BLock 1 Chemistry: essential concepts

Pregunta	Respuesta
What is electronegativity?	The tendency to gain electrons
What are normal oxides?	Compounds in which the oxygen atoms are not bound to themselves. UNlike the peroxide ion - O2^2- or super oxide O2^-
What do oxides of Li, Na, K, Ca dissolve in water to give? Are they acid or base?	Metal hydroxides with the dissolved cations and anions M+ and OH- They are bases.
What do ionic sloids consist of?	They do not consist of molecules but of an array of ions.
DO sodium ions react readily? Why is this useful?	No. They carry negative ions such as carbonate or hydroxide into solution and do not react with the substances meant to react with the negative anions.
Name properties of alkali metal halides.	Fomula MX. All white crystaline solid. High melting temperatures All produce electrical conducting melts. Dissolve in water to give colourless electrical conductive solutions.
What are the oxides of alkali metals?	Li2O is Li^+ and O^2- Sodium is Na2O2 which has the peroxide ion O2^2- KO2, RbO2 and CeO2 are formed of the O2^- (superoxides - two O bonded together)
What compounds are formed when alkali metals are heated in H gas?	Hydrides - colourless crystals
Name the states and some properties of the halogens.	Fluorine almost colourless gas Chlorine greenish yellow gas Bromine reddish brown liquid Iodine purplish solid All volatile and form diatomic molecules
What is the valency of the halogens and what is the formula for their reactions with Al, and H?	1. AlF3 (ionic) AlCl3 (layered) Al2X6 for Br and I HX
Hydrogen Fluoride causes burns but is less volatile than the other halides. Why?	Hydrogen bonds form between the adjacent molecules between H and F atoms.
What do hydrogen halides dissolve in water to give?	HF is a weak acid. (As a result of hydrogen bonds forming) The others are strong acids.
Give a high valency found in an interhalogen compound between I and F?	IF7
Why do all oxides of bromine have no practical value?	The decompose at or below room temp.
What are halogen oxides liable to do?	Decompose, often explosively on heating or shock of impact.
What character do all of the transition elements, the lanthinoids and actinoids share?	They are all metals
What are the main group semimetals and what properties define them?	B, Si, Ge, As, Sb and Te. They have the appearance of metals but their chemical properties resemble non metals.
What is different about the trend in the reactions of fluorine?	It does not follow the reactivity trend in the periodic table. It is more reactive than oxygen and chlorine.
metals and semi metals have a pattern of increasing valencies. How is this not true for non metals?	Non metals often form several oxides or fluorides where the element has a number of different valencies.
Apart from oxygen the valency down groups 1,2 and 13-16 is constant. This is not true for the halogens. What are the maximum valencies for their oxides and fluorides?	F-1 Cl-7 Br-5 I-7
For hydrides the pattern of valencies acroos a period is different. What pattern does it display generally?	1234321
What are isotopes?	Atoms with the same atomic number but different atomic masses
What is the relative atomic mass measured in?	The mass of the atom relative to the mass of 1/12 of the carbon isotope with mass number 12.
What is the chemistry of an element governed by?	The number of electrons
How many electrons occupy the s, p and d levels?	2, 6 and 10
What is the principle quantum number n?	It represents the overall energy of each orbital. The overall energy increases with distance from the nucleus.
What is the orbital quantum number l?	It is the number that determines angular momentum and describes the shape of the orbital. It distinguishes s(l=0) p(l=1), d(l=2) and f(l=3)
What is the magnetic quantum number m?	Describes the number of orientations each orbital can have. For the purposes of the module ml can be -l or +l - that 2/+1 values.
How many electrons can each level with a given n, l and m (sub)l have. What property is this related too?	2 electrons. It is related to a property called spin (visualised clockwise or anticlockwise)
When an orbital has two electrons what is their spin? What are these two electrons said to be?	One clockwise and one anticlockwise. They are said to be paired.
What does Hund's rule say about the configuration of electrons in the ground state?	In an energy diagram each box of a particular energy level is filled with one electron first then another of opposite spin is added starting from the lowest energy level.
What form do elemental noble gases take? What other properties do they have?	monotomic, inert, full electron subshell
What is the first ionisation energy?	The enthalpy change (positive) when one a valence electron is removed, ionising the atom.
What happens to the 1st ionisation energy with increasing atomic mass?	It increases. Increase in nuclear charge wins out over increase in electron repulsion from other electrons.
What is an octet?	A full set of valence electrons in the s and p subshell.
How can you predict whether a compound will be ionic or covalent?	By considering the electronegativity of the elements that make it. similar negativities means they share. If one is much more electronegative it takes the electron forming an ionic bond.
Why does electronegativity increase across a period?	The positive charge of the nucleus is more able to attract the outer electrons and this also makes it more electronegative.
What is the guideline for predicting ionic bonds?	Elements less than 1.9 would be expected to form ionic bonds with elements higher than 2
Describe metallic bonding.	Metal sites in a crystal are occupied by M+ ions. The electrons are not tied to one ion but move freely as an electron gas. This is why they can conduct electricity. Also - the electrons are in the spaces between the positive ions and hold them together like a glue.
What are alloys?	Two elements with low electronegativity are bonded metallically and share all the electrons. Most have no definite formula but best described as a solid solution.
Where are the highest electronegativities found?	Top right of the periodic table.
What do 2 elements with low but similar negativities form?	Alloys.
What do elements with high but similar electronegativities form?	covalent compounds
What do combinations of low and high electronegativities form?	Ionic compounds
What is the traditional definition of oxidation and reduction?	Oxidation - addition of oxygen, loss of hydrogen, loss of electrons, increase in oxidation number Reduction - loss of oxygen, addition of hydrogen (and to a double bond), gain of electrons, decrease in oxidation number
If oxidation number goes up from one side of the equation to the other, has the atom been oxidised or reduced?	Oxidised
If oxidation number goes down has the atom been oxidised or reduced?	Reduced
What are the four steps for balancing redox equations?	1. calculate oxidation number. 2.Make total change in oxidation number zero. 3. Balance elements not undergoing redox. 4. Check charges balance.
What is Arrhenius's definition of an acid?	An acid is a substance that contains hydrogen and when dissolved in water releases H+ ions.
What state symbol is 'amm' in an equation?	Dissolved in liquid ammonia.
How can Arrhenius's definition be extended?	An acid is a substance from which a proton can be removed.
Arrhenius defined a base as a substance that gives hydroxide ions when dissolved in water. How can it be extended?	A base is a substance that can accept a proton from an acid.
So what is the bronsted-Lowry definition?	An acid gives a proton and a base accepts it.
What is a dative bond?	When two electrons in a pair are both donated to form a covalent bond it is a dative bond.
How are dative bonds drawn?	As an arrow going from the donator to the recipient.
What is the definition of a Lewis Acid and a Lewis Base?	Rather than thinking of an acid donating a proton as with Bronsted-Lowry. A Lewis acid can accept a non bonding pair of electrons from the base. A Lewis base donates the non bonding pair of electrons.
What are resonance structures?	Resonance structures are alternate structures possible for an atom or ion. The species is a composite or hybrid of all the possible resonance structures. Experimentally equal bond lenghths, (where unequal lengths are expected) support this idea
Name the shapes molecules such as the fluorides can take?	Linear coordination (BeF2) 180 degrees trigonal planar (BF3) 120 degrees tetrahedral(CF40) 109.5 degrees trigonal bipyramidal (PF5) horizontal-120, vert-90 degrees. Octahedral (SF6) 90 degrees pentagonal bipyramidal.(IF7) 72 degrees
What are the two kinds of position in the molecule shapes of the previous question?	'Equatorial' on the horizontal plane and 'axial' at right angles to it
Why are these molecule shapes adopted?	the electrons on each atom repulse each other and try to get as far away from one another as possible.
What are the four steps for deciding on a molecule's shape.	1. count the number of bonded and non bonded electrons. 2. Divide the non bonded electrons into pairs as far as possible. 3. Count each bonded pair and non bonded pair as a repulsion axis. 4. Decide which structure would minimise inter-axis repulsion.
What is the order that repulsion axes vary?	Non-bonded to non-bonded pairs > Non-bonded to bonded pairs > bonded to bonded pairs.
What is the order that repulsion varies taking double and triple bonds into account?	Triple bonded > non bonded about equal to double bonded > single bonded
Will repulsion axes of single electrons be stronger or weaker than any two electron axis?	Weaker
When deciding on laternatives for distributions of repulsion axes what rules should be followed?	1.Repulsive effects vary - non bonded pair-non bonded pair>non bonded pair- bonded pair> bonded pair-bonded pair. 2.Multiple bonds exert more repulsion than single bonds. 3. IN trigonal bipyrimidal arrangements non bonded pairs tend to occupy equatorial rather than axial positions.
What is a dipole?	2 separate but equal charges between two atoms in a molecule.
What is the dipole moment?	The extent of separation of the charge. See equation 11.1 Dipole moment = positive charge x distance of separation
In ionic bonds, ions are held together by?	Electrostatic forces
What is a dipole-dipole interaction?	The interaction between dipoles on adjacent polar molecules.
What are charge-dipole interactions?	When molecules with a dipole interact with ions.
What is a London Dispersion Force?	An induced or transient dipole. It may in turn induce a transient dipole in another molecule. It is very weak and short range. Ability increases down the periodic table.
What is hydrogen bonding?	Hydrogen bonds are a result of dipoles too, between electronegative atoms. Hydrogen bonding increases down a group.

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