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Chapter 1 Prep - Chapter 1, page 7. Chapter 1 Prep - Chapter 1, page 13. mercury (II) iodide. aluminium oxide. 3. a) b) c) d) 4. a) b) c) d) 5. a) b) c) d) 6. a) b) c) d) 7. a) b) c) d) 8. a) b) c) d). sodium phosphide.

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chapter 1 prep chapter 1 page 13
Chapter 1 Prep - Chapter 1, page 13

mercury (II) iodide

aluminium oxide

  • 3. a) b)

c) d)

4. a) b)

c) d)

5. a) b)

c) d)

6. a) b)

c) d)

7. a) b)

c) d)

8. a) b)

c) d)

sodium phosphide

calcium bromide

FeS

ZnO

MgI2

CoCl3

sulfur hexafluoride

dinitrogen penta-oxide

phosphorus pentachloride

carbon tetrafluoride

H2O never call it this!

SO3

N2O4

N2O

potassium phosphate

ammonium chloride

lithium perchlorate

sodium hydrogen carbonate

MgOOCCOO

KClO

NaCN

(NH4)2SO4

chemistry 20

Chemistry 20

Chapter 1

PowerPoint presentation by

R. Schultz

robert.schultz@ei.educ.ab.ca

1 1 forming and representing compounds
1.1 Forming and Representing Compounds
  • Chemical bonding theories developed by observing chemical reactions and physical properties of natural substances
  • Many patterns have been observed – one set, page 17 of Inquiry into Chemistry
  • You studied all of these in Science 10:
    • Metals found in combination with non-metals
    • Metals in pure form are solids

ionic compounds

1 1 forming and representing compounds1
1.1 Forming and Representing Compounds
  • Non-metals combine to form solids, liquids, and gases
  • Only Noble Gases exist as individual atoms(we write metals as single atoms, but this is not how they exist)

• Watch Chemical Families Video

molecular compounds

1 1 forming and representing compounds2
1.1 Forming and Representing Compounds
  • Lewis Dot Diagrams:
  • show valence electrons only
  • valence electrons arranged into orbitals
  • Orbital: area of space where an electron of a given energy is most likely found - not what it is doing
  • What parts of atom does atomic symbol represent? (2 things)

nucleus

inner, non-valence electrons

1 1 forming and representing compounds3
1.1 Forming and Representing Compounds
  • Main group elementswill always have 4valence orbitals
  • Each orbital can hold maximum of 2 electrons
  • Electrons in completely filled orbital called lone pair
  • Electrons in half-filled orbital called bonding electrons

Fig 1.5, p. 19

1 1 forming and representing compounds4
1.1 Forming and Representing Compounds
  • To draw a Lewis Dot Diagram of an element:
    • Write the element symbol
    • Count # of valence electrons
  • Each side of the symbol represents 1 of the 4 valence orbitals
    • Start on 1 of the sides, proceed around putting 1 electron on each, not doubling up until you have to
1 1 forming and representing compounds5

bonding electrons

lone pairs

1.1 Forming and Representing Compounds
  • Example: oxygen (6 valence electrons)

Now you can start doubling up – electrons repel each other so 1 electron per orbital is more stable than 2

O

It doesn’t matter which side lone pairs and bonding pairs are (it depends where you start counting from) important thing is that O ends up with 2 lone pairs and 2 bonding electrons

1 1 forming and representing compounds6

use sides not corners

O

1.1 Forming and Representing Compounds
  • Please don’t do your Lewis Diagrams like this:
  • or like this:

electron pairs should be parallel to the symbol sides

O

1 1 forming and representing compounds7
1.1 Forming and Representing Compounds
  • Electronegativity – find on periodic table
  • Do BLM 1.1.3B – Lewis Diagrams of Atoms
  • Correct
  • Note that Noble Gases have the stable octet electron configuration
1 1 forming and representing compounds8
1.1 Forming and Representing Compounds
  • The stable octet configuration is what atoms attempt to achieve through bonding
  • Atoms can get the stable octet by transferring electrons or by sharing them
1 1 forming and representing compounds9

to get the stable octet for each

1.1 Forming and Representing Compounds
  • Ionic compounds – transferring electrons
  • In reactions between metals and non-metals,
    • metals tend to lose electrons
    • non-metals tend to gain electrons

We’ll discuss why later in the chapter

1 1 forming and representing compounds10

Na +

Cl

electron transfer

If I ask you to do this on an assignment, quiz, or test, you must show everything circled in red

1.1 Forming and Representing Compounds
  • Example:

+

Na

+ Cl

both have stable octet (Na has 8 electrons in the previous valence level)

neither has stable octet

1 1 forming and representing compounds11

2+

Ca

F

+2

On an assignment, quiz, or test, it is sufficient to do the following:

F

2+

+ 2

Ca +

Ca

F

F

1.1 Forming and Representing Compounds
  • Example:

+

+ F

F

Ca +

F

Ca +

F gets the stable octet, but not Ca, transfer the 2nd electron to another F

Note that the coefficients CaF2 are the same as those in the balanced formula!

1 1 forming and representing compounds12
1.1 Forming and Representing Compounds
  • Bonds between ions, formed by electron transfer are called ionic bonds
  • Do question 6b, d, e on page 21
1 1 forming and representing compounds13
1.1 Forming and Representing Compounds
  • Molecular compounds – sharing electrons
  • Bonds formed by sharing electrons called covalent bonds
  • Covalent bonds exist between non-metallic atoms in a molecule and between atoms within a polyatomic ion (e.g. SO42-)
1 1 forming and representing compounds14
1.1 Forming and Representing Compounds
  • Drawing Lewis Structures for Molecular Compounds:
  • Start by counting the number of bonding electrons on each atom involved
  • The atom with the most bonding electrons is the central atom
  • Sometimes there will be more than 1 central atom
  • Start with the central atom, bonding other atoms to it, until it has the stable octet
1 1 forming and representing compounds15

H

1.1 Forming and Representing Compounds
  • Examples:
  • H2O

O

H•

1 bonding electron

2 bonding electrons:central atom

Note that O gets the stable octet

H ends up with 2 – that’s what it needs

H•

O

1 1 forming and representing compounds16

H

1.1 Forming and Representing Compounds
  • It is unnecessary to put circles around the atoms as your text does – I find they just make the diagrams messy and hard to read – even when typed out

O

H•

1 1 forming and representing compounds17
1.1 Forming and Representing Compounds
  • A correct Lewis structure will always have a stable octet for every element other than H
  • When doing these diagrams, make electrons on adjacent atoms look different – different colour, different symbol, etc. Even if the atoms are atoms of the same element!
1 1 forming and representing compounds18

H

H

H

C

H

C

H

H

1.1 Forming and Representing Compounds
  • Further example:
  • C2H6

H•

C

central atom

Note that both C’s get the stable octet

Also note that I have made electrons on the 2 C’s different colours, since they are adjacent, and all H’s the same since they aren’t adjacent

1 1 forming and representing compounds19
1.1 Forming and Representing Compounds
  • Do BLM 1.1.4B – Lewis Diagrams of Molecules up to and including question 10
  • Try question 11, but you will likely have some difficulties – I will show how to do this type with next set of examples
1 1 forming and representing compounds20

stable octet on everything!

••

Cl

••

••

••

••

Si

F

C

F

••

••

Cl

••

••

••

1.1 Forming and Representing Compounds
  • Extra examples:
  • SiCF2Cl2 – always start with most symmetric arrangement

C

••

Cl

Si

••

••

••

••

••

Si

F

F

C

F

••

••

••

••

Cl

••

Cl

••

••

Si and C don’t have stable octet. Share the other 2 electrons (circled in grey)

1 1 forming and representing compounds21

••

••

P

Si

H

P

1.1 Forming and Representing Compounds
  • Example: HSiP

••

Si

H

P

Si

Si has 6; P has 6 - share more electrons!

H•

Single, double, and triple covalent bonds are possible

Experimental evidence indicates they actually exist

1 1 forming and representing compounds22

••

O

••

••

••

S

O

O

••

••

O

••

1.1 Forming and Representing Compounds
  • Example: SO42- (polyatomic ion) – you will not be required to do these but I want to show you an illustration

• extra electron

Note: you could draw a Lewis Diagram with the extra electrons in other spots, but they there has to be 2 extra electrons to make SO42- stable

1 1 forming and representing compounds23
1.1 Forming and Representing Compounds
  • Extra Practice – Practice Problems 7 – 17, page 27
  • Answers – page 728 – They don’t use colours or symbols to differentiate electrons, but this is a requirement for you
1 1 forming and representing compounds24

••

••

••

••

••

••

••

••

O

S

O

••

1.1 Forming and Representing Compounds
  • Resonance – page 27

actual structure is a cross between the two

••

••

••

••

••

••

••

••

O

S

O

••

Experimentally, bonds are identical

These diagrams show resonance more clearly than the ones in your text

You will not be required to draw resonance diagrams, but you should know the concept and be prepared to answer multiple choice questions concerning it

1 1 forming and representing compounds25

+

H

••

H

N

H

H

1.1 Forming and Representing Compounds
  • Coordinate covalent bonds – bonds where both electrons come from the same atom
  • e.g. NH4+
1 1 forming and representing compounds26
1.1 Forming and Representing Compounds
  • Structural formula – not the actual structure
  • Based on Lewis diagram – electron pairs are dropped and bonds replaced by lines

H

H

H

H

H

C

H

C

H

C

H

C

H

H

H

H

1 1 forming and representing compounds27
1.1 Forming and Representing Compounds

••

Cl

••

••

Cl

••

••

Si

F

F

C

Si

C

F

F

••

••

Cl

••

Cl

••

••

••

Si

Si

H

P

H

P

1 1 forming and representing compounds28
1.1 Forming and Representing Compounds
  • Structural formulas are very useful and we will use them, but don’t confuse them with molecular structure – Chapter 2
  • Do question 8a, c, e, f, g, h, j page 31 – Lewis Diagram and structural formula for each
  • Modeling – chapter 2, after VSEPR theory
1 1 forming and representing compounds29
1.1 Forming and Representing Compounds
  • Metallic Bonding – theory now, relationship to properties in Chapter 2
  • Metallic Bonding Handout - review

Fig 1.16, page 32

shows Mg atoms having released their valence electrons to the electron cloud to become Mg ions in the metal crystal

1 1 forming and representing compounds30
1.1 Forming and Representing Compounds
  • Remember, metals do not exist as individual atoms – if they did they would be gasesThey exist as metal ions in a crystal of delocalized valence electrons
  • Analogy: Rice Krispee squares
1 1 forming and representing compounds31
1.1 Forming and Representing Compounds
  • Nomenclature Review: Question 9, page 34
  • Identify each as ionic or molecular, and provide the correct name
1 2 the nature of chemical bonds
1.2 The Nature of Chemical Bonds
  • Electronegativity: relative measure of an atom’s ability to attract shared electrons in a covalent bond

Generalizations?

metals low; non-metals high

F highest; Fr lowest

 from left to right

 from top to bottom

noble gases have none – not zero

1 2 the nature of chemical bonds1
1.2 The Nature of Chemical Bonds
  • Note 2 things about this diagram:

atoms get smaller as you go across a row from left to right!! (but …….)

electronegativity is inversely related to atomic size – small atoms  large electronegativity; large atoms  small electronegativity (Noble Gases excepted)

fig 1.19, page 37

1 2 the nature of chemical bonds2
1.2 The Nature of Chemical Bonds
  • Atomic radius  as you move left to right because valence electrons for a given period all occupy same set of orbitals – outer radius is ~ fixed – but, as you move left to right nuclear charge  attracting valence electrons closer (attractive force and )
  • Because of the small size and large charge, F has the highest electronegativity (attraction for shared electrons
  • Atomic radius  as you move from top to bottom since each period is filling of a new set of orbitals with larger radius
1 2 the nature of chemical bonds4
1.2 The Nature of Chemical Bonds
  • Atoms can share electrons or transfer electrons to obtain the stable octet electron configuration
  • If electronegativities are close or equal you can predict electrons will be shared
  • If electronegativities differ by more than a certain limit you can predict electrons will be transferred
  • But, ………..
1 2 the nature of chemical bonds5
1.2 The Nature of Chemical Bonds
  • non-polar covalent bond: a covalent bond where electrons are shared equally
  • polar covalent bond: a covalent bond where electrons are shared unequally
  • a polar covalent bond is said to have a bond dipole – since electrons are shared unequally, one end of the bond is partially + (δ+); other end partially – (δ-)
  • there are 2 poles ……
1 2 the nature of chemical bonds6
1.2 The Nature of Chemical Bonds
  • Bond dipoles also designated by symbolExamples 10a, 11a, page 41
  • Examples 10d, 11d, page 41

δ+

δ-

C - F

ΔEN = 4.0 – 2.6 = 1.4

polar covalent*

ΔEN = 3.4 – 1.9 = 1.5polar covalent according to chart*

we would normally call this ionic (continuum)

Cu - O

*chart, page 40 (next slide)

1 2 the nature of chemical bonds7

know this number!

1.2 The Nature of Chemical Bonds

Page 40

do questions 10 and 11 b, c, e, f, h, page 41

1 2 the nature of chemical bonds8
1.2 The Nature of Chemical Bonds
  • Another picture – page 88
1 2 the nature of chemical bonds10
1.2 The Nature of Chemical Bonds
  • Review: Chapter 1 Review, page 44

good questions:1, 3 (what does each component of the diagram represent?), 7*, 8, 12, 14, 15 a, b, d, i, j, 16 (all but a and h), 17, 18, 19-24 (for question 24 draw bond dipole arrows for polar covalent bonds)

* no multiple bonds here – also do C2HF, N2