Chapter 2 + 3 Flashcards
describe the nuclear atom
• Nucleus is made of both neutrons and protons, with electrons arranged around the nucleus in shells.
does a proton and a neutron have the same mass
• A proton has virtually same mass as a neutron
• Accurate measurements show that neutron has slightly greater mass, by factor of 1.001375, but so close to 1 that chemists assume 1:1 ratio
relative charge on proton
positive
relative charge on neutron
0
relative charge on electron
negative
relative mass of proton
1
relative mass of neutron
1
relative mass of electron
1/1836
proton exact charge
+1.60217733 x 10^-19 C
electron exact charge
-1.60217733 x 10^-19 C
define isotope
different atomic forms of the same element, with different number of neutrons, but the same number of protons
symbol for mass number
A
symbol for atomic number
Z
why does isotopes of the same element have the same chemical properties but different physical properties
• Different isotopes still have the same number of electrons, so their chemical properties don’t change.
- physical properties change due to higher mass = higher mp, higher bp, higher density.
does chemical properties change between isotopes of the same element
no - same electron number
does physical properties change between isotopes of the same element
yes - different number of neutrons = heavier
what is an ion
a charged atom
what is a cation
positive ion
what is an anion
negative ion
what type of ion is it when there are more electrons then protons
anion
what type of ion is it when there are more protons then electrons
positive
What is ‘u’
• One atom of carbon-12, mass of 1.992646538 x 10 kg, but we call this an atomic mass of u.
What is the mass of carbon in terms of ‘u’
12u
Charge on an atom
Neutral
What is the number of protons called
Atomic number
How to calculate mass number
number of protons + number of neutrons
Symbol for mass number
A
Symbol for atomic number
Z
What are isotopes
Isotopes are atoms of the same element that contain the same number of protons and electrons but a different number of neutrons
Properties of isotopes
the same chemical properties but different physical properties
Why do isotopes of an element have the same chemical properties
because they have the same number of electrons in their outer shells
Electrons take part in chemical reactions and therefore determine the chemistry of an atom
Why do isotopes of an element have different physical properties
they only add mass to the atom
As a result of this, isotopes have different physical properties such as small differences in their mass and density
Define relative atomic mass
• relative atomic mass, Ar, is the weighted mean mass of an atom of an element relative to 1/12th of the mass of an atom of carbon-12.
Define isotopic mass
• relative atomic mass, Ar, is the weighted mean mass of an of an isotope relative to 1/12th of the mass of an atom of carbon-12.
Relative atomic mass formula
How does a mass spectrometer work
• A sample is placed in mass spectrometer
• Sample is vaporised, ionised to form positive ions
• Ions are accelerated, heavier ions move more slowly and are more difficult to deflect than lighter ions, so ions of each isotope are separated.
• ions are detected on a mass spectrum as a mass-to-charge ratio m/z.
• Each ion reaching the detector adds to the signal, so the greater the abundance, the larger the signal.
• For an ion with one positive charge, this ratio is equivalent to the relative isotopic mass, which is recorded on x -axis of spectrum.
What are the ions detected as
The ions are detected as a mass-to-charge ratio, written as bevelled m over z
What ions do metals form
Positive
Non-metal ions that are positive
ammonium, NH4+, and hydrogen, H+
Non metal ions make
Negative ions
silver (I)
Ag+
Ammonium
NH4 +
Zinc (II)
Zn 2+
Hydroxide
OH -
Nitrate
NO3 -
Sulfate
SO4 2-
Carbonate
CO3 2-
Hydrogen carbonate
HCO3 -
Phosphate
PO4 3-
Nitrite
NO2 -
Manganate (VII)
MnO4 -
Sulfite
SO3 2-
Dichromate (VI)
Cr2O7 2-
What is a polyatomic ions
an ion that contains atoms of more than one element bonded together
What is a binary compound
contains two elements only
Ions that copper for,
cu+ and cu 2+
Ions that iron form
iron 2+ and iron 3+
Symbol for solid
S
Symbol for liquid
L
Symbol of gas
g
Symbol for aqueous
(aq)
What do ions do in aqueous solutions
They dissociate
What are spectator ions
The ions that do not take part in the reaction
What does an ionic equation show
shows only the ions or other particles taking part in a reaction, and not the spectator ions
What state are acids
Aqueous
What state are alkalis / salts
Depends on solubility
If soluble = aqueous
Soluble table
Insoluble salts
Symbol for number of moles
n
Symbol for Avagadros constant
N (subscript A)
Avagadros constant = number
6.02 x 10^23 g mol-1
Define molar mass
the mass of substance that contains the same number of fundamental units as exactly 12.00 g of carbon-12
the mass of 1 mole of a substances
Number of moles + molar mass + given mass formula
What is the molar gas volume
the volume occupied by one mole of any gas, at room temperature and pressure
What is the molar volume
24 dm3
Molar gas volume Formula
Volume = amount in mol × molar volume. (24)
Molecular formula for ethanoic acid
C2H4O2
What is molecule formula
shows the number and type of each atom in a molecule
What is the empirical formula
shows the simplest whole number ratio of the elements present in one molecule of the compound
How to find the molecular formula
The molecular formula can be found by dividing the relative molecular mass of the molecular formula by the relative formula mass of the empirical formula
Multiply the number of each element present in the empirical formula by this number to find the molecular formula
What is a compound that contains water if crystallisation called
hydrated compound
What is water if crystallisation
is when some compounds can form crystals which have water as part of their structure
What is the compound which doesn’t contain water of crystallisation called
anhydrous compound
Is the The conversion of anhydrous compounds to hydrated compounds reversible
YES = by heating the hydrated salt
How can the degree of hydration be calaculated
The mass of the hydrated salt must be measured before heating
The salt is then heated until it reaches a constant mass
The two mass values can be used to calculate the number of moles of water in the hydrated salt - known as the water of crystallisation
Method to find the hydrated salt
Colour change in the hydrates salt experiment
• When blue crystals of hydrated copper (II) sulfate are heated, bonds holding the water within the crystal are broken and the water is driven off, leaving behind white anhydrous copper (II) sulfate.
• (without water, the crystalline structure is lost, and a white powder remains. It is difficult to remove the last traces of water; hence it will often be a very pale blue instead)
Assumptions of hydrated salt experiment
Assumption 1 = all of the water has been lost
Assumption 2 = no further decomposition
Why might you not realise all water has not been lost
If the hydrated and anhydrous forms have different colours, you can be fairly sure when all of water has been removed.
• - However, you only see surface of crystals and some water could be left inside.
• - If the hydrated and anhydrous salts have similar colours, this is hard to determine.
How to improve the fact that all the water has not been lost
heat to constant mass – crystals are reheated repeatedly until mass of residue no longer changes, suggesting water has removed.
What is the kinetic theory of gases
states that molecules in gases are constantly moving
What assumptions does the kinetic theory of gases male
That gas molecules are moving very fast and randomly
That molecules hardly have any volume
That gas molecules do not attract or repel each other (no intermolecular forces)
No kinetic energy is lost when the gas molecules collide with each other (elastic collisions)
The temperature of the gas is related to the average kinetic energy of the molecules
Gases that follow the kinetic theory of gases are called…
Ideal gases
Limitations of the ideal gas law
At very low temperatures and high pressures real gases do not obey the kinetic theory as under these conditions:
Molecules are close to each other
There are instantaneous dipole- induced dipole or permanent dipole- permanent dipole forces between the molecules
These attractive forces pull the molecules away from the container wall
The volume of the molecules is not negligible
Real gases therefore do not obey the following kinetic theory assumptions at low temperatures and high pressures:
There is zero attraction between molecules (due to attractive forces, the pressure is lower than expected for an ideal gas)
The volume of the gas molecules can be ignored (volume of the gas is smaller than expected for an ideal gas)
What is the ideal gas equation
How to convert from Celsius to kelvin
add 273 to the Celsius temperature - e.g. 100 oC is 373 Kelvin
Why may percentage yield not be 100%
- Other reactions take place simultaneously
- The reaction does not go to completion
- Products are lost during separation and purification
Percentage yield formula
What is atom economy
shows how many of the atoms used in the reaction become the desired product
The rest of the atoms or mass is wasted
Formula for atom economy
What is the atom economy in addition reactions
100%
What does atom economy account for that percentage yield doesn’t
Waste Products
Principles of green chemistry
What are the key ideas of green chemistry
- to find reaction pathways with high percentage yield and high atom economy
What is the limiting reactant
The reactant that is NOT in excess - will be used up first
what is meant by avagadros constant
number of carbon 12 atoms that are needed to make 12g of carbon 12
Carbon - 12
Mass spectrometer
B
C
A
B
B
D
