Chemistry S1

Proton

• nucleus

• +1

• 1.6726 × 10^-27 kg

• 1 amu

Neutron

• nucleus

• 0

• 1.6749 × 10^-27kg

• 1 amu

Electron

• energy levels

• -1

• 9.109 × 10^-27kg

• negligible amu

Atomic Number (Z)

• identity of an element

• # of p⁺

Mass Number (A)

• # of p⁺ + # of n⁰

• always a whole #

Element Symbol

Isotopes

• Atoms of the same atomic number but different mass number 

• Same chemical properties (same behavior in reactions), different physical properties (e.g. BP, MP, etc) 

Radioisotopes

• Isotopes with an unstable nuclei.

• Emits ALPHA, BETA and GAMMA as they change to become more stable.

Relative Atomic Mass

The weighted average of all naturally occurring isotopes of an element relative to carbon-12. 

The Mass Spectrometer

• An analytical instrument used to measure the masses of the isotopes of an element and their abundances.

• It determines the composition of an unknown molecular substances.

Solid Sphere Model

John Dalton 1803

• indivisible

• unqiue elements

Plum Pudding

J. J. Thompson 1904

• exsitence of electrons

• atoms are a positive cloud

Nuclear Model

Ernest Rutherford 1911

• positive charge in the center

• electrons in orbits

• gold foil experiment

Planetery Model

Niels Bohr 1913

• electrons in fixed orbits and E levels

• no E emittence

Quantum Model

Erwin Schrodinger 1926

• clouds of possibility

• uncertain positions, movement in waves

Gold Foil Experiment Results

• electrons mostly pass right through → atom are mostly empty space

• electrons are bounced at small angles → there is a dense center

• electrons are deflected from the center → the center is positively charged and repels the positive charge of the alpha particles

Electron Transition

The distance of travel when an electron emits radiation and falls down to a lower E level 

3 characterisitcs of light

1. wavelength

2. frequency

3. energy in J

Electromagnetic spectrum

Gamma rays - x rays - UV - Visible light - infared - microwave - radio waves

Visible light spectrum

(400nm) VIBGYOR (700nm)

Emission Spectrum

• breaks down light

• shows colors produced on a black background

Continuous Spectrum

Shows the whole spectrum of visible light

Discontinuous/ Line Spectrum

Shows certain discrete colors of visible light produced

Formation of Electron Spectrum

1. electron absorbs energy while it is at ground state

2. electron jumps to a higher corresponding E level at an excited state, unstable status

3. electron falls to a lower E level while emitting the proportional value of energy

Bohr Model proposes that

• electrons occupy around the nucleus

• electrons can exist at E levels, but not in between them

• only certain defined energy values are possible for each E level

Higher E levels…

converge at n = ∞. When an electrons goes there, it is lost to that atom.

Hydrogen Emission Spectrum

Hydrogen Line Emission Spectrum

UV → falls to n=1 (highest E)

VL → falls to n=2

IR → falls to n=3 (lowest E)