Electron-Dot Notation

Electron-Dot Notation

How does the interaction between nuclei & valence electrons affect how atoms interact together?


Valence electrons are responsible for chemical bonding. Group 1: Alkali metals have 1 valence

electron Group 2: Alkali-earth metals have 2 valence

electrons Electron-Dot Notation:

It only shows the valence electrons of an atom, which are indicated by dots placed around the element’s symbol.


1. Write the symbol2. Put one dot for each valence electron.3. Don’t pair up the e- unless you have

to.

X

Electron Dot Notation: Nitrogen

Nitrogen has 5 valence electrons.

First we write the symbol. NThen add 1 electron

at a time to each side, until they are forced to pair up.

Mg

Write the electron dot notation for…Remember:# Valence Electron = # electrons on outermost ring (last ring) Na Mg C O F Ne He

1s22s22p63s1

1s22s22p63s2

1s22s22p2

1s22s22p4

1s22s22p5

1s22s22p6

1s2

Na

C

O

F

He

Ne

Electron-Dot Notation: Cations

Metals (L side of the Periodic Table) tend to lose electrons to attain greatest stability (8 valence electrons – Octet Rule). This results in forming positive ions, cations.

Example:

Na 1s22s22p63s1 - 1 valence electronNa+ 1s22s22p6 – 8 valence electrons

Ca

Electron Dot Notation for Cations Elements that have few valence electrons will

tend to lose them, forming positive ions: cations.

Calcium: 20 e- Ca2+: 18 e-

1s22s22p63s23p64s2 1s22s22p63s23p6Ca40.078

20

Ca2

+

Electron Configurations for Anions

Nonmetals (R of the periodic table) tend to gain electrons to attain stability This results in forming negative ions,

anions.

Sulfur S 1s22s22p63s23p4 - 6 valence

electrons S2- 1s22s22p63s23p6 – 8 valence

electronsS S2

-

Common Monatomic Ions: pg. 221Group 1: 1+ Group 2: 2+ Group 13:

3+

Lithium Li+

Beryllium Be2+

Aluminum Al3+

Sodium Na+

Magnesium Mg2+

Potassium K+

Calcium Ca2+

Rubidium Rb+

Strontium Sr2+

Cesium Cs+

Barium Ba2+

Group 17 1-

Group 16 2-

Group 15 3-

Fluoride F-

Oxide O2-

Nitride N3-

Chloride Cl-

Sulfide S2-

Phosphide P3-

Bromide Br-

Iodide I-

Elements down a group have similar charges.

Group 1 (Alkali) elements produce 1+ ionsGroup 2 (Alkali-earth)elements produce 2+ ionsGroup 13 elements produce 3+ ions

Group 14 elements produce 4- ionsGroup 15 elements produce 3- ionsGroup 16 elements produce 2- ionsGroup 17 (Halogens) elements produce 1- ionsGroup 18 (noble gases) elements (STABLE!) – do not produce ions

Ionic Bonding & Ionic Compounds

Ionic Bonding

Ionic Compounds: Composed of a cation and an anion that are bonded together Ionic compounds are called salts.

Properties of Ionic Compounds: Crystal Lattice Ionic Compounds consists of positive and negative ions held together by ionic bonds. They are ordered in a rigid structure, called a

crystal lattice. Crystal Lattice: a repeating arrangement of ions in

the solid. Ionic compounds have high melting points -

because of strong forces between ions It requires a lot of energy to melt an ionic compound

Ionic Bonding - Crystal Lattice

Crystal Lattice: Table Salt, NaCl

Table salt

Ionic solids are Brittle

+ - + -+- +-

+ - + -+- +-

Force + - + -

Strong repulsion breaks crystal apart.

Ionic Bonding

Ionic Bonding: Formed when atoms completely give up electrons to other atoms, transferring of electrons.. To achieve stability 8 valence electrons.

Ionic Bonding

Na

Cl

transfer of electron

+ -

NaCl

Example: Sodium & Chloride

• Sodium: Group 1, 1 valence electron

• Chloride, Group 17, 7 valence electrons

• Sodium will give up its 1 valence electron so that it can achieve stability, meanwhile chlorine gains 1 to achieve stability

•Mutual Benefits!

Ionic Bonding

-

-

-

-

-

- -

-

-

-

-

- -

-

-

n = 2

Na1 valence electron

n = 3

n = 3

+

-

-

-

-

-

- -

--

-

- -

-

- -

-

Cl7 valence electrons

Na+

8 valence e-

Cl-

8 valence electrons

NaCl

Transfer of electrons to achieve a stable octet (8 electrons in valence shell).

--

-

-

-

--

-

-

-

-

-

-

- -

-

-

-

- -

-

-

- -

-

Calcium gives up two valence electrons – one to each fluorine atom.

Chemical Formulas

Chemical Formulas indicate the number of atoms of each kind in a compound.

CaCl2

Binary Compound: Two Types of atomsCalcium Chloride

1 Calcium atom

2 Chloride atoms

“ Chlorine” becomes ‘Chloride” when it gains electrons

Cations always come first

1 2

CaCl2

Ca Cl

Ca Cl

2+ 1-

1. Write out names with space

2. Write symbols & charge of elements

3. criss-cross charges as subscripts,drop the + and - signs

4. combine into formula(“1” is never shown)

Calcium Chloride

Formulating Binary Ionic Compounds:

Criss-Cross RuleSteps

Step 1: Aluminum Oxide

Step 2: Al3+ O2-

Step 3: Al O2 3

Step 4: Al2O3

Criss-Cross Rule: Aluminum OxideNote: The name of the cation is given first, then the anion.

Step 1: Magnesium Oxide

Step 2: Mg2+ O2-

Step 3: Mg O2 2

Step 4: Mg2O2

Step 5 MgO(Reduce to lowest terms) :

Criss-Cross Rule: Magnesium Oxide

IrBr3BaS

Criss-Cross RuleCriss-cross rule:

** Warning: Reduce to lowest terms.

Al2O3

Al3+ and O2–

Al2 O3

Ba2+ and S2–

Ba2 S2

Ir3+ and Br1–

Ir1 Br3

Ca +2

P -3Ca

+2

P

All the electrons must be accounted for!

+2

Ionic Bonding

Ca -3

Ionic Bonding

Ca3P

2Formula Unit

Ca2+

Ca2+

Ca2+

P3-

P 3-

Ca2

+

P3- Ca2+

P3- Ca2

+

Polyatomic Ions

Ionic bonding can occur with polyatomic ions, because sometimes, a cation or an anion can be a polyatomic ion…which is -

A charged group of atoms, resulting from an excess of electrons ( - ) or a shortage of electrons (+)

Stays together, functions as a unit

Common Polyatomic Ions

Writing Formulas with Polyatomic Ions

Binary Compounds: Formulas http://www.chemfiles.com/flash/

formulas.html

Bonding Activity – Why the criss-cross rule?

O2-

K1+

K1+

Mg2+

Br1-

Br1-

K Br

potassium atom bromine atom

e- e- Br1-K1+

potassium ion bromide ionpotassium bromide

K Br

potassium atom bromine atom

e-

Br1-K1+

potassium ion bromide ion

KBr

MgBr2 K2Omagnesium bromide potassium oxide

Ca2+

Al3+

K1+

Pb4+

Br1-

O2-

N3-

K1+

K1+

Mg2+

Br1-

Br1-

PO43-

S2-

Cu2+

OH1-

OH1-NH41+

NO31-

?

Review: Naming Ionic Compounds

Rules of Naming Ionic Compounds(1) The name of cations do not change.Examples: Sodium, Na+ Hydrogen, H+

(2) The ending of monatomic anions change to –ide.

Examples: Chlorine Chloride, Cl-

Nitrogen Nitride, N3-

The name of polyatomic ions do not change.

Examples: Bromate, BrO3- Carbonate, CO3

2-

Rules of Naming Ionic Compounds(4) Some cations have multiple charges. These

are represented by roman numerals. This system of naming is called the Stock system.Examples: Lead (IV): Pb4+ Lead (II): Pb2+

Lead(IV) oxide vs. Lead (II) oxidePb4+ O2- Pb2+ O2-

Pb2O4 Pb2O2

PbO2 PbO

We must use the Stock system to distinguish which lead we are referring to.

Nomenclature: Binary Compounds – Stock System

Ion Stock Ion Stock

Fe2+ Iron II Fe3+ Iron III

Cu+ Copper I Cu2+ Copper II

Au+ Gold I Au3+ Gold III

Sn2+ Tin II Sn4+ Tin IV

Pb2+ Lead II Pb4+ Lead IV

Hg+ Mercury I Hg2+ Mercury II

Cr2+ Chromium II Cr3+ Chromium III

Mn2+ Manganese II Mn3+ Manganese III

Practice:Formula Name

1 BaO ____________________

2 ________________ sodium bromide

3 MgI2 ____________________

4 KCl ____________________

5 ________________ strontium fluoride

6 ________________ cesium fluoride

barium oxide

NaBr

magnesium iodide

potassium chloride

SrF2

CsF

Practice:

Which iron is used in these chemical formula? Fe2O3 Iron(III) oxide FeS Iron(II) sulfide

Which copper is used in this chemical formula? Cu(ClO4)2 Copper(II) perchlorate

Which gold is used in this chemical formula?Au2O

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Electron-Dot Notation