Atomic Structure + Periodic Table

Atomic Structure + Periodic Table

1. Atoms

   • Nucleus
     • Contains protons and neutrons
     • Has a positive charge
     • Most of the mas is the nucleus
   • Electrons
     • Moves around the nucleus in the shells
     • Negatively charged
     • Tiny
       • Have virtually no charge
   • Protons = number of electrons
     • Atoms are neutral, have no charge (unlike ions)
     • Same number of protons as electrons
       • charge is same
         • Cancel out
     • Ion
       • Protons + electrons different numbers
         • e.g 2- charge has 2 more electrons
   • Atomic number and mass number
     • nuclear symbol tells you its a atomic number and mass number
     • Atomic number show how many protons
     • Mass number is total number of protons and neutrons
     • To find number of neutrons subtract atomic number from mass number

2. Elements

   • A element is a substance made up of atoms that have the same number of protons
   • Elements consist of atoms with same atomic number
     • Atoms can have different numbers of protons neutrons and electrons
     • Number of protons decide what type of atom it is
       • e.g. one proton in nucleus is hydrogen, 2 protons is helium etc.
     • if a substance only contains atoms with the same number of protons its called an element
     • all atoms of a particular element have the same number of protons and elements
   • Isotopes
     • They are different forms of the same elements, which have same number of protons, different number of neutrons
     • Same atomic number, different atomic mass
       • E.g. a pair of isotopes are carbon-12 and carbon-13
     • Relative atomic mass is the average mass taking into account the different masses and amouns of all isotops that make up the elements

3. Compounds

   • Atoms join together to form compounds
     • Elements react, atoms combine with other atoms
     • Compounds form 2 or more elements, atoms in each are fixed proportion and held together by chemi
     • Making bonds involves atoms giving away electrons, taking or sharing electrons
       • Only electrons are involved
     • difficult to separated original elements of compound out again - chemical reaction is needed
     • Compounds formed from a metal and a non metal consists of ions
       • Metal atoms lose electrons to form positive ions
       • Non metal atoms gain electrons to form negative ions
       • Opposite charges = strongly attached
       • Called ionic bonding
         • E.g. Sodium chloride, magnesium oxide
     • Compounds formed non-metals consist of molecules, each atom shares electrons with another atom, called covalent bonding
       • E.g. hydrogen chloride gas
     • Properties of compound are different to original one
       • E.g. iron (lustrous magnetic metal) and sulphur (a nice yellow powder) react, compound formed iron sulphide (dull grey solid lump)

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