Structure, bonding , and propertiejn s.ppt

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KS3 Chemistry
Structure, bonding,
& properties

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Do Now
Why is an atom
termed electrically
neutral

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Proton number and the periodic table 05/09/24
WALT: describe how proton number
gives an element its position on the
periodic table
KEYWORDS: Protons, Electrons,
Electronic Structure, Shells, Electronic
configuration.

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Starter 12/05/23
Define proton number
in your own words.

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Summary: the atom so far
The nucleus is:
made up of protons and neutrons
positively charged because of the
protons
dense – it contains nearly all the
mass of the atom in a tiny space.
Electrons are:
very small and light, and negatively charged
able to be lost or gained in chemical reactions
found thinly spread around the outside of the nucleus,
orbiting in layers called shells.

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How many protons?
The atoms of any particular element always contain the same
number of protons. For example:
The number of protons in an atom
is known as its atomic number
or proton number.
It is the smaller of the two numbers
shown in most periodic tables.
hydrogen atoms always contain 1 proton;
carbon atoms always contain 6 protons;
magnesium atoms always contain 12 protons,

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What’s the atomic number?
What are the atomic numbers of these elements?
11
sodium
26
iron
50
tin
9
fluorine

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How are electrons arranged?
Electrons are not evenly spread but exist in layers called
shells. (The shells can also be called energy levels).
The arrangement of electrons in these shells is often
called the electron configuration..
Note that this diagram is not drawn to scale – the atom is
mostly empty space. If the electron shells were the size
shown, the nucleus would be too small to see.
1
st
shell
2
nd
shell
3
rd
shell

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How many electrons per shell?
Each shell has a maximum number of electrons that it can
hold. Electrons will fill the shells nearest the nucleus first.
1
st
shell holds
a maximum of
2 electrons
2
nd
shell holds
a maximum of
8 electrons
3
rd
shell holds
a maximum of
8 electrons
This electron arrangement is written as 2,8,8.

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Electronic Structure
•Using numbers to represent the electron
arrangement is known as the electronic
structure of an atom
Electronic Structure of
this atom is
2,8,8

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Pattern in the Electronic Structures

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Classwork
Draw the electron
configuration for the
first 20 elements.

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Do Now 09/09/24
Write the definition for
electron configuration.

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Making ions 11/09/23
WALT: Describe how
ions are made
KEYWORDS: ion, cation,
anion

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Starter 12/05/23
The goat is licking salt, sodium chloride. Why?

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From atoms to ions
How can reactive metal atoms become stable positive ions?

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How do atoms form ions?
An ion is an atom or group of atoms that has
an electrical charge, either positive or negative.
Atoms have an equal number of protons and electrons and
so do not have an overall charge.
Atoms with incomplete outer electron
shells are unstable. By either gaining or
losing electrons, atoms can obtain full
outer electron shells and become stable.
When this happens, atoms have an unequal number of
protons and electrons and so have an overall charge.
This is how atoms become ions.
How does an atom become a positive or negative ion?

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Positive and negative ions?
The electron configuration of an atom shows how many
electrons it must lose or gain to have a filled outer shell.
An atom that loses electrons has more protons
than electrons and so has a positive overall charge.
This is called a positive ion (cation).
An atom that gains electrons has more electrons
than protons and so has a negative overall charge.
This is called a negative ion (anion).
Atoms with a nearly empty outer shell, will lose electrons
to obtain a full outer shell.
Atoms with a nearly full outer shell, will gain electrons
to obtain a full outer shell.

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How do atoms form positive ions?
An atom that loses one or more electrons
forms a positive ion.
Positive ions have a small ‘+’ symbol and a number by this
to indicate how many electrons have been lost.
This number is usually the same as the number of electrons
in the atom’s outer shell. For example:
Metal atoms, such as sodium, magnesium
and iron, form positive ions.
lithium ion [ 2 ]lithium atom 2.1
aluminium atom 2.8.3 aluminium ion [ 2.8 ]
magnesium atom 2.8.2 magnesium ion [ 2.8 ] = Mg
2+
= Li
+
= Al
3+

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How do atoms form negative ions?
Negative ions have a small ‘-’ symbol and a number by this
to indicate how many electrons have been gained to fill their
outer shell. For example:
An atom that gains one or more electrons
forms a negative ion.
The name of the ion is slightly different to the atom’s name.
Non-metal atoms, such as chlorine,
oxygen and nitrogen, form negative ions.
chlorine atom chloride ion [ 2.8.8 ] = Cl
-
oxygen atom oxide ion [ 2,8 ]
nitrogen atom nitride ion [ 2,8 ]
2.8.7
2.6
2.5 = N
3-
= O
2-

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Calculating ion charges
What is the charge on the ion of each element?
+2 +2+1 -3 -1
2.8.8.21 2.8.5 2.7 2.2
calciumhydrogenphosphorusfluorineberylliumElement
Electron
shells
Charge
on ion

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Classwork
1. Most ions have eight electrons in the outer shell.
Explain why. 2 marks
2. Write the chemical formula for each ion below. Use
the periodic table to find the chemical symbols of the
elements:
a.A potassium ion, with a charge of+1.
b.A magnesium ion, with a charge of +2.
c.A bromide ion, with a charge of -1
3 marks
Homework: Due 18
th
September, 2023

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Do Now 18/09/23
Draw the electronic configuration of a
fluorine ion and predict its charge.
Explain your prediction

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Inside ionic compounds 12/09/24
WALT: Define the terms ionic
bonding, ionic compound,
and giant ionic structure
KEYWORDS: ionic bonding

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Why do atoms form bonds?
Starter

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What is ionic bonding?
Compounds that contain ions are called ionic
compounds. These compounds are usually
formed by a reaction between a metal and a
non-metal.
Why do these substances react together and form bonds?
The metal and non-metal atoms have incomplete outer
electron shells and so are unstable.
Electrons are transferred from each metal atom to each
non-metal atom. The metal and the non-metal atoms form
ions with completely full outer shells and become stable.
The positive and negative ions are strongly attracted to each
other. This electrostatic attraction is called ionic bonding.

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How are ionic bonds formed?
Sodium chloride is an ionic compound formed by the reaction
between the metal sodium and the non-metal chlorine.
Sodium has 1 electron
in its outer shell.
Chlorine has 7 electrons
in its outer shell.
2.8.7 [2.8.8]
-
+
Cl Cl
-
2.8.1 [2.8]
+
Na Na
By losing this electron,
it has a filled outer shell
and forms a positive ion.
By gaining an electron
from sodium, it has a
filled outer shell and
forms a negative ion.

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How are ionic bonds formed?
The positive sodium ions and the negative chloride ions
are strongly attracted to each other.
-
Cl
It is this electrostatic attraction that forms ionic bonds in
sodium chloride and other ionic compounds.
Na
+

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Giant ionic structure
In an ionic compound, millions and millions of ions are
packed together in a regular cubic arrangement, joined by
ionic bonds.
The structure of the ionic
lattice affects the properties
of the ionic compound.
The giant ionic structure will
continue to build in this way
until there are no more ions
left to add.
This forms a giant 3D
structure called a
giant ionic structure.

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Why do ionic compounds form crystals?
Ionic compounds such as sodium chloride, form crystals, with
a cubic shape. This is due to the structure of the ionic lattice.
All ionic compounds form lattices and crystals when solid.

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Heating ionic compounds
Why are ionic compounds solid at room temperature and
have high melting points and boiling points?
Larger ionic charges produce stronger ionic bonds and so
much more heat is required to break the ionic bonds in
magnesium oxide than in sodium chloride.
sodium chloride
magnesium oxide
Compound
Ion
charges
Melting
point (
o
C)
Boiling
point (
o
C)
1
+
and 1
-
2
+
and 2
-
801 1,413
2,852 3,600
strong
ionic bonds
hold ions
together
Ionic bonds are strong and a
lot of heat is needed to break
them.

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How can ionic compounds conduct electricity?
When liquid (molten), the ions
can break free of the lattice
and are able to move. The ions
are charged particles and so
can carry an electric current.
As solids, ionic compounds
cannot conduct electricity
because their ions are
bonded together in the lattice.
ions in
solid state
cannot
move
ions in
molten state
can move
and conduct
electricity
Ionic compounds are usually soluble in water because water
molecules have a slight electrical charge and so can attract
the ions away from the lattice. When dissolved, the ions are
free to move and can carry an electric current.

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Why are ionic compounds brittle?
Ionic compounds are brittle – they shatter when they are hit.
When the lattice is hit, a layer
of ions is shifted so that ions
with the same charges are
lined up together.
These like charges repel
each other and so split
the ionic lattice causing
it to shatter.
repulsion
force
Ionic bonds are strong, so why does this happen?

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Classwork
1. Write the definitions for the terms ionic
bonding, ionic compound, and giant ionic
structure 3 marks
2. Explain these physical properties of an ionic
compound:
a.It has a high melting point
b.It is brittle
4 marks

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Do Now 25/09/23
Explain why some elements come
together to form ionic compounds

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Covalent bonding 25/09/23
WALT: Describe covalent
bond and draw dot –and-
cross diagrams
KEYWORDS: covalent bond

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What is a molecule?
Starter

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What is a covalent bond?
Non-metal elements usually just need one or two electrons
to fill their outer shells. So how do they form a bond?
The shared electrons join the atoms together. This is called
a covalent bond.
The two non-metal atoms cannot form a bond by transferring
electrons from one to another. Instead, they share electrons.
Each atom now
has a full, stable
outer shell.
incomplete
outer shells
Cl
Cl
Cl
Cl

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What are simple covalent structures?
Covalent molecules that contain only a few atoms are
called simple covalent structures.
weak bonds
between
molecules
strong bonds
within
molecules
Most substances that contain simple covalent molecules
have low melting and boiling points and are therefore liquids
or gases at room temperature, e.g. water, oxygen, carbon
dioxide, chlorine and hydrogen. Why?
The covalent bonds within these molecules are strong but
the bonds between molecules are weak and easy to break.

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Two common ways to represent a covalent bond are:
Only outer shells of electrons are involved in bonding, so the
inner shells do not always have to be included in diagrams.
A covalent bond consists of a shared pair of electrons.
covalent bond
Cl
simplified
dot and
cross
diagram
Cl
How is a covalent bond drawn?
Cl Cl

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Can compounds contain covalent bonds?
Covalent bonding can also occur between atoms of different
non-metals to create molecules of covalent compounds.
How is a covalent bond formed in hydrogen chloride (HCl)?
H Cl
H Cl
Hydrogen and chlorine both need one more electron to fill
outer shells. By sharing one electron each, they both have
a stable outer shell and a covalent bond is formed.

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How is the ratio of atoms calculated?
To calculate the ratio of atoms in a stable covalent compound:
For example, how
many nitrogen and
hydrogen atoms
bond together in an
ammonia molecule?
1. Work out how many electrons are needed by each
non-metal element to complete its outer electron shell.
2. Work out the ratio of atoms that will provide enough

shared electrons to fill all the outer shells.
N H
(2.5)(1)
3
electrons
needed
electron
configuration
ratio of
atoms
element
1
1 3

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H
Covalent bonding in methane
How do carbon and hydrogen atoms form covalent bonds
in a molecule of methane?
C H
(2.4)(1)
4
electrons
needed
electron
configuration
ratio of
atoms
element
1
1 4
H
H H
C

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Covalent bonding in carbon dioxide
How do carbon and oxygen atoms form covalent bonds in
a molecule of carbon dioxide?
C O
(2.4)(2.6)
4
electrons
needed
electron
configuration
ratio of
atoms
element
2
1 2
O OC
A double bond is when two pairs of electrons are shared.
In carbon dioxide there are two double bonds
– one between each oxygen atom and the carbon atom.

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Activity
A fluorine atom has 7 electrons in its
outer shell. Draw a diagram to show
the bonding in a fluorine molecule, F
2
.

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What are the properties of covalent compounds?
low melting and boiling points;
usually soft and brittle – they
shatter when hit.
The properties of a covalent compound, such as iodine, are:
Why do covalent compounds have these properties?
The weak forces of attraction between the molecules can
be broken by a small amount of energy. This means that
the molecular solids are soft and brittle and melt and boil at
low temperatures.
cannot conduct electricity.

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What are giant covalent structures?
In some substances, such as sand, diamond and graphite,
millions of atoms are joined together by covalent bonds.
All the bonds are covalent, so giant covalent structures have
very high melting and boiling points, and are usually hard.
The covalent bonds in these substances do not form
molecules but vast networks of atoms called giant covalent
structures.

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Diamond
Diamond is made only from carbon atoms. Draw the dot
and cross structure of diamond

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What are the properties of diamond?
In diamond, all the electrons in the outer shell of each
carbon atom (2.4) are involved in forming covalent bonds.
This affects the properties of this allotrope of carbon:
Diamond is very hard – the
hardest natural substance.
Diamond has a very high
melting and boiling point
– a lot of energy is needed
to break the covalent bonds.
Diamond cannot conduct
electricity – there are no
free electrons or ions to
carry a charge.

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Sand
Silicon(IV) oxide, which is also known as silicon dioxide,
SiO
2
, is what you lie on when you go to the beach. Not your
towel… sand!
The structure formed extends in all directions to make a
giant covalent macromolecule.

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Classwork
1. Explain why a substance with simple
molecules has a lower melting point than a
substance with a giant covalent structure.
2. Draw the dot and cross structure of
hydrogen sulfide, H
2S.
Next lesson: Giant metallic

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Metallic structures 28/09/23
WALT: Describe giant
metallic structures
KEYWORDS: delocalized

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Bonding in metals
The delocalized electrons
surround the positive metal ion.
A strong electrostatic force of
attraction is formed between
the positive metal ions and
negative delocalized electrons,
which act in all directions to
form a giant metallic lattice
.
Lithium (Li) is in Group I of the Periodic Table. Each atom
has only one electron in its outermost shell. The outermost
electrons from each lithium atom become delocalized, or
split away, from the atom. This leaves a positive lithium

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Properties of metals
As the metallic lattice is held together by strong
electrostatic forces of attraction, a lot of energy is needed
to separate the metal atoms to melt or boil the metal.
Therefore, metals have high melting points and boiling
points.
What conclusion can you draw from the table?
Melting and boiling point

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Properties of metals
The delocalized electrons in the metallic lattice are free to
move throughout the structure and so metals are good at
conducting electricity.
Electrical conductivity
Why is the electrical
conductivity of
magnesium higher than
the electrical
conductivity of lithium?

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Properties of metals
Metals are malleable because all the metal ions in the
metallic lattice are identical, and therefore the same size.
When a force is applied to the metal, the layers of the
metal ions, with their delocalized electrons, are able to
move and slide past the other layers. This prevents the
metal structure from breaking; instead, it bends
Malleability and ductility

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Classwork
1.Name the two types of particle in a giant
metallic structure, and the force that
holds these particles together.
2. Explain why most metals have high
melting points.
Next lesson: Test 2

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Do Now 09/10/23
Why is the electrical conductivity of Gold higher
than the electrical conductivity of aluminium?

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Life saving compounds 09/10/23
WALT: Describe an application
of science
KEYWORDS: ionic compounds,
covalent compounds

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Group these compounds under ionic and covalent
compounds
Starter

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Diarrhoea
Diarrhoea takes water out of
the body. It removes vital
ions, including sodium,
potassium, and chloride
ions.
If the water and ions are not
replaced, diarrhoea may
cause dehydration. Badly
dehydrated people may die.

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ORS
The sachet contains
oral rehydration salts
(ORS). There is a
mixture of these
substances:
• sodium chloride
• potassium chloride
• trisodium citrate
• glucose.
Group the substances under ionic and covalent
compounds

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What causes diarrhea

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When should you see a doctor

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How to stop diarrhea

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Classwork
Explain how ORS prevents
deaths from diarrhoea.
Next lesson: Recap of all lessons