ATOMIC THEORY

ATOMIC THEORY

1. John Dalton

   • A pure element is made up of atoms
   • The atoms of each element are different sizes and mass
   • Atoms are the smallest particles that take part in a chemical reaction.
   • A pure element is made up of atoms
     • The atoms of each element are different sizes and mass
       • Atoms are the smallest particles that take part in a chemical reaction.

2. Kinetic Theory of Matter

   • Molecules - atoms of different elements that have combined to make a compound.
   • Matter is made up of small particles - Atoms or molecules
   • Particles are moving all the time.
   • Higher the temperature - the more they move
   • Heavier particles move slower than lighter particles at the same temperature
   • Molecules - atoms of different elements that have combined to make a compound.
   • Matter is made up of small particles - Atoms or molecules
   • Particles are moving all the time.
   • Higher the temperature - the more they move
   • Heavier particles move slower than lighter particles at the same temperature

3. Atomic Structure

   • All atoms consist of: Protons Neutrons Electrons
   • A single atom is so small that it cannot be weighed on a balance. An atom can be COMPARED to another using a MASS SPECTROMETER
   • Carbon - The element used for comparisons on a MASS SPECTROMETER. Carbon has a relative atomic mass of 12 - written as carbon-12
   • SUB ATOMIC PARTICLES
     • ELECTRONS - Negatively charged particles
     • PROTONS - Positively charged particles
     • NEUTRONS - Neutral particles No positive or negative charge
     • Nucleus - centre of atom - made up of protons and neutrons
     • Electrons orbit nucleus - little mass
     • Protons & Electrons have equal and opposite charges.
     • Neutrons are electrically neutral - no charge
   • A single atom is so small that it cannot be weighed on a balance. An atom can be COMPARED to another using a MASS SPECTROMETER
     • Carbon - The element used for comparisons on a MASS SPECTROMETER. Carbon has a relative atomic mass of 12 - written as carbon-12
   • ELECTRONS - Negatively charged particles
     • PROTONS - Positively charged particles
       • NEUTRONS - Neutral particles No positive or negative charge

4. Atomic number and Mass Number

   • Number of protons in nucleus decides the element. Number of protons is known as the atomic number. symbol = Z
   • Protons and neutrons make up the total mass of atom. Electrons are so small they can be ignored.
   • Mass of an atom - depends on the number of protons and neutrons. This is called the mass number Symbol = A
   • Atomic number (Z) = number of protons in nucleus
   • Mass number (A) = number of protons + neutrons in nucleus
   • Number of Neutrons = mass number - atomic number (A-Z)
   • Number of protons in nucleus decides the element. Number of protons is known as the atomic number. symbol = Z
     • Protons and neutrons make up the total mass of atom. Electrons are so small they can be ignored.
       • Mass of an atom - depends on the number of protons and neutrons. This is called the mass number

5. Number of electrons:

   • Energy level 1 = 2 electrons
     • Energy level 2 & 3 = 8 electrons

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