Organic Chemistry Lecture 1 Flashcards
Why is organic chemistry used?
To design new drugs
To manufacture and quality control of known drugs
The formulation of drugs into preparations that can be administered to patients e.g. dosage forms such as injections, tablets and creams
Understanding how drugs work at molecular levels
Research in the pharmaceutical, pharmacological, biomedical and other health sciences
What does an atom consist of?
A dense positively charged nucleus surround by negatively charged electrons at a relatively large distance
What does the nucleus of an atom contain?
Subatomic particles called:
Neutrons (electronically neutral)
Protons (positively charged)
Describe the structure of an atom
The nucleus of an atom is made up of subatomic particles called protons (positively charged) and neutrons (neutrally charged). This is called the nucleus
The volume around around the nucleus is occupied by orbiting electrons (negatively charged)
What is the atomic number?
The number of protons in the atoms nucleus. This is equal to the sum of electrons present in a neutral atom
What is the mass number?
The sum of protons and neutrons in an atoms nucleus
How can you calculate the number of neutrons present in an atom?
Neutrons = mass number - atomic number
13
C
6
How many:
Protons?
Neutrons?
Electrons?
6 protons
7 neutrons
6 electrons
What is an isotope?
Atoms of a given element that have the same atomic number
Same number of protons but different number of neutrons
Therefore, they have different mass numbers
What are the isotopes of carbon?
12 13 14
C C C
6 6 6
Carbon 14 is present in trace amounts, this isotope is radioactive and is used in the carbon dating of ancient objects
What is the atomic weight?
The atomic weight (or atomic mass) of a naturally occurring element is the average mass of its atoms. For carbon, the atomic weight is 12.011 atomic mass units.
What is the molecular weight?
Molecular weight of a compound is the sum of the atomic weight of all atoms in the molecule
According to the quantum mechanical model, electrons behave as ……?
Waves
Behaviour of a specific electron in an atom is described by the mathematical expression called …..?
Wave equation
What is the solution of wave equation termed as?
Wave function
The square of wave function (psi)2 gives the probability of….
Finding an electron at a particular point. Referred to as the atomic orbital
(Shell is a collection of orbitals)
What is the shell of an atom refer to?
The collection of orbitals
What are the three quantum numbers that define the atomic orbital?
The principle quantum number, n
The orbital angular momentum quantum number, i
The magnetic quantum number, m
4th quantum number, thespian angular momentum m2 but this is not needed to define the wave function
What does different values of the principle quantum number (n) mean and what values can n be?
Different values of n divides orbitals into groups of similar energies called shells,
N can take values of 1,2,3,4,5,6,7…………..
What does the orbital angular momentum number (i) mean?
This gives information about the shape of the orbital
Values of i depend on values of n such that 1=0,1,2…. And n-1
The different possible values are given letters rather than numbers, namely s,p,d,f
0=s
1= p
2=d
3=f
What does the magnetic quantum number, m, show?
M determines the spatial orientation of the angular momentum I
Determines where the orbitals are in space and its value depends on the value of i
Such that m=+i to -i
M1= i,i-1,1-2……..-2
The values of mi are given as suffices on the letters defining the angular momentum quantum numbers i.
What does the spin quantum number, ms, mean?
Refers to the orientation (or spin) of the electron with respect to an external magnetic field
Can take the values +1/2 or -1/2
It is significant in determining electron configuration
What are the four kinds of electron orbitals?
S, p, d and f
Describe an s orbital
Spherical with the nucleus at the centre
Describe the p orbital
Dumbbell-shaped with nucleus at the middle
In each shell, starting at the second, there are three perpendicular p orbitals, px, py and Pz, these all have the same energy
The lobes of a p orbital are separated by a region of zero electron density, a node.
How are orbitals grouped?
Orbitals are grouped in electron shells of increasing size and energy
How many electrons can be contained within each orbital?
2
How many orbitals does the first shell contain and how many electrons are held here?
First shell contains one s orbital, denoted 1s which holds two electrons
How many orbitals are contained within the second shell and how many electrons can this hold?
The second shell contains four orbitals, one s orbital (2s) and three p orbitals (2p) which can hold a total of eight electrons
How many orbitals are contained within the third shell and how many electrons can this hold?
The third shell contains nine orbitals, one s orbital (3s), three p orbitals (3p) and five d orbitals (3D), which holds a total of 18 electrons
Draw an example of an electron configuration diagram
See lecture notes
What is ground state electron configuration?
The most stable, lowest energy electron configuration of a molecule or atom
Describe the aufbau principle:
Building up principle:
Electrons in the ground state of an atom occupy the orbitals of lowest energy such that the total electronic energy is minimised
Lowest energy orbitals fill first e.g. 1s -> 2s -> 2p ->3s
Describe the Pauli exclusion principle:
‘No Two electrons in an atom may possess identical sets of the four quantum numbers n,i,m and ms
Only two electrons of opposite spins can occupy an orbital
Describe Hunds rule
In filling a set of degenerate orbitals, the number of unpaired electrons is maximised and such unpaired electrons will posses parallel spins
Using an energy level diagram, write the ground state electronic configuration for the following elements:
12 1 23 19 C H Na+ F-
6 1 11 9
Draw diagrams
Why do atoms bond?
Atoms bond because the compound that results is more stable and is lower in energy than the separate atoms due to attraction between the oppositely charged ions, nuclei and shared electrons
What is chemical bonding?
Bonding that occurs in the outer most electron shell of an atom
Eight electrons in valence shell import special stability to noble-gas elements in 8a
Octet rule states: atoms gain, lose or share electrons as to have eight electrons in their outer shell
The main group elements are governed by their tendency to take on electron configuration of the nearest noble gas.
This leaders to ionic bonding
What does the octet rule state
Atoms gain, lose or share electrons so as to have eight electrons in their outer shell
What are some problems with the octet rule?
It applies only to first row and roughly p block compounds
The rule often breaks down e.g. PCL5, NO and BF3
Does not predict the strength of bonds
Only predicts how many bonds will be formed and even that is often wrong
How does ionic bonding work?
In ionic bonding, the elements of note or accept electrons to achieve noble gas configuration
Alkali metals in groups 1A (Na, Li and Mg) achieve noble gas configuration by losing their single s electron from their valence shell to form a cation
Halogens in group 7a (Br, Cl, F, O) gain a p electron to fill their valence shell and achieve noble gas configuration leading to the formation of an anion
The ions are held together by an electrostatic attraction, like in Na+ and Cl- forming an ionic bond
Electrostatic force of attraction between two oppositely charged ions formed as the result of electron transfer
How does covalent bonding work?
Covalent bond is a pair of electrons shared between atoms.
In covalent bonds, atoms share electrons until they reach noble gas configuration
This was proposed by Lewis in 1916 and called the octet rule
The octet rule stares that atoms gain, lose or share electrons so as to have eight electrons in their outer shell
What are Lewis structures?
Electron dot structures
Simple way of indicating covalent bonds in molecules (here atoms valence electrons are represented by dots)
What does the number of covalent bonds depend on?
The number of covalent bond as depends on how many additional valence electrons are needed to reach noble base configuration
What are lone pair electrons
Valence shell electron pairs which are not used for bonding are called lone pairs
Lone-pair electrons can act as nucleophiles and react with electrophiles
