What are the key learning points about the periodic table?
- Dmitri Mendeleev developed an early version of the periodic table that places A pure substance which is made from only one type of atom. Elements are listed on the periodic table. An element cannot be broken down into anything simpler by chemical means. with similar properties in the same vertical group.
- The alkali metals (Group 1) are a group of highly reactive metals that have distinctive observations when they react with water.
- The noble gases (Group 0) are a group of non-reactive gases.
What were early attempts to classify the elements?
An element is a substance that is made up of only one type of The smallest particle of an element. We often think of atoms as tiny spheres, but in fact they are made from smaller particles called protons, neutrons and electrons., that cannot be broken down into simpler substances by chemical means.
Early chemists attempted to classify the elements according to their atomic weights – what we now call atomic mass.
They could see that The mass of the atom compared with that of the carbon-12 isotope, which has a mass of exactly 12. These masses use the symbol Ar or RAM. of the elements increased by steps.
Many elements were unknown, so these early tables were incomplete.
They also contained errors – some elements that were not similar were placed together.
What was Mendeleev’s periodic table?
In 1869, the Russian chemist, Dmitri Mendeleev published a periodic table that forms the basis of the one we use today.
Mendeleev’s periodic table was different from those of other scientists in the following ways:
He arranged the elements in order of increasing atomic weight.
He left gaps where no element fitted the repeating pattern. These gaps were for undiscovered elements.
He was able to predict the properties of undiscovered elements.
What does the modern periodic table look like?
Scientists continued to revise Mendeleev’s periodic table.
- The modern periodic table is arranged in order of increasing atomic number, rather than atomic mass.
- There are now over 100 elements and no gaps in the periodic table.
- A group of unreactive elements – the The elements in Group 0 of the Periodic Table, named for their lack of chemical reactivity. – were discovered at the end of the 1800s and added as a group to the modern periodic table.
- The modern periodic table includes A metal that is located in between Group 2 and Group 3 of the periodic table and has brightly coloured compounds., actinides and lanthanides.
Key fact
Each element in the periodic table is a substance that consists of only one type of atom.
The elements cannot be broken down into simpler substances by chemical means.
Structure of the periodic table
What are groups and periods?
The modern table is called a “periodic” table because the elements with similar properties appear at regular intervals.
- The vertical columns are called groups.
- The horizontal rows are called periods.
What are metals and non-metals in the periodic table?
There are many divisions in the periodic table, but one of the most important is between the metals and the non-metals.
The metal elements are on the left of a ‘stepped line’ that runs below boron (B), silicon (Si), arsenic (As), tellurium (Te), and astatine (At).
You can tell the difference between the metals and non-metals by looking at their properties.
| Properties of a typical solid metal | Properties of a typical solid non-metal |
|---|---|
| Good conductor of electricity. | Poor conductor of electricity. |
| Good conductor of heat. | Poor conductor of heat. |
| Generally high melting points. | Generally low melting points. |
| Malleable (can be hammered into shape). | Brittle (breaks when hammered). |
| Ductile (can be drawn out into wires). | Brittle (snaps when stretched). |
| Sonorous (makes a ringing sound when struck). | Not sonorous. |
What is the state of the different elements at room temperature?
All the metals are solids, except mercury – it is a liquid.
The non-metal elements hydrogen nitrogen, oxygen, fluorine, chlorine and all the noble gases (Group 0) are gases.
Bromine, a non-metal, is a liquid.
Every other element is a solid.
What does a group number mean?
Elements in the same group have the same number of Subatomic particle, with a negative charge and a very small mass relative to protons and neutrons. in their outer shell.
For example, every element in Group 1 has 1 electron in the outer An energy level around the nucleus where electrons can be found orbiting..
| Group | Name | Metal / Non-metal | Reactive / Non-reactive | |
|---|---|---|---|---|
| 1 | Alkali metals | Metal | Reactive | |
| 2 | Alkaline earth metals | Metal | Reactive | |
| 7 | Halogens | 1 | Non-metal | Reactive |
| 0 | Noble gases | Non-metal | Non-reactive |
What are periods in the periodic table?
Elements in the same period have the same number of electron shells.
For example, all the elements in period 3 will have 3 electron shells.
This can be seen by looking at their electronic configurations:
Sodium (2.8.1), aluminium (2.8.3) and chlorine (2.8.7).
Each configuration consists of 3 numbers.
Question
What group number and period number of the periodic table will an atom with electronic configuration of 2.5 belong to?
Answer
An atom with electronic configuration 2.5 will belong to Group 5 (number of electrons in outer shell) and Period 2 (number of shells).
What are the key properties of Group 1 – the alkali metals?
The Group 1 elements all have similar physical and chemical properties because they all have one electron in the outer shell of their atoms.
Low density - the first three (lithium, sodium and potassium) can all float on water.
Very soft - they are easily cut with a knife.
Shiny when first cut, but tarnish rapidly in air.
Low melting points.
How reactive are Group 1 metals?
Group 1 metals are very reactive.
Always use tweezers when lifting alkali metals.
Always use a safety screen.
Always wear safety glasses.
Always use small pieces of metal.
Key fact
They must be stored under oil to prevent them reacting with the air or water vapour.
All Group 1 elements react with water to produce a metal hydroxide and hydrogen.
This is the equation for the reaction between sodium and water:
sodium + water → sodium hydroxide + hydrogen
2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g)
Question
Write a word equation for the reaction of potassium with water.
Answer
potassium + water → potassium hydroxide + hydrogen
How do Group 1 metals react with water?
All Group 1 metals react with water.
There are some common observations and some differences:
Lithium, sodium and potassium are less dense than water so they float on the surface of the water.
The metals move about the surface of the water and fizz as hydrogen gas is produced.
They will all release heat as they react as the reactions are exothermic and they will eventually disappear.
The solution remaining at the end will be colourless.
Sodium also melts to form a silvery-grey ball on the surface of the water.
Potassium will do this as well but it is hard to see as the reaction is so fast and also potassium burns with a lilac flame and crackles as it explodes at the end of the reaction.
Group 1 metals all react in the same way, because each of them loses an electron to form a positive ion with a stable electronic configuration – a full outer shell.
For example, sodium loses one electron to form a sodium ion, Na+, with a full outer shell.
Group 1 metals become more reactive as you move down the group.
These The smallest particle of an element. We often think of atoms as tiny spheres, but in fact they are made from smaller particles called protons, neutrons and electrons. are larger because they have more shells.
The larger the atom, the further the outer electron is from the nucleus.
The force of attraction between the The central part of an atom. It contains protons and neutrons, and has most of the mass of the atom. The plural of nucleus is nuclei. and the Subatomic particle, with a negative charge and a very small mass relative to protons and neutrons. is less than for smaller atoms, and the outer electron is lost more easily.
Key fact
Most compounds containing Group 1 elements are white and dissolve in water to give colourless solutions.
What are the properties of Group 0 – the noble gases?
Group 0 elements have stable electronic configurations – full outer shells of electrons – and are therefore unreactive.
The Group 0 elements are all colourless gases.
All noble gases have low boiling points.
Their boiling points increase as we move down the group.
WATCH: The periodic table
The periodic table, containing all the known elements, arranged in groups and periods
This is the periodic table.
There really is no more useful tool for getting your head around chemistry.
It lists all known elements, arranged in different ‘groups’, to help us make sense of their properties.
The key thing to remember is that an element’s group number is the same as the number of electrons it has in its outer shell.
An exception to this rule is the noble gases in group zero, which have a full outer shell of electrons.
Because of this rule, all elements in the same group react in a similar way.
So, the atoms of Group 1 elements all have one outer electron.
The atoms of Group 7 elements all have—guess what—seven outer electrons.
Group 1 elements are called the alkali metals.
They’re soft and shiny when freshly cut, but they quickly tarnish as the metal reacts with oxygen in the air.
This is because they’re very reactive.
When a Group 1 element reacts with water, it produces a metal hydroxide solution and hydrogen gas.
Let’s try it with lithium.
So… on with eye protection and gloves.
Here I’ve got some lithium.
And then I’m just going to cut a little bit off…
And do you see how quickly it tarnishes—how quickly it’s changing colour?
Here we’ve got some water.
And if I put some universal indicator in… like this…
You’ll see that it’s green.
And that means it’s neutral.
But let’s see what happens when we put the lithium in.
Well, you can see it’s reacting with the water straight away.
It’s steadily fizzing away there.
It’s transferring its energy to its surroundings by heating.
And can you see the little purple trail there?
That universal indicator is showing us that the water now contains an alkali—in this case, lithium hydroxide.
So let’s try it with another Group 1 metal—sodium.
As you can see, it reacts far more vigorously than lithium.
Why is that?
Well, sodium is below lithium in Group 1, and the reactivity of the alkali metals increases as you go down the group.
Potassium is even more reactive—woah—look at it!
Remember, Group 1 atoms have one electron in their outer shell, and when they react, they lose it and form a positive ion.
As you go down Group 1, the atoms have more shells of electrons, meaning the outer electron gets further away from the positive nucleus.
It’s easier to lose—and that means the metal becomes more reactive.
Group 7 elements are reactive non-metals called the halogens.
They exist as diatomic molecules—two halogen atoms joined by a covalent bond.
They are:Fluorine, a very pale yellow gas;Chlorine, a pale green-yellow gas;Bromine, a red-brown liquid;and iodine, a shiny purple-black solid.
As you go down Group 7, the elements become darker.
At room temperature they go from gas to liquid to solid because their melting points increase.
You can compare the reactivities of halogens using displacement reactions.
A more reactive halogen can replace a less reactive one in its compounds.
Chlorine is more reactive than iodine.
Pop some chlorine solution into potassium iodide solution, and the mixture changes to brown as iodine is displaced and colourless chloride ions form.
The atoms of Group 7 elements have seven electrons in their outer shell.
They share one with another atom to form molecules.
In reactions, each atom gains an electron to complete its outer shell, forming a negative ion.
As you go down Group 7, the reactivity of the elements decreases.
The atoms have more filled electron shells, so the outermost shell gets further from the positive nucleus, and it’s more difficult to attract and gain an electron.
And of course, groups are just one aspect of the periodic table.
It’s amazing how much information is in it.
It really is elementally powerful.
How much do you know about the periodic table?
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