unit 4; chemistry

— Concept 4; Covalent Bonds —

Objectives

Explain the connection between electronegativity and the formation of a covalent bond. — A covalent bond forms when 2 atoms share electrons to become a stable electron configuration. If the atoms involved have similar electronegativities they will share electrons more or less equally making a covalent bond.

Differentiate between polar covalent and nonpolar covalent bonds. Give an example of each. A polar covalent bond happens when 2 atoms have different electronegativities causing an unequal sharing of electrons. An example is water (H2O), oxygen is more electronegative than hydrogen. A Nonpolar Covalent bond is when 2 atoms have similar electronegativities and cause an equal share of electrons. An example is a bond between 2 hydrogen atoms (H2).

Explain how the VESPR theory impacts drawing Lewis structures for molecular compounds. The VESPR theory predicts the shape of molecules based on the repulsion between electron pairs around a central atom. Electron pairs arrange themselves as far apart as possible to minimize repulsion. In Lewis structures, this theory helps determine the 3D arrangement of atoms in molecules.

Vocabulary

Covalent compound – a chemical compound formed by the sharing of electron pairs between atoms between nonmetals.

Covalent bond – a type of chemical bond where two atoms share one or more pairs of electrons to be stable in their outer electron shells.

Molecule – two or more atoms covalently bonded together.

Diatomic elements – molecules composed of only two atoms, of the same or different chemical elements. The seven diatomic elements that naturally occur are hydrogen (H2), nitrogen (N2), oxygen (O2), fluorine (F2), chlorine (Cl2), bromine (Br2), and iodine (I2).

— Concept 5; Molecular Geometry —

Objectives

Explain VESPR theory — The VESPR theory is used to predict the shape of molecules based on the repulsion between electron pairs around a central atom, electron pairs will arrange themselves as far apart as possible to minimize repulsion

List what constitutes an electron domain — Electron domain: the space occupied by e-

could be:

- Bonding pair = e- shared in a bond

- Lone pair = e- not in a bond

- Multiple bonded pairs of e- (like in a double or triple bond)

Create a chart to distinguish between different types of molecular shapes. Include the name, what determines the shape, an example of a compound, and a picture or model as a visual reference.

Linear

What Determines the Shape: 2 electron domains

Carbon dioxide (O2).

O–O

Trigonal Planar

3 electron domains

Boron trifluoride (BF3).

F

|

B---F

|

F

Tetrahedral

4 electron domains

Methane (CH4).

H

|

H---C---H

|

H

Trigonal Bipyramidal

5 electron domains

Phosphorus pentachloride (PCl5)

Cl

|

Cl---P---Cl

| |

Cl Cl

Octahedral 🡪 6 electron domains

Ex. SF6

Bent 🡪 4 electron domains

2 bonding pairs, 2 lone pairs

Ex. H2O

Trigonal pyramidal 🡪 4 electron domains

3 bonding pairs, 1 lone pair

Ex. NH3

• Tetrahedral 🡪 4 electron domains

  • 4 bonding pairs, 0 lone pairs

  • Ex. CH4

vocabulary

Electron domain – the space occupied by e-

Lone pairs – e- not in a bond

Bonding pairs – e- shared in a bond

— Concept 6; Intermolecular Forces —

Objectives

Summarize the connection between chemical bonds, polarity, intermolecular forces, and properties of substances.

1. Chemical Bonds: These forces hold atoms together in a molecule. They include ionic bonds (transfer of electrons) and covalent bonds (sharing of electrons).

2. Polarity refers to the distribution of electrical charge over the atoms in a molecule. A molecule is polar if there is a significant difference in electronegativity between its atoms, resulting in partial positive and negative charges.

3. Intermolecular Forces: These are forces of attraction or repulsion between molecules. They include hydrogen bonds, dipole-dipole interactions, and London dispersion forces. The strength of these forces depends on the polarity of the molecules involved.

4. Properties of Substances: The type and strength of intermolecular forces affect the physical properties of substances, such as boiling point, melting point, solubility, and viscosity. For example, substances with strong hydrogen bonds (like water) have higher boiling points compared to those with weaker London dispersion forces (like methane).

In summary, the type of chemical bonds determines the polarity of molecules, which in turn affects the intermolecular forces. These forces then influence the physical properties of the substances.

each determines what bond is formed and what properties the molecule will have

for each and notate the partial charges in the polar molecule. Label the direction of the dipole in the polar molecule

Polar Molecule: Water (H₂O)

1. Lewis Structure:

- Oxygen (O) is the central atom with two hydrogen (H) atoms bonded to it.

- Oxygen has two lone pairs of electrons.

δ+ H:O: H δ+

δ-

Non-polar molecule:

Methane (CH₄)

1. Lewis Structure:

- Carbon (C) is the central atom with four hydrogen (H) atoms bonded to it.

- There are no lone pairs on the carbon atom.

```

H

|

H - C - H

|

H

Explain how electronegativity and symmetry can be used to predict polarity

BEND + SNAP Bend is based on bond electronegativity difference which determines if the atom is polar or not and snap uses symmetry to determine if there atom is polar or not

Explain why polar molecules have the strongest intermolecular forces.

positive + negative charges (aka unequally shared e-) act like a magnet

Rank the different types of intermolecular forces from strongest to weakest. Explain your ranking.

hydrogen bond, dipole-dipole, london dispersion.

Explain how even a perfectly stable noble gas can be impacted by intermolecular forces. You may need to draw a picture to support your explanation.

they are monoatomic and unpolarized

Describe the impact of intermolecular forces on the properties of substances, such as viscosity and boiling point.

as the IMF strength increases, the melting and boiling point of a substance also increases

Create a summary chart to distinguish between the types of molecular forces

LDF

Dipole-Dipole

Hydrogen bonding

Be able to rank compounds based on their polarity using BEND

Be able to predict a compound polarity using electronegativity and symmetry

Be able to identify partial charges in a compound using electronegativity and proper notation

Be able to predict the type of intermolecular force(s) at work when given a description, model, data table, or example.

Be able to rank substances based on the strength of the intermolecular forces at work when given a description, model, data table, or example.

Vocabulary

polar molecules = have particle charges in different locations within the overall molecules. EX H2O

nonpolar molecules = no partial charges because the e- are equally shared. EX O2

intermolecular forces (IMF) = the attractive forces between particles in a substance

dipole-dipole force = the short-range attractive force between polar molecules

dipole = formed in a molecule when equal and opposite charges are separated by a short distance.

hydrogen bonding = when a hydrogen atom bonded to a highly electronegativity atom (like N, O, or F) is attracted to an unshared pair of e- of an electronegative atom in a nearby molecule.

London dispersion forces = an intermolecular attraction resulting from an instantaneous and temporary dipole created from the constant motion of e-

viscosity = a fluids resistant to movement

boiling point = the amount of kinetic energy needed to overcome the force of attraction between liquid particles.