Physical Chemistry Flashcards
What are the two types of molecular bond?
Ionic and covalent
Define an atom
The smallest part of an element which can take part in chemic reactions
Define an element
A group of atoms all having the same atomic number
Define a molecule
A combination of atoms which is the smallest unit of a chemical substance that can exist whilst still retaining the properties of the original substance
Define atomic number and mass number
Atomic number: The number of protons in each atom of an element Mass number: The total number of protons and neutrons in the nucleus
Describe the make up of an atom
A nucleus of neutrons and protons, surrounded by a cloud of negatively charged electrons
Where does the mass of an atom lie?
Almost all of the mass of an atom lies in the nucleus
How is the charge of an atom determined?
The total number of protons (positive charge) minus the total number of electrons (negative charge)
Define an isotope
Same number of protons (and therefore same element) with a different number of neutrons
Define a radio-isotope
An isotope which releases particles (i.e. is radioactive)
Explain the difference between carbon 12 and carbon 14
Carbon 12 - 6 protons, 6 neutrons, not radioactive Carbon 14 - 6 protons, 8 neutrons, radioactive
How are mass number and atomic number traditionally written?
Mass number: Superscript Atomic number: Subscript. e.g 12 6C
What is the relative mass and charge of each of the three constituents of an atom?
Proton Mass: 1 Neutron Mass: 1 Electron Mass: 1/1836 Proton charge: +1 Neutron charge: 0 Electron charge: -1
Electrons are arranged around the atom in a pattern called _______
Shells
From innermost to outermost, what are the shells of an atom?
K, L, M, N, O, P, Q.
How are shells filled?
In alphabetical order
Give the number of electrons each shell from K to N can hold
K - 2 L - 8 M - 18 N - 32
Explain the theory of sub-shells
Each shell has subshells; s, p, d and f shells. s shells can contain two electrons p shells can contain six electrons d shells can contain ten electrons f shells can contain fourteen electrons
At what shells are each sub shell located?
s sub-shells - in every shell p sub-shells - every shell after the K shell d sub-shells - every shell above the K and L shells f sub-shells - every shell above the M sub shell
Explain how an atom with 50 electrons would be arranged using the spdf sub-shell arrangment
1s2, 2s2, 2p6, 3s2, 3p6, 3d10, 4s2, 4p6,4d10, 4f4
Define “valency”
The number of atoms of hydrogen that one atom of an element can combine with or replace
True or false: an atom can have only one valency
False - can have multiple valency states
What is the connection between periodic table groups and valency?
The same groups have the same valency; group 1 all have a valency of +1, group 2 = +2, group 3 = +3 and group 4 = +4 etc.
Give the difference, in terms of electron transfer, between an ionic and a covalent bond
ionic - complete loss or gain of electron(s) from atom to another covalent - two atoms “share” electron(s) to give both a full shell.
What is special about the inert gases?
They have full electron shells and are at their most stable; therefore they do not gain or lose electrons and do no react with other elements
Why is carbon the most important element in terms of organic chemistry?
It can both lose or gain electrons to gain stability
What is the point of a bond?
To allow formation of a stable outer shell
In terms of sodium and chlorine, explain what is happening when an electrocovalent (ionic) bond is formed
sodium loses 1 electron, giving it a charge of +1. It now has a full shell (2, 8) in its outermost orbit, taking on the electron configuration of neon (stable gas) Chlorine picks up the electron that sodium has lost and becomes a chloride ion, with an outer shell which is also full (2, 8, 8) and takes on the configuration of argon (stable gas). the chlorine atom now contains a negative charge of -1. The positive charge of the sodium ion and the negative charge of the chloride results in a strong attraction and therefore a bond between the two ions, sufficient enough to maintain the crystalline structure. Ionic compounds are very stable and require a very large amount of heat energy to convert to liquid or gas - therefore they are usually solids at room temperature
True or false: Carbon can lose or gain electrons to become stable
True - can lose 4 electrons so that shell K is the outermost shell and full with 2 electrons, or can gain 4 so that shell L is the outermost shell and full with 8 electrons
How many types of covalent bond are there? Define the difference
single - one pair of electrons shared double - two pair of electrons shared triple - three pair of electrons shared
Methane is an example of which kind of covalent bond?
single bonds - carbon gains 1 electron from each hydrogen atom, taking on the configuration of neon while each hydrogen takes on the configuration of helium. Each bond shares one pair of electrons.
In terms of bonds/shape/state of matter/vaporisation/conductance/solubility, compare and contrast ionic and covalent bonds
Bonds - Ionic no sharing therefore non-directional/covalent sharing therefore direction Shape - ionic no particular shape/covalent definite shape therefore able to have isomers State of matter - ionic solid and usually crystalline/ covalent usually highly volatile liquids or gases Vaporisation - ionic not easily vaporised/covalent easily vaporised Conductance - ionic when melted good conductor/covalent poor conductor Solubility - ionic readily dissolves in water/covalent not readily soluble in water
Dative bonds: What are they?
A type of covalent bond in which both electrons of the shared pair come from the same atom.
Give an example of a dative bond
Ammonium chloride; also possesses covalent and ionic bonds. Bond between NH3 and hydrogen ion is dative as the hydrogen ion possesses no electrons to transfer
Van der Waals Forces - define them
Attraction and repulsion of weakly charged areas to similar areas in neighbouring molecules
Why do Van der Waals forces occur?
Particles which are neutral can have permanent dipoles or have dipoles induced by the interaction with particles which has a permanent dipole. These dipoles then attract each other and Van der Waals are the electromagnetic forces between these particles.
True or false: Van der Waals forces are weak forces and as thus the melting point of substances held by them is quite high
False - Van der Waals forces are weak but this means their melting point is relative low and they tend to be softer than those held by ionic or covalent bonding
Graphite is an example of Van der Waals interactions - how?
It is made of sheets formed from covalent bonds between carbon atoms and each sheet is held to the next one by Van der Waals forces
What is a highly electronegative atom?
An atom which has a high propensity to attract electrons and become a negative ion
Hydrogen bonds - explain them
Weak electrostatic bond between the positive nucleus of the hydrogen atom in a covalent bond and the unshared pair of electrons in a highly electronegative atom of a neighbouring molecule
Give examples of highly electronegative atoms
Oxygen, sulphur, nitrogen
True or false - the high boiling point of water and crystalline structure of ice is due to Van der Waals interactions
False - these are due to hydrogen bonds forming between molecules of water, with the free pair of electrons on the oxygen atom on one molecule of water being attracted to the positive nucleus (proton) of hydrogen on another molecule
Explain hydrophobic bonding
Individual water molecules are attracted to each other by hydrogen bonds. Any molecule added to water will disrupt the structure. If the substance has polarity or is ionised it will spread easily and form bonds with the water molecules. If however electron distribution is even (i.e. not ionised or polarised) then the energy released by making new bonds is less than that required for breaking of hydrogen bonding. Therefore the additive becomes most stable by collecting together and leaving as much of the water as possible, undisturbed.
An example of a hydrophobic bond can be demonstrated by something readily available in your home: what is it?
Oil - when added to water it will remain grouped together, only being broken up temporarily by very vigorous stirring.
Why are hydrophobic and hydrogen bonds physiologically important?
Areas of membranes and proteins which do not have polarity do not attract water, allowing water to maintain bonds with other water molecules. Therefore the hydrophobic areas remain vacant promoting the movement of non-polar hydrophobic molecules into these sites.
Hydrophobic areas and molecules do not attract each other - explain
There is no net polarity or force present to allow for movement. However these molecules and areas become grouped. This is not due to any attraction or force but is actually due to the displacement of hydrophobic molecules by water and other hydrophilic molecules.