Download Understanding the Properties of Elements – Chapter 5

The Properties of Compounds (Ch. 6)
Ionic Compounds (6.1)
Ion = ___________________________________
An atom is the most stable when it has a full _________ ________, with eight
electrons (two if there is only one shell). This is known as a _________ _______.
9 p+
10 n
11 p+
12n
Sodium
Fluorine
In the space below draw the “unit” that results.
Also observe the photos and Bohr diagrams on p. 223 for sodium chloride
Valence electrons are furthest from the positive nucleus, so they are the most
loosely held and are therefore _________ ___ __________ _________
_____.
One valence electron is transferred from sodium to fluorine.
This makes the sodium _________ charged and the fluorine __________
charged. They will attract each other, because opposite charges attract.
The result is __________ ___________ (NaF), an ingredient in toothpaste.
Sodium is an ________ ________ and fluorine is a ________. Other alkali metal
and halogen compounds form one-to-one compounds.
e.g.
LiF, LiCl, LiBr, LiI
NaCl, NaBr, NaI
KF, KCl, KBr, KI
The first element is a _______ and the second is a ____________.
These are all _________ ___________.
So is magnesium oxide (MgO), in which the two outermost electrons of magnesium
are transferred to the outermost shell of oxygen.
_____________________________________________________.
An ionic bond is a link in which electrons are transferred.
Ionic bonds form between metal atoms and non-metal atoms.
Sodium fluoride and sodium chloride (table salt) are examples of ionic compounds.
Properties of ionic compounds: show crystal models
Strength of ionic bonds
Structure
State
Melting point
Boiling point
Solubility
Conductivity
Ion Charges
An ion charge is ______________________________________ in its ion form.
This occurs when electrons are _________ or _________ to achieve a stable
octet (or duet) in the valence shell.
e.g. Lithium ion → _________________________
Magnesium ion → _______________________
Nitrogen → _______________________
Naming Ionic Compounds
1. Name the metal ion first.
2. Name the non-metal ion second. The end of its name will change to “-ide”.
3. If the proportion of one element to the other is not 1:1, a subscript is required
to indicate the proportion of the element that is more abundant.
e.g. For 1 Magnesium atom, there are 2 chlorine atoms: MgCl2.
Examples: Polyatomic ions: sulfate SO42-, carbonate CO32-, phosphate PO43-, nitrate NO31Formula Positive ion (metal) Negative ion (non-metal)
Name
Properties of Ionic Compounds
Read pages 225 to 227.
1. Describe what is meant by a crystal lattice.
2. Why does a typical ionic compound dissolve in water?
3. Describe the importance of soluble ionic compounds in the
human body.
4. Explain why ionic compounds are
a) poor conductors when solid.
b) good conductors when dissolved in water.
5. Compare the electrical conductivity of pure water, tap
water, and salt water.
Molecular Compounds (Covalent Compounds)
Molecular compounds are made up of ___________ ________ instead of ions.
Instead of electrons being transferred from one atom to the other, they are
_______. Strong _______ _ _________ are formed when electrons are shared.
Electrons are shared so that each atom has enough for a _______ ______ (or
pair, in the case of hydrogen).
For example, oxygen has six electrons in its outer shell, so it requires two more.
It can share electrons with (for example):
2 H atoms → H2O
Notice only valence
electrons are shown.
H
O
H
Hwk: Draw Models: H2, O2, CO2, H2O, N2, CH4, CH3OH (methanol), CH3CH2OH
(ethanol), H2SO4, (CH3)2CO (acetone; hint: CH3COCH3)
__________ __________ are elements whose atoms combine in pairs to form
molecules.
e.g. H2, O2, N2
H2
O2 – 2 pairs of electrons are N2 – 3 pairs of electrons
are shared in a triple bond
shared in a double bond
Double and triple bonds are extremely strong.
A covalent bond is a link in which electrons are shared.
Covalent bonds form between non-metal atoms and other non-metals atoms.
Naming Molecular Compounds
Names show:
 which elements are in the compound
 the number of atoms of each element in one molecule; Greek prefixes are
used.
1 – mono
4 – tetra
2 – di
5 – penta
3 – tri
(also hexa, hepta, octo, nona ………)
“Mono” isn’t used for the first element in the name.
e.g. carbon monoxide, not monocarbon monoxide
examples: N2O → dinitrogen monoxide
PBr3 → phosphorus tribromide
CCl4 → carbon tetrachloride
Practice: Name these:
CO
____________
CI4
__________________
OF2
__________________
PCl3
__________________
N 2O 3
__________________
Properties of molecular compounds
Strength of covalent
bonds
Strength of physical
interactions between molecules
Structure
State
Melting point
Boiling point
Solubility
Conductivity
CS2 → carbon disulphide
PF5 → phosphorus pentafluoride
Plastics and Polymers
Plastics are made of very large molecules called polymers.
polymer = a giant molecule made of many repeating identical or very similar
subunits (monomers) linked together by strong covalent bonds
e.g.
• plastics
• DNA
• starch
• some proteins, such as hair
• synthetic fibres, such as nylon, polyester
• rubber
Polyethylene is a plastic made of many ethylene monomers.
It’s used in plastic bags, bottles, pipes. And so on.
Ethylene: a colourless gas; C2H4
Polyethylene: …..CH2-CH2- CH2- CH2- CH2- CH2-……...
High density polyethylene:
Environmental Concerns (p. 239)
1. Why do plastics pose problems for the environment?
2. Can all types of plastics be recycled?
3. What happens to the chemicals in plastics when they are put in landfills?
4. It takes twice as much energy to make one paper grocery bag as it does to make
one plastic bag. A paper bag holds up to three times as much as one plastic bag.
Make a table that compares the advantages and disadvantages of each.
Paper
Plastic
Advantages
Disadvantages