Atoms

Elements, Molecules, Compounds, Mixtures

How Atoms are made

1.The Structure of the Atom

Below is a picture of the Calcium Atom

Below is another diagram

If we look we can see that these diagrams are actually very similar. They have a clump of balls in the middle, then smaller ones in orbits around the middle.

Count the number of balls in each of the rings in each of the diagrams. Is there a pattern?

The clump of balls is called the Nucleus

The balls in the orbits are called Electrons

The balls in the middle are of two types, as shown with their different colours

The red ones represent Protons. The blue ones are neutrons

So, the nucleus consists of Protons and Neutrons

The electrons squeeze into the orbits, with the first orbit being so small and close to the nucleus that it can only hold 2 electrons. All the other orbits can hold 8.

Electrons fill up the orbits starting with the one closest to the nucleus. Once that has 2, then the electrons go into the next orbit, until it is full. So, once that orbit has 8 electrons, the left over electrons will go into the next orbit, until it is full. Filling up each orbit until it is full, before filling up the next.

The number of electrons in each orbit is called the electron configuration

So if we have 7 electrons, then 2 electrons will go into the first orbit, leaving 5 for the next orbit. The electron configuration will be: 2, 5

If we have 16 electrons, then 2 will go into the first orbit, 8 will go into the next orbit, leaving 6 for the final orbit. The electron configuration will be 2, 8, 6

Calcium has 20 electrons, so it will have (you can check in the diagrams above) 2 electrons in the first orbit, 8 in the next, 8 in the following, then just 2 in the last. Giving Calcium an electron configuration of 2, 8, 8, 2

Hydrogen has 1 Electron, so its Electron Configuration will be: 1

Helium has 2, so its EC will be: 2

Oxygen has 8, its EC will be: 2, 6

If we look into the middle of the Calcium atom model, we will see the red balls. If we can count them we will find that there is 20 of them. These 20 balls are called Protons (they are not really colored red, they just are for the model so you can tell them apart form the other ones)

The number of protons determines what atom it is. If you add an extra proton then it is no longer Calcium, rather it becomes Scandium.

If we remove a proton, then it is no longer Calcium, rather it becomes Potassium.

Because the number of Protons determines the type of Atom it is, we call this number the Atomic Number. Each atom has its own Atomic Number depending on how many Protons it has. Oxygen has an Atomic Number of 8, this is because it has 8 Protons.

So if an atom has 1 proton, then it is given the Atomic number 1. If it has 2 protons, then it has the atomic number 2.

The atom with 1 proton and the Atomic number 1 is called Hydrogen.

The atom with 2 protons and the atomic number 2 is called Helium

Protons have a positive charge. Sometimes you will see them with the symbol +.

To keep them balanced, there is a negative charged thing called the Electron

Electrons sometimes have a negative symbol - in diagrams

For the Atom to have no charge overall, that is, no positive or negative, then the number of negatives must equal the number of positives

So, for Hydrogen with its atomic number 1 and its 1 positive proton, then it needs 1 negative electron

For Helium, atomic number 2, which means 2 positive protons, so it needs 2 negative electrons

For Oxygen, atomic number 8, which means 8 protons, it needs 8 electrons

For Calcium, and you can check in the diagrams above. It looks to me like Calcium has the Electron configuration of 2, 8, 8, 2. This adds up to 20 Electrons. This means it must have 20 Protons and thus it must also have an Atomic Number of 20

You'd have noticed in the diagrams above, that there was another type of ball in the middle of the Calcium atom. These are Neutrons. These Neutrons have No charge, that is they are Neutral. Neutrons are Neutral. So, sometimes in diagrams they will have a 0 in them, to indicate that they are not positive or negative, rather they have 0 charge.

The Neutrons plus the Protons make up everything that is in the middle of the Atom

The middle of the atom is known as the Nucleus (meaning center)

So, the Neutrons + Protons are the Nucleus.

The number of things in the Middle of the atom is given the name Mass Number

So, the Mass number is the number of things in the Middle.

Of the things in the middle, one of them is the Protons. We know the number of protons due to the Atomic number. So if we have the Mass number and we subtract the Atomic number, then what is left is the number of Neutrons.

Neutrons = Mass number - Atomic number

Hydrogen has an Atomic number 1, and Mass number 1. So, it has 0 Neutrons

Helium has an Atomic number 2, and a Mass number 4. So, it has: 4-2=2. 2 Neutrons

Neutrons keep the nucleus stable. An atom can have more Neutrons or less Neutrons, this is why the mass number is usually not a whole number. These Atoms that have a different number of Neutrons than normal are called "Isotopes"

2. Atom Number and Mass Number

Understand and use the mass number and atomic number of an element

Atomic Number = Number of Protons

Atomic Number = Number of Electrons in a neutral Atom

Mass Number = Number of things in the Middle

Mass Number = Number of Protons + Number of Neutrons

Mass Number = Atomic Number + Number of Neutrons

Number of Neutrons = Mass Number - Atomic Number

Sodium is a very good one to practice with.

You'll notice that the 2 diagrams above have the 11 in 2 different positions. This is because one is American and one is European. But it doesn't matter

What matters is that you know that the Big number, the Massive number is the Mass number. Sometimes this is not a whole number, due to 'Isotopes', but you can round the number to the nearest whole number

You'll also note that the small number, the tiny number, the atomically small number is the Atomic Number. This is always a whole number

From these two numbers, the Atomic number and the Mass number, you can work out all of the subatomic particles that the sodium atom has

It has an tiny Atomic Number of 11. So it will have 11 Protons. It will thus also have 11 Electrons

The massive Mass Number is all of the things in the middle. Only Protons (of which there is 11) and Neutrons are in the middle. So, we can round the 22.99 to 23. Then we can go 23 - 11 = 12. Thus, there are 12 Protons.

We can also figure out the Electron Configuration, as we know that we need to fill up each orbit before going to the next. And we know that the first orbit can only hold 2 electrons, whilst the rest hold 8. So, there are 11 Electrons (atomic number 11). So, 2 in the first orbit, 8 in the next, that leaves 1 for the last. Thus, the electron configuration

We can summarize as follows

Na = Sodium

Atomic Number 11. Mass Number 23. Protons = 11. Electrons = 11. Neutrons = 12. Electron Configuration = 2, 8, 1

Have a play with the Element Math Game below, its really good practice :-)

3. Periodic Table

Relate atomic structure of an element to its position on the Periodic Table

Atoms have certain numbers of protons.

If an atom has one proton then it is Hydrogen. If it has 2, then it is Helium. 3 is Lithium. 4 is Beryllium. 5 is Boron. 6 Carbon. 7 Nitrogen. 8 Oxygen. 9 Fluorine. 10 Neon. 11 Sodium. 12 Magnesium. 13 Aluminum. 14 Silicon 15 Phosphorus. 16 Sulfur. 17 Chlorine 18 Argon 19 Potassium. 20 Calcium.

Because these are nice whole numbers, you can arrange them in a long row, like in the Periodic Table song.

Whenever we have just one type of atom, such as Calcium, we call it an Element.

The Elements are then arranged based on their reactivity. Although, it turns out that this is determined by how many electrons they have in their last orbit. These outermost Electrons are called Valence Electrons

The Valence Electrons are the ones that can interact with the world.

If they just have 1 Valence Electron, or 7 Valence Electrons, then they are most reactive. Like Sodium. Sodium has an Atomic number of 11, so it has an Electron Configuration of 2, 8, 1. Because it has just 1 Valence Electron, it is very reactive.

Scientists saw the patterns in reactivity, and worked on trying to group these atoms

Dmitri Mendeleev figured it out and created the Periodic Table.

The periodic Table has grown since he created it, as new atoms have been discovered

Have we reached the end of the Periodic Table?You mightn't know that 2019 is the International Year of the Periodic Table, but Professor Allan Blackman certainly does. He's doing all he can to ensure people can enjoy the Periodic Table in all its glory.

Below is an extremely good YouTube clip explaining everything about the periodic table. Watch it :-)

In the periodic table, we have Columns and Rows

The Column represents the number of Valence Electrons that all of the Atoms in that column have

The Rows represent how many orbits contain Electrons

Columns are called Groups (number of Valence Electrons)

Rows are called Periods (number or Orbitals)

Luckily for us, we only learn up to the first 20 elements, so we don't have to worry about the transition metals that start at number 21

There are 7 Periods, we just look at the first 3

There are 18 Groups but because the Transition metals (green on the periodic table below) take up 10 groups, we subtract 10 to find out how many valence electrons the element has. For example Carbon is in group 14 - so it has; 14-10 = 4. Four valence electrons

So, if we pick any of the first 20 we can work out its number of orbitals and its number of valence electrons.

Oxygen is in Period 2 and Group 16. So it has 2 orbitals and 6 Valence Electrons

Helium is in Period 1 and Group 18. So, it has 1 Orbital and 2 Valence Electrons

Neon is in Period 2 and Group 18.

Sodium (Na) is in Period 3 and Group 2. So it has 3 Orbitals and 2 Valence Electrons

We can also predict the Period and the Group if we have the atomic number and can figure out the Electron Configuration. For instance, Calcium has the Atomic Number 20. So, it has 20 electrons. Its Electron Configuration will be 2, 8, 8, 2. Thus it has 4 Orbitals and 2 Valence Electrons (the electrons in its last orbital). So, Calcium will be in Period 4 and Group 2

A harder one; Aluminum. Aluminum has the Atomic number 13. So, 13 electrons. The electron configuration would be 2, 8, 3. Thus 3 Orbitals and 3 Valence electrons. Aluminum will be in Period 3 as it has 3 orbitals and it will be in group 13. We have to add 10 to the 3 as it is on the other side of the gap made by the transition metals

Side note, transition metals have valence electrons in multiple orbitals. That makes them very confusing. But the first 20 are tidy, so we just learn those ones

Periodic Table

A YouTube clip on each of the first 20 Elements

Incredible Lecture with Dr Peter Wothers

Below is an Amazing Lecture about the Elements of the Periodic Table. This Royal Society of Chemistry Lecture travels around the world and sells out. There are heaps of demonstrations and brilliant explanations. Grab something to eat. Chill out and watch it

Have a go playing the game below

4. Elements, Compounds and Mixtures

Explain the nature of a substance using its chemical make-up

Elements

There are just 92 Naturally occurring Elements in the Universe.

They are the Elements in the Periodic Table song

Elements are like Lego Blocks, all the Lego Blocks of the same size and colour are an Element

Oxygen is an Element. Its just Oxygen with nothing else stuck onto it.

We can stick 2 oxygen atoms together, like two lego blocks of the same size and colour, and we get molecular Oxygen ( a little lump of Oxygen (molecule is latin for little lump))

The individual atom is an element. And, clusters of the same type of atoms also make an Element.

Hydrogen gas in a floating and exploding balloon is H2. This means that the gas molecules (little lumps) are just lots of two Hydrogen atoms stuck together in pairs, floating around

Same with Gold, if we stick more and more Gold Atoms together, we just get a bigger lump of gold

A gold nugget just contains the atom gold, so it is just gold. It is the element gold

But, like lego blocks, you can stick different blocks of different sizes and colours together

Water is a good example. It is H2O. But what does this mean, H2O?

H stands for Hydrogen, 2 means 2 hydrogen atoms

O stands for Oxygen

So, H2O has 2 Hydrogen atoms and 1 Oxygen atom all stuck together as a little lump of just 3 atoms. This is a compound

Molecule

Molecule is Latin for Little Lump

We use the word Molecule for little lumps that are so little that we cant see them with our eyes

A Molecule can be an element

A Molecule can be a compound

Compounds

Compounds are whenever 2 or more different types of atoms have bonded together

There are only 92 naturally occurring elements in the universe, but these can combine to form billions of different compounds.

Water, H₂O is a molecule that is a compound

We will often drop the word 'molecule' and just say 'compound'

Carbon Dioxide CO₂ is a compound

Carbon Monoxide CO₃ is a compound

Sugar, C₆H₁₂O₆ is a compound

Oxygen O₂ is a molecule of the element oxygen

Here, we will drop the word 'element' instead of the word molecule

Ozone O₃ is a molecule of oxygen

A lump of Gold is Au, there are millions of Au atoms stuck together, so we wont worry about a number. To indicate this we will say, we have a lump of the Element Gold - here we don't say Molecule, because molecule means little lump, and this is a lump that is so big that we can see it, so it is not a little lump, it is just a lump.

Methane CH₄ is a compound.

We can work out how many of each atom is in a molecule by looking at the number immediately after each letter - if there is no number, then it means that there is just one of these

So looking at our examples from before:

H₂O = Hydrogens 2, Oxygen 1

CO₂ = Carbon 1, Oxygen 2

C₆H₁₂O₆ (sugar) = Carbons 6,

Hydrogens 12, Oxygens 6

CH₄ = Carbon 1, Hydrogen 4

The letters are arranged usually alphabetically. So, a, b, … C₆H₁₂O₆

Unless it is a Metal and a non-metal compound. Then it is the metal first then the non-metal. E.g. MgCO₃ - magnesium (metal) carbonate (non-metal)

Pure Substance

Pure Substance: Element

Gold

If I buy a Gold gansta chain to wear to school, I want it to be pure gold. This would be a pure substance. The only atoms it would contain is ... gold. Gold is on the periodic table, so it is an element. It cannot be broken chemically. So, my

Gold is a pure substance and it is an element.

Pure Substance: Compound

Water

I take a glass or water

The water has nothing else in it

The water is a Pure Substance

If I zoom into the water I will see that each molecule is H2O, that is it has 2 Hydrogen atoms and 1 Oxygen atom. H2O is a compound.

A compound can be broken into parts chemically.

If you run an electrical current through water, the H2O will break apart, with the Hydrogens gathering around the negative electrode, and the oxygens gathering around the positive electrode. Hydrogen is a pure element as is Oxygen

Water is a pure substance and it is a compound

Mixtures

Heterogeneous Mixture: Suspension

Flour water

If I take my cup, and add some Flour to it, it is a mixture

I can stir the flour in the cup. If might look uniform, however, if I look very closely, I will see the bits of flour floating in the water. The flour is suspended in the water, floating around in it. If I leave the cup overnight, I will find that all the flour will settle to the bottom of the cup. Because the flour can float, suspended in the water, this is a Suspension!

Also, if you look at the flour water under a magnifying glass, you will see bits of flour and clear area with no flour - because it is not the same everywhere, it is called Heterogenous.

So Flour water is a heterogeneous mixture and it is a suspension

Heterogeneous Mixture: Colloid

Milk

Milk is an interesting one, if you look at it it looks all the same everywhere, so it is appears homogenous. However, if you look at it under a strong microscope, you will see that it is actually small white balls of fat and protein floating in water. So it is actually Heterogenous.

If you leave it sit overnight, the fat and protein will not sink to the bottom. They are too small. The particles are smaller than the particles in a suspension so the effect of gravity is unable to pull them past all the water molecules, so they can not sink to the bottom.

The molecule sizes are halfway between the Solution and Suspension.

Milk is a Colloid

Milk is a Heterogeneous Mixture and is a Colloid

Homogeneous Mixture: Solution

Salt water

If I take my cup of water, and add some salt to it, it is no longer a pure substance. Rather it is a mixture.

If I stir the water and it all dissolves and disappears, then I have a Solution. The reason it disappears is because the molecules are so small. If the molecules are so small that you cannot see them, even with a microscope then it is a solution.

So Salt water is a mixture and it is a solution

Food colouring

If I take my cup of water and add some food colouring, it is no longer a pure substance, again it is a mixture.

Once the food colouring as diffused to all parts of the cup of water, then the colour is the same everywhere. If I take take 2 drops from the cup, one drop in an eye dropper from the top of the cup, and on from the bottom, and I look at the drops, the will be the same colour. Things that are the same are said to be Homogeneous. 'homo' means the same. 'hetero' means different.

So food colouring in water is a homogenous mixture

If we look at the food colouring under a microscope, we can not see the molecules that give the food colouring its colour - because they are too small even for a microscope. So, they food colouring in water is a Solution!

So food colouring in water is a homogeneous mixture

In fact, Coca Cola is also a Solution!!