chemistry - atomic theory 5

what did neils bohr do

showed that the amount of energy an electron possessed was of a definite quantifiable amount

prior to bohrs theory

electrons able to possess any amount of energy and are found anywhere around the nucleus

what did bohr show

amount of energy an electron possesses is a definite quantifiable amount

electron capacity formula

2(n)²

what happens when white light is passed through a prism

light splits up into an array of colours called the spectrum/continuous spectrum as it consists of a continuous range of colours/wavelengths

what did bohr carry out his experiments with

hydrogen discharge tube

what happened when bohr passed the light coming out of the discharge tube through a prism

he saw that only a few wavelengths were present in the resultant spectra - coloured lines were seperated by black regions

what did the black regions in bohrs results correspond to

colours that were absent in the line

what did bohr call his results

emission line spectrum

what did bohr notice in his experiements

each element had its own characteristic line spectrum

what does the spectrum consisting of a series of lines indicate to bohr

that only certain energy emissions are possible

what did bohr conclude from his experiement

• electrons revolve around the nucleus of an atom in certain allowed orbits / shells

• when in a shell electron has a definite amount of energy

• energy level is an exact amounts of energy that an electron has when it is close to an atom

• dependent on distance from nucleus

• when electron stays in an energy level, amount of energy remains same, when it absorbs energy, it jumps from a lower to a higher energy level

• as electron can only fall back to certain definite energy levels, only fixed amounts of energy can be given off

enzymes in their excited state are

unstable and temporary

what does energy level depend on

dependent on distance from the nucleus, electron has little energy when close to the nucleus, and more energy when it is far from the nucleus

Atomic Emmision spectrum of hydrogen

1. Hydrogens one electron occupies lowest available energy level (ground state)

2. when energy is given, electron is promoted to higher energy level (unstable and temporary)

3. as electron falls back to lower level, energy emitted as photon

4. each line seen on spectrum is the result of an electron moving to a lower energy level

5. each transition has definite energy and appears as a line of a particular colour on the line emission spectrum (each line has a definite frequency)

6. this indicates that only a limited number of energy changes are possible within the structure of an atom

photon

fixed amount of light energy or other forms of electromagnetic radiation

why do different elements have unique atomic spectra

due to differing numbers of electrons giving rise to different electron transitions from higher to lower energy levels

why do different metals produce different flame colours

different metals have different numbers of electrons, and therefore different arrangements of electrons, different electron transitions occur from one energy level to another, thus different frequencies and wavelengths appear

what is an emission spectrum

a series of coloured lines against a dark background

limitations to bohrs theory

• failed when applied to atoms with more than one electron

• did not take wave particle duality into account

• does not allow for uncertainty

• does not explain the discovery of sublevels

bohrs nucleur model of the atom

• electrons revolve around nucleus in fixed paths called orbits

• in an orbit, electrons have a fixed mount of energy

• energy that an electron has in its energy level is an exact, fixed value

what did louis victor de broglie propose

electrons may behave as waves as well as particles

what did schrodinger do

math equation to work out probability of finding an electron in a sublevel in an atom, equations were solved to give us shapes of four types of orbitals - spdf

heisenbergs uncertainty principle

states that its impossible to know both the position and velocity of an electron at the same time as electrons move in a wave motion

atomic orbital

region in space around nucleus of an atom, in which there is a high probability of finding an electron

energy level

exact amount of energy an electron has when it is in an atom

energy sublevel

subdivision of a main energy level, ggroup of atomic orbitals with the same energy

what sublevels does energy level one have

s

what sublevels does n = 2 have

s, p

what sublevels does n = 3 have

s, p, d

what sublevels does n = 4 have

s, p, d, f

sublevel capacity of s

2

sublevel capacity of p

6

sublevel capacity of d

10

sublevel capacity of f

14

orbital capacity of s

2

orbital capacity of p

2

orbital capacity of d

2

orbital capacity of f

2

aufbau principle

electrons occupy lowest available energy level

hunds rule of maximum multiplicity

when two or more orbitals of equal energy are available, electrons fill them singly before in pairs

paulis exclusion principle

no more than two electrons can occupy an orbital

sodium flame test colour

amber / yellow

potassium flame test colour

lilac

copper flame test colour

blue - green

lithium flame test colour

crimson

strontium flame test colour

red

barium flame test colour

yellow - green

appartus for flame test

safety glasses, Bunsen burner, platinum wire

materials for flame test

concentrated HCL solution (two batches), salts of sodium, lithium, copper, potassium, calcium

method for flame test

1. nichrome wire cleaned by dipping it into concentrated hcl (batch one)

2. heated to red hot in bunsen flame until no flame colour observed

3. wire dipped into clean sample of hcl and into salt to be tested

4. wire held in busen flame

5. colour of flame noted and recorded

6. procedure repeated with other salts, ensuring wire was cleaned thoroughly each time

how many orbitals does 3d contain

5

how many orbitals does p contain

3

how many orbitals does f contain

7

why the arrangement of electrons in the main energy levels in a calcium atom is 2,8,8,2 and not 2,8,10

because the 4s sublevel is of lower energy than the 3d sublevel, which is why electrons occupy it first