.
 Remember: All atoms “like” to have a full valence
shell
 The shared pairs (“bonding pairs”) of electrons are
usually drawn as a straight line
 “lone pairs” are the electrons not shared
Naming Ionic Compounds:
 name of an ionic compound = cation anion-ide
 Ex.1: magnesium and oxygen
 cation anion-ide
 Magnesium ox + ide
 Magnesium oxide
Magnesium
 Ex.2: what is the name of Ca3N2?
oxide is used as
a drying agent.
 Ca = calcium; N = nitrogen
 Drop the end of the anion and add –ide
 Calcium nitride
 Ex.3: What is the name of BaCl2?
 Barium chloride
Water, H2O
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Writing formulas for Ionic Compounds
Remember: positive charges must = negative charges
Ex.1: What is the formula for magnesium phosphide?
 Magnesium is Mg2+ Phosphorous is P3–
 Lowest common multiple of 2 and 3 is 6
 3 Mg2+ ions & 2 P3– ions (6 +ve’s & 6 –ve’s)
 Magnesium phosphide = Mg3P2
Ex.2: What is the formula for calcium oxide?
Calcium is Ca2+
Oxygen is O2–
2+
1 Ca ion
&
1 O2– ion
Calcium oxide = CaO
Ionic Compound with a Multivalent Metal
 Multivalent: some transition metals have
more than one charge.
 Roman numerals are used after the metal
name to indicate which ion was used
Ex. 1 What is the formula manganese(III) sulphide?
 This manganese is Mn3+ Sulphur is S2–
 Lowest common multiple of 3 and 2 is 6
 2 Mn3+ ions and 3 S2– ions
 Mn2S3
Drawing Formula Diagrams
 Examples:
 Lithium nitride
 Barium sulphide
You try!
What is the name for TiF4?
 Titanium can be Ti4+ or Ti3+ Fluorine is F–
 From the ratio in the formula you can find out it is
Ti4+
 1 Ti4+ ion and 4 F– ions
 Titanium (IV) fluoride
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Polyatomic Ions
 are made up of several atoms joined together by
covalent bonds
 The whole group has a + or – charge, not
individual atoms.
 Ex.1 What is the formula of sodium sulphate?
Ex.2: What is the name of the compound KClO?
ClO– = hypochlorite
K+ = potassium
Potassium hypochlorite
Ex.3: What is the formula for Calcium nitrate?
and
NO3Ca2+
Ca(NO3)2
Na+ and SO42–
Na2SO4
Naming Simple Covalent Compounds
 Prefixes are used before the atom name to
indicate the number of atoms in the molecule.
* Note the brackets around NO3 show there are two
of the nitrate ions present
Examples:
 Examples:
CO = carbon monoxide
CO2 = carbon dioxide
 What is the name of the molecule Si3P6?
 Trisilicon hexaphosphide
Write the most metallic atom
(furthest left) first, then add -ide
to the end of the second atom’s
name
 What is the chemical formula for the
molecule trinitrogen tetrachloride?
 N3Cl4
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How do you know which type it is?
 To determine whether a compound is ionic or
covalent:
- Examine the formula
• Ionic compounds start with a metal or the
ammonium ion
• Covalent compounds start with a non-metal
4.3 Chemical Equations
 A Chemical change means new compounds are
formed.
 Law of Conservation of Mass: matter is not
created or destroyed; atoms are just
rearranged.
mass of reactants = mass of products
number of each = number of each
atom in reactants atom in 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)!

Chemical reactions can be written in different ways.
 A word equation:
Nitrogen monoxide + oxygen  nitrogen dioxide
 A symbolic equation:
State of matter
2NO(g) + O2(g)  2NO2(g)
Writing and Balancing Chemical Equations
 word equation
 uses the names of the chemicals
- Letters indicate the
state of each compound
Coefficients
- indicate the ratio of
compounds in the
reaction
- here, there is twice as
much NO and NO2 than
there is O2
(aq) =aqueous/
dissolved in water
(s) = solid
(l) = liquid
 Example:
K
+
O2

K2O
The word equation is:
Potassium metal + oxygen gas
 potassium oxide
(g) = gas
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Tips and Tricks
 A skeleton equation shows only the formulas of the
elements/compounds
 Shows atoms, but is not balanced
 K(s) + O2 (g)  K2O(s)
 A balanced chemical equation shows the correct
number of each atom
 Balancing ensures that the number of each atom
is the same on both sides of the reaction arrow
 Always use the smallest whole number ratio
 4K(s) + O2 (g)  2K2O(s)
 Use the chemical symbol to
represent single elements.
 Be careful of diatomic and
polyatomic elements
such as O2, P4 and S8
 The “special seven” are all
diatomic elements (hockey
stick & puck)
 H2, N2, O2, F2, Cl2, Br2, I2
Balancing Equations Examples
Balance the following:
__Sn(NO2)4 + __K3PO4  __KNO2 + __Sn3 (PO4)4
Balance the following:
___ C2H6 + ___ O2  ___ CO2 + ___ H2O
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