Definitions Flashcards
READ THE MATHEMATICS 3 TIMES
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What are isotopes?
Atoms with the same number of protons but differing number of neutrons
what are isobars?
Atoms with the same atomic weight but differing number of protons and electrons
what are isotones?
Atoms with the same number of neutrons but differing atomic weights?
what does the first quantum number represent?
n, the energy level quantum number, describes the proximity to source of attraction.
the higher the energy level, the further away the electron can be found
what does the second quantum number represent?
l, the Angular quantum number, determines the shape of the electron cloud.
l=0, spherical shape (s orbital)
l=1, p orbitals
l=2, d orbitals,
l=3, f orbitals
L ranges from 0 to n-1
what does the third quantum number represent?
m, the Magnetic quantum number, determines the orbitals orientation in space.
Values range from -L to L
what does the fourth quantum number represent?
s, the Spin quantum number, is used used to explain behavior of individual electrons as if they were spinning clockwise or anticlockwise.
has value of plus/minus half
what are the 5 Goldschmidt rules of element distribution?
- If two ions have the same radius and the same charge, they would enter solid solution in each mineral with equal ease in amounts roughly proportional to their abundance. The ionic radii must not differ more than 15%; substitution is limited or rare if radii differ by 15 to 30% and non-existent of the difference is more.
- When two ions possessing the same charge but different radii compete for a lattice site, the ion with the smaller radius would be incorporated preferentially because the smaller ion forms a stronger ionic bond.
- When two ions having different charges but similar radii compete for the same lattice site, the ion with the higher charge forms a stronger ionic bond and would be incorporated preferentially
- Ions whose charge differ by one unit may substitute for one another provided electrical neutrality of the crystal is maintained by coupled substitution.
- Nature of bond, i.e. degree of covalence should not change.
What are the three types of molecular orbitals and which is the strongest?
Sigma, s, constructed from s-AO (strongest)
Pi, p, constructed from p-AO
Delta, d, constructed from d-AO
what is electronegativity and how does it vary across the periodic table?
Electronegativity describes the power of an atom to attract electrons to itself in a chemical bond
Electronegativity increases towards the right and decreases towards the bottom of the periodic table
describe the difference between ionic and covalent compounds in terms of PARTICIPATING ELEMENTS
IONIC
Commonly between two elements with quite different electronegativity’s, usually a metal and a nonmetal
COVALENT
Commonly between two elements with similar electronegativity’s, usually nonmetals. Homonuclear molecules (such as Cl2 comprised of only one element) are covalent
describe the difference between ionic and covalent compounds in terms of MELTING POINT
IONIC
They are solids with high melting points (typically > 400°C). Ionic compounds do not exist as gases in nature
COVALENT
They are gases, liquids, or solids with low melting points (typically < 300°C)
describe the difference between ionic and covalent compounds in terms of SOLUBILITY
IONIC
Many are soluble in polar solvents such as water, and most are insoluble in nonpolar solvents such as carbon tetrachloride (CCl4 ).
COVALENT
Many are insoluble in polar solvents, and most are soluble in nonpolar solvents such as carbon tetrachloride (CCl4)
describe the difference between ionic and covalent compounds in terms of ELECTRICAL CONDUCTIVITY
IONIC
Molten compounds and aqueous solutions are good conductors of electricity because they contain charged particles (ions)
COVALENT
Due to lack of charged particles, liquid and molten compounds do not conduct electricity, and aqueous solutions are usually poor conductors of electricity
what is metallic bonding?
Describes bonding that exists among atoms within the crystal structure of a metallic element
Most metallic elements display closed-packed structures
what is van der Waals bonding?
Weak attractive and repulsive forces among the molecules
what is a hydrogen bond?
forms between H atom in a polar bond such as O-H and an electronegative element such as O, N and Cl
what are the four groups in Goldschmidt’s classification?
Siderophile (iron loving) elements
Chalcophile (sulphur loving) elements
Lithophile (rock loving) elements
Atmophile elements, which are normally found in the gas phase
what is meant by chemical equilibrium? Recall the equations.
A reaction attains equilibrium when the rate of forward reaction becomes equal to the rate of the reverse reaction
The properties of the system will not change with time
what is the Le Chatelier Principle?
This is nothing more than a description of the equilibrium constant
If a system in equilibrium is disturbed by some external influence, the system will react in such a way as to alleviate the disturbance.
what is a homogeneous reaction in terms of thermodynamics?
A homogeneous thermodynamic system is defined as the one whose chemical composition and physical properties are the same in all parts of the system, or change continuously from one point to another.
In a system of this kind, acted upon by the force of gravity, both the composition of the system and its physical properties will continuously change from one point to another.
what is a heterogeneous reaction in terms of thermodynamics?
A heterogeneous system is denned as one consisting of two or more homogeneous bodies.
The homogeneous bodies of a heterogeneous system are referred to as phases.
Each phase is separated from other phases by interfaces, or boundaries, and in passing over such a boundary the chemical composition of the substance or its physical properties abruptly change.
This phase boundary must not be regarded as a mathematical surface but as a thin layer separating the phases, a layer where the properties of one phase pass, or turn, rapidly into the properties of the other phase.
what is the basis behind henrys law? Recall the equation
Henry’s law relates the fugacity of the gas to its activity in solution
Recall the variance equation. what do the three possible values of this equation tell us about the system?
When f = 0, the system is described by an ‘invariant point’
When f = 1, the system is described by ‘uni-variant curves’
When f = 2, the system is described by ‘di-variant curves’
state the first law of thermodynamics. Recall the equations
The energy in a system can neither be created, nor destroyed, only transferred from on form into another
The definition of energy is the ability to do work, thus, with energy comes the proceeding of geochemical reactions
The change in the internal energy, ∆U, of the studied thermodynamic system during a process is equal to the difference between heat, Q, and word done, W.
state the second law of thermodynamics
Any process leads to a change in order of the system, or entropy
The higher the randomness, the higher its entropy; the more organized a system, the lower its entropy
what is entropy? Recall the equations
Entropy is a measure of the spontaneous dispersal of energy at a specific temperature in a system
Entropy is highest in gaseous phases and lowest in solid phases
what are the two implications of the second law of thermodynamics?
Naturally occurring, or “spontaneous” processes will always proceed towards the state that has the least potential energy
Spontaneous chemical reactions increase the disorder in the system. We know from the first law of thermodynamics that energy cannot be lost, but it can change forms. What is lost, when a reaction is finished, is energy that is useful for doing more work
how can the change in enthalpy be determined? recall the formula
The change in enthalpy due to a reversible or irreversible change in the state of a system via a process can be determined by measuring the heat absorbed (or released) by the system during that change at constant pressure.
what is enthalpy? Recall the formula
The total heat content of a system.
It is equal to the internal energy of the system plus the product of pressure and volume.
what value is the change in enthalpy for an exothermic reaction?
heat is outputted, so the change in enthalpy is negative
what value is the change in enthalpy for an endothermic reaction?
heat is inputted, so the change in enthalpy is positive
where is enthalpy stored and how is it released?
Enthalpy is stored in chemical bonds: forming bonds liberates energy and breaking bonds requires energy.
Bond enthalpy is the enthalpy change required to break and separate 1 mole of bonds in a molecule of a gaseous compound.
The strength of the bonds in the reactants and products decides whether a reaction is exothermic or endothermic.
what is heat capacity? recall the formula
The heat capacity of a substance is the amount of heat required to raise the temperature of 1 mol of substance by 1 ̊C
how many heat capacities describe a system? recall the formulae
A system has two values of heat capacity, one for heat being added at constant pressure and one for heat being added at constant volume
if volume is constant, he heat absorbed equals the change in internal energy.
if pressure is constant, the heat absorbed goes into both temperature rises and expansion
what is gibbs free energy and how can we compute it? recall the formula.
∆G expresses the ability of substances to react and the extent to which reactions will go
The free energy is not directly measurable for any system, but its value can be computed from its enthalpy and entropy
what are the three key points about the gibes free energy?
Negative ∆G indicates that the reaction is exergonic and spontaneous.
If the reactants have a lower ∆G than the products, there will be an increase in free energy, and the reaction is
non-spontaneous.
• In this situation, energy (in the form of heat, light, etc.) will be required for the reaction to take place.
A spontaneous reaction will not necessarily occur on its own.
• This is because an initial activation energy is needed to start the reaction and even a spontaneous reaction
may need some form of energy input.
why is chemical potential used in thermodynamics? recall the relevant formula
To extend the application of the auxiliary thermodynamic functions to systems that may undergo a change in composition
The chemical potential of a constituent i is its partial molar free energy at constant temperature and pressure.
what does the extent of a reaction allow us to do?
To find conditions of equilibrium at constant temperature and pressure for a reaction in terms of chemical potentials
what is activity a measure of? recall the formula
Activity is a measure of the effective concentration of a species in a mixture.
By convention, activity is treated as a dimensionless quantity, although its actual value depends on customary choices of standard state for the species. The activity of pure substances in condensed phases (solid or liquids) is
normally taken as unity (the number 1).
what does the activity of a species depend upon?
Activity depends on temperature, pressure and composition of the mixture, among other things
