Unit 3

Bond Dipole

Separation of electrical charge created when atoms with different electronegativities form a covalent bond; a type of polar bond.

Permanent Dipole

Permanent separation of electrical charge in a molecule resulting from unequal distributions of bond and/or lone pairs of electrons.

Polar Bond

bonds between atoms, in which there are an unequal distribution of electronsin a covalent bond.

Polar Molecules

Unequal distributions of electric charge that give rise to certain molecular shapes

• in the molecule, certain regions have more positive charge/s and ones with more negative charge/s

• POLAR MOLECULES WILL ALWAYS HAVE A PERMANENT DIPOLE.

Difference betwen Polar bonds and Polar molecules

• POLAR BONDS: Unequal electrons between bonds (Smaller)

• POLAR MOLECULES: Unequal charge between atoms ( larger)

Dipole moments

• A molecule’s polarity

  • determined by the degree to which the molecule aligns with a

    strong electric field.

  • Units = debyes (D)

Valence bond theory

Overlap: Bonds forming when 2 obrtials on different atoms, occupy the same region of space

electron density

probability of finding an electron within a specific volume around a nucleus

internuclear axis:

Imaginary line connecting the nuclei of two atoms in a chemical bond

The formation of chemical bond leads to increased ____ along the _______

electron density, internuclear axis

Sigma Bond

a covalent bond in which the highest electron density lies between the two atoms along the bond axis

pi ($\pi$) bond:

covalent bond, in which electron density is greatest above and below.

Hybridization

mixing of atomic orbitals (like s and p ) within an atom to create new, equivalent "hybrid orbitals"

• The mixing results in the formation of a new set of wave function, defining four equivalent hybrid atomic orbitals

Sp³ hybrid orbitals

Four hybrid orbitals, that have a tetrahedral orientation produce by mixing one s, and three p orbitals

Sp² hybrid orbitals

Three hybrid orbitals in a trigonal planar orientation formed by mixing one s and two p orbitals

Sp¹ Hybrid Orbitals:

Two hybrid orbitals on opposite sides of the hybridized atom formed by mixing one s and one p orbital

Molecular recognition

The process by which molecules interact with other molecules to produce a biological effect.

Molecules with Multiple Central Atoms

In certain atoms, there are more than one central atoms.The hybridization of and geometry around each carbon must be determined independently.

Intermolecular force

• Forces that exist BETWEEN molecules and hold them together in the liquid or solid phase.

  • attraction between two molecules and/or ions

  • weaker than intramolecular forces and act over longer distances.

  • influences the physical properties of all substances.
    
    

    

Intramolecular forces:

• forces INSIDE atoms

• hold atoms together within a molecule.

  • Exist separate like intermolecular

    

• Shorter distance between molecules

• Stronger bonding force between molecules.

Boiling points

• The temperature at which an molecule turns into its gaseous form    

  • The temperatures at which a liquid's vapor pressure equals external pressure

TREND BETWEEN BOILING POINTS AND ATOMIC NUMBER

• As atomic number increases, so does boiling points

  • the stronger the particles’ attractions for each other, the more energy needed to separate them—and, in turn, the higher the boiling points.

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Temporary dipoles:

• Separation of charge produced in an atom or molecule by a momentary uneven distribution of electrons, also referred induced dipole

  • only intermolecular force present in between nonpolar molecules.

• The presence of temporary dipoles in atoms and molecules creates an electrostatic way for them to interact with other atoms and molecules.
  
  

  

London Dispersion force

• intermolecular force between atoms or molecules, cause by temporary dipoles'

  • London dispersion forces become stronger, as atoms and molecules become larger

Polarizability

• the tendency of molecules to generate induced electric dipole moments when subjected to an electric field

  • Greater polarizability leads to stronger temporary dipoles and stronger intermolecular interactions

  • London dispersion forces become stronger, as atoms and molecules become larger

Strength of London Dispersion forces depend on….

• Number of electrons- strength increase if electrons increase,

• Size of atoms/molecules

• Shape of molecules
  
  

  

Hydrocarbons

a compound whose molecules contain only carbon and hydrogen atoms

Alkane

• hydrocarbon, in which each carbon atom is bonded to four other carbon or hydrogen atoms

  

Constitutional Isomers:

• Compounds with the same molecular formula, but different connections between the atoms in their molecules.

  • More branching in the structure leads to a smaller surface area, which causes a decrease in the London dispersion forces between molecules.

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Viscosity

• London dispersion forces, also influence viscosity of liquids

• Viscosity: measure of a fluid’s resistance to flow.

  • Intermolecular forces increase, Viscosity increases

    

Viscosity for liquid alkanes

• viscosity of liquid alkanes increases as the number of carbon atoms and the molar mass increases.

  

Dipole–Dipole Interactions

• attractions between the partial positive end of one polar molecule and the partial negative end of another

  • Polar molecules have an overall dipole moment and the partial negative charge on one molecule is attracted to the partial positive charge on another molecule.

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Hydrogen bonding

• Hydrogen bonding: dipole-dipole attraction between a positive H atom, covalently bonding to on highly electronegative atom ( N,O, or, F ), another very electronegative atom.

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Hydride

• Where hydrogen combines with another element, to form an new element or compound.

  • Water (H₂O)

  • Ammonia(NH₃)

  • Titanium

  • NaH

hydroxyl groups

• (-OH) are composition of oxygen and hydrogen, where a oxygen atom is bonded covalently to a hydrogen atom,

  • The presence of hydroxyl groups (-OH) allow for hydrogen bonding, resulting in higher boiling points.

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Ion-Dipole interaction

• an attractive force between an ion, and a molecule that has a permanent dipole

  • * Cations and anions can interact with molecules that have a permanent dipole.

  • *Ionic salts can interact with polar water molecules, causing them to dissolve in water

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Sphere of Hydration

• When ions dissolve in water, they become surrounded by a number of water molecules, which are organized in multiple layers.

  • The dissolved ions are referred to be hydrated.

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• Inner sphere: The water molecules closet to the ions, will form ion-dipole interactions

• Outer sphere: The water molecules outside the inner sphere, will form hydrogen bonding to the inner spheres water molecules

The strength of intermolecular forces present in between molecules affects:

• State of matter

• solubility

• Boiling point

• Physical properties of substances

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solution (in solubility)

• homogeneous mixture of two or more substances.

  • The complete mixture of the solute and solvent- the product

solvent

• Compound of a solution, for which the largest number of moles are present

  • The component that dissolves the other part of the solution

    • The liquid dissolving it

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Solute

• any component in a solution other than the solvent,

  • The component that dissolves in the solvent

    • The powder,or substance dissolving

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Solubility

• Maximum quantity of a substance that can dissolve in a solution

  • the maximum amount of a solute that can dissolve in a specific amount of solvent

Miscible

• the ability of two or more liquids to mix together in any proportion, forming a single, uniform solution without separating into layers.

  • Strength and number of interactions among solute particles and interactions of solvent molecules determine solubility.

  • Nonpolar solutes may dissolve in water due to dipole-induced dipole interactions.

    • The dipole in water can induce a dipole in oxygen, causing it to be slightly soluble

Solute-Solvent interactions:

• Attractive forces (ion-dipole or hydrogen bonding), that occur between particles of a solute and a solvent, determining solubility.

Polar solutes | Polar solvents interactions

• Polar solutes tend to dissolve polar solvents, due to strong dipole-dipole interactions, between the molecules of both. This is refereed to

  • like dissolves like

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Non-polar solutes | Polar solvents interactions

• Nonpolar solutes dont dissolve or dissolve very little in polar solvents because the interaction is much weaker than the interactions that keep the solute molecules attracted to each other, and solvent molecules are attracted to other solvent molecules

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Non-polar solutes | non-polar solvents interactions

• Non-polar solutes and non-polar solvents dissolve easily in one another, because of the dipole-dipole interaction between the 2- same reason for polar and polar.

  • like dissolve like

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Ketones

• organic compounds defined by a carbonyl group (C tripple bonded to O) bonded to two carbon atoms

• Ketones become less soluble in water as the length of the carbon chain increases

  

Mole

• Si unit for expressing the number of atoms in exactly 12 grams of carbon-12

  • 1 mole = $6.022\cdot10^{23}$ particles (Avogadro’s constant)

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Conversions using Avogadro’s constant

Avogadro’s constant can be used to convert between number of particles and number of moles of a substance (VICE VERSA)

Molar mass

• The mass (in grams) of one mole of a substance (atom,molecule, formula unit)

  • Same numerical value as mass in u.

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Conversions among Moles, Mass, and Particles

(check image)

Average atomic mass

• Weighted average of masses of all isotopes of an element.

  • Calculation : multiplying natural abundance of each isotope by its mass in unified atomic mass units, and then summing the products

  • Natural abundance: Proportion of a isotope.Expressed as a percentage typically

    • (Natural abundance * mass) + …..

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Molecular Mass

• The molecular mass is the sum of all the average atomic masses of the atoms that are bonded

  • Sum of all atomic masses

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Formula Mass

Mass in unified atomic mass units of one formula unit of an ionic compound

Formula Unit

• Smallest electrically neutral unit of an ionic compound

Stoichiometry

• The balancing in a chemical reaction.

  • the number atoms of each Element must be the SAME on the reactant side and the product side of the arrow.

Law of conservation

• the law stating that: all chemical equations must be balanced

  • Total number of atoms of each element, must be the same amount on the left and right side

  • (Number of atoms, must be same on both sides)

  • The masses of the products must equal masses of the reactants.
    
    

    

Steps to Balance Chemical Equations

1. Write a preliminary expression containing a single particle (atom, molecule, or formula unit) of each reactant and product with a reaction arrow separating reactants from products. Include phase symbols indicating physical states.

   (Write equation of each reactant and product on both sides, separating them with a arrow, and indicating what states each atom is in)

2. Check whether the expression is balanced by counting the atoms of each element on each side of the reaction arrow.

   (Check if both sides are balanced, if not continue)

3. Choose an element that appears in only one reactant and one product and balance it first.

   

4. Choose coefficients for the other substances so that the number of atoms for each element is the same on both sides of the reaction arrow.
   (add more of that substance through coefficents, inorder to balance it)