1. Draw and label all the parts of the atom in the given drawing.

2. An Introduction to Atoms
Created by J. Smith, October 2012
electron
proton
neutron
electron cloud
An Introduction to Atoms
This presentation will provide a basic introduction to atoms. It will include things such as:
- why atoms are important in the world around us,
- the basic structure of an atom,
- what gives the atom its mass and size,
- the electrical charge of the atom and its various parts, etc.

3. Contents How are matter and atoms related? What are atoms made of?
What gives an atom its mass and size?
How do the electrons move?
What is the electrical charge of an atom?
What are the energy levels of an atom?
What is atomic theory and the current atomic model?
Review
We will start off by looking at how matter and atoms are related.
Created by J. Smith, October 2012

4. Why are atoms important?
Why should we care about atoms?
The air we breathe
The plants around us
The mountains
The “man-made” structures
Created by J. Smith, October 2012
Everything in this beautiful world is made up of matter.
What’s the big deal - why do we spend time learning about atoms and why are atoms so important?
Everything that exists in this world is made up of matter. The food you eat, the air we breathe, even your body is made up of matter. All the “stuff” around us is made up of matter.

5. Matter and atoms All the stuff around us is matter.
Aah! I get it! Everything is made of matter ... And atoms make up all matter!
Exactly! That is why atoms are so important! ... If we understand atoms, we can understand our world around us a bit better.
Created by J. Smith, October 2012
All the stuff around us is matter.
In science, matter is anything:
that has mass
takes up space (volume)
All matter on earth is made up of atoms.
All the “stuff” around us is made up of matter. Matter is anything that takes up space and has a mass.
But what makes up matter? Atoms! Which means everything around us is made up of atoms. Humans, water, air, trees, food - you name it - it’s made up of atoms. So, knowing about atoms is important, it helps us to understand our world a bit better.

6. Atoms ? An atom is the basic, or smallest, unit of matter.
So, what are atoms?
Huh ...?
If you found a piece of matter ... for example a piece of gold ... Au
Created by J. Smith, October 2012
if you kept breaking it down into smaller
you would eventually be left with a gold atom that you could not break down into anything smaller.
and smaller
and smaller bits
Atoms
An atom is the basic, or smallest, unit of matter.
Everything that exists is made up of atoms.
Atoms are the tiniest or smallest “building blocks” of everything around us. If you were able to break down anything that exists around us - and you kept breaking it into smaller and smaller bits - you would eventually be left with an atom that you couldn’t break down any further (under normal circumstances). The atom is the smallest (or most basic) building block (or unit) of matter.

7. Atoms - the smallest building blocks
What’s this stuff made of?
Don’t know ... but let’s break it down into its smallest part to find out.
But, I can’t see anything now!!!
Mmm! I think we can break it down further
Created by J. Smith, October 2012
Atoms are really, really tiny. It would take at least about two million atoms placed side by side to make a period or full-stop in a sentence on a piece of paper.

8. Contents What are atoms made of? How are matter and atoms related?
What gives an atom its mass and size?
How do the electrons move?
What is the electrical charge of an atom?
What are the energy levels of an atom?
What is atomic theory and the current atomic model?
Review
Let’s move onto the structure of atoms - or what atoms are made up of.
Created by J. Smith, October 2012

9. What are atoms made of? and An atom is made up of: an electron cloud
nucleus
electron
proton
neutron
Created by J. Smith, October 2012
An atom is made up of:
an electron cloud
a nucleus
What is an atom made up of? An atom is made up of an outer electron cloud and a nucleus. This nucleus of the atom is not to be confused with the nucleus found in a living cell. While a cell’s nucleus contains DNA material, the nucleus of an atom contains proton and neutrons.

10. The atom’s subatomic particles
and
electron (e-)
protons
neutrons
Created by J. Smith, October 2012
The electrons are found in the electron cloud.
The nucleus contains:
the protons
the neutrons
Atoms are extremely small. But, there are even tinier particles inside the atom - called subatomic particles. The subatomic particles include the electrons, protons and neutrons. There are also some other “things” that make up subatomic particles, but we will get to those later. In an atom, the electrons “swarm” in a cloud around the small nucleus. The nucleus is made up of neutrons and protons.

11. The nucleus
protons
neutrons
nucleus
The proton have a positive electrical charge (+1 or 1+).
The neutrons have no charge, they’re neutral.
Created by J. Smith, October 2012
The centre of the atom, or the nucleus, is relatively densely packed - with protons and neutrons clustered (or squashed) together.
Each proton has a positive electrical charge of one (shown as 1+ or +1).
The neutrons are neutral and have no charge.
Usually (but not always) there are the same number of protons as there are neutrons in the nucleus of an atom.
(Notes to teacher: Isotopes will be covered in another presentation. There are also other smaller particles within the protons and neutrons but these are not covered in this presentation and will be covered in another presentation.)

12. Contents What gives an atom its mass and size?
How are matter and atoms related?
What are atoms made of?
What gives an atom its mass and size?
How do the electrons move?
What is the electrical charge of an atom?
What are the energy levels of an atom?
What is atomic theory and the current atomic model?
Review
What do you think would give an atom its mass?
What would give and atom its size?
Clue: it’s something that you find inside the atom (and there are different parts that give an atom its mass versus those that give the atom its size).
Created by J. Smith, October 2012

13. The mass of an atom
Most (> 99%) of the mass of an atom is in the dense nucleus (i.e. protons + neutrons).
A proton has a mass of about times greater than the mass of an electron.
An electron is so so tiny, it hardly has any mass.
It makes up less than 0.06% of the total mass of an atom.
Created by J. Smith, October 2012
If you thought an atom was tiny, an electron is much, much smaller than an atom ... it is minuscule. An electron has hardly any mass. A proton has a mass that is about 1800 times larger than an electron’s mass. Electrons make up less than 0.06% of the total mass of an atom.

14. The size of an atom p n e-
The atom is at least 10,000 times bigger than the nucleus
The atom is at least 100,000 times bigger than a proton
The atom is at least 100,000,000 times bigger than an electron
The nucleus of the atom is much, much much smaller than the total size of the atom.
It is the cloud of electrons around the nucleus that gives the atom its size .
Wow! so, most of the atom is in fact made up of empty space!
Created by J. Smith & Jem O’, October 2012
While the protons and neutrons in the nucleus make up most of the mass of the atom, when it comes to the size of an atom it is the electron that is largely responsible for the size of an atom.
Whilst the electrons are extremely small compared to the protons and neutrons in the atom, the space that the electrons and the electron cloud occupy is huge - relative to the nucleus of the atom. So, most of the atom is taken up by the electron cloud, which consist of tiny, tiny electrons whizzing about in space - therefore an atom is mostly empty space - and so, most of matter is empty space
The size of the atom is at least 10,000 times larger than the nucleus of the atom!
It’s where the electrons whizz about in space.

15. pea (represents the nucleus)
The atom’s size
pea (represents the nucleus) .
speck of dust (represents the electron)
larger than a full sized sports field (represents the size of the atom)
Created by J. Smith, October 2012
To get a feel for the size of the nucleus in relation to the size of the atom: if a pea represented the nucleus of an atom, the size of an electron would be smaller than a speck of dust ... however, the size of the total atom would be larger than the full size of a major sports stadium. What makes up this extra space is the electron cloud (i.e. the space in which the electrons whizz about in the atom).

16. Mass versus size of an atom
protons
neutrons
nucleus
electron cloud
So, the nucleus makes up the mass of the atom.
But, it is the electron cloud that makes up the size of an atom!
Created by J. Smith & Jem O’, October 2012
To recap, it is the nucleus which makes up the mass of the atom. Remember the nucleus is made up of protons and neutrons.
It is the electron cloud that makes up the size of the atom.

17. Contents How do the electrons move? How are matter and atoms related?
What are atoms made of?
What gives an atom its mass and size?
How do the electrons move?
What is the electrical charge of an atom?
What are the energy levels of an atom?
What is atomic theory and the current atomic model?
Review
Let’s look at how the electrons move around in the atom.
Created by J. Smith, October 2012

18. So, what creates the electron cloud?
electron (e-) e-
movement of the electron around the nucleus
So, what creates the electron cloud?
The electrons (e- ) have a negative electrical charge (-1 or 1-).
It’s the electrons that are zooming around ... really, really fast ... in the space outside the nucleus that make up the electron cloud
Created by J. Smith & Jem O’, October 2012
Electrons are found in the electron cloud around the nucleus of an atom.
The electrons are negatively charged (i.e. have a negative electrical charge). An electron is considered to have a charge of -1 or 1-.
The electrons move at high speeds in the electron clouds.

19. The movement of electrons
Electrons whizz around so quickly! They can zoom about at speeds similar to the speed of light!
electron orbit
electron (e-)
electron cloud
Yes, but electrons don’t move in orbits around the nucleus, but in a complex pattern that forms the electron cloud.
old model
new model
Created by J. Smith & Jem O’, October 2012
Electrons can move at speeds similar to the speed of light (i.e. 186,000 miles per second, or 299,339 km per second).
The electron does not move around the nucleus in orbits, like the planets move around the Sun. At one time, people believed this was the way the electrons moved. The movement of the electron around the nucleus appears to be more chaotic, however there is a complex pattern in which the electron moves. There are regions around the nucleus in which there are higher probabilities that electrons will be found. This high-energy region of electrons looks a bit like clouds or clusters of electrons. The electron cloud term is used by scientists to describe the pattern formed by the electrons in their movement around the nucleus. The path an electron travels is not the same each time they go past the nucleus.
Each electron has a negative charge. Electrons circle the nucleus billions of times per second. As the electron circle the nucleus, they also spin (a bit like the way the earth spins around its imaginary axis as it circles the sun). (Note to teacher: We will go into further details on the electron spin in another presentation.)

20. Contents What is the electrical charge of an atom?
How are matter and atoms related?
What are atoms made of?
What gives an atom its mass and size?
How do the electrons move?
What is the electrical charge of an atom?
What are the energy levels of an atom?
What is atomic theory and the current atomic model?
Review
We have looked at the electrical charges of the different parts of the atom. Now we will look at the overall electrical charge of an atom. We will also look at:
- the forces of attraction and repulsion of these charged particles in an atom and
- what stops the nucleus from blowing apart and
- what stops the electrons from spinning off the atom and whizzing away from it.
Created by J. Smith, October 2012

21. Electrical charge of the atom
The proton (p+) have a positive electrical charge (+1 or 1+).
The neutrons (n0) have no charge - they’re neutral.
The electrons (e-) have a negative electrical charge (-1 or 1-). - +
If an atom has the same number of electrons as it does protons there is no electric charge overall for the atom. The number of negative electrons balances the number of positive protons.
4p+ + 4e- + 4no = 0 4
= 0
Created by J. Smith, October 2012
positively charged protons in nucleus
negatively charged electrons in electron cloud
no charge or neutral neutrons in nucleus
An atom that has the same number of electrons and the same number of protons is balanced in terms of electrical charge and overall the atom has no electrical charge. So for example, an atom that has 1 negative electron and 1 postive proton (and of course 1 neutral neutron) has no overall positive or negative charge as the +1 and -1 balance each other out to 0. Similarly, an atom with 4 electrons, 4 protons an 4 neutrons also, overall, is neutral (i.e. 4 + (-4) + 0 = 0) and has neither an overall positive or negative for the atom as a whole.
It is possible for an atom to either lose or gain an electron and then the atom will have either a positive or negative overall charge. (Note to teacher: We will go into further details on this concept in another presentation.)

22. What stops the nucleus from blowing apart?
I know that like charges will repel like charges. So, if there are 2 positive protons in the nucleus why don’t they repel each other and split the atom apart?
forces of repulsion +
Well ... normally the protons don’t fly apart - even though they repel each other - that’s because there’s a strong “nuclear glue” type of strong force in the nucleus that holds them together. So the protons are usually crammed together in the nucleus, together with the neutrons.
forces of “nuclear glue”
(strong force ... gluon)
Created by J. Smith & Jem O’, October 2012
Each proton has a positive electric charge of 1. OK, so maybe you’re thinking if there is a nucleus with say 2 protons and 2 neutrons - the overall charge of the nucleus will be positive ... a charge of 2+ (even though the two negative electrons are spinning in the electron cloud will balance the overall charge of the atom out to neutral). But, what about those positive protons squeezed close together in the nucleus? You know that like electrical charges will repel each other - so why doesn’t the nucleus split apart when the two positively charged protons get too close to each other and repel each other?
The nucleus doesn’t blow apart, because of a very strong force within the protons and neutrons that act like a type of “nuclear glue”, called gluon. (Note to teacher: This is to do with quarks and this will be covered in more detail in another presentation).

23. What stops the electrons from spinning off the atom?
Created by J. Smith, October 2012 ?
OK, but what about the electrons? I mean, the electrons are moving almost at the speed of light. So, what stops the electrons from whizzing off, away from the atom? n - +
Aha! The forces of attraction between the electrons and the protons in the atom stop that. Remember, opposite charges attract. So, the negatively charged electrons are attracted to the positively charged protons.
forces of attraction
The electrons move extremely fast in the electron cloud. They whizz around at speeds approaching the speed of light. Why do the electrons stay in the atom in the electron cloud and not whizz off the atom and continue travelling away from the atom at the speed of light? The answer again lies in the electric charge!
The protons (in the nucleus of the atom) which are positively charged and the electrons (in the electron cloud of the atom) which are negatively charged are attracted towards each other ... due to their opposite charge. Remember, that opposite electrical charges attract!
Why do the different negative electrons in the atom not repel each other. Well, they probably do ... but, remember the proton is so much larger than the electron, that the forces of attraction of the positive proton towards the negative electron will be much greater than the forces of repulsion between two negative electrons due to the size of the proton.

24. Contents What are the energy levels of an atom?
How are matter and atoms related?
What are atoms made of?
What gives an atom its mass and size?
How do the electrons move?
What is the electrical charge of an atom?
What are the energy levels of an atom?
What is atomic theory and the current atomic model?
Review
We are going to look at the energy levels of an atom. This will be important to understand as future lessons, especially chemical interactions, will build on this.
Created by J. Smith, October 2012

25. The electron’s energy
Created by J. Smith, October 2012
Scientists have a theory that electrons with the same energy share the same energy levels in the atom. These energy levels are often called shells.
Those electrons that are further away from the nucleus have more energy.
Electrons can have different amounts of energy in an atom.
Electrons closer to the nucleus have less energy.
electron
nucleus
electron shell
energy shells
Different electrons in the atom can have different amounts of energy. Those electrons with a lot of energy tend to be further away from the nucleus. They will need more energy to withstand the opposite forces of attraction of the protons in the nucleus. Those electrons closer to the nucleus will have lower energy levels. Some electrons in an atom have similar amounts of energy. A model or diagram that scientists use for explaining the electrons energy is called the shell model. Electrons are arranged in the atom around the nucleus in different energy levels (or energy shells). Electrons with the same energy levels are found in the same shell.

26. Created by J. Smith & Jem O’, October 2012
Each shell in the atom contains a certain number of electrons.
1st energy shell (K-shell)
energy shell
1st energy shell (also known as K-shell)
can contain a maximum of 2 electrons
2nd energy shell (L-shell)
3rd energy shell (M-shell)
2nd energy shell (also known as L-shell)
can contain a maximum of 8 electrons
3rd energy shell (also known as M-shell)
can contain a maximum of 18 electrons ?
Huh! Shell ??
The atom’s shells
According to the current theory, only a certain number of electrons can be in each energy level or energy shell at the same time. The first energy shell can only take a maximum of 2 electrons. The second shell can accommodate up to 8 electrons, and the third shell can take up to 18 electrons, etc.
In theory, the shell closest to the nucleus has to be filled first before the electrons can appear in the next energy level. Once the 1st shell is full with electrons, then electrons start to fill the 2nd energy level. Once the 2nd energy level is filled, the electrons start to fill the 3rd energy level, etc. ... Some energy shells can take up to 32 electrons!
(Note to teacher: there are also sub-shells, but this is not covered in this presentation).

27. The atom’s shells Hydrogen (1 electron) Carbon (6 electrons) Sodium
Created by J. Smith & Jem O’, October 2012
Hydrogen
(1 electron)
Carbon
(6 electrons)
Sodium
(11 electrons)
Different types of atoms have a different number of electrons whizzing about in the shells around the nucleus
Depending on the type atom, there will be a different amount of electrons in the energy shell levels, for example:
- a hydrogen atom only has 1 electron, so there will only be 1 electron in its 1st energy shell
- a carbon atom has 6 electrons, so there will be 2 electrons in its 1st energy shell + 4 electrons in its 2nd energy shell.
- a sodium atom has 11 electrons, so there will be 2 electrons in its 1st energy shell + 8 electrons in its 2nd energy shell + 1 electron in its 3rd energy level
This is important as the number of electrons in a shell in an atom will affect the way the atom will interact with other atoms. An atom with full shell is less likely to interact with other atoms than an atom with unfilled shells. This will be covered in more detail in another presentation relating to chemical interactions.
Electrons are very important, they are key players in the chemical bonding process and of course, an essential component of electricity. (Note to teacher: chemical bonding is covered in another presentation).

28. Contents What is atomic theory and the current atomic model?
How are matter and atoms related?
What are atoms made of?
What gives an atom its mass and size?
How do the electrons move?
What is the electrical charge of an atom?
What are the energy levels of an atom?
What is atomic theory and the current atomic model?
Review
We will look at atomic theory and the current atomic model to see how our understanding of the atom has developed over the centuries to our current or standard atomic model (this is the model that scientists use nowadays to explain what the structure of the atom is and how atoms work or interact with other things.)
Created by J. Smith, October 2012

29. Atomic theory and models
Created by J. Smith & Jem O’, October 2012
± BC
1808
1897
1904
1911
1913
1920’s
1932
2012
Democritus Ancient Greeks
(couldn’t be divided further)
Dalton Billiard ball Model
Thomson
Plum pudding model
(electrons)
Nagaoka Saturn’s rings
(electrons revolve around positive central sphere)
Rutherford (Confirmed nucleus + protons + random electron orbits)
Bohr (electrons in shells)
Electron cloud
(electrons in electron cloud around nucleus)
Chadwick (neutrons)
Present Modern Model (quantum cloud - probability of electrons in could around nucleus) - + n
The atomic model has evolved over the years and scientists have built on previous theories.
The theory about the structure of an atom has developed over hundreds of years. This theory has been revised and changed as more evidence has been collected. Various models were used to help explain the theories of the atom’s structure.
1) Early Greek Theory:
Around 2,500 years ago, Democritus (an ancient Greek philosophers) was the first to use the term ‘atom’. He thought that matter could be keep on being divided until it was so tiny, it could no longer be divided and he called this tiny particle the atom. (The word atom comes from the ancient Greek word ‘atomos’, which means uncuttable or indivisible ... i.e. cannot be divided or broken down any further.)
2)Dalton’s model (the ‘billiard ball model’)
Around 1808, a British chemist called John Dalton thought atoms were tiny, smooth, solid ball (similar to a hard billiard ball - but minuscule). Through experiments, he also proposed that:
- all matter is made of atom
- atoms of the same element are identical
- different atoms of different elements have different masses, etc
3) Thomson model (the ‘plum pudding’ model)
Around 1900, the British scientist J J Thomson, through experiments proposed that there were smaller parts inside atoms. He ‘discovered’ the electron. He found that atoms contained negatively charged particles that were held in a positively charged framework or sphere of the atom. He thought the electrons were embedded or scattered in the positive sphere or ball of the atom (a bit like raisins are scattered through a christmas pudding / plum pudding, or blueberries are scattered through a muffin).
4) Nagaoka Model
In 1904, Hantaro Nagaoka who was a Japanese physicists, proposed the atom had a massive positive sphere in the centre of the atom and that the electrons revolved around the positive central sphere bound by electrostatic forces (a bit like the way Saturn’s rings move around the planet Saturn due to gravitational forces).
5)The Rutherford model
In 1911, Ernest Rutherford a New Zealand-born British chemist and physicist, confirmed through his experiments that there was a positively charged nucleus in the centre of the atom and that most of the mass was located in the centre of the nucleus. However he did not agree with the charged rings in Nagaoka's model but though that the electrons orbited randomly around the nucleus. He also proposed that most of the atom was made up of empty space. Later, Rutherford called the positively charged parts in the atom’s nucleus protons.
6) Bohr model
In 1913, a Danish physicist called Niels Bohr found electrons only have a certain amount of energy and suggested that electrons didn’t move about randomly, but that the electrons orbited the nucleus of an atom in specific layers or shells (like planets orbiting the sun - or like layers of an onion). He proposed that electrons could move from one shell to another and when they did this, the atom would either absorb or give off energy.
7) The electron cloud
In the 1920’s, scientists proposed that electrons do not move in orbits around the nucleus ... instead they move in a cloud like region around the nucleus.The movement of electrons is related to its energy level, so those electrons with higher energy will be more loosely held by the nucleus than those with lower energy levels.
8)Chadwick model
In 1932, James Chadwick (a British physicist) discovered the existence of neutrons, which helped to explain why the total mass of an atom was heavier than just the protons plus the electrons.
9) Current Model / The present modern model
Currently we use the cloud model and Chadwick’s discovery of the neutron to describe the model of the atom, with:
- a nucleus in the centre containing protons and neutrons
- electrons to be found in a cloud around the nucleus, with the probability of the electron to be found in a certain area (of the cloud around the nucleus) depending on the energy level of the electron.

30. Contents Review How are matter and atoms related?
What are atoms made of?
What gives an atom its mass and size?
How do the electrons move?
What is the electrical charge of an atom?
What are the energy levels of an atom?
What is atomic theory and the current atomic model?
Review
Finally, we will have a quick review - to recap on the main points that have been covered in this presentation.
Created by J. Smith, October 2012

31. Review Yikes! I don’t know if I can remember all of this!
Created by J. Smith & Jem O’, October 2012
Yikes!
I don’t know if I can remember all of this!
Its easy! You just need to remember :
Everything in this world is made up of atoms.
Electrons
Protons
Neutrons
The electron cloud
The nucleus
Atoms are made up of:
containing
have an electrical charge of -1
have an electrical charge of +1
have zero electrical charge (0)
creates the size of the atom
creates the mass of the atom - + n
Review
You have learnt that:
- Everything in this world is made up of matter .... and all matter is made up of atoms .... therefore everything in earth is made up of atoms.
- Atoms are made up of three main subatomic particles:
1. the electrons (which spin and whizz around the nucleus in an electron cloud)
2. protons (found in the nucleus)
3. neutrons (found in the nucleus)
- The electrical charge of an atom depends on the balance of the subatomic particles:
- the electrons have a change of -1
- the protons have a charge of + 1
- the neutrons are neutral and have zero charge
- if the number of protons and electrons in an atom are equal (balanced) there is no overall charge in the atom.
- if an atom loses an electron - the atom will become positively charged, or if it gains electrons the atom will become negatively charged
- Electrons are extremely tiny and travel so quickly (almost at the speed of light). They move around in the electron cloud in different energy levels.
- The protons have a mass of almost 1800 times more than the electrons
- The electrons zooming around in the electron cloud are responsible for creating the size of the atom
- The protons + neutrons in the nucleus of the atom are responsible for creating the mass of the atom
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