Electron Configurations – a Review and More…

Electron Configurations e- configuration notation: Reminder – this notation uses # of e- in a sublevel as a superscript over the sublevel (block) designation Write complete e- configuration notation for elements 2, 6, & 16 He: C: S:

Electron Configurations e- configuration notation (noble gas shortcut): Reminder – this version uses a noble gas (group 18) “core” instead of beginning at 1s Write noble gas shortcut for elements 12, 21, & 35. Mg: Sc: Br:

Electron Configurations e- dot notation: simplest notation, only shows valence e- (e- that may be lost, gained, or shared when chemical compounds are formed - they are from s & p blocks) Draw dot diagrams for elements 1-10

Ion Formation…

Valence electrons: outer shell electrons that may be lost, gained, or shared when chemical compounds are formed

Ion Formation… Octet rule: atoms are most stable when they have a filled outer shell of valence e- (usually 8 e-) noble gases have this configuration without any help – other atoms lose, gain, or share e- to fill their outer shell

Ion Formation… Ions: Atoms that have either gained or lost e -. –Gain of e - gives a negative ion called an anion. –Loss of e - gives a positive ion called a cation.

Ion Formation… Ion examples: The magnesium ion is Mg 2+. How many p + and e - does it have? The oxide ion is O 2-. How many p + and e - does it have? An ion has 7 p + and 10 e -. What ion is it? An ion has 4 p + and 2 e -. What ion is it?

Bonding

Chemical Bonds link between atoms due to mutual attraction of nuclei for e-

Chemical Bonds Why bond??? Bonding can result in lower potential energy (this is usually associated with a release of energy) Lower energy gives greater stability (greatest completed energy level)

Chemical Bonds Bonds are classified by how the valence e- are distributed around nuclei of combined atoms

Types of Chemical Bonds Ionic bond – results from electrostatic attraction between positive and negative ions (usually done when metal bonds w/ nonmetal)

Types of Chemical Bonds Ionic bond Created by transfer of e- from one atom to another Active metals readily give up their e-, usually to a nonmetal atom Oppositely charged ions are formed by this process of transferring e- Cation: + charged ion Anion: - charged ion

Types of Chemical Bonds Ionic bond Forming ionic bonds: e- are transferred from atom with lower EN value to one with higher value

Types of Chemical Bonds Ionic bond Forming ionic bonds: How can you determine if bond is ionic? See if atoms are active metal & non-metal or look up EN values to get difference. (if EN difference is 1.7 to 4.0, ionic bond)

Types of Chemical Bonds Ionic bond Types of ions Monoatomic – single element with charge Polyatomic – 2 or more elements with charge

Types of Chemical Bonds Ionic bond Ionic compound – composed of positive & negative ions combined so that the positive & negative charges are equal in number (Ex. NaCl instead of Na 2 Cl or NaCl 2 )

Types of Chemical Bonds Covalent (molecular) bond – results from the sharing of e- between two atoms (usually done w/ nonmetal atoms) The e- are not always equally shared (like tug of war)

Covalent Bonds Bonds between 2 unlike atoms are never completely covalent Non-polar covalent – e- are shared equally ( which only happens between two identical atoms) Polar covalent – e- are not equally shared (due to differences in electronegativity)

Covalent Bonds May share 1 or more pairs of e- Single bond – single pair of shared e- between two atoms Double bond – two pairs of shared e- between two atoms Triple bond – three pairs of shared e- between two atoms

Covalent Bonds Atoms that are bonded covalently form stable particles called molecules Ex. CO 2, P 2 O 5, NH 3, etc. 7 diatomic molecules to know - H 2, N 2, O 2, F 2, Cl 2, I 2, Br 2

Covalent Bonds Molecular compound – chemical compound whose simplest formulas are molecules

Comparing Properties… Ionic Compounds Held together tightly (due to attraction of charges) –High melting point –High boiling point –Hard & brittle crystalline solids –Dissolve in water –Carry a current (very well) in water

Comparing Properties… Molecular Compounds Most are not tightly held –Most have low melting point (due to weak attractions between molecules) –Most have low boiling point –Usually soft, amorphous solids –Some dissolve in water –Do not carry current well in water

Determining Bond Type… Using Periodic Table Metal Element (left of staircase) + Nonmetal Element (right of staircase) –Ionic Bond Two Nonmetal Elements (right of staircase) –Covalent Bond

Determining Bond Type… Using Electronegativity Values 1.Page 161 has a EN chart –Determine the EN difference between the two elements in the bond 2.Go to page 176 and find the chart of bond types. Use the EN difference to determine type of bond (greater difference = more ionic character). –Nonpolar covalent: difference of 0 to 0.3 –Polar covalent: difference of 0.3 to 1.7 –Ionic: difference of 1.7 to 4.0

Determining Bond Type… Using Observed Properties from Lab Activity

Representing Compounds - Ionic Empirical formula or Formula unit – indicates lowest whole number ratio of cations to anions in any sample of an ionic compound (ex. NaF = 1 Na + ion + 1 F - ion)

Representing Compounds - Ionic Empirical formula or Formula unit – simplest unit indicated by the formula of any compound (ex. NaF = 1 Na + ion + 1 F - ion) This “unit” doesn’t represent something that can be isolated, it is only the smallest possible ratio to make a neutral electrical charge # of ions in one formula unit depends on the charges of the ions to be combined (ex. B + F, Na + Cl, K + O, etc)

Representing Compounds - Ionic Just a thought… Can you use the periodic table to determine the charge of an ion?

Representing Compounds - Ionic Determining formula units by the crisscross method Ca + Br K + P Al + O Ca + O Al 3+ + OH 1- Mg 2+ + PO 4 3-

Representing Compounds - Molecular Molecular formula – shows the types and numbers of atoms combined in a single molecule of a compound Ex. CO, H 2 O 2, SO 3, O 2

Representing Compounds - Molecular Structural formula – shows kind, number, arrangement, and bonds (single, double, or triple) of the atoms in a molecule (or polyatomic ion) Ex.

Representing Compounds - Molecular Lewis structures - diagrams that show valence e- as dots, the inner e- and nucleus are included in the letter symbol for the element being represented

Representing Compounds - Molecular Lewis structures Reminder… Group 1 Group 2 Group 13 Group 14 Group 15 Group 16 Group 17 Group 18

Representing Compounds - Molecular Lewis structures –Structures of individual elements may be joined to form compounds –pairs of dots (or a dash) between symbols represent bonds (or electron pairs), dots adjacent only to one symbol are unshared e- –Lone (unshared) pair of e- – pair of e- that is not involved in bonding, but instead belongs exclusively to one atom

Representing Compounds - Molecular Lewis structures Ex. F 2, NH 3, H 2 O, CH 4, O 2, CO 2, N 2, CH 2 O, C 2 H 2, PI 3 (must draw structures)

Representing Compounds - Molecular Lewis structures Octet exceptions: Less than full octet Ex: Boron compounds such as BF 3 More than full octet – atoms beyond 2nd period, most often S & P (extra e- go to 3d level) Ex: SF 4