electron configurations – a review and more…. electron configurations e- configuration notation:...

Electron Configurations – a Review and

More…

Electron Configurationse- 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 Configurationse- 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 Configurationse- 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…

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 BondsWhy bond???• Bonding can result in lower

potential energy (this is usually associated with a release of energy)

•Lower energy gives greater stability (greatest stability @ completed energy level)

Chemical BondsBonds 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)


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


Ionic bondForming ionic bonds: e- are

transferred from atom with lower EN value to one with higher value


Ionic bondForming 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)


Ionic bondTypes of ions• Monoatomic – single element

with charge• Polyatomic – 2 or more

elements with charge


Ionic bondIonic compound – composed of

positive & negative ions combined so that the positive & negative charges are equal in number (Ex. NaCl instead of Na2Cl or NaCl2)


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. CO2, P2O5, NH3, etc.•7 diatomic molecules to know - H2, N2, O2, F2, Cl2, I2, Br2

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 Values1. 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

Activity1.

2.

3.

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)


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)


Just a thought…

Can you use the periodic table to determine the charge of an ion?


Determining formula units by the crisscross method

•Ca + Br•K + P•Al + O•Ca + O•Al3+ + OH1-

•Mg2+ + PO43-

Representing Compounds - Molecular

• Molecular formula – shows the types and numbers of atoms combined in a single molecule of a compound

•Ex. CO, H2O2, SO3, O2


• Structural formula – shows kind, number, arrangement, and bonds (single, double, or triple) of the atoms in a molecule (or polyatomic ion)

•Ex.


• 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


• Lewis structures

Reminder…Group 1Group 2Group 13Group 14

Group 15Group 16

Group 17

Group 18


• 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


• Lewis structuresEx. F2, NH3, H2O, CH4, O2, CO2,

N2, CH2O, C2H2, PI3

(must draw structures)


• Lewis structuresOctet exceptions:Less than full octet

•Ex: Boron compounds such as BF3

More than full octet – atoms beyond 2nd period, most often S & P (extra e- go to 3d level)

•Ex: SF4

electron configurations – a review and more…. electron configurations e- configuration notation:...

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