Chemistry C2 GCSE AQA - UNIT 1

Atomic Structure

• Centre nucleus contains protons and neutrons.
• Protons = POSITIVE CHARGE
• Neutrons = NO CHARGE
• Electrons = negative charge
• Therefore the overall atom has NO OVERALL CHARGE
• Atoms of the same element contain the SAME NUMBER OF PROTONS
• This is called the PROTON NUMBER

The Arrangement of Electrons in Atoms

• Electrons shown on diagrams as dots or crosses
• Lowest energy level holds TWO ELECTRONS
• The rest hold EIGHT ELECTRONS
• Elements in the same group on the periodic table hold the SAME number of ELECTRONS in their HIGHEST ENERGY LEVEL

Chemical Bonding

• Nobel gases are UNREACTIVE - as their atoms are in a stable arrangement (Group 8)
• Other elements can achieve this by GAINING or LOSING electrons to form ions
• An ion is an atom/group of atoms that has LOST/GAINED electron/s.
• Therefore it is CHARGED

Ionic Bonding

• Holds OPPOSITELY CHARGED ions together in GIANT STRUCTURES
• Strong ELECTROSTATIC forces of attraction act in all directions.
• Each ion is surrounded by opposite charge - held in place
• Example of Ionic Bonding -
  • Mg (2+) + Cl (-) > MgCl(2) as twice as many chloride atoms are needed

Properties of Ionic Compounds

•  
  • HIGH melting points - tight structure, strong electrostatic forces
  • A LARGE amount of energy is needed to break these forces to overcoem the attraction

Covalent Bonding

• If BOTH atoms need to GAIN electrons to get a full outer energy level.
• They SHARE electrons in a covalent bond

Properties

• LOW melting/boiling points
  • Not much energy needed to break inter-molecular forces
• INSULATORS of electricity, (do not conduct)
  • No free moving charged particals (ions)
• WEAK inter-molecular forces
• STRONG intra-molecular forces

Bonding in Metals

• Atoms in a metallic element are ALL the SAME size.
• They form GIANT STRUCTURES, layers of atoms arranged in regular PATTERNS
• The electrons in the highest energy level DELOCALISE - results in strong electrostatic forces between these electrons and the positively charged metal ions