Group 0 - The Noble Gases

What are the noble gases?

The noble gases are helium, neon, argon, krypton, xenon and radon (radioactive).


Properties of the noble gases

• They are all non metals
• They were discovered after Mendeleev had invented the periodic table
• Colourless gases
• Exists as monatomic gases, e.g. Ar, Ne, He etc. 
• Very unreactive
• Also called Group VIII
• Very steady electron structures that are difficult to change
• Other elements try to get these electron configurations by under going chemical reactions
• Their outer electron shells are full

Compounds of helium, neon and argon have never been found, but recently, compounds of xenon and krypton with fluorine and oxygen have been found, e.g. XeF.

Uses of argon, neon and helium

Neon is used in lasers and neon lights.

Argon gas is the gas used in lightbulbs that stops the tungsten filament reacting with air.

Helium is used in balloons and medical procedures, e.g. MRI machines.

You can separate helium from natural gas by liquefying the other elements.

You can also obtain the other noble gases by the fractional distillation of liquid air.

Group VII - The Halogens

What are the elements?

The elements in Group VII are fluorine, chlorine, bromine, iodine and astatine (radioactive).
Chlorine, bromine and iodine are the only elements in this group that you need to have an in depth knowledge of.



Properties of chlorine, bromine and iodine

• They exist as diatomic molecules, e.g Br₂
• Their colour darkens as you move down the group - chlorine is pale green, bromine is red-brown and iodine is purple-black
• They form molecular compounds with other non-metals, e.g. HCl
• As you move down the group they gradually change state, chlorine is a gas, bromine is a liquid and iodine is a solid.
• When they react with hydrogen they produce hydrogen halides, for example HCl,  and hydrogen halides produce acidic solutions when dissolved in water, for example HCl becomes hydrochloric acid
• When they react with metals they produce ionic metal halides, 2FeCl₃ (iron(III) chloride) is an ionic metal halide

Electronic structure and reactivity

The reactivity decreases as you go down the group, this is unlike what happens in Groups I and II, the order of reactivity is below:

Image courtesy of http://isbchem1.pbworks.com

When the halogens react, they gain an extra electron. This is because they have 7 electrons in their outer shell (we know this because they're in Group VII) so to fill their outer shell it's easiest to gain 1 electron, rather than loose 7. When that 1 extra electron, they then have the electron configuration of a noble gas.

The reason chlorine is more reactive than iodine is because chlorine is a smaller atom, so the electrons in the outer shell are held in closer to the nucleus. As you go down the group, the outer electron shell will get further away and will be held less securely.

Uses of fluorine, chlorine, bromine and iodine

Florine - used for toothpaste and in drinking water

Chlorine - kills bacteria in drinking water, an ingredient in PVC plastic and is in bleach

Bromine - used in medicines, fire retardants and disinfectants

Iodine - used in medicines, disinfectants and is also used as a photographic chemical

Group 1 - The Alkali Metals

What are the elements?

The elements in Group I are:

• Lithium
• Sodium
• Potassium
• Rubidium
• Caesium 
• Francium (radioactive)

For IGCSE you need to be aware of all of these metals, but you only need to know the details about the first three.

All of these metals have to be kept under oil, because they're very reactive, so they can't come into contact with air or water.

Properties of lithium, sodium and potassium:

• Soft metals
• Good conductors of electricity
• Low densities
• Low melting points
• When freshly cut by a knife, they have a shiny surface
• Burn in air, forming white oxides, the white oxides form alkaline solutions of the metal hydroxide when dissolved in water
• React vigorously with water, making an alkaline solution of the metal hydroxide and hydrogen gas
• React vigorously with halogens (e.g. chlorine) forming metal halides (e.g. sodium chloride)
• Potassium reacts the most with water, then sodium and lithium reacts the least with water

Gradual changes (like the one above) are called trends, trends allow chemists to predict things about elements that they have not yet observed.

The further down the group you go, the more reactive the metals are, so obviously francium is the most reactive. For more information on this look at the post on The Periodic Table 

When the Group I elements react, they loose an electron, becoming more stable because their electron configuration is now the same as that of a noble gas. 

The Periodic Table and Electronic Structure

History

The Periodic Table was invented in 1969 by the Russian scientist Dmitri Mendeleev (at that time, Professor of Chemistry at St. Petersburg University).

He arranged the 63 elements (all that were known at that time) by increasing atomic mass, leaving gaps where he predicted that elements, that were undiscovered at that time, would fit into the table.

Mendeleev arranged is so that elements that have similar properties are in the same groups.

This is the Periodic Table supplied by www.cie.org.uk
So this is probably the most reliable one you can find!

Key Terms


Groups = the vertical columns in the Periodic Table

Periods = the horizontal rows in the Periodic Table

Modern Periodic Table

There are currently 118 known elements!

Elements are arranged by proton number in the modern Periodic Table and elements with similar priorities are still in the same groups.


Groups:

There are eight groups of elements:

• Group I
• Group II
• Group III
• Group VI
• Group V
• Group VI
• Group VII
• Group 0 (sometimes known as Group VIII)

Group I is known as the alkali metals, Group II as the alkaline earth metals, Group VII as the halogens and Group 0 as the inert gases or noble gases.

The big block of elements between Groups II and III are the transition metals.

Periods:

The periods are numbered 1-7, going down the periodic table.

Across each period the properties of the elements change:

Courtesy of Bryan Earl and Doug Wilford's
Cambridge IGCSE Chemistry Third Edition

Metals and non-metals:

The bold line that starts beneath boron divides the Periodic Table into two parts.

The elements on the left of the line are metals and the elements on the right are non-metals.

Metalloids is the name given to the elements that are on this dividing line, they are metals that have properties of both metals and non-metals.

Electronic Structure and The Periodic Table

The group that an element is in determines how many electrons it has in it's outer shell.

N.B. This does not apply to the elements in Group 0, they have either 2 or 8 electrons

So the elements in Group I have 1 electron in their outer energy level and the elements in Group II have 2 electrons in their outer energy level, and so on and so on.

As you move down a group, the metallic characteristics of the elements increases, this happens because the outer energy shell becomes further away from the nucleus, as do the electrons in it. So there's less attraction between the outer energy shell's electrons and the nucleus, due to distance, so the electrons in the outer shell are easier to loose.
This doesn't happen in Group VII, in this group the reactivity DECREASES as you go down the group.

Acids and Alkalis - Basic

What are acids and alkalis?

Acids are all: sour, corrosive and soluble in water
All alkalis are the chemical opposite of acids, have a soapy feel and can remove the sharp taste from acids.

Examples of acids:

• Vinegar
• Orange juice
• Lemons and limes

Examples of alkalis:

• Bleach
• Toothpaste
• Washing powder
• Milk of magnesia

Indicators

Indicators are used to test if a substance is acidic, they change colour when added to acids or alkalis. Many indicators are actually dyes that have been extracted from a natural source, e.g litmus. The table below helpfully shows some common indicators and the colours that they turn when you add them to acids or alkalis.

Universal Indicator

The universal indicator is used to find out how acidic or alkaline a substance is.

It's a mix of several different indicators and it can be used as a paper or as a liquid, it turns a different colour depending on what acid or alkali is added to it. You then match up the colour of the universal indicator with something called the pH scale. 

The pH scale.
Image courtesy of https://www.chinesemedicineliving.com

Each colour on the pH scale corresponds to a number, and the number tells you the pH level of the substance you're testing. For example, the pH of pure water is 7.

What the pH level tells you about a substance

• pH of less than 7 - acid
• pH of 7 - neutral
• pH of more than 7 - alkaline

pH meter
Image courtesy of http://www.conrad-electronic.co.uk

Another method of measuring the pH of a substance is to use a pH meter.

When you place the electrode into the solution, the electronic display shows the pH level.