Chemical Bonding - PowerPoint PPT Presentation

Chemical Bonding

Unit 3 – Lecture 1

No one wants to be alone…

• Most atoms are not found alone in quantity in the universe, they are bonded to other atoms
• All atoms except the ones in Group 18 (the Noble Gases) have an unstable electron configuration
• Atoms will gain, lose, or share valence electrons until they become stable

• Elements will gain, lose, or share electrons to fill their valence shells with 8 e-s
• major groups (1,2,13-17) gain, lose or share until 8 or zero valence e-s
• zero valence electrons means that layer is stripped and the full inner layer is exposed, making them stable

• An Electron-Dot Diagram allows us to draw atoms and show their valence electron configuration
• Write the element’s symbol
• Begin placing dots around the symbol equal to the number of outer-shell electrons
• 1 to a side, then double up

• …show valence e- configuration
• element symbol in center
• surround with # of dots equal to valence e- number
• e-s pair if have more than 4

• Oxidation number:
• charge on the atom after an atom gains, loses, or shares electrons to become stable
• the + or – number tells you how many e-s the atom gained or lost
• positive = surplus loses e-s
• negative = deficit  gains e-s

Oxidation/Charge Numbers

+1 +2 ----------------------------------------- +3 +/-4 -3 -2 -1 0

• Mg
• valence electrons?
• oxidation number?
• how many e-s gained, lost or shared?

• Ge
• valence electrons?
• oxidation number?
• how many e-s gained, lost or shared?

• Cl
• valence electrons?
• oxidation number?
• how many e-s gained, lost or shared?

• Ion – a charged particle
• positively charged particle = cation
• negatively charged particle = anion

• Ionic bond – typically formed btw metal & non-metal
• one atom loses 1 or more e-s
• Metal
• one atom gains 1 or more e-s
• Non-metal
• attraction between the + and – charge ions cause them to bond with a lot of electromagnetic force

• Compounds with Ionic Bonds
• are created from elements on opposite sidesof the Periodic Table
• large difference in electronegativity
• example: NaCl
• form repeating units

• Compounds with Ionic Bonds
• dissolve into aqueous solutions easily
• soluble [solid dissolves in liquid]
• miscible [liquid dissolves in liquid]
• dissociation – particles are pulled apart by water

• Compounds with Ionic Bonds
• can have very strong bonds which cause them tohave unusually high melting and boiling points
• exist usually as solids at room temperature

• Covalent Bond – formed between atoms which share valence e-s to complete their octet
• once bond is formed, atoms are stuck until they bond to something else [do not dissociate].

• Compounds with Covalent Bonds
• are created from elements somewhat close to each other on the Periodic Table
• can be liquids or solids at room temp
• do not dissolve easily into aqueous solutions
• immiscible
• form distinct molecules

• Metallic Bond – formed between metals
• positive nuclei arrange into crystal latticeelectrons flow freely from atom to atom
• sometimes called a “sea of electrons”
• this accounts for physical properties of metals, such as strength, malleability, ductility, thermal and electrical conductivity, opacity, and luster.

• Compounds with Metallic Bonds
• have strength, malleability, ductility, thermal and electrical conductivity, opacity, and luster because of flow of electrons
• are solid at room temp

• Compounds with Metallic Bonds
• may lose e-s to substances outside of the bond
• causes corrosion or oxidation [rusting]
• usually happens with oxygen

“I’m not stealing, I’m sharing unequally…”

• Electronegativity – the ability of an atom to pull electrons to itself
• ie, how well an atom holds onto its own electrons or steals from others
• increases ↑ the PT
• increases  PT

• Reactivity for Metals
• increases  and  from the stair step
• Cesium/Francium = most reactive metals
• Reactivity for Non-Metals
• increases  and  from the stair step
• Fluorine = most reactive non-metal

• Polar-Covalent Bonds – form when atoms in covalent bond do not share e-s equally.
• one end of compound = slightly negative
• one end of compound = slightly positive

• Polarity & Solubility
• “Like Dissolves Like”
• polar & ionic solutes dissolve in polar solvents
• non-polar solutes dissolve in non-polar solvents
• remember, “surround & separate”
• polar cannot dissolve non-polar
• non-polar cannot dissolve polar

• Most atoms bond because…
• lonely too many valence e-s too few valence e-s
• What number of valence e-s is suitable for most atoms?
• 2 8 0 6
• What model is used to show valence e-s on an atom?
• Bohr Lewis Wave Scale
• Atoms which have more or less e-s than normal are…?
• ions positrons negatrons
• How do atoms become stable?
• gain e-s lose e-s share e-s all of these

• Atoms which have gained e-s are called…?
• anion cation ion
• Atoms which have lose e-s are called …?
• anion cation ion
• Ionic bonds are held together by a … force.
• strong nuclear strong electromagnetic
• weak nuclear weak electromagnetic
• Atoms far apart on the PT will usually bond ….
• ionically covalently metallically not at all

• Covalent bonds are formed when atoms..
• gain e-s lose e-s share e-s all of these
• Ionic bonds are formed when atoms …
• gain e-s lose e-s share e-s all of these
• Groups 3-12 will use which type of bond?
• ionic covalent metallic none of these
• Which part of a metallic bond explains why metals are lustrous and good conductor of electricity?
• crystal lattice “sea of electrons”
• nuclear density metals aren’t good conductors…

• Atoms with a strong attraction to their electrons are …?
• positronicgravometricthaleonic electronegative
• What is the most reactive nonmetal?
• Cl F O S
• A covalent bond where the atoms do not share evenly is called a … bond
• polar equatorial longitudinal latitudinal
• Most atoms are found … in nature.
• bonded unbonded free free-range

• What is the rule concerning how polar and nonpolar bonds react?
• “Opposites Attract” “Like Repel” “Like dissolves like” “Surround and Separate”
• How does oxidation affect a metal?
• strengthens it weakens it does not affect it
• Which of these is the most electronegative?
• O Cl F Ar
• When all atoms share electrons equally in a covalent bond, it is called
• polar non-polar ionic metallic

• Draw the Lewis diagram for Selenium (Group 16, Period 4, Atomic # 34).
• Which group of elements loses electrons most easily?
• group 1 group 3 group 15 group 17
• How many dots should be drawn around the element Oxygen in its Lewis diagram?