Atomic Structure and the Periodic Table

Atomic Structure and the Periodic Table

1. Atoms

   • Radius of about 0.1 nanometers. Nucleus in the middle of atom, protons and neutrons, radius of around 1*10^-14m, positive charge because of protons, almost whole mass of atom concentrated in nucleus.
   • Electrons: move around nucleus in shells, negatively charged and tiny - cover lots of space, volume of orbits determines size of atom, no mass.
   • Neutral, same number of protons and electrons, charge on electrons = charge on protons, opposite so charges cancel out, ion - number of protons doesn't equal number of electrons - has charge.
   • Nuclear symbol tells the atomic (proton) number and mass number, atomic number - how many protons, mass number - total number of protons and neutrons in atom, get number of neutrons by taking away atomic number from mass number.

2. Elements

   • Number of protons in nucleus decide what atom it is: atom with one proton in its nucleus is hydrogen and an atom with two protons is helium. If substance only contains atoms with same number of protons - element, all atoms of particular element have same number of protons, different elements have different number of protons.
   • Atoms represented by symbols e.g. C = carbon, O = oxygen, Mg = magnesium, Na = sodium, Fe = iron, Pb = lead.
   • Isotopes - different forms of same element, same number of protons but different number of neutrons, same atomic number but different mass numbers. Relative atomic mass used instead of mass number - average mass : different masses and abundances.
     • Relative atomic mass = Sum of (isotope abundance * isotope mass number) / sum of abundance of all the isotopes.

3. Compounds

   • Compounds: two or more elements, atoms of each in fixed proportion and held by chemical bonds. Making bonds involves atoms giving away, taking or sharing electrons, usually difficult to separate - chemical reaction needed. Compound - metal + non-metals consists of ions, metal lose electrons - positive ions, non-metals gain electrons - negative ions, opposite charges of ions - strongly attracted - ionic bonding. Compound - non-metals consists of molecules, atom shares electron with another atom - covalent bonding . Different characteristics to elements.
   • Compounds - formula e.g. Sodium chloride = NaCl.

4. Mixtures and Chromatography