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.
• https://www.youtube.com/watch?v=8hgz0iJih7I&noredirect=1 (Embed)

Structure of the atom

• 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
• 
• Caption: Structure of the atom

Protons and Neutrons

• 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. (>>>>>>)
• 
• Caption: From: profmattstrassler.com

Atomic numbers

• Atomic Number: Number of protons in the atom
• Mass Number: Number of protons + Number of neutrons
• this means:
• Number of neutrons in an atom = Mass number MINUS Atomic number
• 
• 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)
• 
• Caption: Flourine

The Periodic Table

• 
• Caption: Periodic Table of the Elements

Isotopes

• 
• 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