M2S1: Atoms and Moles

Mass number

Total num proton + neutron

Atomic number

Num protons in nucleus of atom

Isotope

Isotopes of an element same num protons, diff num neutrons

What did JJ Thomson do?

• 1897

• Took measurements of the charges of an atom, concluded atoms must contain smaller, negatively charged particles

• Plum pudding model - positively charges sphere with negative electrons embedded in it

What did Ernest Rutherford do?

• 1909

• Alpha particle scattering experiment

  • Fired alpha particles at thin sheet gold

  • Due plum pudding model, expect most deflect but most passed through

• Nuclear model - tiny positively charged nucleus surrounded by ‘cloud’ negative electrons, most mass concentrated at centre = mostly empty space

• Later discovered protons

What did James Chadwick do?

Discovered neutron

What does Bohr’s model include?

• Electrons exist fixed orbit

• Each shell had fixed energy

• Electron moves between shells = electromagnetic radiation emitted/absorbed

• Energy of shells fixed = radiation fixed frequency

Relative atomic mass

(Ar) is the weighted mean mass of an atom of an element compared to 1/12 of the mass of carbon-12

Relative isotopic mass

Mass of an atom of any isotope of an element compared to 1/12 of the mass of an atom of carbon-12

Mass spectra

Isotopic abundance in form of graph, produced by mass spectrometers

Relative molecular mass

(Mr) is the average mass of a molecule compared to 1/12 of the mass of an atom of carbon-12

Relative formula mass

Average mass of a formula unit compared to 1/12 of the mass of an atom of carbon-12

Avagadro constant

6.02 × 10²³

Molar mass

• The mass of one mole of something

• (gmol^-1)

• Same numerical value as Mr

Number of moles formula

n = m/Mr

Number of gas moles (1)

n = v/24 (dm³)

Number of gas moles (2)

pV = nRT

C to K

C + 273

Number of moles in a solution

n = c x v