Introduction to the Atom

The Atom

The Atom is the smallest part of an element, that still has the properties of that element, i.e. it cannot be broken down any further.

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NUCLEUS: the central section of the atom made up of sub-atomic particles called protons and neutrons ELECTRONS: sub-atomic particles that revolve around the nucleus in paths called orbits this movement of electrons creates an electron cloud

Structure of the atom

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Caption: : Structure of the atom

Protons have a positive charge (Charge = +1) Electrons have a negative charge (Charge = -1) Neutrons are neutral (No charge) Usually atoms are electrically neutral which means that the number of protons in the atom is equal to the number of neutrons.Protons and neutrons have the same mass, but electrons are 2000 times smaller than the mass of proton. (>>>>>>)

Protons and Neutrons

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Caption: : From: profmattstrassler.com

Atomic Number: Number of protons in the atomMass Number: Number of protons + Number of neutronsthis means:Number of neutrons in an atom = Mass number MINUS Atomic number

Atomic numbers

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Caption: : Helium: Atomic number = 2, Mass number = 4

Describing atoms

The atomic number of fluorine is 9 and its mass number is 19. (rounded from 18.998, see left) How many (a) protons, (b) electrons and (c) neutrons does a neutral fluorine atom have? (a) 9 protons(b) 9 electrons (same number as the number of protons)(c) 10 neutrons (19 – 9)

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Caption: : Flourine

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Caption: : Periodic Table of the Elements

The Periodic Table

Isotopes

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Scientists used to think that all atoms of a particular element were identical. We have discovered that some elements have two or  three different types of atom.They will all have the same number of protons but they could have a different number of neutrons. e.g. some atoms of carbon have 6 neutrons, while other atoms of carbon have 7 neutrons, and others have 8 neutrons. We say these atoms are isotopes of each other. Isotopes are atoms that have the same atomic number but a different mass number