Module 2 Flashcards
Relative Isotopic Mass?
The mass of an isotope of an atoms of an element relative to 1/12 of carbon-12.
Relative Atomic Mass
The weighted mean mass of an atom of an element relative to 1/12 of the mass of the carbon-12 atom.
How to use a mass spectrometer?
-Place sample in the mass spec
-Sample is vapouriest and then ionised to form positive ions.
-The ions are accelerated. The heavier ions move more slowly and are more difficult to deflect that lighter ions so the ions of each isotope are separated.
-the ions are then detected on the mass spec as a mass-to-charge ratio m/z. The greater the abundance, the greater the signal.
What does the Avogadro Constant represent
Number of atoms/particles
Relative Formula Mass
Compares the mass of a formula unit with the mass of an atom of carbon-12.
What is water of crystallisation?
When crystals have a crystalline structure where they are hydrated.
What are the assumptions made when you find the formula of a hydrated salt?
- All of the water has been lost
- There was no further decomposition
Equation that involves concentration and moles
n = c x V
What are the conditions of RTP
20c/ 293 k
101 kPa
What is molar gas volume?
Volume per mole of gas molecules at stated temp and pressure.
24dm3mol-1
What is the ideal gas equation?
pV = nRT
What does ‘R’ stand for in the ideal gas equation?
Ideal Gas constant = 8.31 Jmol-1K-1
What is a limiting reagent?
The reactant that is not in excess will be completely used up first and stop the reaction.
How is a salt formed?
By a base replacing a H+
Atomic Orbitals
A region around the nucleus that can hold up two electrons in opposite spins.
How is a covalent bond different to an ionic?
The attraction is localised as it acting solely between the share pair of electrons.
Average Bond Enthalpy
A measurement of covalent bond strength.
What does a solid line represent in shapes of molecules?
A bond in the plane of the paper
A solid wedge?
Bond comes out of the plane of the paper
Dotted wedges?
bonds go into the plane of the paper
Angle - 109.5. BPs - 4
Tetrahedral
Angle - 107 BPs - 3. LPs- 1
Pyramidal
Non-linear
2 lone pairs
2 bonds pairs
104.5.
[there 4 pairs overall but two are lone pairs so 109.5 - 2(2.5) as for every lone pair you subtract 2.5 from the angles]
Linear
Angle - 180
2 Bond pairs
Angle- 120. BPs- 3
Trigonal Planar
Octahedral
90 angle
5 bond pairs
Why is SF6 an octahedral shape?
This is because the 6 fluorine atoms are positioned at the corners of an octahedron.
What is electronegativity?
The attraction of a bonded atom for the pair of electrons in a covalent bond.
Bond Polarity of non-polar bonds.
The bonded electron pair is shared equally, they have the same or similar electronegativity.
The bond is a pure covalent bond.
They don’t mix with water or polar solvents
What is polar bond?
A bonded electron pair that is shared unequally between the bonded atoms.
Results in a polar covalent bond.
What is a polar molecule?
^A molecule with 2 or more atoms may have 2 or more polar bonds.
What are intermolecular forces?
I weak interactions between dipoles of different molecules.
Describe induced dipole-dipole interactions [london forces]
They exist between all molecules. They are formed by
- movement of electrons produces changing dipole in a molecule.
-an instantaneous dipole will exist at any moments [its position is always constantly changing]
-the instantaneous dipole induces a dipole on a neighbouring molecule.
-induced dipole will further induce dipoles on other neighbouring molecules.
Describe the strength of London forces
The large the induced dipole, the greater the dipole-dipole interactions, and therefore the stronger the attractive force between the molecules.
Describe permanent dipoles
A permanent dipole occurs when there is an electronegative atom [so if it is two F atoms it will cancel out and therefore only have london forces and are non-polar].
Describe simple molecular substances
Made up of simple molecules
Has a definite molecular formula such as neon, hydrogen and water.
They form a regular structure called a simple molecular lattice. The molecules are held in place by weak intermolecular forces, and covalent bonds are present in between the atoms.
Describe hydrogen bonds
A special type of permanent dipoles, that is found in between molecules that are a hydrogen atom attached to an electronegative atom.
The hydrogen bond acts between a lobe pair of electrons on an electronegative atom in one molecule and a hydrogen atom in another molecule.
What are anomalous properties of water?
-solid ice is less dense than water, this is because there are more hydrogen bonds holding in the water and therefore are held apart in an open lattice structure, the water molecules in the ice are further apart and so solid ice less dense and floats on water. Four hydrogen bonds can form on a oxygen atom.
- It has a high melting point and boiling point, water has both london forces and hydrogen bonds to overcome and therefore it requires a lot of energy to break them down.
- high surface tension and cohesion
- high viscosity
