IB SL Chemistry - Structure 1

Compounds

Atoms of different elements chemically bonded together in fixed rations.

Mixtures

More than one element of and can be separated by physical methods./A combination of two or more pure substances that retain their individual properties- homogeneous and heterogeneous.

What are physical and chemical properties dependent on?

The bonding and arrangement of atoms.

Elementary substances

Contain atoms of only a single element.

Pure substance

Has a definite and uniform chemical composition- element or compound.

Homogeneous mixture

Where the components are evenly distributed throughout, resulting in a uniform appearance and composition to the nake eye.

Heterogeneous mixture

Where the components are not evenly distributed, and the different substances are visibly distinguishable.

Sublimation

The phase transition of a substance directly from the solid state to the gaseous state, without passing through the liquid phase. (Opposite of deposition.)

Deposition

The direct transformation of a substance from its gaseous state to a solid state, without passing through the liquid phase. (Opposite of sublimation.)

When changing states of matter, temperature is used to…

help change the physical state, rather than increase/decrease the temperature because temperature is a measure of the average kinetic energy of particles.

What is an important difference between the Kelvin and Celsius temperature scale at zero?

The Kelvin scale starts at absolute zero (0K = -273C).

Filtration

The mixture is poured through a paper filter or other porous material.

Crystallization

Dissolved in hot water, the solution cools and crystals are formed (and later isolated by filtration).

Distillation/Evaporation

The mixture is heated up until one or more of its components vaporize(s).

Paper chromtography

Used to separate substances as components in inks.

The mobile phase

Te fluid that carries the sample through the stationary phase. It's the phase that is constantly moving, responsible for transporting the components of the sample.

The stationary phase

The fixed, non-moving phase that interacts with the mobile phase as it passes through the system. It's the component that doesn't move during the separation process.

Isotopes

Atoms of the same element but with different number of neutrons.

Subatomic particles

Protons, electrons and neutron.

Picometer

1pm = 10^-12m

Elementary charge

The charge from a single electron: 1.602 × 10^-19C

Three key facts about the nucleus:

1) It is very small compared to the atom itself, 2) it is a highly dense structure containing virtually all of the mass of the atom, and 3) it has a positive charge.

Relative atomic mass (A_r)

The number of neutrons and the number of protons.

What is the relationship between the atomic number of an element and its number of protons?

The number of protons = the atomic number.

The relative atomic mass (A_r) of an element is not a whole number because…

it is the average of all isotopes of that element.

Natural Abundance

The percentage of its atoms among all atoms of the given element found on Earth.

Equation for the relative atomic mass (A_r) of an element.

A_r= [(A of isotope 1 x NA of isotope 1) + (A of isotope 2 x NA of isotope 2)] / 100

Mass spectrometer

An instrument used to detect the relative abundance of isotopes in a sample.

Emission spectrum

Colorful lines against a dark background (hot gas).

Absorption spectrum

Dark lines against a colorful background (cold gas).

Electromagnetic radiation (EM)

The energy of the radiation is inversely proportional to the wavelength, λ.

How fast do EM waves travel?

The speed of light, c = 3.00 × 10⁸ms^-1

What is the relationship between wavelength and frequency of the radiation?

c = f x λ

Characteristics of high energy EM waves:

Short wavelengths and high frequencies.

Characteristics of low energy EM waves:

Long wavelengths and low frequencies.

Quantization

The idea that EM radiation comes in discrete packets, or quanta, or discrete energy levels.

Photon

A quantum of energy.

What is the relationship between a photon and the frequency of radiation?

E = h x f, where E is the specific energy possessed by the photon (in joules) and h is Planck’s constant, 6.63 × 10^-34Js.

Heisenberg’s uncertainty principle

It is impossible to precisely know the location and momentum of an electron simultaneously.

Atomic orbital

A region in space where there is a high probability of finding an electron.

What is the relationship between the principal quantum number, n, and atomic orbitals?

These energy levels are split into sub-levels comprised of atomic orbitals

What is the relationship between the principal quantum number, n, and the distance from the nucleus?

As n increases, the orbitals are further away from the nucleus.

What are the four atomic orbitals in increasing energy order?

s, p, d, f and then theoretical levels.

What are the four atomic orbitals in decreasing energy order?

(Theoretical levels), f, d, p and s.

What is the shape of an s orbital?

A sphere.

What is the shape of an p orbital and how many orbitals does it have?

A dumbell with 3-p orbitals: p_x, p_y and p_z.

How many orbitals does d have?

Five.

How many orbitals does f have?

Seven.

Orbital diagram

Used to represent how electrons are arranged in atomic orbitals.

Pauli exclusion principle

Only two electrons can occupy the same atomic orbital and those electrons must have opposite spins.

Degenerate orbitals

Orbital sub-levels with equal energy on the same overall orbital level.

What is a “ground state” orbital?

When n=1, the most stable orbital.

What is an “excited state” orbital?

When n= 2, 3,…, unstable and spontaneous.

Equation for the maximum number of electrons in each orbital

2n²

Aufbau principle

The lowest available energy orbitals fill before higher energy orbitals do.

Valence electrons

The atom’s outermost electrons

What is the exception with 3d transition elements?

All elements with 3d valence electrons tend to lose two 4s electrons to form 2+ ions.

What is the electron configuration of Mn and Mn²⁺?

Mn: 1s²2s²2p⁶3s²3p⁶4s²3d⁵ and Mn²⁺: 1s²2s²2p⁶3s²3p⁶3d⁵

What is the electron configuration of Sc and Sc³⁺?

Sc: 1s²2s²2p⁶3s²3p⁶4s²3d¹ and Sc³⁺: 1s²2s²2p⁶3s²3p⁶

Hund’s rule

Every degenerate orbital in a sub-level is singly occupied before any orbital is doubly occupied and that all electrons in singly occupied orbitals have the same spin.

What happens when an electron in the orbit with the lowest energy level absorbs a photon of the right mount of energy?

It moves to a higher energy level and remains at that level for a short time.

What happens when an electrons returns to a lower energy level and what does that represent?

It emits a photon of light and that photon represents the energy difference between the two levels.

What equation shows the relationship between electron energy (E_n) in joules and the energy level number (n)?

E_n=-R_H(1/n²)

What is R_H?

The Rydberg constant: ~2.18 × 10^-18J

What is Avogadro’s constant (N_A)?

1 mole = 6.02 × 10²³

What is relative molecular mass (M_r) and how do you find it?

The ratio of the mass of a molecule to 1/12th of the mass of a Carbon-12 atom. To find the M_r of a molecule, you need to add together the A_r values for all atoms in that molecule.

What are hydrates?

Compounds in which water molecules for coordination bonds with the ions.

What is molar mass, M?

The mass of one mol of that substance.

What is the difference between a molecular formula and an empirical formula?

Molecular: shows the actual number of atoms of each element in the molecule of that substance. Empirical: shows the simplest ratio of atoms of the different elements that are present in that substance.

What is the difference between the solvent and solute of a solution?

Solvent: usually the major component of the solution, so the properties of the whole solution are similar to that of the solvent- normally water. Solute: the other substance present in the solution.

What is the relationship between concentration of solution and the amount of solute?

A more concentrated solution has a large proportion of solute, so it has a high ratio of solute to solvent. And the opposite is true for a more diluted solution.

What is molar concentration, c (also known as molarity)?

The ratio of the amount of solute to the volume of the solution:

c_solute = (n_solute)/(V_solution)

What is mass concentration, P_solute?

The ratio of the mass of the solute to the volume of the solution:

P_solute = (m_solute)/(V_solution)

What equation should you use to calculate the concentration of a solute in a new solution?

c₁ x V₁ = c₂ x V₂

Spectrophotometry

A technique based on the measurement of the intensity of visible, ultraviolet and near-infrared radiation, used to determine the concentrations of colored substances in solutions.

What is absorbance in spectrophotometry and how does it relate to a calibration curve?

Absorbance is a value describing the amount of light absorbed by the sample and those absorbances are plotted against concentrations, producing a calibration curve.

Colorimetry

A technique used to determine the concentrations of colored substances in solutions but only limited to visible light, contrary to spectrophotometry.

True or False: Molecules of gas are not in constant random motion.

False- Gas molecules are not stationary. They move in a straight line until they collide with another gas molecule or the side of a container.

What does it mean for collisions between molecules to be perfectly elastic?

That both the kinetic energy and momentum of the system are conserved and no energy is lost from the system as molecules collide.

What are the values for standard temperature and pressure (STP)?

273.15K (0C) and 100kPa

True or False: The volume occupied by gas molecules is negligible compared to that volume of the container they occupy.

True

True or False: There are strong intermolecular forces between gas particles.

False- For an ideal gas, the IM are negligible compared the the kinetic energy of the molecules.

True or False: The kinetic energy of the molecules is directly proportional to Kelvin temperature.

True.

Boyle’s law

At constant temperature, the pressure of a given amount of gas is inversely proportional to its volume. p₁ x V₁ = p₂ x V₂

What are the conditions for ideal gas behavior?

Low pressure and high temperature- allows for IM forces to be negligible.

In what conditions do gases deviate from ideal gas behavior, forcing IM to become significant?

Low temperature and high pressure- collisions are no longer elastic and Boyle’s law no longer applies, respectively.

What is the molar volume of an ideal gas, V_m?

22.7 dm³ mol^-1

What is the Combined Gas law?

Where pressure is inversely proportional to volume and directly proportional to absolute temperature: (p₁V₁)/T₁ = (p₂ x V₂)/T₂

What is the Ideas Gas equation?

pV = nRT, where R is the universal gas constant R= ~8.31 J K^-1 mol^-1.