Leaving Cert Chemistry - Assignment 1 (LC HL Q5)

Atomic Structure and Periodic Table, including trends, bonding, Radioactivity

what is diffusion?

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

briefly outline the contributions of greek philosophers to the discovery of the atom

all matter is made of tiny particles called atoms

no experiments

four elements - earth, fire, air, water

atomos - indivisible

briefly outline the contributions of john dalton (1766-1844) to the discovery of the atom

experiments on gases

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 of a kind atoms

5. atoms can join together to form compounds

briefly outline the contributions of william crookes (1832-1919) to the discovery of the atom

investigated cathode rays in a vacuum tube

two experiments

1. the maltese cross - saw something was hitting the back of the glass

2. the paddle wheel

concluded that radiation was coming from the negative terminal - cathode rays

they moved in straight lines towards anode

cathode rays cause the glass to fluoresce

briefly outline the contributions of george stoney (1826-1911) to the discovery of the atom

named electrons

briefly outline the contributions of jj thomson (1856-1940) to the discovery of the atom

investigated cathode rays

attracted to positive plate

cathode rays consist of negatively charged particles - electrons

plum pudding model

briefly outline the contributions of robert millikan (1868-1953) to the discovery of the atom

measured charge of electron

oil drop experiment - charged oil drop suspended between two charged plates

e/m calculated (charge/mass)

briefly outline the contributions of ernest rutherford (1871-1937) to the discovery of the atom

scattered alpha particles at a thin sheet of gold foil

nucleus

briefly outline the contributions of james chadwick (1891-1974) to the discovery of the atom

bombarded beryllium with alpha particles

observed a chargeless radiation emitted from the nucleus - neutrons

state two assumptions of daltons atomic theory

1. electrons revolve around the nucleus in fixed paths called energy levels

   1. electrons normally occupy the lowest available energy level

outline the experiment performed by crookes to discover cathode rays

maltese cross

• saw something that was hitting the back of the glass

• investigated the negative terminal of a - bettery in a vacuum tube (empty space)

the paddle wheel

• established cathode rays

outline the experiment performed by jj thomson to discoverthe charge on cathode rays

investigated if cathode ray consisted of charged particles

observed cathode rays attracted to positive plate

concluded that cathode rays consist of negatively charged particles - electrons

what are cathode rays?

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

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

oil drop experiment

investigated the size of a charge on the electron

charged oil drop suspended between two charged plates

e/m calculated (charge/mass)

outline thomsons 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

complete the table, which shows the properties of sub-atomic particles

proton: +1, 1, nucleus

neutron: 0, 1, nucleus

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

outline bohrs atomic theory based 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/quanised

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

when an atom absorbs energy, electrons jump from 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 characteristic colour given off by lithium when heated in the flame test

crimson

state the characteristic colour given off by potassium when heated in the flame test

lilac

state the characteristic colour given off by barium when heated in the flame test

green

state the characteristic colour given off by strontium when heated in the flame test

red

state the characteristic colour given off by copper when heated in the flame test

blue-green

state the characteristic colour given off by sodium when heated in the flame test

yellow

define energy level

a region of definite energy within the atom that electrons 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

state what each symbol represents in the equation E₂ - E₁ = hf

E₂ = energy of electron in excited state

E₁ = energy of electron in ground state

h = Plancks constant

f = frequency of the light emitted

define atomic orbital

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

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

balmer series

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

paschen series

how is an atomic absorption spectrum produced?

created when electrons transition from a low energy level to a high energy level 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 bohr’s theory

only worked for hydrogen

subsequent discoveries:

1. energy sublevels

2. wave nature of the electron

3. uncertainty principle

4. orbitals

name this

s orbital

name this

p orbital

define an element

a simple substance that cannot be broken into anything simpler

what method did humphrey 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 three

the atomic weight of the middle one was approximately 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 eight element repeated properties

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 properties of undiscovered elements

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

state two differeces between mendleev’s periodic table and the modern periodic table of elements

1. mendeleev - in order of 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 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 accouunt, compared to the carbon-12 isotope

a sample of chlorine is found to consist of 75% Cl-35 and 25% Cl-37. Calculate the average mass of an atom of chlorine

35.5

what is an isotope?

atoms of the same element (atomic number) wih 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: electrons 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 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

write the electron configuration of hydrogen

1s¹

write the electron configuration of helium

1s²

write the electron configuration of lithium

1s² 2s¹

write the electron configuration of berryllium

1s² 2s²

write the electron configuration of boron

1s² 2s² 2p¹

write the electron configuration of carbon

1s² 2s² 2p²

write the electron configuration of nitrogen

1s² 2s² 2p³

write the electron configuration of oxygen

1s² 2s² 2p⁴

write the electron configuration of fluorine

1s² 2s² 2p⁵

write the electron configuration of neon

1s² 2s² 2p⁶

write the electron configuration of sodium

1s² 2s² 2p⁶ 3s¹

write the electron configuration of magnesium

1s² 2s² 2p⁶ 3s²

write the electron configuration of aluminium

1s² 2s² 2p⁶ 3s² 3p¹

write the electron configuration of silicon

1s² 2s² 2p⁶ 3s² 3p²

write the electron configuration of phosphorous

1s² 2s² 2p⁶ 3s² 3p³

write the electron configuration of sulphur

1s² 2s² 2p⁶ 3s² 3p⁴

write the electron configuration of chlorine

1s² 2s² 2p⁶ 3s² 3p⁵

write the electron configuration of argon

1s² 2s² 2p⁶ 3s² 3p⁶

write the electron configuration of potassium

1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹

write the electron configuration of calcium

1s² 2s² 2p⁶ 3s² 3p⁶ 4s²

write the electron configuration of scandium

1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹ 4s²

write the electron configuration of titanium

1s² 2s² 2p⁶ 3s² 3p⁶ 3d² 4s²

write the electron configuration of vanadium

1s² 2s² 2p⁶ 3s² 3p⁶ 3d³ 4s²

write the electron configuration of manganese

1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁵ 4s²

write the electron configuration of iron

1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶ 4s²

write the electron configuration of cobalt

1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁷ 4s²

write the electron configuration of nickel

1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁸ 4s²

write the electron configuration of copper

1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s¹

write the electron configuration of zinc

1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s²

write the electron configuration of gallium

1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p¹

write the electron configuration of germanium

1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p²

write the electron configuration of arsenic

1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p³

write the electron configuration of selenium

1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁴

write the electron configuration of bromine

1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁵

write the electron configuration of krypton

1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶

write the electron configuration of chromium

1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁴ 4s¹

define atomic radius

half the distance between the nuclei of two atoms o 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. additiion of a new energy level

2. screening effect of inner electrons

give two reasons why the valus 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 remove the most loosely bound electron from a netural gaseous atom in its ground state

give two reasons why the values of first ionisation energy decrease as you go down 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 electrons, resulting in higher ionisation energy