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Topic 1a - Principles of Chemistry - Coggle Diagram
Topic 1a - Principles of Chemistry
History of the Atom
Plum pudding model
From his Experiments, JJ Thompson concluded that atoms weren't solid spheres
His measurements of charge and mass showed that an atom must contains even smaller negatively charge particles - electrons
His theory is known as the plum pudding model and has a positively charged ball with negatively charged electrons
At the start of the 19th century, John Dalton thought that atoms where solid spheres and said that different spheres make up different elements
Rutherford
Ernst Rutherford conducted the famous gold foil experiment, they fired positively charged alpha particles at an extremely thin sheet of gold
They expected that particles would pass through the sheet or be slightly deflected as the positive charged of the atom was thought to be spread out
Most of the particles did go through, but some were deflected more than expected
Rutherford concluded that an atoms has a tiny positively charged nucleus at the centre, where most of the mass is concentrated, and a cloud of electrons surround it
Bohr
If the atoms had a cloud of electrons, the electrons would be attracted to the nucleus, causing it to collapse
Bohr proposed that electrons orbit the nucleus in fixed shells, with fixed energy levels
Protons and neutrons
Protons
Experiments showed that the nucleus could be further divided into smaller particles, each of which has the same charge as a hydrogen nucleus
This was the proton
Neutron
There was evidence for neutral particle in the nucleus
This was the neutron
The atom
Made from 3 sub-atomic particles
Protons = Relative charge = +1 Relative mass = 1
Neutrons = Relative Charge = 0 Relative mass = 1
Electrons = Relative Charge = -1 Relative mass = 1/2000
Isotopes
Atoms of the same element, which have the same number of protons but a different number of neutrons
Isotopes have the same atomic number but a different mass number
Isotopes of an element have the same chemical properties because they have te same number of valence electrons so react in a similar way
Relative atomic mass( Ar)
The average mass of one atom of the element
If an element has one isotope, its Ar will be the same as the mass number.
Ar = sum of (isotope abundance X isotope mass number) /
sum of abundance of all the isotopes
Ar values take into account the relative abundance or percentage fo each isotope in a sample of an element.
Mendeleev's periodic table
Arranged in atomic mass
Left gaps for elements which hadn't been discovered, he also predicted their properties
Grouped elements with similar chemical properties in colums
He swapped the places of some elements so that elements with similar properties lined up
Group 0 was missing from Mendellev's table
Elements in the same group have the same amount of electrons in their outer shell, which gives them similar chemical properties
Metals - lose electrons in order to be more stable, so they become positive ions
Non-Metals - gain electrons in order to become more stable, and become negative ions
Modern periodic table
Arranged in atomic number (The number of protons on the nucleus of an atom
Period number (row) tells you how many electron shells the element has
Group number (column) tells you how many electrons are in the outer shell of the element
Non-metals are found in the top right
Metals make up the rest of the table
Electron configuration
Electrons occupy shells (energy levels)
1st shell can contain a maximum of 2 electrons
2nd shell can contain a maximum of 8 electrons
3rd shell can contain a maximum of 8 electrons