Module 2: Foundations in Chemistry Flashcards
Definition of Relative Isotopic Mass?
The mass of one atom of a particular isotope relative to the mass of 1/12th of a carbon-12 atom.
How do you calculate Relative Atomic Mass?
You multiply the % Abundance by the mass number then add the abundance all together and divide by 100.
Definition of a mole?
A mole is the amount of substances that contain as many particles as there are atoms in 12g of carbon-12.
When working out Water of Crystallisation how do you find x?
You divide the moles of water by the moles of the salt.
Percentage uncertainty formula?
(number of readings x max error/actual reading ) x100
Volume of gas (cm3)
V =n x 24000
Volume of gas (dm3)
V=n x 24
What is the Limiting Reactant in a reaction?
The reactant that is used up first and stops the reaction.
Ideal Gas Equation?
pV=nRT
cm3 to m3
x10-6
dm3 to m3
x10-3
oC to K
+273
kPa to Pa
x103
What is a salt?
A salt forms when the H+ ion in an acid is replaced by a metal ion or NH4+ ion.
What is an orbital?
A region around the nucleus which can hold up to two electrons with opposite spins.
What is First Ionisation Energy?
Energy required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous ions.
First ionisation energy of X?
X(g) –> X+(g) + e-
Factors affecting Ionisation Energy?
- Atomic Radius
- Shielding
- Nuclear Charge
Why does Ionisation Energy decrease as you go down a group?
As you go down a group:
* Atomic radius increases
* Shielding from electrons increases
* So despite an increase in nuclear charge
* less energy required to remove an electron
Why does Ionisation Energy generally increase as you go across period?
As you go across a period:
* Nuclear charge increases
* Electrons are removed from the same shell with similar shielding
* Nuclear attraction increases
* Atomic radius decreases
* More energy is required to remove an electron.
Why do Beryllium and Boron not follow the increase in Ionisation energy trend?
An electron is being removed from the 2p subshell in Boron and 2s in Beryllium, since it’s being removed from a higher energy subshell it is easier to remove.
Why is Oxygen’s ionisation energy less than that of Nitrogen’s?
Paired electrons repel eachother, making it easier to remove an electron so it requires less energy to remove an electron from Oxygen.
What is an ionic bond?
The electrostatic attraction between oppositely charged ions.
If a molecule has 2 bonding pairs and 0 lone pairs shape and degrees?
Linear 180o
If a molecule has 3 bonding pairs and 0 lone pairs, shape and degrees?
Trigonal planar 120o
If a molecule has 4 bonding pairs and 0 lone pairs what is the shape and angle?
Tetrahedral 109.5o
If a molecule has 6 bonding pairs and 0 lone pairs what is the shape and degrees?
Octahedral 90o
If a molecule has 3 bonding pairs and 1 lone pair what is the shape and degrees?
Trigonal pyramedial 107o
If a molecule has 2 bonding pairs and 2 lone pairs what is the shape and degrees?
Non-linear 104.5o
Predict the bond angle in ammonia NH3 molecule. 3 bond pairs and 1 lone pair
- Electrons repel eachother as much as possible.
- Lone pairs repel more than bonded pairs.
- NH3 has 3 bond pairs and 1 lone pair.
- Gives a bond angle of 107o and Trigonal pyramedial shape.
Definition of Electronegativity?
The tendency of a covalently bonded atom to draw the pair of bonding electrons towards itself.
How do London forces exist?
- Fluctuations in electron density within a molecule or atom
- Produce an instantaneous dipole moment
- This induces a dipole moment in an adjacent atom
- The two dipole moments create a weak temporary force of attraction.
Why do larger molecules require more energy to break?
As molecular size increases the number of electrons increase, this makes London forces stronger as atomic or molecular mass increases.
Why are Hydrogen bonds relatively strong?
N, O and F atoms are:
* highly electronegative attracting electrons away from H atom
* have at least a lone pair of electrons after bonding.
Why is ice less dense than water?
In ice, water molecules are held apart from each other in a lattice occupying less space.
Why does water have a relatively high surface tension?
Water molecules have a strong attraction for eachother.
What is a metallic bond?
The electrostatic attraction between a metal cation and the delocalised sea of electrons.