Notes for Atoms
Year 10 Chemistry
Summary Notes Atoms
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The current idea of the atom
o has been developed over the years by;
o Ancient Greeks, Dalton, Thomson, Rutherford, Bohr, Chadwick, Schroedinger etc.
o You just need to be aware of their basic contribution.
Current Simplified Theory
o Atom is the building block of matter, the smallest part of an element.
o Atom consists of a nucleus and electron shells.
o Nucleus is tiny, dense centre of atom.
o Protons are there in the nucleus.
 They are positive and have 1 unit of atomic mass.
 The atomic number Z is the number of protons, (and also the atoms number
in the periodic table.)
o Neutrons are there in the nucleus.
 They have no charge and have 1 unit of atomic mass.
 The mass number A is the number of protons + the number of neutrons.
 Number of neutrons = A – Z.
o Isotopes
 Have the same number of protons but different number of neutrons.
 They are the same element with the same chemical properties, but they
have different mass.
o Electrons
 The number of electrons will = Z for a neutral atom.
 If electrons are added or removed the atom has a charge (it is called an ion).
 Are organised in shells called: K, L, M, N …..
 The shells to be filled (for elements up to Ca) K=2, L=8, M=8, N=2.
 We fill the shells from inner shell K.
 Example Silicon Z = 16. K, L, m  2, 8, 4
 The shells are actually energy levels. Light is absorbs or emitted if electrons
jump from 1 shell to another.
 This is how we get colours and flame tests. (It also explains the spectacular
colours in fireworks)
 The electron shells are also used to explain chemical properties and the
position of elements in the periodic table.
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Notes for Atoms
The diagram on the left
shows the electron
arrangement for Calcium
o
The periodic Table:
 It is organised in order of increasing atomic number.
 The atomic number is the element’s number.
 The number of electron in the outer shell tells us the Group number.
(Which column it is in)
 The number of shells tell us the period number (which row it is in.)
 The metals are on the left, non-metals on the right.
 Each group has similar properties, some are given special names.
 Group 8 is special because it has a stable outer shell.
 Other elements tend to react in a way that can give them the same
electron structure as the Noble gases.
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Notes for Atoms
Isotopes of Hydrogen
Isotopes of Carbon
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References
o Text book Ch 2.1, 2.2, 2.6.
o Stleonards Links site, Y 10 science Chemistry
o Any suitable searches from Google or you tube.
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