Download Elements, Mixtures and Compounds

Lesmahagow High School
Structure Bonding & Properties
Lesmahagow High School
National 4/5 Chemistry
Name
Chemical Changes & Structure:
Structure, Bonding & Properties
Through gaining an understanding of the structure of atoms and
how they join, I can begin to connect the properties of
substances with their possible structures.
SCN 4-15a
Atomic structure and bonding related to properties of
materials.
National 4
Atomic structure and bonding related to properties of
materials.
National 5
Page 1 of 34
Lesmahagow High School
Structure Bonding & Properties
Learning Outcomes – Structure, Bonding & Properties
Circle a face to show how much understanding you have of each
statement:  if you fully understand enough to do what the
outcome says,  if you have some understanding of the
statement, and  if you do not yet understand enough to do
what the statement says. Once you have completed this, you
will be able to tell which parts of the topic that you need to
revise, by either looking at your notes again or by asking for an
explanation from your teacher or classmates.
National 4 Learning Outcomes
By the end of this topic I will be able to:
1.
State that every element is made up of very
tiny particles called atoms.
  
2.
Describe the atom as having a very small
positively charged nucleus with negatively
charged electrons moving around outside
the nucleus.
  
3.
Describe the location and charge of the proton,
neutron and electron.
  
4.
State the relative masses of the proton,
neutron and electron.
  
5.
State that an atom is neutral because the
positive charge of the nucleus is equal to the
sum of the negative charges of the electrons.
  
6.
State that an atom is neutral because the
numbers of protons and electrons are equal.
  
Page 2 of 34
Lesmahagow High School
Structure Bonding & Properties
7.
State that atoms of different elements are
different and have a different number on the
Periodic Table called the atomic number.
  
8.
State that the electrons in an atom are
arranged in energy levels.
  
9.
State the electron arrangements of the first
20 elements.
  
10.
Explain the structure of the Periodic Table in
terms of the atomic number and chemical
properties of the elements.
  
11.
State that elements with the same number of
outer electrons have similar chemical properties.
  
12.
State that an atom has a mass number which
equals the number of protons plus neutrons.
  
13.
Calculate the number of neutrons, protons and
electrons from the mass number and atomic
number, and vice versa.
  
14.
State that atoms can be held together by
bonds.
  
15.
State that atoms can lose, gain or share
electrons to achieve a stable electron
arrangement.
  
16.
Describe the covalent bond in terms of nonmetal atoms sharing pairs of outer electrons.
  
17.
State that a molecule is a group of (usually)
non-metal atoms held together by covalent
bonds.
  
Page 3 of 34
Lesmahagow High School
Structure Bonding & Properties
18.
State that a diatomic molecule is made up of
two atoms.
  
19.
Give examples of elements which exist as
diatomic molecules.
  
20.
State that covalent compounds can exist as
molecules and also as giant covalent network
structures.
  
21.
State that an ion is an atom which has either
lost or gained electrons to become a charged
particle.
  
22.
Describe that an ionic compound forms when
metal atoms join to non-metal atoms by
transferring electron(s) from the metal to
the non-metal, forming a giant lattice of
oppositely charged ions held together by
ionic bonds.
  
23.
Describe the ionic bond in terms of an
attraction between oppositely charged ions
(e.g. between a positive metal ion and a
negative non-metal ion).
  
24.
State that the chemical formula gives the
number of atoms of each element in a
molecule of a covalent substance.
  
25.
State that the chemical formula gives the
ratio of atoms of each element in a giant
covalent network substance.
  
26.
State that the chemical formula gives the
ratio of ions of each element in an
ionic substance.
  
Page 4 of 34
Lesmahagow High School
Structure Bonding & Properties
27.
State that metal elements and carbon
(graphite) are conductors of electricity and
that most non-metal elements are nonconductors of electricity.
  
28.
State that covalent compounds (in any state)
do not conduct electricity.
  
29.
State that ionic compounds (made from metal
ions and non-metal ions) do not conduct
electricity in the solid state but do conduct
when dissolved in water or when molten.
  
30.
State that electric current is a flow of
charged particles.
  
31.
State that electrons flow through metals and
ions flow through solutions and ionic melts.
  
32.
State that electrical energy chemically changes
a molten ionic compound or a solution which
conducts by breaking ionic bonds.
  
33.
Explain why an ionic melt /solution conducts
but the solid does not.
  
34.
State that solid compounds can be ionic
lattices or covalent networks and that
compounds which exist as liquids or gases at
room temperature are covalent molecules.
  
Page 5 of 34
Lesmahagow High School
Structure Bonding & Properties
National 5 Outcomes
35.
I can explain what an isotope is and state that
  
most elements exist as a mixture of isotopes
36.
I can state what is meant by relative atomic
mass and explain why the relative atomic mass of
an element is rarely a whole number
  
37.
I can state that there are two different types of
bonding (ionic (ionic and covalent) when elements join
together, which affect the properties of their
compounds
  
38.
I can state that atoms of non-metal elements form
covalent molecules
  
39.
I can state that covalent compounds (solid, liquid, in
solution) do not conduct electricity
  
40.
I can state that ionic compounds do not conduct
electricity when solid, but they do conduct when
dissolved in water and when molten
  
41.
I can show covalent bonding as a sharing of electrons
  
42.
I can state the covalent bond is a result of two
positive nuclei being held together by their common
attraction for the shared pair of electrons and covalent)
when elements join together, which affect the
properties of their compounds
  
43.
I can show covalent bonding as a sharing of electrons by
drawing non-metal atoms joined in a molecule
Page 6 of 34
  
Lesmahagow High School
Structure Bonding & Properties
44.
I can use diagrams to show the shape of simple twoelement molecules.
45.
I can state that atoms of non-metal elements
form covalent compounds.
  
46.
I can state that a covalent network structure consists
of a giant lattice of covalently bonded atoms.
  
47.
I can describe the bonds between covalent molecules
as weaker than the covalent bonds within molecules.
  
48.
I can state that ionic solids exist as networks/lattices
of oppositely charged ions (charged particles).
  
49.
I can state what is meant by ‘valency’ of an element.
  
50.
I can write the chemical formulae of two element
compounds.
  
51.
I can explain what the endings –ide, -ate and –ite mean.
  
52.
I can state that a diatomic molecule is made up of two
atoms and I can name the seven diatomic elements.
  
53.
I can write formulae for compounds using prefixes,
including mono-, di-, tri-, tetra-.
  
54.
I can work out chemical formulae using valencies.
  
55.
I can state that metal elements (solids, liquids) and
carbon (graphite) are conductors of electricity
because they contain mobile/delocalised electrons.
  
56.
I can state metallic bonding is the electrostatic
force of attraction between positively charged ions
and delocalised electrons.
  
Page 7 of 34
  
Lesmahagow High School
Structure Bonding & Properties
57.
I can explain why ionic compounds do not conduct
electricity when solid, but they do conduct when
dissolved in water and when molten.
58.
I can state that when ionic compounds dissolve in
water, the lattice breaks up completely.
  
59.
I can write formulae for compounds involving complex
ions, eg Na2SO4.
  
60.
I can write a word equation for a chemical reaction.
  
61.
I can write simple symbol equations from word equations.
  
62.
I can identify and use state symbols appropriately.
  
63.
I can write formulae equations and balance them to
show the relative number of moles of reactant(s)
and product(s).
  
64.
I can calculate the gram formula mass of a
substance from the relative atomic masses of the
elements within it .
  
65.
I can state that the gram formula mass of any
  
substance is known as one mole.
66.
I can calculate the number of moles from the
mass of a substance and vice versa.
67.
I can calculate the mass of a reactant or product
using a balanced equation.
Page 8 of 34
  
  
  
Lesmahagow High School
Structure Bonding & Properties
Rates of Reactions – Summary notes
National 4 Summary Notes
Atoms & Atomic Number
In order to understand the properties of elements and compounds
we must look in detail at their atoms.
Everything that exists is made up of atoms. An element is a
substance that is made up of atoms of only one kind. It is difficult
to imagine anything as small as an atom. 100 million of them side by
side will only measure about 1 cm3. A single atom is so small that it
cannot be weighed on a balance. There has to be a special scale to
measure the mass of something so light. The mass of an atom is
measured on the relative atomic mass scale. Since this is a
relative scale, it has no units. The relative atomic mass for some
elements are found in the Data Booklet.
There are over 100 different elements. All the atoms of one
element are different from atoms of other elements. Each
different atom has a 'number'. This is called the atomic number.
All atoms of the one element have the same atomic number and
atoms of different elements cannot have the same atomic number.
Elements are arranged in the Periodic Table in order of increasing
atomic number.
Structure of the Atom
Atoms themselves consist of
even smaller particles
(sub-atomic particles) called
protons, neutrons and
electrons. The numbers of
these particles vary from
element to element.
Page 9 of 34
Lesmahagow High School
Structure Bonding & Properties
Protons and neutrons are found in a 'core' at the centre of the
atom. This is called the nucleus. The nucleus is very small and heavy
compared to the size of the rest of the atom; which is made up of
mostly empty space.
Protons have a positive charge and neutrons do not have a charge,
i.e. they are neutral. Therefore the nucleus has a positive charge
(due to the protons within it). Electrons move outside of the
nucleus. They have a negative charge, equal and opposite to that of
protons. Atoms are neutral overall, i.e. they are neither positive nor
negative. This is because the total positive charge of the protons in
the nucleus is equal to the total negative charge of the electrons,
i.e. the positive and negative charges balance each other.
The masses of the sub-atomic particles are measured on the atomic
mass scale. On this scale, protons and neutrons have a mass of one
atomic mass unit (amu). Compared to protons and neutrons, even on
this scale, electrons have a very small ( almost zero) mass.
Atomic Number & Mass Number
The atomic number and the mass number provide all the
information necessary to calculate the number of protons, neutrons
and electrons in an atom.
The atomic number tells us the number of protons in an atom of an
element. Since atoms are neutral and the charge on an electron is
equal and opposite to the charge on a proton, the atomic number
also gives the number of electrons in an atom.
The mass number of an atom is the number of protons (atomic
number) plus the number of neutrons in the atom. Note that the
mass number of an atom cannot be found in the Data Booklet, you
will be given it. If you want to calculate the number of neutrons in
an atom it is the mass number minus the atomic number.
Page 10 of 34
Lesmahagow High School
Structure Bonding & Properties
Some people get mixed up which number is which for an atom.
Just remember the mass number is always bigger than the atomic
number (think massive).
Electron arrangement
Most of the atom is empty space and electrons move through this
space. The electrons do not however move in a haphazard fashion;
they are arranged in a particular way. Electrons are arranged in
shells. There is a limit to the number of electrons each shell can
hold.
The first shell (nearest the nucleus) can hold 2 electrons.
The second shell can hold 8 electrons.
The third shell can hold 8 electrons (for the first twenty
elements).
Electrons always fill the shells nearest the nucleus first. The
electron arrangement of atoms of all elements is given in the Data
Booklet.
From second year we know that group 1 is called the alkali metals,
group 2 is the alkaline earth metals, group 7 is the halogens and
group 8/0 is the noble gases.
Page 11 of 34
Lesmahagow High School
Structure Bonding & Properties
All the atoms of elements in the one group have the same
number of electrons in the outer shell and this number is equal
to the group number, e.g. 1 outer electron for all the atoms of
the group 1 alkali metals and 7 outer electrons for all the
atoms of the group 7 halogens. The chemical reactions of an
element depend on the number of electrons in the outer shell.
This is why all elements in a group have similar chemical
properties, e.g. all the alkali metals are very reactive.
The noble gas family of group 8 all have a full outer electron
shell. Helium only has two electrons so it has a full 1st (and only)
electron shell, all the others have 8 outer electrons just like
their group number, meaning a full outer electron shell. It is
this full outer electron shell which gives the noble gases their
stability and means they do not react with other elements to
form compounds.
helium 2
krypton 2, 8, 18, 8
xenon 2, 8, 18, 18, 8
Bonding
Not all elements in the periodic table join with other elements
to form compounds. The noble gases have a full outer electron
shell (which is very stable) meaning they do not form
compounds. The other elements in the periodic table have an
unstable electron arrangement which means that they do form
bonds to other elements forming compounds, since this helps
them to achieve a stable electron arrangement like a noble gas.
Page 12 of 34
Lesmahagow High School
Structure Bonding & Properties
To achieve a stable electron arrangement atoms can lose, gain
or share electrons.
When particles in elements or compounds join this ‘join’ is called
a bond. There are two main kinds of bonds which we will learn
about; covalent and ionic. The type of bonding depends on the
types of elements which are joined together. Covalent bonding
is normally when non-metal atoms join together and ionic
bonding is when a metal and a non-metal are joined.
Covalent Bonding
Covalent bonds form when atoms of non-metal elements join
with other atoms of non-metal elements by sharing outer
electrons. The shared electrons lie in an overlap region so that
they are close enough to each element giving each element a full
outer electron shell (and stability) like a noble gas. Covalent
bonds can form between two atoms of the same element
(forming an element) or can form between atoms of different
elements (forming a compound).
It is possible for more than one covalent bond to form between
atoms. We commonly represent a single covalent bond (one
shared pair of electrons) in a simple diagram as a single line.
Double covalent bonds (two shared pairs of electrons) are
Page 13 of 34
Lesmahagow High School
Structure Bonding & Properties
represented by a double line and triple covalent bonds (three
shared pairs of electrons) are represented by a triple covalent
bond.
A group of non-metal atoms held together by covalent bonds is
called a molecule. Molecules made up of only two atoms are
called diatomic molecules, e.g. hydrogen chloride. HCl (one
carbon atom and one chlorine atom), and carbon monoxide, CO,
(one carbon atom and one oxygen atom).
Certain elements normally exist as diatomic molecules. Since
diatomic molecules contain two atoms, the chemical formula for
an element that is made up of diatomic molecules is X2 (where X
is the symbol for the element), e.g. hydrogen is written H2. The
seven common elements that exist as molecules made up of twoatom units are hydrogen (H2), oxygen (02), nitrogen (N2),
fluorine (F2), chlorine (Cl2), bromine (Br2) and iodine (I2).
In five elements including hydrogen the two
atoms in the molecule share electrons to form
a single covalent bond. In oxygen, the two
atoms in the molecule share electrons to form
a double covalent bond. In nitrogen, the two
atoms in the molecule share electrons to form
a triple covalent bond.
The memory aid HON7 can be used to remember the 7 diatomic
elements (i.e. Hydrogen, Oxygen, Nitrogen and the top 4
elements in group 7). Or I Bring Clay For Our New House.
Page 14 of 34
Lesmahagow High School
Structure Bonding & Properties
Ionic Bonding
In covalent bonding atoms shared outer electrons to achieve a
stable electron arrangement like a noble gas.
In ionic bonding electrons are lost
(transferred) from metal atoms and gained
by non-metal atoms to form charged
particles called ions. Since electrons have a
negative charge, metal atoms will be left
with a positive charge and non-metal atoms
will have gained a negative charge.
These oppositely charged ions are attracted to one another and
when they join this is called an ionic bond.
The transfer of one electron from the lithium atom to the
chlorine atom gives the lithium ion the stable electron
arrangement of helium (2) and the chloride ion the stable
electron arrangement of argon
(2, 8 ,8). The formula for
lithium chloride is LiCl.
Note that when lithium chloride actually
forms it is not just one single lithium ion
which bonds on to one single chloride ion
but a huge number of each ion bonding
together to form a huge structure called
an ionic lattice. We will learn more about
Page 15 of 34
Lesmahagow High School
Structure Bonding & Properties
the nature and properties of ionic lattices
in future.
Chemical Formulae
The chemical formula represents different things depending on
the type of bonding present in the substance.
When the substance is a covalent molecule (with a fixed and
usually small number of atoms) the formula gives the number of
actual atoms of each element in the molecule.
When the substance is a giant ionic compound (with no fixed
number of ions) the formula gives the ratio of the different
ions of each element in the substance.
There is another type of covalent substance which exists,
called covalent network. This type of substance is a giant
structure with no fixed number of non-metal atoms all bonded
together by covalent bonds. The formula for this type of
compound gives the ratio of atoms of each element in the
substance. We will look at the covalent network in more detail
during NAT 5 chemistry.
Chemical Formulae From Diagrams/Models
The easiest way to work out a chemical formula is by counting
the number of each kind of atom. This method of working out
formulae is only for covalent molecules as these are the only
substances with a fixed number of atoms. Note that each
symbol is written with the number of atoms of that element
written as a subscript immediately after the symbol. When
formulae are written from diagrams or models the order in
which the different symbols are placed is not important.
Page 16 of 34
Lesmahagow High School
Structure Bonding & Properties
O
H
H
2 hydrogens
and 1 oxygen
3 carbons and
8 hydrogens
Formula H2O
Formula C3H8
Most chemical formulae have to be worked out from the name
of the compound.
Chemical Formulae From Names Including A Prefix
Sometimes the name of a compound contains a prefix which
allows us to write the formula. Prefixes such as mono (one), di
(two), tri (three), tetra (four), penta (five), hexa (six) when
present before the name of an element tell you how many atoms
of that element are in the compound.
E.g. carbon dioxide contains one carbon and two oxygens (CO2).
and diphosphorus pentachloride contains two phosphorus atoms
and five chlorine atoms.
Valency Method For Writing Formulae
If and only if the name of the compound does not contain a
prefix the chemical formula should be worked out by using the
valency method. Valency is the combining power of an element
i.e how many bonds that element can form.
The valency of an element can be found from the group number
in the Periodic Table.
Group
Valency
Group 1 Group 2 Group 3 Group 4 Group 5 Group 6 Group 7
1
Page 17 of 34
2
3
4
3
2
1
Lesmahagow High School
Structure Bonding & Properties
Note that the group 8 noble gases do not have a valency
because they are unreactive and do not form compounds.
Transition metals can form ionic compounds when joined with
non-metals. The metals in this block are a bit unusual as they
have no group number to give you the valency the valancy can
change.
For transition metals the valency of the metal ion is given in
roman numerals inside brackets immediately after the name or
symbol of the metal. If no roman numeral is given, the valency
is assumed to be 2.
e.g. In iron(II) oxide the valency (combining power) of the
iron ion
is 2 but in iron (III) oxide the valency of the iron
ion is 3.
The steps for the valency method are summarised by
remembering SVSDF.
Step 1 –
Step 2 –
Step 3 Step 4 –
Step 5 -
e.g.
S
V
S
D
F
Write the Symbol for each element.
Write the Valency for each element.
Swap the valencies over.
Divide both numbers to get the smallest possible
whole numbers.
Write the Formula (including the symbol and
numbers as subscripts).
silicon
Si
4
2
1
SiO2
Page 18 of 34
oxide
O
2
4
2
e.g.
S
V
S
D
F
Iron (III)
Fe
3
2
2
Fe2O3
oxide
O
2
3
3
Lesmahagow High School
Structure Bonding & Properties
Note that the subscript 1 when it appears for an element (like
for silicon above) is not written. Note also that sometimes it is
not possible to divide the numbers any further in step 4 (like
for iron oxide above).
Remember; never use valency method when a compound
name contains prefixes.
Properties of Substances
The different types of compounds have different properties
including state at room temperature and the ability to conduct
electricity.
State at Room Temperature
Most elements are solid at room temperature. There are two
liquid elements, bromine and mercury.
The state of a compound at room temperature is an indication
of the type of bonding in the compound. If a compound is solid
at room temperature that compound could be a giant ionic
lattice or a giant covalent network. Any compounds which exist
as liquids or gases at room temperature must be covalent
molecules.
Conductivity
Electricity is a flow of charged particles. What happens when
a substance is included as part of an electrical circuit gives
information about the particles in the substance and the way
they are held together.
The terminals through which the electrical current enters and
leaves the substance under test are called the electrodes.
Page 19 of 34
Lesmahagow High School
Structure Bonding & Properties
These are usually made of graphite, a form of carbon that
conducts electricity but is comparatively unreactive.
Elements and compounds that conduct electricity are
conductors.
Elements and compounds that do not conduct electricity are
non-oonductors or insulators.
Elements: Conductors Or Non-Conductors?
The elements in the Periodic Table can be divided into metals
and non-metals. Atoms are made up of a nucleus that contains
positive particles. Negatively charged particles called electrons
move around outside the nucleus. In metals, the outer
electrons are loosely held and can move from atom to atom.
The flow of electricity in metals is a flow of the loosely held
electrons in a definite direction.
This only happens with metal
elements and is therefore why
most non-metals do not conduct
electricity.
The one exception to this
rule is carbon in the form of
graphite. This is because
there are also some free
moving
(delocalised)
electrons
between
the
layers in the structure of
graphite.
Covalent Compounds: Conductors Or Non-Conductors?
Covalent compounds are (usually) made up of atoms of only nonmetal elements held together by covalent bonds. For a
substance to conduct electricity it must have charged particles
Page 20 of 34
Lesmahagow High School
Structure Bonding & Properties
which can flow. Covalent substances do not have mobile
charged particles therefore do not conduct electricity.
Ionic Compounds: Conductors Or Non-Conductors?
Compounds that contain both a metal and a non-metal element
are called ionic compounds. Ionic compounds are made up of
charged particles called ions. In the solid, the forces of
attraction keep the ions locked together. Since ions in a solid
are unable to move, the solids do not conduct electricity (since
no flow of charged particles). When an ionic substance is
dissolved in water to form a solution or when an ionic solid is
heated until it melts, the lattice is broken up. Ions therefore
become free to move and so the substance is able to conduct
(it now has charged particles which can flow).
Properties of Compounds summary
Covalent
Ionic
Non-conductors
Small forces between molecules
Low melting/boiling points
Less dense than ionic compounds
Soluble in covalent liquids
Liquid over a narrow temp. range
Often liquids or gases at room temp
Conductors if molten or in solution
Strong forces between ions
High melting/boiling points
Denser than covalent compounds
Soluble in polar liquids (e.g. water)
Liquids over a wide temp. range
Always solid at room temperature
Page 21 of 34
Lesmahagow High School
Page 22 of 34
Structure Bonding & Properties
Lesmahagow High School
Structure Bonding & Properties
Writing Equations Using Symbols & Formulae
An equation using symbols and formulae gives more information
than a word equation. It shows the nature of the substances
involved when they are reactants and products. These
equations are usually combined with state symbols after the
formulae of substances.
The following state symbols are used;
(s) solid
(l)
liquid
(g) gas
(aq) dissolved in water i.e. aqueous
Example
Zinc metal reacts with copper (II) chloride solution to produce
zinc (II) chloride solution and copper metal.
The word equation for this reaction:
Zinc + copper (II) chloride  zinc (II) chloride + copper
This equation can be written using symbols and formulae as:
Zn (s) + CuCl2 (aq)  ZnCl2 (aq) + Cu (s)
Note that zinc and copper are both elements which are not
diatomic so we just use their symbol from the periodic table.
Copper (II) chloride and zinc (II) chloride are both compounds
with no prefix in their names so we must use SVSDF to work
out their formulae.
The flow diagram on the next page can be used when writing
equations involving symbols and formulae. It should be followed
for each substance in the equation in turn.
Page 23 of 34
Lesmahagow High School
Structure Bonding & Properties
National 5 Summary notes
Isotopes & Relative Atomic Mass
A sample of chlorine gas actually contains two different types
of atom – both types of atom have the same atomic number (so
same number of protons) but a different mass number (or
number of neutrons)
These different types of atoms – with the same atomic number
but a different mass number – are called isotopes.
Calculation of Relative Atomic Mass
An individual atom has a mass number. Relative atomic mass is
the average mass of all isotopes present, taking into account
their relative proportions.
E.g. 75% of chlorine have the mass number 35 and 25% of
chlorine have a mass of 37.
Relative Atomic Mass = total mass of all atoms in the sample
Number of atoms in the sample
= (75 X 35) + (25 X 37) = 35.5
100
Shapes of molecules
Bonds that are formed give molecules a distinctive shape. The
shapes are caused by the repulsion of electrons that are in the
Page 24 of 34
Lesmahagow High School
Structure Bonding & Properties
bonds. Particles with the same charge move away from each
other. The electrons in a covalent bond repel the electrons in
other covalent bonds causing them to move as far away from
each other as possible.
Tetrahedral molecules – Methane (CH4) is an example of a
tetrahedral molecule. Other molecules with a similar formula
have the same shape e.g. CCl4 (carbon tetrachloride)
Pyramidal molecules – Ammonia (NH3) is an example of a
pyramidal molecule.
Linear molecules – Hydrogen fluoride (HF) is an example of a
linear molecule.
Bent molecule – water (H2O) is an example of a bent shaped
molecule
Page 25 of 34
Lesmahagow High School
Structure Bonding & Properties
Complex Ions
A complex ion contains more than one kind of atom e.g.
carbonate, CO32-. These can be found in the data booklet on
bottom of page 4.
Name of ion
Overall
Formula
charge
Ammonium
+1
NH4+
Hydroxide
-1
OH-
Permanganate
-2
MnO42-
Dichromate
-2
Cr2O72-
Formulae for Ionic Compounds with Complex ions
You must use valency rules to work out the formula of
compounds that end in –ite or –ate. It is useful to write the
formula for the ion in brackets
e.g.
Ammonium Sulphate
S (NH4+) (SO42-)
V
1
2
S
2
1
D
(Divide not needed here)
F (NH4+)2(SO42-)
Page 26 of 34
Lesmahagow High School
Structure Bonding & Properties
Word equations
A word equation is a statement showing the reactants on the
left separated by an arrow from the products on the right.
For example, zinc combines with oxygen to form zinc oxide.
The word equation for this is:
zinc
+ oxygen
zinc oxide
Word Equations to Chemical Equations
When we know what the reactants and products are we can
change the word equation into a chemical equation. You swap
the words for chemical formula.
e.g. for the word equation:
zinc
+ oxygen
zinc oxide
1. Look for the symbol for zinc in the data booklet page 4
(Zn). Zinc is NOT one of the diatomic elements so
appears on it’s own.
2. Look for the symbol for oxygen (O). Oxygen is one of the
diatomic elements for the chemical formula is O2.
3. The chemical formula for zinc oxide can be worked out using
the valency method on page 19.
The chemical equation would be:
Zn
Page 27 of 34
+
O2
ZnO
Lesmahagow High School
Structure Bonding & Properties
Balancing Chemical Equations
Remember that the number of atoms present at the start of
the reaction are the same atoms present at the end. We should
be able to see this in a chemical equation.
Example
N2
+
H2
NH3
This equation is not balanced. There are 2 nitrogen atoms on
the left hand side, but only 1 on the right. Also, there are only
2 hydrogen atoms on the left, but 3 on the right. The answer
to this is that substances do not always react in a 1:1 ratio,
producing 1 product molecule.
In this case, 2 molecules of ammonia are formed, which
accounts for the 2 nitrogens originally present.
N2
+
H2
2 NH3
The 6 hydrogens needed to form the ammonia must come from
not 1, but 3 hydrogen molecules.
N2
+
3 H2
2 NH3
The equation is now balanced.
Formula Mass
The formula mass of a substance is the sum of the relative
atomic masses of all the atoms shown in the formula.
e.g. Sodium Nitrate has the formula NaNO3
This represents one sodium atom, one nitrogen atom and three
oxygen atoms.
Page 28 of 34
Lesmahagow High School
Structure Bonding & Properties
Use page 4 of data booklet to add masses of the atoms
together
1 x Na = 1 x 23 = 23
1 x N = 1 x 14 = 14
3 x O = 3 x 16 = 48
Formula Mass = (23 + 14 + 48) = 85g
For complex ions it is often easier to keep brackets round ions
to help work out formula mass. Remember that all atoms shown
inside a bracket must be multiplied by number outside bracket
e.g. (NH4+)2(SO42-)
So . (NH4+)2 shows 2 nitrogen atoms and 8 hydrogen atoms
(SO42-) shows 1 sulphur and 4 oxygen atoms
Use page 4 of data booklet to add masses of the atoms
together
2 x N = 2 x 14 = 28
1 x S = 1 x 32 = 32
4 x O = 4 x 16 = 64
8xH =8x1=8
Formula Mass = (28 + 32 + 64 + 8) = 132g
The Mole
One mole of a substance (n) is the formula mass expressed in
grams.
To find the mass of 1 mole, work out the formula mass in grams
e.g.
Page 29 of 34
Lesmahagow High School
Structure Bonding & Properties
1 mole of HCl = 1 xH + 1 x Cl = 1 +35.5 = 36.5g
0.2mole of NaCl = 0.2 x(1 xNa + 1 x Cl) = 0.2 x (23 + 35.5) =
11.7g
In the second example the number of moles (n) x mass of 1
mole (m) gives us the answer.
Using the triangle below we can convert moles into mass and
vice versa:
m
n
FM
M = mass of a substance
n = number of moles
FM = Formula Mass
Cover what you are asked to find and use the letters left e.g.
how many moles are present in 18g of water?
n = m / FM = 18 / 18 = 1 mole
Mole and Mass Calculations in balanced equations
By using the formula masses in grams (moles) we can deduce
what masses of reactants to use and what mass of products
will be formed Example 1
What mass of oxygen will react with 1 mole of carbon and
how much carbon dioxide is formed ?
Page 30 of 34
Lesmahagow High School
Structure Bonding & Properties
carbon
+
oxygen
carbon
dioxide
Balanced Equation
C
+
O2
CO2
No moles in equation
1 mole
1 mole
12
2 x 16
1
mole
Formula mass
+
12+(2x16)
Mass in calculation
12g
32g
44g
So we need 32g of oxygen to react with 12g of carbon and
44g of carbon dioxide is formed in the reaction.
Example 2
What mass of carbon dioxide will I get when 5 grams of
calcium carbonate reacts with excess HCl ?
Balanced Eq: CaCO3 + 2HCl
CaCl2
+
CO2 +
H20
No moles eq: 1 mole
Formula mass 40+12+(3x16)
100g
So 5 g
Page 31 of 34
1 mole
12+(2x16)
44g
5/100 x 44 = 2.2g
Lesmahagow High School
Structure Bonding & Properties
Structure, Bonding & Properties
National 4 Glossary
Word
Meaning
(aq)
Dissolved in water.
(g)
Gaseous state
(l)
Liquid state
(s)
Solid state.
Ammeter
A device used to measure the quantity of electricity
flowing in a circuit.
Atom
The smallest particle of an element that can exist on
its own.
Atomic mass unit
The mass of one proton or one neutron (shorthand
amu).
Atomic number
The number of protons in the nucleus of an atom.
Bond
Force of attraction between particles which holds
them together.
Circuit
A pathway for electricity.
Conductor
Substance which allows the passage of electricity
through it.
Covalent
Two or more non metal atoms joining together by
sharing outer electrons.
Covalent network
A massive structure made of lots of non-metal atoms
held together by strong covalent bonds.
Delocalised
electrons
Electrons which are free to move as they do not
belong to any one atom.
Diatomic
Two atoms joined together in a molecule.
Electricity
A flow of charged particles. Either electrons in wires
or ions in a solution or ionic melt.
Page 32 of 34
Lesmahagow High School
Word
Structure Bonding & Properties
Meaning
Electrode
A solid rod which conducts electricity. Can be made of
graphite or a metal.
Electron
Sub atomic particle with a negative charge and
negligible mass. Found outside the nucleus in electron
shells.
Electron
arrangement
The way electrons fill electron shells.
Electron shells
Area where electrons are orbiting.
Formula
The symbols and numbers that represent the ratio of
different atoms/ions in a substance.
Graphite
A covalent network made of carbon atoms. It has
delocalised (free moving) electrons which allow it to
conduct electricity.
Insulator
A substance which does not allow the passage of
electricity through it.
Ionic compound
When a metal and non metal join together by transfer
of electrons. Oppositely charged ions are formed
which bond (attract) together.
A massive three dimensional structure where the ions
are held firmly in place by strong ionic bonds.
Ionic lattice
Ions
Atoms which have lost or gained electron(s) to become
either positively or negatively charged.
Mass number
The sum of protons and neutrons in the nucleus of an
atom.
Metallic bonding
Type of bonding which exists in metal elements.
Molecule
A small group of non-metal atoms that are chemically
joined together by covalent bonds. Has a definite
number of atoms.
Not charged.
Neutral
Page 33 of 34
Lesmahagow High School
Word
Neutron
Nucleus
Structure Bonding & Properties
Meaning
Particle with no charge and mass of 1 amu. It is
located in the nucleus.
Centre of an atom containing protons and neutrons.
Outer electrons
Electrons located in the outer electron shell (furthest
from the nucleus)
Power pack (lab
pack)
A source of electricity for use in experiments.
Prefix
A few letters placed before a word e.g. mono, di, tri,
tetra, penta, hexa.
Proportion / Ratio
The quantity of one substance compared to another.
Proton
Positively charged subatomic particle with mass of 1
amu. It is located in the nucleus.
Stable
Has a full outer shell of electrons.
Valency
The combining power of an element (i.e. the number of
bonds an atom/ion forms in order to achieve a full
outer shell of electrons like a noble gas).
National 5 Glossary
Word
Balanced Equation
Meaning
Complex ion
Same number of atoms on the left hand side of an
equation as on the right hand side.
Ion which contains more than one type of atom
Formula mass
The sum of the relative atomic masses of all the atoms
shown in the formula.
Mole
One mole of a substance (n) is the formula mass
expressed in grams.
Page 34 of 34