Foundations In Chemistry Flashcards
If an atom has 2 bonded electron pairs what is its bond angle and name?
Linear
180 degrees
If an atom has 3 bonded electron pairs what is its bond angle and name?
Trigonal planar
120 degrees
If an atom has 4 bonded electron pairs what is its bond angle and name?
Tetrahedral
109.5 degrees
If an atom has 5 bonded electron pairs what is its bond angle and name?
Trigonal bipyrimidal
90 degrees and 120 degrees
If an atom has 6 bonded electron pairs what is its bond angle and name?
Octahedral
90 degrees
Define electronegativity
The tendency of a bonded atom to attract the electrons around it
Define polar bond
When the bonded electron pair is unequally shared between the atoms
What is a dipole
Partial charge resulted from the unequal sharing of electrons between molecules
Define intermolecular forces
Weak interactions between dipoles of different molecules
How does an induced dipole dipole form?
Fluctuation of electron density in molecule induces an instantaneous dipole which induces another dipole which results in a weak attraction
Why do simpler molecules not readily dissolve in water ?
Little interaction between molecules in Lattice and the polar solvent molecules due to no polarity in covenant lattice
Why do smaller/simpler molecules have lower melting/boiling points ?
•Usually have London forces which require less force to be broken
•less electrons results in smaller induced dipoles therefore easier to break
What is an orbital ?
An area of probability of which two electrons with opposite spins can be found within a sub shell
What is a dative bond
Shared pair of electrons supplied by one atom in a bond
Define isoelectric
An Atom has same number of protons but different number of electrons
Why is 4s sub shell filled before 3d?
4s is a lower energy level than 3d electrons fill lower energy levels first
Why must electrons have opposite spin?
To counteract the repulsion between the two negative charges
Why do ions dissolve in water ?
Water is an polar solvent. The dipole charges on the water are more favourable than the charges of the ions
Define a covelant bond
Electrostatic forces between the nuclei and shared electron pair
Define electron density
Probability of an electron being present with in a given area of an electron
When does a covalent bond become an ionic bond ?
When the electronegativity difference is larger than 1.8 on the Pauling scale
What happens to a covenant molecule when there is a lone pair of electrons in the outer shell?
Each lone electron pair will reduce bond angle by 2.5 degrees
What two factors affect electronegativity
•atomic radius increase electronegativity decreases
•more unshielded protons higher electronegativity
Define an acid
Compound that releases H+ ions in aqueous solution
Define a base
Substance that accepts H+ ions from an acid
Define an alkali
Releases OH- ions in aqueous solution
Why are titrations used ?
To calculate the concentration of an acid of unknown concentration by neutralisation with a know concentration of an alkali
Define oxidation number
Number of electrons lost shared or gained by an atom in a compound
What are the exceptions for the oxidation numbers of hydrogen, oxygen and chlorine
Hydrogen — metal hydrides(-H)
Oxygen — peroxides (-1) and fluorine (+2)
Chlorine — compounds with Oxygen or Flourine
Define oxidation and reduction in terms of oxidation number
Oxidation-Increase in oxidation number
Reduction-Decrease in oxidation number
Define oxidising agent and reducing agent
•Oxidising agent: Oxidises something else resulting in reducing itself
•Reducing agent :Reduces something else resulting in oxidising itself
Define disproportionation
Redox reaction in which same element is both oxidised and reduced
