General Chemistry

Matter

– anything that has mass and occupies space.

Matter is made up of small particles
The particles have spaces between them:
1. Inter-Particle Spaces
2. Inter-Molecular Spaces
Particles attract each other
1. Intermolecular Forces
2. Intramolecular Forces
Particles of matter are in constant motion

Kinetic Molecular Theory of Matter

Intermolecular Forces

these are attractive forces between atoms/molecules, and these become stronger as the particles move closer together.

Intramolecular Forces

are forces that holds atoms together in a molecule, also known as bonds.

Solid

- Definite shape
- Constant Volume
- Nearly incompressible
- Particles are very close to each other
- Particles vibrates in fixed position relative to one another

Intermolecular Spaces of solids are very small. Intermolecular Forces are stronger

Kinetic Molecular Model of Solid:

Intermolecular Spaces of liquids larger than solids. Intermolecular Forces is less /weaker than solids.

Kinetic Molecular Model of Liquid:

Liquid

- No definite shape. It takes the shape of the container.
- Constant Volume.
- Slightly compressible
- Particles are neither too close nor too far from each other.
- Particles moves freely among themselves, but clump together.

Gas

- No definite shape. It takes the shape of the container.
- No definite volume
- It can be expanded or compressed
- Particles are far apart
- Particles are independent of one another.
- Particles move in random motion

Intermolecular Spaces of Gases are very large. Intermolecular Forces are very weak.

Kinetic Molecular Model of Gas:

Chemical Bonds

– force of attraction that holds two atoms together in a molecular or ion pair.

Octet Rule

– bonds are formed either by transferring or sharing of electrons to achieve a stable configuration. Elements tend to bond in such a way that each atom has eight electrons in its valence shell, giving it the same electronic configuration as a noble gas.

Ionic Bonds and Covalent Bonds

Types of Chemical Bond:

Ionic Bonds

– formed between metal and nonmetal elements. When Metals lose electron, it becomes positively-charged (Cation) while nonmetals become negatively-charged (Anion) when it accepts electrons. Ionic bonds involve in the attraction between the two charged Ions.

Cation

positively-charged ion

Anion

negatively-charged ion

Ionic Bonds

This bond holds the ions together in an Ionic compound.

Covalent Bonds

also called molecular bond

Covalent Bonds

It is a chemical bond that involves the sharing of electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs. Formed between two nonmetal atoms with identical or relatively close electronegativity values.

Single Covalent Bond

─ two atoms share one pair of electrons.

Double Covalent Bond

─ two atoms share two pairs of electrons.

Triple Covalent Bond

─ two atoms share three pairs of electrons.

Molecular Compound

– the compound that consists of atoms bonded together by shared electrons.

Diatomic Gases

─ Made up of atoms of the same elements (Ex. F2, O2, N2).

Binary Acids

─ Hydrogen, a nonmetal element, shares electron with Halogens to form binary acids and to achieve stability. (Ex. HF, HCl, HBr)

1. Diatomic Gases
2. Binary Acids

Examples of Molecular Compounds:

Bond Polarity

– electron sharing in covalent bonds may be equal or not between two atoms.

Polar & Nonpolar

2 kinds of covalent bonds

Nonpolar Covalent Bond

– electrons are equally shared between atoms. This means their electronegativities are almost the same. (Ex. H2, F2, Cl2, Br2 O2, & N2 ─ Diatomic gases)

Polar Covalent Bond

– electrons are shared unequally, resulting in one atom being partially negative (δ-) and the other being partially positive (δ+). (Ex. HF)

Electronegativity

– the tendency for an atom to attract electrons to itself when it is chemically combined with another element.

F (4.0)
O (3.5)
N (3.0)
Cl (3.0)

Four most electronegative elements:

Electronegativity Difference

– provides an estimate to determines the type of chemical bond the most likely to exists in a compound.

Non-polar Covalent

─ bond formed when difference in electronegativity is 0.

Polar Covalent Bond

─ formed when electronegativity difference is less than 1.5 but not equal to 0.

Ionic Bond

─ formed when difference in the electronegativity is equal to or greater than 1.5

Dipole Moments

occur when there is a separation of charge. They can occur between two ions in an ionic bond or between atoms in a covalent bond; arise from differences in electronegativity. Arrow points toward the more e-neg atom.

Dipole Moments

measure of the polarity of the molecule, direction of the polar bond in a molecule.

Dipolar Molecule or Dipole

– a molecule that has 2 poles (charged regions), like H-Cl.

Nonpolar Molecules

– Dipole moments are symmetrical and cancel out.

Polar Molecules

– Dipole moments are asymmetrical and don’t cancel. Therefore, they have asymmetrical shape (lone pairs) or asymmetrical atoms.

Geometry

– arrangement of atoms in a molecule.

Intramolecular Forces

– are the forces that hold atoms together within a molecule.

Inter-Ionic Forces

– are forces that hold ions together.

Intermolecular Forces

– are forces that exist between molecules.
– this force holds the molecules together which can be attractive or repulsive. – – these attractive forces are much weaker than bonding forces.
– determines the physical properties of molecules like their boiling point, melting point, density, and enthalpies of fusion and vaporization.
– are accountable for the properties of substances.
– explain why substances exist as solids, liquids, or gases at room temperature.

1. Dipole-Dipole
2. Ion-Dipole
3. Dispersion / London Forces
4. Hydrogen Bond

Four Types of Intermolecular Forces (involving covalent molecules)

1. Dipole-Dipole
2. Ion-Dipole
3. Dispersion / London Forces

Van Der Waals Forces

Johannes Diderik Van Der Waals

– was born on November 23, 1837 in Leyden, The Netherlands.
– in his 1873 thesis, Van Der Waals noted the non-ideality of real gases and attributed it to the existence of intermolecular interactions.

Dipole-Dipole Forces

– attractive forces existing between polar molecules (molecules that exhibit dipole moment), such as HCl.

Dipole-Dipole Forces

These forces occur when the partially positively charged part of a molecule interacts with the partially negatively charged part of the neighboring molecule. All polar molecules have a partial negative end and partial positive end which are attracted to each other.

Dipole

– the existence of partial positive and partial negative poles because there is unequal sharing of electron between H and Cl atoms.

Dipole-Dipole Forces

This force is weaker than ionic and hydrogen or covalent bonds.

Ion-Dipole Forces

exist in the attraction between a charged particle called ion (which can be a positively charged cation or a negatively charged anion) and a polar (dipole molecule).

Ion-Dipole Interaction

An ion is a charged atom because it has gained or lost one or more electrons. It can be either positively charged cation or negatively charged anion. The partial charges at the ends of the dipole molecules make an ______________.

Dispersion or London Forces

– are the weakest attractive force that are formed due to the temporary dipoles induced in non-polar molecules.

Dispersion or London Forces

This force is also called induced-dipole attraction.

Induced Dipole

distortion will result in temporary dipoles in the nonpolar molecule which is called ________.

Induced Dipole

– is the separation of the positive and negative charges in a nonpolar molecule due to its nearness of an ion or polar molecule.

Dispersion or London Forces

- exists when the electrons in two adjacent atoms attract and induce temporary dipoles.

Dispersion or London Forces

- exist between all types of molecules, whether ionic or covalent —polar or nonpolar.

Induced Dipole Force

– forces between nonpolar where electrons are evenly distributed; no dipole.

Induced Dipole-Induced Dipole Force

molecules that have induced dipoles may also induce neighboring molecules to have dipole moments, so a large network of induced dipole-induced dipole interactions may exist.

Ion-Induced Dipole Interaction

– when the induced dipole is due to the interaction between an ion and non-polar molecule.

Dipole-Induced Dipole Interaction

– when the induced dipole is due to the interaction between a polar and nonpolar molecule.

Hydrogen Bond

– is a special kind of dipole-dipole interaction that occurs specifically between a hydrogen (H) atom bonded to either an Oxygen, Nitrogen, or Fluorine atom (highly electronegative atoms, F, O, and N).

Hydrogen Bond

partially positive end of hydrogen is attracted to the partially negative end of the oxygen, nitrogen, or fluorine of another molecule.

Hydrogen Bonding

is a relatively strong force of attraction between molecules, and considerable energy is required to break hydrogen bonds.

Hydrogen bonding

plays an important role in biology; for example, hydrogen bonds are responsible for holding nucleotide bases together in DNA and RNA.

Surface Tension

– could be defined as the property of the surface of a liquid that allows it to resist an external force, due to the cohesive nature of the water molecules.
– it is the measure of the elastic force in the surface of a liquid.
– it is the amount of energy required to stretch or increase the surface of a liquid by a unit area.
– it is manifested as some sort of skin on the surface of a liquid or in a drop of liquid.

Manifestations of Surface Tension:

- Formation of a meniscus
- Capillary action which results from a combination of:
1. Cohesion
2. Adhesion

Capillary Action

– it is the tendency of a liquid to rise in narrow tubes or be drawn into small openings such as those between grains of a rock.
– also known as capillarity, is a result of intermolecular attraction between the liquid and solid materials.

Capillary Action

– straw lowered into water

Cohesion

– is the attraction between like molecules, cohesive forces.

Adhesion

– is an attraction between unlike molecules (such as those in water and in the particles that make up the glass tube), adhesive forces
– these forces also define the shape of the surface of a liquid in a cylindrical container (the meniscus!)

Adhesion, because they stick to the container, not with each other.

Water is having?

Cohesion, because they stick with each other, not in the container.

Mercury is having?

Viscosity

– a measure of a fluid’s resistance to flow.
– units: N.s/m2
– the higher the viscosity the greater the resistance to flow.
– varies inversely with temperature
– stronger intermolecular forces produce higher viscosities.

Glycerol

– high viscosity due to:
• three hydrogen bonding sites
• molecular shape

Vapor Pressure

– the pressure exerted by a vapor in equilibrium with its liquid state in a closed container.
– liquid molecules at the surface escape into the gas phase.
– these gas particles create pressure above the liquid in a closed container.

Closed System (constant temperature)

As liquid continues to vaporize, a point is reached: for every molecule that vaporizes, one condenses.

Equilibrium

When Vaporization = Condensation we have reached ___________

Vapor Pressure

– the pressure of a gas at equilibrium with the liquid in a closed system.
– is a characteristic property

1. Sealed container – Closed system
2. Constant condition ([ ], T, P, V)

Vapor Pressure Equilibrium will only be reached with:

• Compares vapor pressure to normal atmospheric pressure.
• Measures difference in height on both sides

Vapor Pressure can be measured by a manometer:

Pvap = Patm – h

(vapour pressure < air pressure)

Pvap = Patm + h

(vapour pressure > air pressure)

• Intermolecular forces
• Temperature
• Pressure

Vapor Pressure is influenced by:

Intermolecular forces

– stronger attraction restricts phase change

→ less energy needed to break IMF → easier for all particles to phase change (regardless of temperature) → increasing rate of vaporization → increasing vapor pressure.

weaker Intermolecular Forces (vapor pressure)

→ more energy needed to break IMF → harder for all particles to phase change (regardless of temperature) → decreasing rate of vaporization → decreasing vapor pressure.

stronger Intermolecular Forces (vapor pressure)

Volatile (Volatility)

– compounds that easily vaporize (have low IMF – Intermolecular forces).

Temperature

– energy is required to phase change.

→ increases the kinetic energy of all particles → increasing the number of particles with the energy to break IMF → increasing rate of vaporization → increasing vapor pressure.

increasing temperature (vapor pressure)

→ decreases the kinetic energy of all particles → decreasing the number of particles with the energy to break IMF → decreasing rate of vaporization → decreasing vapor pressure.

cooling/decreasing temperature (vapor pressure)

True

Vapor Pressure increases with increasing temperature

as the liquid gains kinetic energy, the molecules can overcome the intermolecular forces of attraction

As temperature increases, the amount of vapor generated by a liquid in a closed container increase. This occurs because ___________________ that are prevalent in the liquid phase.

Pressure

forces particles into liquid state

→ added force restricting particle motion → harder for all particles to phase change (regardless of temperature) → decreasing rate of vaporization → decreasing vapor pressure

increasing pressure (vapor pressure)

an open system must contend with atmospheric pressure

– air molecules colliding and pushing on the surface of the liquid making vaporization more difficult.

Evaporation

– transition from a liquid to a gas below a substances boiling point.
– occurs when molecules at the liquids surface are moving fast enough to escape into the gas phase.
– also called vaporization.
– requires energy to overcome intermolecular forces between the molecules of the liquid.
– some of the liquid particles have enough kinetic energy to overcome the forces of attraction around them and escape into the gas phase.
– high energy molecules escape the surface.