Unit 1.3

Unit 1.3

1. Atoms

   • Elements contain only 1 type of atom
   • Has a small positive nucleus
   • Surrounded by negatively charged electrons
     • Relative Atomic mass of an electron = 0
   • Contains positive protons and neutral neutrons
     • Protons and neutrons have the same atomic mass
     • Relative atomic mass of a proton = 1
     • R.A.M. of a neutron = 0
   • Atoms are neutral because the number of positive protons is equal to the number of negative electrons

2. Atomic Number

   • Each element has its own atomic number
   • The atomic number is the same as the number of protons the atom of that element has
   • Because atoms are neutral, the atomic number is also the number of electrons in the atom
   • You can find an elements atomic number in the periodic table

3. Electron arrangement

   • Electrons contain energy otherwise they would be pulled back inside the nucleus of an atom
   • Electrons are arranged in ENERGY LEVELS
   • Electrons closer to the nucleus have less energy than ones further away
   • The 1st energy level can hold 2 electrons
     • The 2nd energy level can hold 8 electrons
       • The 3rd energy level, between sodium and argon can hold 8 electrons
   • Electrons with higher atomic numbers have more complicated electron arrangements
   • The electron arrangement of elements affects the chemical properties of that element
     • The noble gases (GROUP 8) have the maximum number of electrons in their outer energy level. Eg. Argon = 2,8,8 and Helium = 2
     • The group 7 halogens have 7 electrons in their outer energy level

4. Mass number

   • Mass number = No. of protons + No. of neutrons
     • Eg. Lithium = 3 protons + 2 Neutrons, so the mass number = 5
   • Nuclide Notation
     • Where the mass number and the atomic no. are written next to the symbol of an element

5. Ions, Isotopes and R.A.M

   • Ions
     • Many atoms react to form the electron arrangement of the nearest noble gas which has a stable arrangement
       • Atoms react by losing or gaining electrons
         • Metal atoms lose electrons and non-metal atoms tend to gain electrons
           • The nucleus dosen't change but when an atom gains or loses electrons it becomes an ion because it will have a charge
           • Therefore metals will form positive ions and non-metals will form negative ions
   • Isotopes
     • Atoms with the same atomic no. (ie. the same element) but a different mass no.
       • Isotopes contain different no.s of neutrons making different mass no.s
   • Relative Atomic Number
     • The averaage mass of an element worked out by taking an average of all the isotopes
       • Found in the data book in a table
       • This dosen't mean that if the RAM of chlorine was 5.5 that one of its isotopes has a mass no. of 5.5

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