Module 2.1 Flashcards
Mass and charge of protons, neutrons and electrons:
Protons: 1 +
Neutrons: 1 0
Electrons: Negligible, 1/1000 -
What does the mass number of an element tell us?
Protons + neutrons number
Average of the mass numbers of the isotopes of that element.
Define isotopes:
Atoms of the same element with different numbers of neutrons and masses.
Why is carbon 12 on the periodic table?
Because it is the most abundant carbon isotope.
Define RMM:
Relative molecular mass
What does (m/z) stand for?
Mass/ ion charged
Describe the current model of the atom:
Protons and neutrons in nucleus, centre of atom.
Electrons orbit in shells.
Nucleus is tiny compared to the volume of the atom.
The nucleus is extremely dense and accounts for most of the mass.
Most of the atom consists of empty space between the nucleus and ‘shells’.
Where is most of the mass in an atom?
In the nucleus
What is most of the volume in an atom?
The orbitals
How do isotopes differ?
Different masses
Different numbers of neutrons
What do isotopes of the same element have in common?
Same number of protons and electrons.
Why do different isotopes of the same element react in the same way?
Chemical reactions involve electrons, isotopes have the same number and arrangement.
Neutrons make no difference to chemical reactivity.
Why do different isotopes have different physical properties?
Densities and rates of diffusion differ because they depend more on mass.
How do we measure mass of element?
We compare different masses using relative mass.
Carbon 12 is the international standard for he measurement of relative mass.
Atomic masses are measured using the unified atomic mass unit.
Carbon 12s mass is defined as 12u, so 1/12 of carbon is 1u.
Define a molecule:
A group of atoms held together by covalent bonds.
What are the uses of mass spectrometry?
Identify unknown compounds
Relative abundance of each isotope of an element
Determine structural info about molecules
How is mass spectrometry carried out?
Causes substances to become positive ions, which are passed through the apparatus and separated according to their mass and charge.
A computer analyses the data and produces a mass spectrometer.
What unit are atomic masses measured in?
Unified mass unit (u)
Who came up with the original atomic theory and when?
Dalton, 1800s
What did Dalton’s theory consist of?
Atoms make up elements.
Atoms cannot be divided, they are solid spheres, different sphere, different element.
All atoms of an element are the same.
Atoms of one element are different from atoms of every other.
Who developed the second model of the atom and when?
Thomson, 1897-1906
What did thomsons model consist of?
Disproved atoms cannot be divided
Proposed negative corpuscles (electron) in a sea of positive charge
‘Plum pudding model’ positive sphere with electrons embedded in it
+tive and -tive charges balance out making a neutral atom.
Who and when discovered the 3rd model of the atom?
Rutherford, 1909-11
What did Rutherford model consist of?
Gold leaf experiment
Shot + alpha particles at a thin gold sheet
‘Plum pudding’ would hardy deflect any
Most were not deflected, a small % by large angles, some backwards towards the source
Came up with nuclear model to reflect his findings
Tiny positively charged nucleus at the centre of the atom, were most of the mass is concentrated. The nucleus is surrounded by a ‘sea’ of positive electrons. Most of the atom is empty space
Who and when was the 4th model of the atom discovered?
Bohr, 1913
What did bohrs model consist of?
If electrons were in a cloud they’d spiral into the nucleus, causing the atom to collapse.
He proposed they exist in fixed orbits, or shells and not anywhere in between. Each shell has fixed energy.
When an electron moves between shells electromagnetic radiation is emitted or absorbed.
Because the energy is fixed, the radiation will have a fixed frequency.
How did bohrs model explain the inert gases?
He said shells have fixed numbers of electrons, this causes an atoms reactivity.
Atoms react in order to gain full shells of electrons, when it’s shell is full, it does not react.
What is Avogadro’s constant?
Number of atoms per mole of the carbon-12 isotope
6.02 x 10^23mol-1
How to find moles from mass and molar mass?
moles = mass / molar mass
Ideal gas equation
What do the letters represent?
PV = nRT P = Pressure V = Volume n = Moles R = Gas constant, 8.314Jmol-1k-1
What is 0 degrees in kelvin?
273
How much volume does one mole of gas take up (at room temperature)?
24000cm^3
24dm^3
Define amount of substance
he quantity that has moles as its unit
Define mole
Amount of any substance containing as many particles as there are in 12g of the carbon-12 isotope
Define Molar mass
mass per mole of a substance
g mol-1
How do you work out amount, in moles of any volume of a gaseous substance?
n = v (dm3) / 24 n = v (cm3) / 24000