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Atomic Structure and Bonding Week 2 Atomic structure and bonding related to properties of materials Nuclide notation. Isotopes and relative atomic mass. Ions. Ionic bonding. Covalent molecular, covalent network and ionic lattices. Physical properties of chemicals explained through bonding. Chemical and ionic formulae including group ions. 1st electron shell holds 2 electrons 2nd electron shell holds 8 electrons 3rd Electron shell holds 8 electrons REMEMBER THE NUCLEUS HAS A POSITIVE CHARGE Subatomic particle Proton Neutron Electron Position in atom Charge Mass In nucleus In nucleus Outside nucleus 1+ 1 No charge 1- 1 0 Is overall Neutral ◦ Because has the same number of positive protons and negative electrons Different elements have different number of protons Recognised as an ATOMIC NUMBER Unique for every element Equals the ◦ Number of protons ◦ Number of electrons (for an atom) The only two particles which have mass in an atom are ◦ Protons ◦ Neutrons BOTH ARE FOUND IN NUCLEUS The only two particles which have mass in an atom are ◦ Protons ◦ Neutrons BOTH ARE FOUND IN NUCLEUS MASS NUMBER = ◦ PROTONS + NEUTRONS NO. OF NEUTRONS = ◦ MASS NUMBER – ATOMIC NUMBER Number of protons = never changes ◦ Is like the elements DNA, will never change Number of neutrons = affect mass of atom ◦ Some heavier, some lighter atoms Number of electrons = affects the mood the element in ◦ Neutral ◦ Positive ◦ Negative Note the numbers are written at LHS of symbol Atomic Number is at the bottom – can be checked using data book if you forget Mass Number (the bigger number) at the top. No. of protons = Atomic Number ◦ = 17 No. of electrons = Atomic Number ◦ = 17 No. of neutrons = Mass No. – Atomic No. ◦ = 37- 17 = 20 Are atoms with the ◦ Same atomic number ◦ But, Different mass number i.e. Different number of neutrons Most elements exist as a mixture of isotopes This is rarely a whole number ◦ WHY? The relative atomic mass is an average of all the different Isotopes taking into account the proportion of each present. Relative Atomic Mass = 36.5 Would expect Average to be = 36 Closer to 37 = Grater proportion of 37 isotope present Relative Atomic Mass = 36.0 This tells you that there is exactly 50% of each isotope present as the average lies exactly in the middle. Charged particles Group 1 – Alkali Metals ◦ Reactive Group 7 – Halogens ◦ Reactive Group 8 (0) – Nobel gases ◦ Unreactive Atoms held together by bonds Bonds are formed so elements can achieve a stable electron arrangement ◦ i.e. a full outer shell like the noble gas elements. REMEMBER GROUP 8 ARE UNREACTIVE AND SO NOT BOND Non-metals only Atoms share electrons Covalent bond held together by ◦ Attraction between the positive nuclei and the negative shared electrons Molecule = group of atoms held together by COVALENT bonds 2 elements bonded together Diatomic Elements ◦ H, N, O, F, Cl, Br, I Diatomic Compounds ◦ CO, NO Low Mp and Bp Because strong covalent bonds not broken Weak forces BETWEEN molecules broken MOLECULAR High Mp and Bp Because strong covalent bonds need to be broken and this required a lot of energy. E.g. Diamond Sand (SiO2) NETWORK (usually) soluble in non-aqueous solvents (usually) insoluble in aqueous solvents(water) NEVER CONDUCT ELECTRICITY!!!! Try CH4 NH3 HCl CO2 – very tricky! Charged Particle Metals – lose electrons – form +ve Ions MP Non-metals – gain electrons – form –ve Ions Between metals and non-metals Bond held together by electrostatic attraction between POSITIVE AND NEGATIVE IONS Crystal Lattice Structure of oppositely charged ions Do not conduct when solid as IONS NOT FREE TO MOVE Conduct when in solution or molten as IONS ARE FREE TO MOVE Solid at room temperature ◦ Strong forces of attraction that need to be broken Soluble is aqueous solvent (i.e. water)