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C1 - Atomic Stucture and Periodic Table (4.1.1 (Size and mass of atoms…
C1 - Atomic Stucture and Periodic Table
4.1.1
Atoms, elements and compounds
Compound - Formed from elements in chemical reactions and can only be seperated back into elements through chemical reations 2+ elements chemically combined in fixed proportions
Element - A type of atom, about 100 different types listed on periodic table
Atom - Smallest form of an element all sustances are made up of atoms
Chemical Reactions - The formation of one or more substances from one or more sustances usally involving energy change
Mixtures
Mixture - 2+ elements or compounds not chemically combined together. The properties of each substance in the mixture are unchanged
Seperation - A mixture can be seperated by several different methods these do not involve chemical reations
Crystalisation - Seperation of a soluble solid and a liquid by evaporating the liquid leaving the crystals of the solid behind.
Simple Distillation - The seperation of a soluble solid and a liquid in a soloution by boiling off the subtance with the lower boiling tempreture then cooling it back to a liquid form. Leaving the solid behind and the liquid in a beaker or seperate container.
Fraction Distillation - The seperation of multiple liquids with different boiling tempretures by evaporating one with a lower boiling point first cooling it removing then repeating for each liquid
Filtration - Seperation of an insoluble solid and a liquid with a filter eg. sand and water
The development of the model of the atom
Before the discovery of the electron, atoms were thought to be tiny spheres that could not be divided.
When electrons were discovered it led to the development of the plum pudding model suggesting the atom is a ball of positive energy with negative electrons embedded in it
After an experiment in which alpha particles were thrown at atoms it was discovered that the the mass of an atom was concentated at the center and that was charged the nuclear model replaced the plum pudding
Bohr adapted the model and suggested that electrons orbit the the nucleus at specific distances.
Later experiments showed that the posative nucleus could besub devided into different paticles with the same amount of charge called protons
James Chadwick proved the existance of neutrons in the nucleus
Relative electrical charges of subatomic particles
Proton +1 Charge
Electron -1 Charge
Neuton 0 Charge
Number of Protons = Atomic Number
Atom 0 Charge
All Atoms of an element have the same number of protons
Size and mass of atoms
Atoms have a radius of 0.1 nm
Almost all mass is in the nucleus
Protons have a relative mass of 1
Neuton have a relative mass of 1
Electrons relative mass is negligible
Protons + Neutrons = Relative Mass Number
Isotopes are atoms with different amounts of neutrons
Relative atomic mass
Average mass of an element taking account of the amount of different isotopes
Electronic structure
Electrons ocupy the lowest avalible energy shell
The elecronic structure can be represented by diagram or numbers eg. 2, 8, 8, 3
4.1.2
Periodic Table
Arranged in order of atomic number
Columns, known as groups have very simular properties
Elements in the same group have the same number of electrons in their outer shell
Development of the periodic table
Before the discovery of protons, neutrons and electrons, scientists attempted to classify the elements by arranging them in order of their atomic weights
The early periodic tables were incomplete and some elements were placed in inappropriate groups if the strict order of atomic weights was followed
Mendeleev overcame some of the problems by leaving gaps for elements that he thought had not been discovered and in some places changed the order based on atomic weights
Elements with properties predicted by Mendeleev were discovered and filled the gaps. Knowledge of isotopes made it possible to explain why the order based on atomic weights was not always correct.
Metals and Non-Metals
Elements that react to form positive ions are metals
Elements that do not form positive ions are non-metals.
The majority of elements are metals. Metals are found to the left and towards the bottom of the periodic table. Non-metals are found towards the right and top of the periodic table.
Group 0
Known as Noble Gasses
Unreactive because they are stable
Full Outer Shell
Boiling Points of this group incease with atomic number
Group 7
Known as Halogens
All have 7 electrons in their outer shell
Non-Metals and Consist of molecules made of pairs of atoms
The higher the atomic number of this group the higher the relative molecular mass, melting point and boiling point but the lower the reactivity
Group 1
Known as the Alkali Metals
Single Electron in Outer Shell
The reactivity increases going down the group