Class 2 How Atoms combine with similar and
Class 2 How Atoms combine with similar and dissimilar atoms • • • Periodic table Electron configurations Energies Bond types and properties. Fall 12
Columns represent groups of similar properties, Group 1 A, alkali metals; 8, inert gases; 7 B halides
Atomic Model Nucleus – Protons +ve charge Neutrons no charge Orbitals – Electrons –ve charge Atoms – protons and electrons balance each other, so no net charge. Ions – Positive or negative charge imbalance Na+ or Cl Quantum mechanical model Replaced this one
Electron States Each Quantum Number Fills up first- 1, 2, 3, 4, 5, 6 etc Chlorine atom, z=17, 1 s 2, 2 p 6, 3 s 2, 3 p 5, electrons = 2+2+6+2+5=17 2 So 1 S 2, then 2 S , 2 p 6, then 3 S 2, 3 P 6, 3 D 10, then 4 S etc – there are some Discrepancies though.
Note 4 s before 3 d Note 4 s 1 3 d 5 Note 4 s 1 3 d 10
Electron Filling of Orbitals 1 s 2 s 2 p 3 s 3 p 3 d 4 s 4 p 4 d Z= 1 s 2 s 2 p 3 s 3 p 3 d 4 s 4 p 1 s 2 s 2 p 3 s 3 p 3 d 4 s 1 s 2 s 2 p 3 s 3 p 4 s 1 s 2 s 2 p 3 s 1 s 2 s 2 p 1 s 2 s 1 s On Ionisation, 4 s levels empties first. 46 36 30 20 12 10 4 2
Filling of Shells • Electrons shells like to be full, half full or empty. • Full shells – inert status, for example helium • Full or empty, between elements by ionic or covalent bonding. • Metallic bonding – sharing of electrons.
Periodic Table • Rows – number of shells 1, 2, 3, 4 etc • Column – number of electrons in outer shell • Columns have like properties as number of electrons in outer shell same. • Atomic number – number of electrons and so protons in atom. • Different number of electrons changes properties and produces elements
Bonding Types • Between like atoms – metallic or covalent • Between different atoms – metallic, ionic or covalent. • Primary – ionic, covalent and metallic. strong • Secondary – hydrogen, van der Waals. weak.
4 s level just below 3 d Ionisation energies for the hydrogen atom
Ionic Bonding Na, z=11, # of electrons and protons, 1 s 2, 2 p 6, 3 s 1 : 2+2+6+1=11 Note 3 s 1, lose this electron, full orbitals then ; alkali metals Cl, z=17, 1 s 2, 2 p 6, 3 s 2, 3 p 5 : 2+2+6+2+5=17 Note 3 p 5, gain one electron, full 3 p 6 orbital, halide ions Na+ ion due to loosing one electron, Cl- due to gaining an electron Ionic bonding between elements with different electronegativities. Elements on right of periodic table highly electronegative, and want to Gain electrons, elements on left electropositive, lose an electron. Directional so brittle type materials. Ordered structure, move one ion Lose order. Crystalline structure from this bonding.
Covalent Bonding Hydrogen 1 s 1, Carbon 1 s 2, 2 p 2, so if hydrogen can share one electron And carbon can share four electrons, both elements will have full orbitals. Four hydrogens share with one carbon in covalent bonds. Molecule of methane gas formed – different elements or same can exhibit Covalent bonds eg carbon. Elements with half full outer orbital. Can be crystalline
Metallic Bonding Ion cores protons And neutrons Electrons shared in a gas cloud as outer orbitals not filled. Lots of empty energy states, such as 3 d etc. Can be single element, eg gold, or mixtures such as brass, or aluminum alloys. No directionality to bonds, so ductile and conductive. Crystalline usually, but not ordered.
Metallic Conductivity Electrons in Electrons out Metals are conductive as the electrons are not specific to an ion Applications – electrical wire, copper circuit boards, thermocouples.
Bond Energy and Properties State 25 C Solid Primary Solids Primary Liquid Solid Primary Gases Secondary Bond energy controls melting point.
Secondary Bonding • Hydrogen – needs presence of hydrogen, single electron effect, non crystalline normally • Van Der Waals – dipole type bonding, due to slight charge imbalance with distance. Non crystalline normally.
Secondary Bonding Positive charge here as electron Favors carbon side Water good example of hydrogen bond Between hydrogen and oxygen covalent Between molecules, hydrogen bond.
Homework • How does calcium and flourine bond to each other? • How does aluminum bond to other aluminum atoms and how does silicon bond to other silicon atoms? • Why are metals conductive?
- Slides: 18