chemistry
Chemistry Higher tier C2a
- Created by: kasia
- Created on: 10-11-11 18:35
Electronic Structure
Electrons
- electrons fill up the shell closest to the nucleus first,
-when this is full they fill up the next one
-the electronic structure is always 2,8,8
-the last number always tells us what group
it belongs to in the periodic table
Compunds and Isotopes
Compounds
-compounds are formed when two or more elements chemically react together
-it is difficult to seperate compounds
-Compounds are chemically bonded
Isotopes
-isotopes are different atomic forms of the same element,which have the same numbrer of protons but a different number of neutrons.
Carbon-14 is unstable and it decays into NITROGEN
Convalent Substances
Simple Molecular Substances
- they form very Strong Convalent Bonds
-The forces of attraction between these molecules are very weak
-Molecular Substances dont conduct electricity
Giant Convalent Structures
-These are similar to Giant ionic structures but they have NO charged ions
-All atoms are bonded to each other by strong convalent bonds
-they do NOT conduct electricty
Metallic Structures
Metal Properties
- in a metal electrons are free to move so metals are good conductors of heat and electricity.
-These electrons also hold the atoms together in a regular structure
-They also alow atoms to slide over each other causing metals to be Malleable
New Materials
Smart Materials
- Smart materials behave differently depending on the conditions
-Dyes change colour depending on temperature or light intensity.
DIfferent formula's (1)
Relative Atomic Mass
all you do is add the masses together and it is used to compare the mass of different atoms for example:
Relative Formula Mass
Different formula's (2)
Empirical Formula
Method:
1. list the two elements
2.Write the Experimental masses
3.Divide by Ar
4.Multiply by 10...then divide by 4
Calculating Masses in reactions
The Mole
The mole
- number of moles= mass(g)
Relative mass of the substance
for example:how many moles are there in 42g of Carbon?
no.of moles=mass (g) =42/12 = 3.5moles
Atom Economy
Total Mr of useful products
total Mr of reactants
Precentage Yield
Precentage yield
precentage yield= actual yield (g)
predicted yield (g)
The amount of product made in the reaction is called the yield
we often find that the actual yield is lower then the predicted yield this is because:
-the reacton is reversible and does not go to completion
-some of the products were lost for exmaple during filtering or evaporation
-there may be side reactions that are producting another product
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