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Topic 1 Atomic Structure and the periodic table By Bethan Poole (1.1 A…
Topic 1 Atomic Structure and the periodic table
By Bethan Poole
1.1 A simple model of the atom, symbols, relative atomic mas electronic charge and isotopes
1.1.4 Relative electrical charges of subatomic particles
Electrical Charges
Proton= +1
Neutron= 0
Electron= -1
Number of protons is equal to the number of electrons - no overall charge
Atomic number
- number of protons
Mass number
- Number of protons and neutrons
All atoms of the same element have the same number of protons
1.1.3 The development of the model of the atom
4.1.3 The development of the model of the atom
Futher developments
Niels Bohr
adapted this nuclear model by suggesting that electons orbit the nucleus at specific distances
The nucleus can be divided into a whole number of smaller particles, each with the same aount of positive charge- They were called Protons
James Chadwick
- 1932- he proved that in the nucleus there was another particle, neutron.
Rutherford and Marsden
Most passed through but not all
Conclusion
Electrons surround this nucleus
Mass of atom concentrated in a central nucleus, which is positively charged
Some were reflected back so
The repelling charge must have been much heavier than the alpha particle
They must have been repelled by the same charge
Some were deflected meaning
They must have come close to a concentration of charge
If the plum pudding model was correct the heavy positively charged alpha particles would pass straight through
1905 Rutherford and Marsden bombarded thin gold foil with alpha particles
Plum pudding model
Electrons were discovered in 1897 by J.J. Thompson, who thought atoms were a ball of positive charge with electrons embedded in it
Atoms were once thought to be tiny spheres that couldn't be divided
1.1.6 Realative Atomic mass
The ratio of the average mass per atom of the element to one-
twelfth the mass of an atom of carbon-12
1.1.2 Mixtures
They consist of two or more elements or compunds-
not chemically combined
Chemical properties are unchanged
They can be separated by physical process
Filtration
Used to separate soluble solids from insoluble solids
e.g.
A mixture of salt (soluble) can be separated from sand (insoluble) by dissolving the salt in water and filtering the mixture
Crystallisation
Used to obtain soluble solids from a solution
(1)
Gently heat the mixture
(2)
The water evaporates leaving the pure salt crystals
Simple distillation
Method
(1)
Use a pH probe or suitable indicator to analyse the pH of the sample
(2)
Set up the equipment
(3)
heat a set volume to 100°C so the water changes from liquid to gas
(4)
The water coolects in the condenser and changes state (from liquid to gas) Collect this pure water in a beaker
(5)
When all the water from the sample hs evaporated, measure the mass of soid that remains to find the amount of dissolved solids present in the sample
Hazards and Risks
Burning yourself on the hot equipment so be careful during and after the heating process
Fractional Distilation
Used to separate mixtures with different boiling points
Chromotography
Used to separate different soluble, coloured components of a mixture
1.1.7 Electronic Structure
Electrons in an atom occupy the lowest available shell or energy level
First 20 elements
The first shell can onlly hold two electrons
The next two shells can hold a maximum of 8 electrons
Electronic structure can be represented by a diagram or numbers
Shows how the electrons are arranged around the nucleus in shells
1.1.1 Atom, elements and compounds
Atoms
All substances made up of atoms
e.g Oxygen = O (one atom of oxygen)
e.g Sodium = Na (One atom of sodium)
Atoms smallest part of an element
Compounds
Chemically bonded atoms
e.g H2O =Water (Contains 2 Hydrogen atoms and 1 Oxygen atom) 2H2 + O2 -> 2H2O
Chemical formulae show: the different elements in a compound and how many atoms of each molecule of the compound contains
#
Chemical reactions always involve the formtion of one or more new atoms
They can only be separated by chemical reactions
Elements
About 100 different elements
Displayed in the periodic table
Element is An element is a substance containing one type of atom
Chemical reactions can be represented by word equations or equations using symbold or fomulae
1.1.5 Size and mass of atoms
Isotopes
- Atoms of the same element with a different number of neutrons
e.g.
Carbon has two common isotopes
carbon-14, contains 6 protons and neutrons
carbon-12, contains 6 protons and 6 neutrons
Mass of particles
Electron= Very small (0)
Neutron=1
Proton= 1
Almost all the mass is the nucleus
Radius of nucleus less than 1/10000 of the atom (1x10-14)
They are very small radius of 0.1nm (1x10-10m)
1.2 The Periodic Table
1.2.3 Metals and non-metals
Elements that react to form positive ions are metals and elements that react to form negative ions are non-metals
Majority are metals
Metals found to the lft and bottom of the periodic table and non-metals found towards the right and top of the periodic table
1.2.4 Group 0
Nobel gases
Full outer shell of electrons
Very stable and very unreactive
Boiling points increase down the group
1.2.2 Development of the periodic table
John Newland
Tried to put a periodic table together in 1864- only 63 elements were known
He arranged them in order of atomic weight- following this meant some elements were in the wrong place
He noticed the repeated patterns though the missing element caused problems
Dimitri Mandeleev
Realised some elements were yet to be discovered
Created his table in 1869- He left gaps for the missing elements
Each element was placed in a verticle column or group with elements of similar properties
He used this to predict the existence and properties of new elements
When subatomic particles were later discovered, it revealed that he had arranged the elements in order of increasing atomic number
1.2.5 Group 1
Alkali metals
1 electron in out shell
Low melting and boiling points- decrease down the group
More reactive down the group- outer electron gets further away from the influence of the nucleus, so can be lost more easily
Stored in oil- react vigorously with water and oxygen
When they react with water a metal hydroxide is formed and hydrogen given off
e.g.
potassium+water-> potassium hydroxide+ hydrogen
2K+2H2O->2KOH+H2
Low density
React with non-metals to form an ionic compound
1.2.1 The Periodic Table
Arranged in order of atomic number
Elements with similar propertes are in columns
Called a periodic table as similar properties occur at regular intervals
Elements in the same group have the same number of electrons in their outer shell- giving them similar properties
1.2.6 Group 7
Halogens
7 electrons in outer shell
Reactivity decrease down the group- outer shells further away from nucleus so less easy to gain an electron
Melting and boiling point increase down the group
1.3 Properties of Transition Metals (Chemistry Only)
1.3.1 Comparision with Group 1 elements
Similar properties to group 1 elements
High melting point
Low reactivity
High density
White or colourless compounds
1.3.2 Typical properties
Centre of periodic table between groups 2 and 3
Form coloured compounds
Ions with different charges
Can be used as catalysts to speed up reactions
Good conductors of heat and electricity
Can be easily bent into different shapes