cm 05a structure of atom
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What are atoms made of?
Atoms are made of small particles called protons, electrons and neutrons.
These particles are called sub-atomic particles.
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Where in the atoms are these sub-atomic particles found?
Protons and neutrons are known as nucleons.
Protons and neutrons are found in the nucleus.
Electrons circle the atoms in areas called shells.
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Structure of an Atom - Electron
Carries a charge of -1
Found in shells which surround the atom
Represented by the symbol, eRepresented by the symbol, e
Has negligible mass or relative mass of
1840
1
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Structure of an Atom - Neutron
Carries no charge (charge = 0)
Has relative mass of 1
Represented by the symbol, nRepresented by the symbol, n
Found in the nucleus which is in the centre of an atom
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Structure of an Atom - Proton
Carries a charge of +1
Has relative mass of 1
Represented by the symbol, pRepresented by the symbol, p
Found in the nucleus which is in the centre of an atom
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The Proton Number and Nucleon Number
An atom contains an equal number of positively charged protons and negatively charged electrons.
All atoms are electrically neutral.
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The Proton Number and Nucleon Number
The proton number is represented by the symbol Z.
The proton number can also tell us the number of electrons in the atom (since atoms are neutral).
It is also known as the atomic number.
The number of protons in an atom is called the proton number.
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An example
For example, the proton number of nitrogen is 7.
Hence, we can deduce that a nitrogen atom has seven protons and seven electrons.
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Different atoms have different proton numbers
Atoms of different elements have different numbers of protons.
Carbon, for example, has a proton number of 6. Any atom with 6 protons must be a carbon atom.
Each element has a unique proton number.
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Nucleon Number
It is represented by the letter A.
Nucleon number is the total number of protons and neutrons in an atom.
Nucleon number (A) Nucleon number (A) = number of protons = number of protons ++ number of neutrons number of neutrons
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Nucleon Number
The nucleon number is also called the mass number.
This is because the mass of an atom depends on the number of protons and neutrons in an atom.
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Representing Proton and Nucleon Numbers
The nucleon and proton numbers can be included when representing an element in symbols.
An element is represented using only the nucleon number e.g. sodium-23 or 23-Na.
Nucleon number in superscript, left of symbol
Na23
11
Proton number in subscript, left of symbol
Chemical symbol