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The Nucleus
Atoms · in the middle of the atom
· contains protons and neutrons
· has a positive charge
Particle Mass Charge · almost the whole mass of the atom
Proton 1 +1 · tiny compared to the rest of the atom
Neutron 1 0 The Electrons
Electron Negligible - 0 -1 · moves around the nucleus in shells
· has a negative charge
· are tiny but their path covers a lot of space
· virtually no mass
· shells explain the whole of chemistry
· The atomic (proton) number tells you how Mass Number
many protons there are.
Atomic Number
· Atoms of the same element all have the
same number of protons, so different
elements have different number of protons. · Natural atoms have no charge overall.
· To get the number of neutrons, subtract · The charge on the electron is the same size
the atomic number from the mass number. but opposite the charge on the protons.
· The mass number is always the biggest · This means the number of protons equals the
number, on the periodic table the mass number of electrons in a neutral atom.
number is the relatively atomic mass. · If some electrons are added or removed, the
atom becomes charged and is then an ion.…read more

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Elements & Compounds
· elements consist of one type of atom only
· isotopes are different atomic forms of the
same element, which have the same number
of protons but a different number of neutrons
· Compounds are formed when two or more
elements chemically react together.
· It is difficult to separate the two original
elements out again.
· The properties of a compound are totally
different from the properties of the original
elements.…read more

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Periodic Table
The periodic table is a table of all known elements and they are in order of ascending atomic
number. It is laid out so that the elements form groups horizontally and periods vertically.
· the group which the element belongs is the same number of electrons it has in its outer shell
· elements in each group all have the same number of electrons in their outer shell
· that is why they have similar properties
· the period which the element belongs is the same number of shells it has
· elements in each period all have the same number of shells…read more

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Electron Shells
Electron Shell Rules
· electrons always occupy shells / energy levels
· the shells closest to the nucleus are always filled first
· only a certain number of electrons are allowed in
each shell: 1stshell-2, 2ndshell-8, 3rdshell-8
· atoms are much happier when they have full electron
shells as they are stable
· in most atoms the outer shell is not full and this
makes them want to react
Electron Configuration
This tells you how many
electrons there are in each shell…read more

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