Chemistry 4

PARTICLE          RELATIVE MASS          CHARGE

PROTON                         1                               +1

NEUTRON                       1                                0

ELECTRON                 0.0005                          -1

PHYSICAL STATE                            STATE SYMBOL

SOLID                                                              (s)

LIQUID                                                              (l)

GAS                                                                  (g)

DISSOLVED IN WATER                                 (aq)

ELEMENT                                          COLOUR FLAME

LITHIUM (Li)                                                 RED

SODIUM (Na)                                 YELLOW/ORANGE

POTASSIUM (K)                                         LILAC

Different elements have different wavelengths and these wavelengths can be recorded as a line spectrum. They have different wavelengths due to their different electron arrangement. This means line spectrums can identify elements.

Elements that have been discovered by the line spectrum:  CAESIUM, RUBIDIUM & HELIUM

1) Dobereiner - TRIADS (3s)

He tried arranging elements in order of relative atomic mass & the middle element of each triad had a relative atomic mass that was the average of the other two.

2) Newlands' Law of Octaves (8s)

He noticed that when you arranged the elements in order of realtive atomic mass, every eighth element had similar properties. Transition metals messed up his pattern. He was also criticised because he mixed up metals and non-metals & he didn't leave any gaps for elements that had not yet been discovered.

3) DMITRI MENDELEEV (present)

He put the elements in order of atomic mass and left gaps for new elements to be discovered. The gaps predicted the properties of undiscovered elements. To start with there was no evidence that the elements did fit together in that way but when new elements were discovered and fit in the gaps it was evidence in favour of the periodic table.

• Elements with similar properties form columns

• The group number tells you how many electrons there are in the outer shell

• The rows are called periods, and each period represents a full shell of electrons

• If you know the properties of one element, you can predict the properties of the rest of the elements in the group

When atoms lose or gain electrons they form charged particled called ions.

Compounds formed between GROUP 1 and GROUP 7 elements are held together by IONIC BONDS

Ionic compounds form a regular or giant lattice. Each lattice forms a single crystal. When ionic compounds become molten or are dissolved in water than can conduct electricity because the ions are free to move. The fat that molten compounds made of metals and non-metals conduct electricity is evidence they're made up of ions.

Easy: When the ions in the compound have the same size charge

EXAMPLE: Find the formula for lithium fluoride.

Lithium ion is Li+ & Fluoride ion is F-

So the formula of lithium fluoride must be: LiF

EXAMPLE: Find the formula for calcium chloride.

Calcium ion is Ca2+ and Chloride ion is Cl-

To balance, you need 2 chloride ions to every 1 calcium ion

So the formula of calcium chloride is: CaCl2

They are shiny when freshly cut but react with oxygen in the air

As you go DOWN Group 1, the alkali metals:

1) become MORE REACTIVE

2) have a HIGHER DENSITY

3) have a LOWER MELTING POINT

4)have a LOWER BOILING POINT

GROUP 1 elements:

Reacting with COLD WATER produces HYDROGEN GAS (squaeky pop test)

2Li(s)   +   2H₂O(l)   →   2LiOH(aq)   +   H₂(g)

Reacting with CHLORINE produces SALTS  

       2Li(s)   +   Cl₂(g)   →   2LiCl(s)

The halogens form diatomic molecules (pairs)

As you go DOWN Group 7, the halogens:

1) become LESS REACTIVE

2) have a HIGHER MELTING POINT

3: have a HIGHER BOILING POINT

ELEMENT                COLOUR (AT R.T.)              STATE (AT R.T.)

FLUORINE                        YELLOW                                GAS

CHLORINE                          GREEN                                 GAS

BROMINE                         ORANGE                               LIQUID

IODINE                                 GREY                                  SOLID

The reactions become less vigorous as you go down the group

REACTIONS WITH ALKALI METALS

Halogens react with alkali metals to make SALTS called METAL HALIDES

REACTIONS WITH IRON

Halogens react with iron to form COLOURED SOLIDS called IRON HALIDES

DISPLACEMENT REACTIONS

A displacement reaction is where a more reactive element pushes out a less reactive element from a compound (this happens within the halogens for example, potassium chloride)

   OXIDISING                           HARMFUL

   HIGHLY FLAMMABLE         EXPLOSIVE

   TOXIC                                 CORROSIVE

• Make sure there is a fire extinguisher - Group 1 elements are very reactive and can combust spontaneously. There can be a violent reaction if they come in to contact with water vapour in the air, so they're stored in oil to prevent this.

• Do not touch alkali metals with bare hands - sweat can cause a reaction that produces heat and a corrosive hydroxide.

• Keep every piece of apparatus completely dry

• Keep away from eyes and skin - alkaline solutions can be corrosive

• Chlorine and Iodine are both very toxic.

• Fluorine is too dangerous to have inside the lab.

• Contact with liquid bromine on the skin must be avoided - corrosive
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• Must be used inside a fume cupboard as the halogens have poisonous vapours
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