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Chemistry

Chemistry. AN ATOM. Atom - smallest unit of all matter, that is composed of 3 sub-atomic particles called protons, electrons and neutrons Proton - the 'heavy' positively-charged particle in the nucleus of an atom

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Chemistry

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  1. Chemistry

  2. AN ATOM Atom - smallest unit of all matter, that is composed of 3 sub-atomic particles called protons, electrons and neutrons Proton - the 'heavy' positively-charged particle in the nucleus of an atom Electron - the very 'light' negatively-charged particle that orbits the nucleus of an atom Neutron - the 'heavy' uncharged particle in the nucleus of an atom

  3. AN ATOM • Uncharged or unreacted atoms have the same number of positive protons and negative electrons. • Approximate size of atoms - Millions of atoms could fit on the sharp point of a needle. Also, if you imagine that an atom is the size of an oval, a proton and a neutron would be the size of footballs in the middle of the oval, and the electron would be the size of a rice grain racing around the running lane.

  4. ATOMIC NUMBER AND ATOMIC MASS • Atomic Number - the number of protons in an unreacted atom • Mass Number - the number of protons and neutrons together

  5. ATOMIC DIAGRAMS • Protons and neutrons are in the nucleus. • Protons are p+ • Neutrons are n • Electrons orbit the nucleus in electron levels or 'rings'. • Electrons are e- • A limited number of electrons are situated in each electron 'ring'. • First ring - maximum of 2 electrons Second ring - maximum of 8 electrons Third ring - maximum of 8 electrons Fourth ring - maximum of 18 electrons Electron rings close to the nucleus are filled first.

  6. ELEMENTS AND COMPOUNDS • Element - An element is a substance composed of the same type of atoms (e.g. gold Au, oxygen O2). • Compound - A compound is a substance made of more than one type of atom (e.g. water H2O, carbon dioxide CO2). • Molecule - A molecule is the smallest particle of either an element or a compound.

  7. INERT OR NOBLE GASES • Inert or Noble Gases are unreactive gases. They do not corrode nor react. • Examples of Noble Gases are: • He - Helium Ne - Neon Ar - Argon Kr - Krypton Xe - Xenon Rn - Radon • The electron rings of these unreactive gases are full, therefore they become stable.

  8. IONS (CHARGED ATOMS) • When atoms react, they may either gain or lose electrons. Electrons have a negative charge. An atom gaining or losing electrons will get an overall charge. • Positive Ions are atoms that have lost electrons (e.g. sodium Na1+) • Negative Ions are atoms that have gained electrons (e.g. chlorine Cl1-) • In chemical reactions, atoms tend to gain or lose electrons to resemble the electron numbers of the stable Noble Gases.

  9. COVALENT AND IONIC COMPOUNDS • Covalent Compound - a compound where electrons are shared between the atoms (e.g. carbon dioxide CO2) • Ionic Compound - a compound formed from the attraction between positive and negative ions. For example in the ionic compound sodium chloride NaCl, the chlorine ion (Cl1-) gains one electron that was given by the sodium ion (Na1+).

  10. VALENCY TABLE • Valency - the charge of an ion or radical which has either lost or gained electrons • Note that metals lose electrons easily to become positive ions. This is why most metals are good conductors of electricity.

  11. WORKING OUT FORMULAE OF IONIC COMPOUNDS (THE CROSS-OVER METHOD) • Step 1 - In the ionic compounds, there are two parts to the ionic compound - the first is a positive ion (usually a metal e.g. Na1+) and the second is a negative ion (e.g. Cl1-). • Step 2 - Using the valency table, write the two ions and their valencies. • Step 3 - Now ignore the positive and negative signs. Cross-over the top valency number to the bottom of the other ion symbol. Do this for both. • Step 4 - Write the completed formulae with those same numbers at the bottom. • Step 5 - If the numbers on each part are the same (e.g. Na1 Cl1 or Mg2 O2), ignore them and rewrite the formulae without them (e.g. Na Cl or Mg O). • Step 6 - Brackets may be used around radicals (groups of atoms that are charged e.g CO3).

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