module 2 Flashcards by ; ;

describe electron-repulsion theory

e. pairs surround a central atom determine the shape of the molecule

e. pairs repel one another

arrangement of e.pairs minimises repulsion and thus holds the bonded atoms in a definite shape

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what is the difference between a lone pair and a bonding pair

lone pair is closer to the central atom and occupies more space

so it repels more stronger than a bonding pair

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describe and explain the shape of a tetrahedral molecule

what is the angle

four bonding pairs
equal repulsion

109.5 degrees

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the bond angle is reduced by how much for each lone pair

2.5 degrees

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what is the bond angle and shape of a molecule with 3 bonding pairs and 1 lone pair

107

pyramidal

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what is the bond angle and shape of a molecule with 2 bonding pairs and 2 lone pairs

104.5

non-linear

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explain the shape of a carbon dioxide molecule

has 4 bonding pairs around central carbon arranged as 2 double bonds so there are 2 bonding regions

2 bonding regions repel one another as much as possible

gives molecule a linear shape

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what is the shape and bond angle for a molecule with 3 bonding regions

trigonal planar

120 degrees

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what is used to compare electronegativity of different elements

pauling scale

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if electronegativity diff is large what bond forms and why

ionic

bonded atom has a greater attraction for the shared pair of electrons

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describe the origin of induced dipoles

movement of electrons produces an instantaneous dipole, with its position constantly changing

the instantaneous dipole induces a dipole on a neighbouring molecule

the induced dipole induces further dipoles on other neighbouring molecules

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what does more electrons mean in terms of the strength of the induced dipoles

larger induced dipoles

more energy is needed to overcome the intermolecular forces

increasing the boiling point

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define the first ionisation energy

energy required to remove one electron from each atom in one mole of gaseous atoms of an element

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give the first ionisation of sodium

Na(g) –> Na+ + e-

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what are the 3 factors affecting the attraction between the nucleus and the outer electrons

atomic radius
higher distance = lower force of attraction

nuclear charge
more protons = greater the attraction

electron shielding
inner-shell electrons repel outer-shell electrons, causing repulsion and reduces attraction

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explain why helium’s second ionisation energy is greater than its first

after the first electron is lost, the other is pulled closer to the nucleus

nuclear attraction on the remaining electron increases and more energy is required to remove the electron

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what happens to ionisation energy across a period

decrease between the end of one period and the start of the next period

zig zag

peak is a noble gas

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describe the trend in first ionisation energy down a group

atomic radius increases

shielding increases

nuclear attraction decreases

first ionisation energy decreases

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describe the trend in first ionisation energy across a period

nuclear charge increases

similiar shielding

nuclear attraction increases

atomic radius decreases

first ionisatin incerases

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when is it easier to remove an electron

when there’s a higher energy level

when is it easier to remove an electron in ionisation energy

when the orbital is occupied by 2 electrons

these electrons repel each other so it’s easier to remove an eelctron

give the equation of the most common type of reaction of calcium

what is calcium’s role in this reaction

redox

Ca -> Ca2+ + 2e-

the alkali metal is the reducing agent because it has reduced another species

what do alkali metal react with oxygen to make

metal oxide

what do alkali metals react with water to make

metal hydroxide + hydrogen

what does a metal and acid form

salt + hydrogen

why does the reactivity of the alkali metals increases down the group

nuclear attraction decreases due to higher atomic radius and more shielding electron is more easily lost

what does the reaction of a group 2 oxide and water form

hydroxide ions + metal ion

what happens when the metal hydroxide is saturated in water

metal and hydroxide ions form precipitae > Ca2+ + 2OH- -> Ca(OH)2 (s)

how can we test the solubility trend in group 2 elements

add a spatula of each group 2 oxide to water in a test tube shake the mixture (forms a saturated solution of the metal hydroxide with precipitate) measure the pH of each solution

what are the uses of group 2 elements

hydroxides neutralises acidity in soil used as antacids for treated indigestion

what is the role of a halogen in redox

oxidising agent it has oxidised another species

how can we identify halogens

solution of each halogen added to aqueous solutions of other halides halogen displacing the halide from solution results in a colour change

how can we tell iodine and bromine in water apart

organic non-polar solvent (cyclohexane) is added and the mixture is shaken

what is the colour of iodine in cyclohexane

violet

what does it mean when a bromide solution turns to colour orange when the halogen is added

halogen added is chlorine chlorine displaces bromide in the solution forming bromine turning the solution orange

what is formed when chlorine and water are reacted

chloric (I) acid (HClO) + HCl

what is formed when chlorine reacts with aqueous sodium hydroxide

NaClO + NaCl + H2O

describe the carbonate test

add nitric acid to substance bubble the gas produced through limewater

describe the sulfate test

add barium ions (as barium nitrate) which react with sulfate ions to form the precipiate BaSO4 (s) (white)

which halides are soluble in dilute ammonia

chloride

which halides are soluble in conc. ammonia

bromide and iodide

what is the sequence of tests to be done for the 3 tests

carbonate sulfate halide

why is the sequence of tests done this way

sulfate nor halide ions don't produce bubbles with dil. acid BaCO3 is also a white ppt. so you have to make sure the substance being tested is not carbonate silver carbonate and sulfate also form precipitates

give the test for ammonium

add NaOH mixture is warmed add universal indicator paper

give the sequence of tests when there is a mixture of ions

carbonate test add nitric acid until the bubbling stops sulfate test add excess Ba(NO3)2 filter

how do perform purification

recrystallisation dissolve impure solid with min. volume of hot solvent cool solution and filter solid wash with cold solvent and dry

how do check purity

obtain melting point compare to known values pure sample has sharp melting point close to data value

What is the number of peaks in the 'H NMR spectrum of HOOCH2СНОНСH2 СООН?

A student reacts 4.50 g of C6H5NH2, with excess CH3COCl in the reaction below. C6H5NH2, + CH3COCl→ C6H5NHCOCH3 + HCl M, (C6H5NH2) = 93.0 M, (C6H5NHCOCH3) = 135.0 The reaction produces 3.25 g of C6H5NHCOCH3. What is the percentage yield of C6H5NHCOCH3?

49.8