3 atomic structure pupils
TRANSCRIPT
OK, we know that all stuff is made up of the 92 naturally occurring _____________
BUT what does each of these elements consist of? _____________________
Atomic Structure
Protons
Electrons
Neutrons
So, what are atoms made up of?
ProtonsThese are found at the centre or NUCLEUS of the atom (so they are nucleons)
Electrons Are found at different distances around the nucleus
NeutronsAre also found in the nucleus of the atom (and are also nucleons)
These are the simplest SUBATOMIC particles.
+-
The simple model of a hydrogen atom was proposed in 1913 by Niels Bohr.
Things get more complicated with bigger atoms - which element is this an atom of?
Extra: Investigate the life and work of this extremely influential physicist
Definitions:
The PROTON NUMBER (AKA: Atomic Number) is the
___________________________________________________________
The proton number tells us which element the atom belongs to.
The NUCLEON NUMBER (AKA: Mass number) is the
__________________________________________________________
Sub-Atomic Particle Relative Mass Charge Discovery
Proton 1909 - Rutherford
Electron 1897 - JJ Thompson
Neutron1920 Rutherford suggests its existence/1932 James Chadwick discovers it
Discovery of the electronhttps://www.youtube.com/watch?v=Rb6MguN0Uj4
Discovery of the Nucleushttps://www.youtube.com/watch?v=dNp-vP17asI
Videos: Basic Atomic Structure
Relative masses and charges of the simplest subatomic particles….
1 +1
-11/1836Approx 0
1 0
Write the symbols for the following elements….
Sodium
Using symbols….
IMPORTANT: By definition, an ATOM is always neutral so it must have the same number of
_________________________ and __________________________
Video: Atomic Number
Read pp22-23 Q1-3
Na1123
Helium
Calcium
Why is Chlorine different from the rest of the elements in your periodic table?
Is reality, Chlorine exists as 2 different atoms….
ISOTOPES
NB1. Isotopes of an element have the same chemical properties because chemical properties only depend on the number of electrons that an atom has!
NB2. The physical properties of isotopes can be different, eg. density,.
Explain why…
_____________________________________________________________
______________________________________________________________
Learn this definition: ISOTOPES of an element are atoms with the same proton number (same number of protons) and different nucleon numbers (different numbers of neutrons).
ISOTOPES can be 2 types: radioactive and non-radioactive
Radioactive isotopes are UNSTABLE and spontaneously break up to give other particles and radiation (which can be high energy and dangerous).
Non-radioactive isotopes are STABLE (they do not change over time).
Radioactive isotopes have very interesting properties and some important uses and applications:
USES of Radioactive Isotopes
Medical uses: To treat cancer - “radiotherapy”
Watch video: Isotopes in MedicineHow are tracers used?
Non-medical uses
- To find leaks in pipes- To kill germs and bacteria in food- Carbon dating- Fuel in nuclear power stations (U-235)
Read pp24-25 Q1-3
Where do the electrons go in the atom?
Electrons go into “shells” or “energy levels” around the nucleus.
Each shell can take a maximum number of electrons, as shown in the following table:
Shell * How many electrons fit?
1 2
2 8
3 18
4 32
*This is the same as the PERIOD in the periodic table (the number down the left hand side or the number of the ROW that the element is in).
At IGCSE level, we only have to be able to say where the electrons are for the first 20 elements.
This is called the ELECTRONIC CONFIGURATION
12
2,1 2,8
2,8,1 2,8,8
2,8,8,1 2,8,8,2
2,2 2,3 Etc
2,8,2 2,8,3 Etc
NB1. The noble gases have a FULL OUTER SHELL of electrons and this makes them very STABLE and very UNREACTIVE.
This is a important point!
Name all of the noble gases
NB2. The electrons in the outer shell are called VALENCY ELECTRONS
You can easily see how many valency electrons an atom of an element has by looking at its GROUP NUMBER - the number at the top of the periodic table.
Element Symbol # of Protons
# of Electrons
# of Neutrons
Electronic configuration
Consider the following table:
Read pp26-27 Q1-3Video: Basic Atomic Structure Revision
Hydrogen H 1 101
Lithium Li 3 3 4 2,1
Potassium K 19 19 20 2,8,8,1
Read pp28-29Definition: What is an ELEMENT?
Elements, Compounds and Mixtures
What are CHEMICAL BONDS?
Put the following substances into the correct column in the table.
Write their chemical formula if you know it…
HydrogenWaterCola Cao (or Nesquik as you prefer. Sobre los gustos…)BromineAirSodium ChlorideAmmoniaCrude OilPetrol (Octane)UraniumCarbon dioxideNitrogenBleachChlorineBrass
ELEMENT COMPOUND MIXTURE
HydrogenBromineUraniumNitrogenChlorine
WaterSodium ChlorideAmmoniaPetrol (Octane)Carbon dioxide
Cola CaoAirCrude OilBleachBrass
Metals Non-Metals
Examples
Physical Properties
Chemical Properties
Metals and Non-MetalsRead pp30-31 and compare and contrast the properties of metals and non-metals in the following table…
pp31-32 Q1-3/Questions pp32-33
- What holds stuff together
Atoms usually form bonds with each other to become STABLE.
There are exceptions to this in the periodic table.
Bonding
Which group of elements are already very stable?
SO,…..when atoms take part in chemical reactions they do so in order to try to achieve the
NOBLE GAS ELECTRONIC CONFIGURATION (NGEC)
Why?
When chemicals react, new BONDS are formed between the particles involved.
There are 3 types of bonding that we will come across:
• Ionic Bonding• Covalent Bonding• Metallic Bonding
IONIC BONDING
Ionic compounds form when metals (left hand side of periodic table) react with non-metals (right hand side of the periodic table).
eg. Sodium and Chlorine
What must Sodium do in order to achieve a stable NGEC?
A SODIUM ION is formed
NB. An ION is charged particle
What must Chlorine do to achieve a NGEC?
A CHLORIDE ION is formed
NB. When a non metal element forms a simple ion, it adopts the ending “ide”
So the electron from the Sodium atom is TRANSFERRED to the Chlorine atom
Once the oppositely charged ions have formed, what do they do?
NB: These diagrams are called “dot and cross diagrams” for obvious reasons. The use of dots and crosses is helpful to show where the electrons came from and where they have gone.
This is called a crystal…..
Once lots of ions are formed, they come together to form a giant 3D structure…
Now let’s do the same with another Group 1 and another Group 7 element
pp34-35 Q1-3
Tricky example: Magnesium and Chlorine
Lithium Fluoride, LiF is formed
Magnesium Chloride, MgCl2 is formed
NB. In most cases you only need to show the outer shell of electrons - the valency shell - when you form ionic compounds
IGCSE QUESTION:
The full diagram would look like this
But only outer shell electrons are required to get the marks
Key ideas:
• Ions form when atoms lose or gain electrons to get a stable NGEC
•Once the ions have formed the opposite charges attract to form an IONIC BOND
•This causes the ions to line up to form a LATTICE of alternating positive and negative charges
•Ionic bonds form between METAL IONS AND NON-METAL IONS
Once you can predict which ions will be formed by atoms of an element, you can use the information to work out the CHEMICAL FORMULAE of IONIC COMPOUNDS
In the following empty periodic table, fill in the ions formed by the elements…
H+
Na+ Cl-
O2-Al3+
Ba2+
P3-
Pb2+
Sn2+
Zn2+
Ag+
Cu2+Cu+Fe2+
Fe3+
1
2 3 4 5 6 7
0
Try to predict the chemical formulae of the following:
1.Lithium Chloride
2.Sodium Bromide
3.Calcium Chloride
4.Potassium Oxide
5.Aluminium Fluoride
6.Aluminium Oxide
The next type of bonding that exists in chemical elements and compounds is…
COVALENT BONDING In this type of bonding, atoms SHARE electrons with each other in order to achieve something closer to a NGEC
Hydrogen molecules Chlorine Molecules
Definition: The VALENCY of an atom is the number of electrons that must be lost or gained in order to achieve a NGEC
EtheneEthanol
Task - memorise the structures of the above molecules so that you can identify them in this online quiz
Carbon DioxideMethanol
Structure and properties of IONIC and COVALENT COMPOUNDS
We need to know the differences between ionic and covalent (sometimes called “molecular”) substances…
Property IONIC COMPOUNDSCOVALENT
COMPOUNDS
Solubility in polar solvents (eg. water) High Low
Solubility in non-polar (organic) solvents (eg. cyclohexane)
Low High
Volatility - is it volatile? (does it easily evaporate?)
Low High
Electrical conductivity when solid Low Low
Electrical conductivity when liquid or in solution High Low
Melting and boiling points High Low
Can we explain the differences in melting and boiling points of IONIC and COVALENT compounds?
A lot of energy is required to break down the strong ionic bonds in the giant 3D lattice so ionic compounds have a high melting point
Only weak intermolecular forces exist between covalent molecules so little energy is needed to melt and boil them!
GRAPHITE DIAMOND SILICON DIOXIDEDescription: Description: Description:
Properties: Properties: Properties:
Uses: Uses: Uses:
pp42-43 Q1-3
Black shiny solid Layers of Carbon atoms Each C atom joined to 3 others Hexagons formed
Transparent colourless crystals Each C atom joined to 4 others A tetrahedral structure formed A 3D giant lattice created
Similar to diamond Tetrahedral structure Each Si atom joined to 4 O atoms Each O atom joined to 2 Si atoms 3D giant lattice created
High mpt and bpt Conducts electricity Layers can slide over each other
High mpt and bpt Very hard
High mpt and bpt Hard
Dry lubricant(locks) Pencil “lead” Motors and generators
Cutting an drilling tools Jewellery
Glass manufacture
The last type of bonding that we need to look at, and is perhaps the most special is…
Metallic BondingEach metal atom donates its valency electrons to form a DELOCALISED SEA OF ELECTRONS.
This sea of mobile electrons flows around a LATTICE OF POSITIVELY CHARGED METAL IONS.
NB. It is the attraction between the lattice of metal ions and the sea of electrons that holds the metal together - this is Metallic Bonding, and acts in all directions
We can use these ideas to explain the curious and wonderful properties that metals have.
They conduct electricity because…
They conduct heat because….
pp44-45 Q1-3 End of chapter questions
They are malleable and ductile because…
Other properties…Many metals have high melting and boiling points as lots of energy is required to overcome the metallic bonding.
Many are also hard and dense
The layers of ions can slide over each other and adopt new shapes. This is possible because the metallic bonding acts in all directions so is not broken as the lattice changes shape.