LEAVING CERT HL CHEMISTRY

Q4, Q5, Q6, Q,7/9 (water, acids, bases, pH and indicators, chemical equilibrium)

define electronegativity

the relative attraction an atom has for the shared pair of electrions in a covalent bond

what contribution did Dobereiner make to the systematic arrangement of the elements?

Dobereiner placed elements with similar chemical properties into groups of three, called triads. In order of atomic weight, the weight of the middle element was approx. halfway between the other two

distinguish between an atomic orbital and a sub level

an atomic orbital is a region in space, arouund the nucleus, where there is a high probability of finding an electron. a sub level makes up part of the main energy levels in an atom

how could you confirm the presence of nitrate ions in a solution?

add freshly prepared, cold, saturated iron(II) sulfate solution, then pour conc sulfuric acid carefully down side of slanting test tube. bron ring at junction of liquids

define relative atomic mass

the average mass of the isotopes of that element, taking their abundances into account compared with the carbon 12 isotope

account for the difference in shapes of the ammonia (NH₃) and boron trifluoride (BF₃) molecules

BF₃ - triangular planar

NH₃ - pyramidal

state charles’ law

the volume of a fixed mass of gas is directly proportional to its temperature, at constant pressure

how could the presence of sulphite ions in aqueous solution be detected?

white precipitate with barium chloride solution which dissolves in dilute hydrochloric acid

how many electrons and neutrons has ^17₃₅ Cl^-?

neutrons: 18

electrons: 18

how many electrons are there in 2.3g sodium metal, Na?

(calculations) 6.6 × 10²³

on what principle is the analytical technique mass spectroscopy based?

mass spectroscopy is based on the principle that positive ios are accelerated through a magnetic field and separated according to their mass

list the types of radiation in order of increasing penetrating power

1. gamma

2. beta

3. alpha

state two ways in which Mendeleev’s periodic table of elements differ from that of Moseley

Mendeleev’s periodic table was organised in order of atomic weight. Moseley’s peiodic table is organised in order of atomic number. certain elements in Mendeleev’s table needed to be reversed to fit their groups, but this isn’t the case in Moseley’s

what are isotopes?

atoms of the same element (same atomic number) with different mass numbers due to different numbers of neutrons in the nuclei

write the electronic configuration of a neutral copper atom

1s² 2s² 2p⁶ 3s² 3p⁶ 4s1 3d¹⁰

state boyle’s law

the volume of a fixed mass of gas is inversely proportional to its pressure, at constant temperature

name the two reagents used to detect the presence of phosphate ions in solution

ammonium molybate

nitric acid

how many atoms are present in two moles of ammonia?

(calculations) 2.04 × 10²⁵

how many protons and neutrons are present in the ion Al⁺³?

neutrons: 14

protons: 13

what type of bonding occurs between (i) hydrogren and oxygen in a molecule of water, and (ii) molecules of water in a molecule of ice?

i) intermolecular

ii) intramolecular

give two common uses of radioisotopes

americium-241 used in smoke detectors (alpha)

carbon-14 used to date artifacts containing carbon (beta)

calculate the relative atomic mass of the element X, whose composition was found to be 70% ²⁰Ne and 30% ²²Ne

(calculations) 20.6

write the electron configuration of (i) a sulphur atom and (ii) the chloride ion

i) sulphur: 1s² 2s² 2p⁶ 3s² 3p⁴

ii) chloride ion: 1s² 2s² 2p⁶ 3s² 3p⁶

state the shape of the following two molecules; (i) CO₂ and (ii) NH₃

i) v-shaped

ii) pyramidal

why does HF have a higher boiling poin than HCl?

HF is made with hydrogen bonds, the strongest type of bond, thus having the highest boilng point. HCl has Dipole-Dipole bonding, weaker bonding than hydrogen bonding, and thus a lower boiling point than HF

what is meant by the term “half-life” of an element?

the time taken for half of the nuclei in a sample to decay

how many atoms are there in 250cm³ of methane at STP?

(calculations) 5.376 × 10²⁵

how many grams of NaOH would be required to make 250cm³ of a 0.1M solution?

(calculations) 40g

name the colour that would be produced in fireworks by salts containing (i) copper metal and (ii) potassium metal?

i) copper: blue-green

ii) potassium: lilac

write the equation of state for an ideal gas

PV=nRT

who is credited with the discovery of the electron?

JJ Thomson

what charge is associated with alpha particles?

double positive charge

what is the trend in the size of atomic radii across the periodic table?

decrease in atomic radius

state three characteristic properties of ionic substances

ionic compounds are:

1. composed of a network of ions in a crystal

2. hard and brittle - high melting and boiling points - solid at room temperature

   1. conduct electricity when dissolved in water or molten - free to move - can carry a current

what is the shape of the methane molecule?

tetrahedral

what is diffusion?

the spontaneous spreading out of a substance due to the natural movement of its particles

greek philosophers contributions

all matter is made of tiny particles called atoms

no experiments

four elements (earth, fire, air, water)

atomos - indivisible

john dalton contributions

experiments on gases

atomic theory

william crookes contributions

investigated cathode rays in a vacuum tube

the maltese cross experiment

the paddle wheel experiment

george stoney contributions

named electrons

jj thomson contributions

investigated cathode rays

plum pudding model

robert millikan contributions

measure charge of electron

oil drop experiment

ernest rutherford contributions

gold foil experiment

james chadwick contributions

bombarded beryllium wutg alpha particles, observed a chargeless radiationemitted from the nucleus - neutrons

state dalton’s atomic theory

1. all matter is made of atoms

2. atoms are indivisible and small

3. atoms cannot be created or destroyed

4. elements are made of one kind of atom

   1. atoms can join together to form compounds

outline the experiment performed by crookes to discover cathode rays

maltese cross: saw that something was hitting the back of the glass. investigating the negative terminal of a battery in a vacuum tube (empty space)

paddle wheel: established cathode rays

outine the experiment performed by jj thomson to discover the charge on cathode rays

investigated if cathode rays consisted of charged particles

observed cathode rays attracted to positive plate

concluded cathode rays consist of negatively charged particles - called these electrons

what are cathode rays?

streams of negatively charged electrons which travel from the cathode to the anode

outline the experiment performed by millikan to measure the charge on an electron

oil drop experiment

investigated the size of a charge on an electron

charged oil drop suspended between two charged plates

e/m calculated (charge/mass)

outline thomson’s plum pudding model of the atom

sphere of positive charge with negatively charged electrons embedded in it

state three observations that rutherford made during his gold foil experiment

1. most alpha particles passed through the gold foil

2. some were deflected at large angles

3. a very small amount were deflected back along their own path - hit the nucleus head on

what is the relative charge, relative mass, and location of (i) protons, (ii) neutrons, (iii) electrons?

i) protons: +1, 1, nucleus

ii) neutron: 0, 1, nucleus

iii) electron: -1, 1/1860, space outside the nucleus

outline bohrs atomic theory basd on the hydrogen emission spectrum

electrons revolve around the nucleus in fixed paths called energy levels

while in a particular energy level, the energy of the electron is fixed (or quantised)

electrons normally occupy the lowest available energy level. they are said to be in their ground state

when an atom absorbs energy, electrons jump rom a lower energy level to a higher energy level. they are then said to be in an excited state, which is temporary and unstable

state the colour given by lithium in the flame test

crimson

state the colour given by potassium in the flame test

lilac

state the colour given by barium in the flame test

green

state the colour given by strontium in the flame test

red

state the colour given by copper in the flame test

blue-green

state the colour given by sodium in the flame test

yellow

define energy level

a region of definite energy within the atom that electrons can occupy

what is meant by the ground state of an atom?

the lowest energy state for an electron

what is meant by the excited state of an atom?

when an electron occupies a higher energy state than the ground state by absorbing enough energy

define atomic orbital

a region in the space of an tom where the probability of finding an electron is relatively high

name the series of lines in the emission spectrum of hydrogen where electron transitions are from higher energy levels to n=2 and give rise to lines in the visible spectrum

balmer series

name the series of lines in the emission spectrum of hydrogen where electron transitions are from higher energy levels to n=1 and give rise to lines in the ultraviolet region of the spectrum

lyman series

name the series of lines in the emission spectrum of hydrogen where electron transitions are from higher energy levels to n=3 and give rise to lines in the infrared region of the spectrum

paschen series

how is an atomic absorption spectrum produced?

created when electrons transition from a low energy to a high energy since they absorb energy

what is a sublevel?

a subdivision of an energy level containing one or more atomic orbitals, all of equal energy

state heisenberg’s uncertainty principle

it is not possible to measure both the position and velocity of an electron, since doing one affects the other

state two limitations of bohrs theory

1. only worked for hydrogen

2. subsequent discoveries: energy sublevels, wave nature of the electron, uncertainty principle, orbitals

define an element

a simple substance that cannot be broken into anything simpler

what method did humphry davy use to discover new elements?

passed electric current through a number of compounds. compounds split into their component elements

what contribution did dobereiner make to the systematic arrangement of the elements?

triads - placed elements with similar chemical properties into groups of threes. the atomic weight of the middle one was approx. halfway between that of the other two

what contribution did newlands make to the systematic arrangement of the elements?

the law of octaves - arranged elements in order of atomic weights, noticed every eighth element repeated propertiesw

what is mendeleev’s periodic law?

when elements are arranged in order of atomic weight, their properties vary periodically

outline mendeleev’s work to construct a periodic table of elements

prioritised chemical properties over atomic weight

left gaps to ensure elements fit into the correct columns

predicted the propertie of undiscovered elements

revesed the order of some elements to make them fit their column

state two differences between mendeleev’s periodic table and the modern periodic table of elements

1. mendeleev - in order of atomic weight. modern - in order of atomic number

2. mendeleev - gaps for undiscovered elements. modern - no gaps

what contribution did henry moseley make to the systematic arrangement of the elements?

used x-rays to discover the number of protons in the nuclei of atoms (atomic number)

placed elements in order of increasing atomic number - no reversing

define atomic number

number of protons in an atom of that element

define mass number

average mass of the isotopes of the element

define relative atomic mass

the average mass of the isotopes of that element, taking their abundances into account, compared with the carbon-12 isotope

what is an isotope?

atoms of the same element (atomic number) with different mass numbers due to different numbers of neutrons in the nuclei

name the five processes that occur in a mass spectrometer

1. vapourisation

2. ionisation

3. acceleration

4. separation

5. detection

describe the five processes that occur in a mass spectrometer

1. vapourisation: the sample is turned into a vapour or gas

2. ionisation: elecrons are removed from the atoms to form positive ions

3. acceleration: through a magnetic field

4. separation: the ions are separated according to their mass

5. detection: both the type and the abundance of each type of ion is detected

state the principle of mass spectrometry

positive ions are accelerated through a magnetic field and separated according to their mass

state the aufbau principle

electrons always occupy the lowest available energy level first

state hund’s rule of maximum multiplicity

where two or more orbitals are available, electrons will occupy them singly before filling them in pairs

state the pauli exclusion principle

no more than two electrons may occupy an orbital and they must have opposite spin

define atomic radius

half the distance between the nuclei of two atoms of the same element that are joined together by a single covalent bond

give two reasons why the values of atomic radius increase as you go down a group in the periodic table

1. addition of a new level

2. screenng effect of inner electrons

give two reasons why the values of atomic radius decrease as you go across a period in the periodic table

1. increase in nuclear charge

2. no increase in screening effect

define first ionisation energy

the minimum energy required to removed the most loosely bound electron from a neutral gaseous atom in its ground state

give two reasons why the values of first ionisation energy decreases as you go own a group in the periodic table

1. increasing atomic radius

2. screening effect of inner electrons

give two reasons why the values of first ionisation energy increase as you go across a period in the periodic table

1. increasing nuclear charge

2. decreasing atomic radius

explain why there are some exceptions to the general trend in first ionisation energy as you go across a period in the periodic table

a completely filled outer sublevel or half filled outer sublevel gives an atom extra stability. thus, it makes it more difficult to remove the most loosely bound electron, resulting in higher ionisation energy

define second ionisation energy

the energy required to remove the most loosely bound electron from a positive ion

represent the second ionisation energy as an equation

Be⁺ → Be²⁺ + e^-

describe the trend in the reactivity of alkali metal as you go down the group

increase:

• increase in atomic radius

• increase in shielding

• decrease in ionisation energy

describe the trend in the reactivity of halogens as you go down the group

decrease:

• increase in atomic radius

• increase in shielding

define electronegativity

a measure of the relative attraction an atom of an element has for the shared pair of electrons in a single covalent bond