Honors Chemistry Final - Sophomore Year

UNIT 5

UNIT 5

Covalent bonding is…

sharing electrons between 2 or more nonmetals

ELECTRONEGATIVITY DIFFERENCE VS BOND TYPE

ELECTRONEGATIVITY DIFFERENCE VS BOND TYPE

Electronegativity difference of an ionic bond

>1.8

Electronegativity difference of a polar covalent

between 0.4-1.8

Electronegativity difference of a nonpolar covalent

<0.4

Covalent bonding =

molecular bonding

What does this mean?

Covalent Bonding means…

Bond = Covalent

Molecular Bonding means…

Particle formed = molecule

In a Covalent Bond…

electrons are shared so that atoms achieve an octet

What are the two types of covalent bond?

Polar and Nonpolar

Polar Covalent bond

electrons are NOT shared equally

Nonpolar covalent bond

electrons are shared equally

Lewis Dot Structures

represent valence electrons using dots

Example of a Lewis dot structures

Carbon - 4 valence electrons

What is a lone pair?

an unshared pair of electrons/dots

what are bonding electrons?

the electrons that are not paired

NAMING COVALENT COMPOUNDS

NAMING COVALENT COMPOUNDS

step 1 for naming covalent compounds

Name the first element, add prefix to indicate the number of atoms

DON’T ADD “MONO” IF THERE IS ONLY ONE OF THE FIRST ELEMENT

Step 2 for naming covalent compounds

Name the second element, change the ending to “ide” Add prefixes to indicate the number of atoms

What Are The Prefixes?

1 mono-

2 di-

3 tri-

4 Tetra-

5 Penta-

6 Hexa-

7 Hepta-

8 Octa-

9 Nona-

10 Deca-

WHEN YOU ADD A PREFIX TO OXYGEN…

DROP THE “a” OR THE “o” AT THE END OF THE PREFIX

NAMING COVALENT COMPOUND PRACTICE

NAMING COVALENT COMPOUND PRACTICE

N₂O₃

Cl₂O₇

BCl₃

CF₄

Dinitrogen Trioxide

Dichlorine Heptoxide

Boron Trichloride

Carbon Tetrafluoride

COVALENT COMPOUND FORMULA PRACTICE

COVALENT COMPOUND FORMULA PRACTICE

Dinitrogen Tetrahydride

Trisilicon Tetranitride

Dichlorine Heptoxide

Phosphorus Pentabromide

N₂H₄

Si₃N₄

Cl₂O₇

PBr₅

DRAW LEWIS STRUCTURES FOR MOLECULES

DRAW LEWIS STRUCTURES FOR MOLECULES

step 1

Count the total number of valence electrons from all atoms in the molecule

step 2

Choose your central atom

(This should be the LEAST electronegative atom in the molecule)

Step 2 Tips

Carbon is ALWAYS the central atom

Hydrogen is NEVER the central atom

Halogen are USUALLY NOT the middle

step 3

Arrange the remaining atoms around the central atom and attach using single bonds

step 4

Add lone pairs to any atoms to achieve octets

What are two elements that DO NOT need an octet and how many electrons do they actually need?

Hydrogen (needs only 2 electrons)

Boron (only needs 6 electrons)

step 5

Adjust using double or triple bonds as needed for the total electrons or octet to match

Examples of drawing structures

Examples of drawing structures

F₂

= 14 total valence electrons

H₂O

2(1) + 6 = 8 total valence electrons

(Hydrogen is never in middle)

(There are 2 shared pairs and 2 unshared pairs)

NH₃

5 + 3(1) = 8 valence electrons

CBr₄

4 + 7(4) = 32 valence electrons

(Carbon is always middle)

PCl₃

5 + 7(3) = 26 valence electrons

How many electrons does each bond count for?

2

What is an octet?

a full set of 8 valence electrons

everyone/every element wants this

The noble gases have this

How do we know when to use double or triple bonds?

How do we know when to use double or triple bonds?

examples

examples

O₂

12 electrons

N₂

10 electrons

CO₂

16 electrons

SiS₂

16 electrons

How Do We Draw Structures For Polyatomic Ions?

It is the same as drawing lewis structures for covalent compounds but…

Add electrons to account for the charge

Add brackets and the charge when structure is complete

examples

examples

PO₄ ^3-

5 + 4(6) + 3 = 32 electrons

ClO₃^-

7 + 3(6) + 1 = 26 electrons

NO₃^-

5 + 3(6) + 1 = 24 electrons

VSEPR THEORY

VSEPR THEORY

vsepr stands for…

Valence Shell Electron Pair Repulsion

what is vsepr theory?

when molecules form the electron pairs in bonds and lone pairs spread as far apart from one another as possible

What do we do for it?

focus on central atom

count the e^- domains surrounding that atom

What are electron domains?

bonds (single, double, or triple) or lone pairs (around the central atom)

examples

examples

CH₄

8 electrons

4 electrons domains (all are bonds)

molecular geometry: tetrahedral

H₂O

8 electrons

4 electron domains (2 lone pairs, 2 bonds)

molecular geometry: tetrahedral bent

HCN

10 electrons

electron domains: 2 (both bonds)

molecular geometry: linear

BF₃

3 +3(7) = 24 electrons

electron domains: 3 (all bonds)

molecular geometry: trigonal planar

EXPANDED OCTET

EXPANDED OCTET

what is an expanded octet?

some electrons in the 3rd period (below 3A-7A) or lower can expand their octet (only when there is no other option)

EXPANDED OCTET IS THE…

EXCEPTION NOT THE RULE

examples

examples

SF₆

6 + 6(7) = 48 electrons

6 bonds, 0 lone pairs

PCl₅

5 + 5(7) = 40 electrons

5 bonds, 0 lone pairs

XeF₄

8 +4(7) = 36 electrons

4 bonds, 2 lone pairs

IF EXTRA ELECTRONS…

ADD TO CENTRAL ATOM

What is an intermolecular force?

attractions that exist between molecules

key words: “between molecules”

what is the imf responsible for?

properties such as:

• melting/boiling point

• surface tension

• solubility

WHAT CAUSES POLARITY IN MOLECULES?

WHAT CAUSES POLARITY IN MOLECULES?

what causes polarity in molecules?

an unequal distribution of electron density, due to a difference in electronegativity values

Nonpolar

No central atom, no lone pair, bonded to all of the same atom it’s nonpolar

ex: H₂, Cl₂, CCl₄, BF₃

Polar

Where you see the dash, that’s the partially positive side

Anytime the central atom is bonded to atoms of different elements, the molecule of polar

anytime there is a lone pair(s) on central atom, the molecule is polar

ex: HCl, CCl₃H, HClH₃

THREE MAIN CATEGORIES OF IMFS

THREE MAIN CATEGORIES OF IMFS

London Dispersion Forces (LDF)

all molecules have LDF between them

the weakest of the three types

the only forces that exist between nonpolar molecules

LDFs are caused by…

the movement of electrons within the electron cloud of molecules

LDFs cause…

temporary dipoles within those molecules

extra info on LDFs…

also known as van Der Waals forces

Instantaneous attraction (why it’s so weak)

more electrons in the electron cloud means stronger LDFs

Dipole-Dipole Attraction

forces between all polar molecules

D-D forces are stronger than LDFs but weaker than Hydrogen bonding

Dipoles in polar molecules are not temporary

ex: PCl₃S

DIPOLES POINT TOWARD…

THE MOST ELECTRONEGATIVE ATOM

Hydrogen Bonding

specific type of Dipole-Dipole

molecules that have hydrogen bonded to Fluorine, Oxygen, or Nitrogen can have hydrogen bond with one another

the strongest IMF

a very strong coulombic attraction

Hydrogen bonding with F,O, or N rule

Must see H-F, H-O, or H-N

F,O,N are the most electronegative atoms on the PT

H = only reactive element with only one energy level

• has a largely unshielded nucleus

Molecular Geometry

Molecular Geometry

2 electron dense areas (*know this)

linear (no lone pairs)

3 electron dense areas (*know this)

trigonal planar (no lone pairs)

bent (1 lone pair)

4 electron dense areas (*know this)

tetrahedral (no lone pairs)

trigonal pyramidal (1 lone pair)

bent (2 lone pairs)

5 electron dense areas

trigonal bipyramidal (no lone pairs)

sawhorse (1 lone pair)

T-shaped (2 lone pairs)

Linear (3 lone pairs)

6 electron dense areas

Octahedral (no lone pairs)

Square pyramidal (1 lone pair)

Square Planar (2 lone pairs)

T-shaped (3 lone pairs)

linear (4 lone pairs)

UNIT 6

UNIT 6

Signs of chemical reactions

temperature change: a gain or loss of energy in the system

change in color

change in odor

producing gas (bubbles)

production of a precipitate

what is a precipitate?

a solid formed by 2 liquids mixing

what do these signs mean?

something new is produced

What are chemical reactions represented by?

Chemical Equations

A + B → C + D

reactants → products

Symbols used in chemical reactions

(s) solid

(g) gas

(l) liquid

(aq) aqueous

→← reversible reaction

triangle over arrow heat is added to reaction

pt over arrow or chemical symbols above an arrow is a catalyst

What is a substance that dissolved in water called?

a solution

What does a catalyst do?

speeds up the reaction but does not take part in the reaction

HOW TO BALANCE CHEMICAL EQUATIONS

HOW TO BALANCE CHEMICAL EQUATIONS