Revision:Atomic Theory - 02

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2.1 The Nuclear atom

2.1.1

• Protons
  • Mass = 1 amu
  • Charge = +1
• Neutrons
  • Mass = 1 amu
  • Charge = 0
• Electron
  • Mass = 1/1840 amu (usually insignificant)
• Charge = -1

2.1.2

Protons and Neutrons form the nucleus of the atom, electrons orbit the nucleus in electron shells.

2.1.3

• Mass number (A) - Number of protons + neutrons.
• Atomic number (Z) - number of proton.
• Isotope - atoms with same atomic number but different mass number (ie different numbers of neutrons)

2.1.4

• A = mass number,
• Z = atomic number,
• X = atomic symbol.

2.1.5

Isotopes may differ in physical properties (mass/density) and radioactivity but not generally in chemical properties.

2.1.6

Atomic masses are the average of the atomic mass of each isotope (isotopic mass) times the isotope's relative abundance. results in non integer atomic masses

2.1.7

• Atomic number = number of protons (or number of electrons - ionic charge),
• mass number - atomic number = number of neutrons.

2.2 Electron Arrangement

2.2.1

Continuous spectrum goes continuously through red, orange, yellow, green, blue, indigo, violet. A line spectrum contains only some individual lines from this spectrum.

2.2.2

Electrons are excited (usually by running an electric current through them). This causes electrons to 'jump' into higher electron shells ( X -> X^* ) this state is only temporary, however, and the electron falls back to it's ground state. This change decreases the energy of the electron, and this energy is emitted in the form of a photon. If this photon falls into the visible spectrum of light, then it produces a visible spectrum. As electrons move further away from the nucleus, the electron shells become closer together in terms of space and energy, and so lines converge towards the end of the spectrum.

2.2.3

The main electron levels go : 2, 8, 18 etc...2ⁿ + 2 for n₀, n₁ and n₂.

2.2.4

Electrons are added from the left...after each shell is filled, move to the next...2, 8, 18...only up to Z = 20 is required.

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