Year 10 Chemistry Atom notes

Notes for Atoms
Year 10 Chemistry
Summary Notes Atoms
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.
Notes for Atoms
The diagram on the left
shows the electron
arrangement for Calcium
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.
Notes for Atoms
Isotopes of Hydrogen
Isotopes of Carbon
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.
Related flashcards
Quantum mechanics

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