Chemistry 3 notes

a detailed set of cards for unit 3 chamistry

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  • Created on: 09-05-10 21:43

The Periodic table

The chemical elements can be arranged in a periodic table. Within the table, elements with similar peoperties are placed together. Like other chemists, Mendeleev listed elements in order of mass but he realised that he needed to leave gaps for the elements that had not been discovered.

The rows across the periodic table are called Periods.

The columns down the periodic table are called the groups. All have similar properties and all have the same number of electrons in the outer shells e.g the halogens, group 7, all have 1 electron missing in the outer shell. and the alkaline metals, group 1, all have 1 electron in the outer shell. this makes both of them very reactive.

Larger atoms lose their electrons more easily and gain electrons less easily

Metals react by losing electrons and non metals react with metals by gaining electrons, thus they form ionic bonds.

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Transition Elements / Metals

-All transition metals have the same basic properties:

-they exist in jiant structures held together by metallic bonds with delocalized electrons

-they are good conductors of heat and electricity due to the delocalized electrons

-they are hard, tough, strong and malleable with high melting points and a high density

-they are not very reactive and do not easily react with oxygen or water making them usefull

-they form good alloys such as steel( carbon and Iron)

-Transition metals form coloured compounds

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Group 7 - Halogens

properties of Halogens

-they are all poisonous non-metals which all have colored vapours

-they have low melting and boiling points and are poor conductors

-They are all diatomic elements joined by covalent bonds

- they all have 7 electrons in their outer shell

-they take part in both ionic and covalent bonding

-The Halogens get less reactive as they go further down the group

-they all form ions with a single negative charge 1-, in these reaction metal halides (ionic salts) are formed e.g NaCl with ionic bonds

-they form covalent bods and share electrons with non-metals such as HCl

-Displacement in reactions occur with Halogens, more reactive elements take the place of less reactive ones e.g Cl2 + 2KBr =2KCl +Br2

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Group 1 Alkali Metals

Properties of Alkali metals

-They are very reactive. they must be stored under oil to stop them reacting with the oxygen in the air. their reactivity increases down the periodic table

- they have a very low density, react readily with the oxygen in the air to form oxides

-they all have very low boiling and melting points, getting lower as you go down the group

-they are all unstable and reactive due to the 1 electron in their outer shells.

- They react with non metals and lose their single electron to form ions carrying a +1 charge e.g. Na+, they only form ionic compounds.

- they all form metal hydroxides when they are dissolved in water and a very alkali solution and Hydrogen gas

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Acids and Alkalis

Strong acids ionize highly in water to produce many Hydrogen (H+) ions.

Strong Alkalis ionize in water to produce many Hydroxide ions (OH-)

Acid facts:

  • ACID + METAL ---->> HYDROGEN + METAL SALT
  • AICD + CARBONATE ----->>WATER + CARBON DIOXIDE + METAL SALT
  • ACID + BASE ---->>METAL SALT + WATER

Universal indicator scale:

Strong acid | Weak Acid | neutral | Weak Alkali | Strong Alkali

|0---------------|------------------|-----7----|--------------------|---------------14|

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Titration

Used to measure the exact volume of Acid to neutralize an Alkali (or Vice Versa).

To show the endpoint we need to use a suitable indicator:

STRONG ACID + STRONG ALKALI --> ANY INDICATOR SUITABLE

WEAK ACID + STRONG ALKALI --> PHENOLPHTHALEIN

STRONG ACID + WEAK ALKALI --> METHYL ORANGE

METHOD:

1. Measure the volume of Alkali into a conical flask using a pipette

2. Add indicator solution

3. Add the right volume of acid using a burette until all of the alkali has been neutralized

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