Download The Fundamental Ideas in Chemistry

The Fundamental Ideas in
Chemistry
The Periodic Table
What do I need to know?
Must
• Recall that all substances are made of atoms
Should
• Explain that an element is a substance made
of only one sort of atom.
Could
• Describe the location of different elements
within the periodic table
Atoms and Elements
All substances are made of ______. A substance
that is made of only one sort of atom is called
an _________. There are about 100 different
_________ which are shown in the __________.
[element, periodic table, elements, atoms]
Examination question
The periodic table of the elements
• In the periodic table elements that have
similar properties are found in the same
vertical column or “GROUP”.
• These all have the same number of OUTER
ELECTRONS.
• We call the rows in the periodic table
“PERIODS” and elements are arranged in
order of increasing ATOMIC NUMBER
• Each element has a different chemical symbol
Periodic table
• As you can see MOST elements are metals
Test your knowledge
Elements are arranged in the ________ ______
according to their ________ ________.
The _________ contain elements with similar
___________.
[properties, periodic table, groups, atomic
number]
Examination question
Chemical symbols
It is important that the first letter of a chemical
symbol is a capital letter and the second letter
(if there is one) must be lowercase eg Ca not CA.
Here are some to learn.
Hydrogen
H
Magnesium
Mg
Zinc
Zn
Lithium
Li
Calcium
Ca
Carbon
C
Sodium
Na
Iron
Fe
Nitrogen
N
Potassium
K
Copper
Cu
Oxygen
O
Sulphur
S
Chlorine
Cl
Neon
Ne
Argon
Ar
Lead
Pb
Silicon
Si
Summary
• Recall that all substances are made of atoms
• Explain that an element is a substance made
of only one sort of atom.
• Describe the location of different elements
within the periodic table
The Fundamental Ideas in
Chemistry – Lesson 2
Atomic structure
What do I need to know?
Must
• Recall that atoms of each element are
represented by a chemical symbol
Should
• Describe the composition of an atom and the
properties of sub-atomic particles
Could
• Explain that atoms of a particular element all
have the same number of protons.
Test Your Knowledge
Write down the chemical symbol
1. Iron
2. Oxygen
3. Sulphur
4. Copper
5. Sodium
Write down the name of these elements
1. Mg
2. N
3. Li
4. K
5. Ne
Structure of the atom
• An atom is made up of protons, neutrons and
electrons.
• The protons are positively charged and are
found in the nucleus
• The neutrons are neutral and are found in the
nucleus
• The electrons are negatively charged and are
found orbiting the nucleus.
Test your knowledge
The particles in an atom are…
-------------------, -------------------, and --------------Niels Bohr discovered…
----------------------------------------------------------------------------------------------------------------------
Test your knowledge
The particles in an atom are…
protons
neutrons , and electrons
Niels Bohr discovered that electrons that orbit
the nucleus have different energy levels.
Summary
• Recall that atoms of each element are
represented by a chemical symbol
• Describe the composition of an atom and the
properties of sub-atomic particles
• Explain that atoms of a particular element all
have the same number of protons.
Fundamental Ideas C1.1
Atomic structure part 2
What do I need to know?
Must
Recall that atoms are made up of protons neutrons and
electrons.
Should
Explain that atoms of an element have the same number
of protons and electrons.
Could
Use the mass number to work out how many neutrons
there are in an atom.
How many particles
MASS NUMBER
ATOMIC NUMBER – elements are
arranged in order of this
How many particles
Number of neutrons
= MASS NUMBER – ATOMIC NUMBER
= 12 – 6
=6
This is the number of protons (6)
This is the number of electrons (6)
We can also get Carbon -13
• How many protons, neutrons and electrons
does carbon-13 have?
Neutrons = mass number – atomic number
=13 – 6
= 7 neutrons
Atomic number = 6
so 6 protons and 6 electrons.
Definitions
• Atomic number – number of protons in the
atom which is characteristic of the element. It
is also the number of electrons in the atom.
• Mass number – the total number of protons +
neutrons
• Number of neutrons can be different even for
the same element. These are called ISOTOPES
Test yourself
• Use a periodic table to work out how many
protons, neutrons and electrons the following
elements have?
Element
Magnesium
Carbon
Hydrogen
Fluorine
Neon
Number of
protons
Number of
neutrons
Number of
electrons
Examination question
Examination question
Examination Question
Summary
Must
Recall that atoms are made up of protons neutrons and
electrons.
Should
Explain that atoms of an element have the same number
of protons and electrons.
Could
Use the mass number to work out how many neutrons
there are in an atom.
The Fundamental Ideas in
Chemistry
Electron Shells
What do I need to know?
Must
• State that electrons occupy different energy
levels
Should
• Explain that electrons occupy the lowest
available energy levels
Could
• Draw the electron arrangement for an element
Electronic structure
Electrons occupy particular _________levels.
The electrons in an atom occupy the ______
available energy levels (closest to the _______).
[nucleus, energy, lowest]
Numbers of electrons
• Successive levels hold a maximum of:
To work out which energy level
1. Look at the atomic number on the periodic
table to work out HOW MANY ELECTRONS
the element has.
2. Put up to 2 of these in the first level
3. Put up to 8 of these in the next level
4. Put up to 8 of these in the next level.
5. The total number must be the same as the
number of electrons the element has.
Electronic structure examples
•
•
•
•
Magnesium has 12 electrons
2 in the first
8 in the second
2 in the third
2,8,2 = 12 overall
Electronic structure examples
•
•
•
•
Chlorine has 17 electrons
2 in the first
8 in the second
7 in the third
2,8,7 = 17 overall
Electronic structure examples
• Hydrogen has 1 electron
• 1 in the first
1 = 1 overall
Drawing diagrams
• We show electronic structure in circles around
the atom with the lowest energy nearest the
nucleus
Electrons and reactions
• The number of electrons in the outer shell
gives an element its reactivity.
• For example one outer electron is VERY
reactive for example Li, Na, K, Rb.
• A FULL shell is called a NOBLE GAS. These are
VERY UNREACTIVE eg He, Ne, Ar, Kr, Xe.
Noble gases
• Unreactive gases with full outer shell can be
used inside light bulbs because they do not
react with the filament.
• If we used air only then the oxygen in the air
would react with the filament and burn it.
Examination questions
Li, Na, K – anything in common?
Alkali metals
• We call the metals in group 1 the “alkali
metals”
• They are very reactive because they all have
ONE outer electron.
• When alkali metals react with water it is very
violent. They are more reactive as you go
down the group.
Test your knowledge
Elements in the same_______ have similar
reactions because they have the same number of
_________in their outer _______ ________.
The number of outer electrons determines how an
atom ______. Atoms with ____outer energy levels
are unreactive. These are called the _____ _____.
They are unreactive because their atoms have
_______ arrangements of electrons .
Summary
• Recall that elements in the same group have
the same number of electrons in their outer
energy level
• Explain that the outer energy level electrons
give an element its properties
• Describe how the number of outer electrons
can mean that a substance is very reactive or
not reactive at all
The Fundamental Ideas in
Chemistry
Elements and compounds
What do I need to know?
Must
State that when elements react their atoms join
with other atoms to form compounds
Should
Describe how bonding involves giving, taking or
sharing electrons.
Could
Explain that compounds involving metals and nonmetals involve ionic bonding and compounds of
only non-metals involve covalent bonding.
Definitions
• An element is a substance made from only
ONE KIND OF ATOM
• A compound is a substance made from one or
more types of atoms CHEMICALLY BONDED
TOGETHER
• A mixture is a number of different elements
or compounds NOT BONDED TOGETHER.
Examination questions
Test your knowledge
When elements react, their atoms join with
other atoms to form________. This involves
giving, taking or sharing _________ to form
_____ or ________. Compounds have different
__________ to the elements that made them.
Why bond?
• Chemical elements bond in order to gain a full
outer shell of electrons.
• This makes them stable
• They can do this by giving electrons away,
gaining electrons or sharing electrons.
Ionic bonding
• This type of bonding generally happens
between METALS and NON-METALS
• It involves the outer electrons of the atoms.
• Electrons are transferred between the two
atoms
• Ions are formed which are attracted to each
other.
Na gives Cl an electron
we call this ionic bonding
Ionic bonding forms IONS which have positive
and negative charges and attract each other
Covalent bonding
• This type of bonding generally occurs between
non-metals
• It involves sharing electrons to gain a full shell
and therefore become stable.
Two H atoms share an electron with O
we call this covalent bonding
Covalent bonding forms MOLECULES
Test your knowledge
Ionic bonding
Compounds formed from _______ and non-metals
consist of positive and negative ____. An _________ is
completely transferred.
Covalent bonding
Compounds formed from _________ and non-metals
consist of ________. Electrons are _______.
Summary
State that when elements react their atoms join
with other atoms to form compounds
Describe how bonding involves giving, taking or
sharing electrons.
Explain that compounds involving metals and nonmetals involve ionic bonding and compounds of
only non-metals involve covalent bonding.
The Fundamental Ideas in
Chemistry
Chemical equations
What do I need to know?
Must
Recall that chemical reactions can be represented by
word equations or symbol equations.
Should
Describe how no atoms are lost or made during a
chemical reaction so the mass of the products equals the
mass of the reactants.
Could
Calculate the mass of a reactant or product from
information about the masses of the other reactants and
products in the reaction.
Word equations
A word equation describes a reaction, for example burning
lithium in air.
lithium + oxygen  lithium oxide
Can you write word equations for the following…
Word equations
1.
2.
3.
4.
The reaction between potassium and oxygen
The reaction between lithium and water
The reaction between calcium and oxygen
The reaction between rubidium and water
Word equations
1. The reaction between potassium and oxygen
potassium + oxygen  potassium oxide
2. The reaction between lithium and water
lithium + water  lithium hydroxide + hydrogen
3. The reaction between calcium and oxygen
calcium + oxygen  calcium oxide
4. The reaction between rubidium and water
rubidium + water  rubidium hydroxide + hydrogen
Symbol equations
Symbol equations use chemical symbols and are
“balanced” to show the actual number of atoms used.
Li + H2O  LiOH + ½ H2
lithium + water  lithium hydroxide + hydrogen
Note that we don’t generally include the numbers in the
word equation.
Change these symbol equations into
word equations
K + H2O  KOH + ½ H2
2Mg + O2  2MgO
Na + H2O  NaOH + ½ H2
Ca + 2H2O  Ca(OH)2 + H2
4Fe + 3O2  2Fe2O3
Change these symbol equations into
word equations
K + H2O  KOH + ½ H2
Potassium + water  potassium hydroxide + hydrogen
2Mg + O2  2MgO
Magnesium + oxygen  magnesium hydroxide
Na + H2O  NaOH + ½ H2
Sodium + water  sodium hydroxide + hydrogen
Ca + 2H2O  Ca(OH)2 + H2
Calcium + water  calcium hydroxide + hydrogen
4Fe + 3O2  2Fe2O3
Iron + oxygen  iron oxide
Balancing equations
• Symbol equations need to be balanced because
the number of atoms reacting at the start MUST
be the same as the number of atoms in the
products.
• An unbalanced reaction cannot properly
represent a reaction because there is an
imbalance in the number of atoms in the
reactants and products.
• The mass of reactants MUST also be the same as
the mass of products.
Is it balanced?
Ca + H2O  Ca(OH)2 + H2
Mg + O2  MgO
Li + H2O  LiOH + ½ H2
C6H12 + 9O2  6CO2 + 6H2O
Is it balanced?
Ca + H2O  Ca(OH)2 + H2
NO!
Mg + O2  MgO
NO!
Li + H2O  LiOH + ½ H2
YES!
C6H12 + 9O2  6CO2 + 6H2O
YES!
Calculating masses
We can predict the mass of product from the mass of
reactants because we know that mass is conserved.
Example
2Mg + O2  2MgO
If 24 g Mg reacts completely with 16g of O2 what mass of
MgO is made?
24 + 16 = 40 g
Calculating masses
2Li + 2H2O  2LiOH + H2
A piece of lithium weighing 7g is allowed to react
with 18g of water. We collect 1g of hydrogen gas in
the test tube.
How much lithium hydroxide has been made?
7 + 18 – 1 = 24 g
Calculating masses
C6H12 + 9O2  6CO2 + 6H2O
If 84g of hexane (C6H12) are burnt completely in
288g of oxygen we measure 108g of water
produced.
How much carbon dioxide was given off?
84 + 288 – 108 = 264 g
How to balance
• When we balance equations we do not
change the small (susbscript numbers)
• eg Ca(OH)2 because this would change the
compound itself
• We do change the LARGE number in front of
the compound
• Eg 2Ca(OH)2 because this changes the
amount.
Summary
Recall that chemical reactions can be represented
by word equations or symbol equations.
Describe how no atoms are lost or made during a
chemical reaction so the mass of the products
equals the mass of the reactants.
Calculate the mass of a reactant or product from
information about the masses of the other
reactants and products in the reaction.